Network Working Group R. Kumar
Request for Comments: 3108 M. Mostafa
Category: Standards Track Cisco Systems
May 2001
Network Working Group R. Kumar
Request for Comments: 3108 M. Mostafa
Category: Standards Track Cisco Systems
May 2001
Conventions for the use of the Session Description Protocol (SDP) for ATM Bearer Connections
ATM承载连接使用会话描述协议（SDP）的约定
Status of this Memo
本备忘录的状况
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
本文件规定了互联网社区的互联网标准跟踪协议，并要求进行讨论和提出改进建议。有关本协议的标准化状态和状态，请参考当前版本的“互联网官方协议标准”（STD 1）。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (2001). All Rights Reserved.
版权所有（C）互联网协会（2001年）。版权所有。
Abstract
摘要
This document describes conventions for using the Session Description Protocol (SDP) described in RFC 2327 for controlling ATM Bearer Connections, and any associated ATM Adaptation Layer (AAL). The AALs addressed are Type 1, Type 2 and Type 5. This list of conventions is meant to be exhaustive. Individual applications can use subsets of these conventions. Further, these conventions are meant to comply strictly with the SDP syntax as defined in RFC 2327.
本文档描述了使用RFC 2327中描述的会话描述协议（SDP）控制ATM承载连接的约定，以及任何相关的ATM适配层（AAL）。所述AAL为类型1、类型2和类型5。本公约清单旨在详尽无遗。单个应用程序可以使用这些约定的子集。此外，这些约定旨在严格遵守RFC2327中定义的SDP语法。
Table of Contents
目录
1. Introduction................................................... 3
1.1 Key words to indicate Requirement Levels..................... 5
2. Representation of Certain Fields within SDP description lines.. 5
2.1 Representation of Extension Attributes....................... 5
2.2 Representation of Parameter Values........................... 5
2.3 Directionality Convention.................................... 6
2.4 Case convention............................................... 7
2.5 Use of special characters in SDP parameter values............. 8
3. Capabilities Provided by SDP conventions....................... 8
4. Format of the ATM Session Description.......................... 9
5. Structure of the Session Description Lines.................... 11
5.1 The Origin Line.............................................. 11
5.2 The Session Name Line........................................ 12
5.3 The Connection Information Line.............................. 13
5.4 The Timestamp Line........................................... 15
1. Introduction................................................... 3
1.1 Key words to indicate Requirement Levels..................... 5
2. Representation of Certain Fields within SDP description lines.. 5
2.1 Representation of Extension Attributes....................... 5
2.2 Representation of Parameter Values........................... 5
2.3 Directionality Convention.................................... 6
2.4 Case convention............................................... 7
2.5 Use of special characters in SDP parameter values............. 8
3. Capabilities Provided by SDP conventions....................... 8
4. Format of the ATM Session Description.......................... 9
5. Structure of the Session Description Lines.................... 11
5.1 The Origin Line.............................................. 11
5.2 The Session Name Line........................................ 12
5.3 The Connection Information Line.............................. 13
5.4 The Timestamp Line........................................... 15
5.5 Media Information Line for ATM connections................... 16
5.5.1 The Virtual Connection ID.................................. 16
5.5.2 The Transport Parameter.................................... 19
5.5.3 The Format List for AAL1 and AAL5 applications............. 21
5.5.4 The Format List for AAL2 applications...................... 21
5.5.5 Media information line construction........................ 22
5.6 The Media Attribute Lines.................................... 27
5.6.1 ATM bearer connection attributes........................... 28
5.6.1.1 The 'eecid' attribute.................................... 30
5.6.1.2 The 'aalType' attribute.................................. 31
5.6.1.3 The 'capability' attribute............................... 32
5.6.1.4 The 'qosClass' attribute................................. 33
5.6.1.5 The 'bcob' attribute..................................... 34
5.6.1.6 The 'stc' attribute...................................... 34
5.6.1.7 The 'upcc' attribute..................................... 35
5.6.1.8 The 'atmQOSparms' attribute.............................. 35
5.6.1.9 The 'atmTrfcDesc' attribute............................. 37
5.6.1.10 The 'abrParms' attribute................................. 39
5.6.1.11 The 'abrSetup' attribute................................. 40
5.6.1.12 The 'bearerType' attribute............................... 41
5.6.1.13 The 'lij' attribute...................................... 42
5.6.1.14 The 'anycast' attribute.................................. 43
5.6.1.15 The 'cache' attribute.................................... 43
5.6.1.16 The 'bearerSigIE' attribute.............................. 44
5.6.2 ATM Adaptation Layer (AAL) attributes...................... 45
5.6.2.1 The 'aalApp' attribute................................... 46
5.6.2.2 The 'cbrRate' attribute.................................. 48
5.6.2.3 The 'sbc' attribute...................................... 49
5.6.2.4 The 'clkrec' attribute................................... 51
5.6.2.5 The 'fec' attribute...................................... 51
5.6.2.6 The 'prtfl' attribute.................................... 51
5.6.2.7 The 'structure' attribute................................ 52
5.6.2.8 The 'cpsSDUsize' attribute............................... 53
5.6.2.9 The 'aal2CPS' attribute.................................. 53
5.6.2.10 The 'aal2CPSSDUrate' attribute........................... 54
5.6.2.11 The 'aal2sscs3661unassured' attribute.................... 54
5.6.2.12 The 'aal2sscs3661assured' attribute...................... 55
5.6.2.13 The 'aal2sscs3662' attribute............................. 56
5.6.2.14 The 'aal5sscop' attribute................................ 58
5.6.3 Service attributes......................................... 58
5.6.3.1 The 'atmmap' attribute................................... 60
5.6.3.2 The 'silenceSupp' attribute.............................. 63
5.6.3.3 The 'ecan' attribute..................................... 65
5.6.3.4 The 'gc' attributes...................................... 66
5.6.3.5 The 'profileDesc' attribute.............................. 67
5.6.3.6 The 'vsel' attribute..................................... 68
5.6.3.7 The 'dsel' attribute..................................... 70
5.6.3.8 The 'fsel' attribute..................................... 72
5.5 Media Information Line for ATM connections................... 16
5.5.1 The Virtual Connection ID.................................. 16
5.5.2 The Transport Parameter.................................... 19
5.5.3 The Format List for AAL1 and AAL5 applications............. 21
5.5.4 The Format List for AAL2 applications...................... 21
5.5.5 Media information line construction........................ 22
5.6 The Media Attribute Lines.................................... 27
5.6.1 ATM bearer connection attributes........................... 28
5.6.1.1 The 'eecid' attribute.................................... 30
5.6.1.2 The 'aalType' attribute.................................. 31
5.6.1.3 The 'capability' attribute............................... 32
5.6.1.4 The 'qosClass' attribute................................. 33
5.6.1.5 The 'bcob' attribute..................................... 34
5.6.1.6 The 'stc' attribute...................................... 34
5.6.1.7 The 'upcc' attribute..................................... 35
5.6.1.8 The 'atmQOSparms' attribute.............................. 35
5.6.1.9 The 'atmTrfcDesc' attribute............................. 37
5.6.1.10 The 'abrParms' attribute................................. 39
5.6.1.11 The 'abrSetup' attribute................................. 40
5.6.1.12 The 'bearerType' attribute............................... 41
5.6.1.13 The 'lij' attribute...................................... 42
5.6.1.14 The 'anycast' attribute.................................. 43
5.6.1.15 The 'cache' attribute.................................... 43
5.6.1.16 The 'bearerSigIE' attribute.............................. 44
5.6.2 ATM Adaptation Layer (AAL) attributes...................... 45
5.6.2.1 The 'aalApp' attribute................................... 46
5.6.2.2 The 'cbrRate' attribute.................................. 48
5.6.2.3 The 'sbc' attribute...................................... 49
5.6.2.4 The 'clkrec' attribute................................... 51
5.6.2.5 The 'fec' attribute...................................... 51
5.6.2.6 The 'prtfl' attribute.................................... 51
5.6.2.7 The 'structure' attribute................................ 52
5.6.2.8 The 'cpsSDUsize' attribute............................... 53
5.6.2.9 The 'aal2CPS' attribute.................................. 53
5.6.2.10 The 'aal2CPSSDUrate' attribute........................... 54
5.6.2.11 The 'aal2sscs3661unassured' attribute.................... 54
5.6.2.12 The 'aal2sscs3661assured' attribute...................... 55
5.6.2.13 The 'aal2sscs3662' attribute............................. 56
5.6.2.14 The 'aal5sscop' attribute................................ 58
5.6.3 Service attributes......................................... 58
5.6.3.1 The 'atmmap' attribute................................... 60
5.6.3.2 The 'silenceSupp' attribute.............................. 63
5.6.3.3 The 'ecan' attribute..................................... 65
5.6.3.4 The 'gc' attributes...................................... 66
5.6.3.5 The 'profileDesc' attribute.............................. 67
5.6.3.6 The 'vsel' attribute..................................... 68
5.6.3.7 The 'dsel' attribute..................................... 70
5.6.3.8 The 'fsel' attribute..................................... 72
5.6.3.9 The 'onewaySel' attribute................................ 73
5.6.3.10 The 'codecconfig' attribute.............................. 75
5.6.3.11 The 'isup_usi' attribute................................. 76
5.6.3.12 The 'uiLayer1_Prot' attribute............................ 76
5.6.4 Miscellaneous media attributes............................. 77
5.6.4.1 The 'chain' attribute..................................... 77
5.6.5 Use of the second media-level part in H.323 Annex C
applications............................................... 78
5.6.6 Use of the eecid media attribute in call establishment
procedures................................................. 78
6. List of Parameters with Representations....................... 83
7. Examples of ATM session descriptions using SDP................. 93
8. Security Considerations........................................ 94
8.1 Bearer Security.............................................. 94
8.2 Security of the SDP description.............................. 95
9. ATM SDP Grammar................................................ 95
References........................................................104
Acknowledgements..................................................109
Authors' Addresses................................................109
Full Copyright Statement..........................................110
5.6.3.9 The 'onewaySel' attribute................................ 73
5.6.3.10 The 'codecconfig' attribute.............................. 75
5.6.3.11 The 'isup_usi' attribute................................. 76
5.6.3.12 The 'uiLayer1_Prot' attribute............................ 76
5.6.4 Miscellaneous media attributes............................. 77
5.6.4.1 The 'chain' attribute..................................... 77
5.6.5 Use of the second media-level part in H.323 Annex C
applications............................................... 78
5.6.6 Use of the eecid media attribute in call establishment
procedures................................................. 78
6. List of Parameters with Representations....................... 83
7. Examples of ATM session descriptions using SDP................. 93
8. Security Considerations........................................ 94
8.1 Bearer Security.............................................. 94
8.2 Security of the SDP description.............................. 95
9. ATM SDP Grammar................................................ 95
References........................................................104
Acknowledgements..................................................109
Authors' Addresses................................................109
Full Copyright Statement..........................................110
SDP will be used in conjunction with a connection handling /device control protocol such as Megaco (H.248) [26], SIP [18] or MGCP [25] to communicate the information needed to set up ATM and AAL2 bearer connections. These connections include voice connections, voiceband data connections, clear channel circuit emulation connections, video connections and baseband data connections (such as fax relay, modem relay, SSCOP, frame relay etc.).
SDP将与连接处理/设备控制协议（如Megaco（H.248）[26]、SIP[18]或MGCP[25]一起使用，以传递建立ATM和AAL2承载连接所需的信息。这些连接包括语音连接、语音带数据连接、清晰通道电路仿真连接、视频连接和基带数据连接（如传真中继、调制解调器中继、SSCOP、帧中继等）。
These conventions use standard SDP syntax as defined in RFC 2327 [1] to describe the ATM-level and AAL-level connections, addresses and other parameters. In general, parameters associated with layers higher than the ATM adaptation layer are included only if they are tightly coupled to the ATM or AAL layers. Since the syntax conforms to RFC 2327, standard SDP parsers should react in a well-defined and safe manner on receiving session descriptions based on the SDP conventions in this document. This is done by extending the values of fields defined in RFC 2327 rather than by defining new fields. This is true for all SDP lines except the of the media attribute lines, in which case new attributes are defined. The SDP protocol allows the definition of new attributes in the media attribute lines which are free-form. For the remaining lines, the fact that the <networkType> field in an SDP descriptor is set to "ATM" should preclude the misinterpretation of extended parameter values by RFC 2327-compliant SDP parsers.
这些约定使用RFC 2327[1]中定义的标准SDP语法来描述ATM级别和AAL级别的连接、地址和其他参数。通常，仅当与ATM或AAL层紧密耦合时，才包括与高于ATM适配层的层相关联的参数。由于语法符合RFC2327，标准SDP解析器在接收基于本文档中SDP约定的会话描述时，应以定义良好且安全的方式作出反应。这是通过扩展RFC 2327中定义的字段值而不是通过定义新字段来实现的。这适用于除介质属性行之外的所有SDP行，在这种情况下定义了新属性。SDP协议允许在媒体属性行中定义自由格式的新属性。对于其余的行，SDP描述符中的<networkType>字段设置为“ATM”这一事实应排除RFC2327兼容SDP解析器对扩展参数值的误解。
These conventions are meant to address the following ATM applications:
这些约定旨在解决以下ATM应用：
1. Applications in which a new SVC is set-up for each service connection. These SVCs could be AAL1 or AAL5 SVCs or single-CID AAL2 SVCs.
1. 为每个服务连接设置新SVC的应用程序。这些SVC可以是AAL1或AAL5 SVC或单个CID AAL2 SVC。
2. Applications in which existing path resources are assigned to service connections. These resources could be:
2. 将现有路径资源分配给服务连接的应用程序。这些资源可以是：
* AAL1/AAL5 PVCs, SPVCs or cached SVCs, * AAL2 single-CID PVCs, SPVCs or cached SVCs, * CIDs within AAL2 SVCs/PVCs/SPVCs that multiplex multiple CIDs. * Subchannels (identified by CIDs) within AAL1 [8] or AAL2 [11] SVCs/PVCs/SPVCs.
* AAL1/AAL5 PVC、SPVC或缓存SVC、*AAL2单个CID PVC、SPVC或缓存SVC、*AAL2 SVC/PVC/SPVC中多路复用多个CID的CID。*AAL1[8]或AAL2[11]SVC/PVC/SPVC内的子信道（由CID标识）。
Note that the difference between PVCs and SPVCs is in the way the bearer virtual circuit connection is set up. SPVCs are a class of PVCs that use bearer signaling, as opposed to node-by-node provisioning, for connection establishment.
请注意，PVC和SPVC之间的区别在于承载虚拟电路连接的设置方式。SPVC是一类PVC，它使用承载信令来建立连接，而不是逐节点提供连接。
This document is limited to the case when the network type is ATM. This includes raw RTP encapsulation [45] or voice sample encapsulation [46] over AAL5 with no intervening IP layer. It does not address SDP usage for IP, with or without ATM as a lower layer.
本文件仅限于网络类型为ATM的情况。这包括AAL5上的原始RTP封装[45]或语音样本封装[46]，没有中间IP层。它不解决IP的SDP使用问题，无论是否使用ATM作为较低层。
In some cases, IP connection set-up is independent of lower layers, which are configured prior to it. For example, AAL5 PVCs that connect IP routers can be used for VoIP calls. In other cases, VoIP call set-up is closely tied to ATM-level connection set-up. This might require a chaining of IP and ATM descriptors, as described in section 5.6.4.1.
在某些情况下，IP连接设置独立于在它之前配置的较低层。例如，连接IP路由器的AAL5 PVC可用于VoIP呼叫。在其他情况下，VoIP呼叫设置与ATM级连接设置密切相关。这可能需要IP和ATM描述符的链接，如第5.6.4.1节所述。
This document makes no assumptions on who constructs the session descriptions (media gateway, intermediate ATM/AAL2 switch, media gateway controller etc.). This will be different in different applications. Further, it allows the use of one session description for both directions of a connection (as in SIP and MGCP applications) or the use of separate session descriptions for different directions. It also addresses the ATM multicast and anycast capabilities.
本文档不假设会话描述由谁构成（媒体网关、中间ATM/AAL2交换机、媒体网关控制器等）。这在不同的应用中会有所不同。此外，它允许对连接的两个方向使用一个会话描述（如在SIP和MGCP应用程序中），或者对不同方向使用单独的会话描述。它还解决了ATM多播和选播功能。
This document makes no assumptions about how the SDP description will be coded. Although the descriptions shown here are encoded as text, alternate codings are possible:
本文件对SDP说明的编码方式不作任何假设。尽管此处显示的描述编码为文本，但也可以使用其他编码：
- Binary encoding such as ASN.1. This is an option (in addition to text encoding) in the Megaco context.
- 二进制编码，如ASN.1。这是Megaco上下文中的一个选项（除了文本编码）。
- Use of extended ISUP parameters [36] to encode the information in SDP descriptors, with conversion to/from binary/text-based SDP encoding when needed.
- 使用扩展ISUP参数[36]对SDP描述符中的信息进行编码，并在需要时转换为二进制/基于文本的SDP编码。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [62].
本文件中的关键词“必须”、“不得”、“要求”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照RFC 2119[62]中所述进行解释。
This document conforms to the syntactic conventions of standard SDP as defined in RFC 2327 [1].
本文件符合RFC 2327[1]中定义的标准SDP的语法约定。
The SDP protocol [1] requires that non-standard attributes and codec names use an "X-" prefix.
SDP协议[1]要求非标准属性和编解码器名称使用“X-”前缀。
In this internet document, the "X-" prefix is used consistently for codec names (Table 2) that have not been registered with the IANA. The IANA-registered codec names listed in [31] do not use this prefix, regardless of whether they are statically or dynamically assigned payload types.
在本互联网文档中，“X-”前缀用于未在IANA注册的编解码器名称（表2）。[31]中列出的IANA注册编解码器名称不使用此前缀，无论它们是静态还是动态分配的有效负载类型。
However, this prefix is not used for the extension SDP attributes defined in this document. This has been done to enhance legibility.
但是，此前缀不用于本文档中定义的扩展SDP属性。这样做是为了提高易读性。
This document suggests that parsers be flexible in the use of the "X-" prefix convention. They should accept codec names and attribute names with or without the "X-" prefix.
本文建议解析器在使用“X-”前缀约定时要灵活。他们应该接受编码解码器名称和属性名称，包括或不包括“X-”前缀。
Depending on the format of their representation in SDP, the parameters defined in this document fall into the following classes:
根据其在SDP中的表示格式，本文档中定义的参数分为以下几类：
(1) Parameters always represented in a decimal format. (2) Parameters always represented in a hexadecimal format. (3) Parameters always represented as character strings. (4) Parameters that can be represented in either decimal or hexadecimal format.
(1) 参数始终以十进制格式表示。（2） 参数始终以十六进制格式表示。（3） 参数始终表示为字符串。（4） 可以用十进制或十六进制格式表示的参数。
No prefixes are needed for classes 1 - 3, since the format is fixed. For class 4, a "0x" prefix shall always be used to differentiate the hexadecimal from the decimal format.
类1-3不需要前缀，因为格式是固定的。对于第4类，应始终使用“0x”前缀来区分十六进制和十进制格式。
For both decimal and hex representations, if the underlying bit field is smaller or larger than the binary equivalent of the SDP representation, then leading 0 bits should be added or removed as needed. Thus, 3 and 0x3 translate into the following five-bit pattern: 0 0011. The SDP representations 0x12 and 18 translate into the following five-bit pattern: 1 0010.
对于十进制和十六进制表示，如果基础位字段小于或大于SDP表示的二进制等效值，则应根据需要添加或删除前导0位。因此，3和0x3转换为以下五位模式：0 0011。SDP表示0x12和18转换为以下五位模式：1 0010。
Leading 0 digits shall not be used in decimal representations. Generally, these are also not used in hexadecimal representations. Exceptions are when an exact number of hex digits is expected, as in the case of NSAP addresses. Parsers shall not reject leading zeros in hex values.
十进制表示中不得使用前导0位。通常，它们也不用于十六进制表示。例外情况是预期十六进制数字的确切数目，如NSAP地址。解析器不得拒绝十六进制值中的前导零。
Both single-character and multi-character string values are enclosed in double quotes (i.e., "). By contrast, single quotes (i.e., ') are used for emphasizing keywords rather than to refer to characters or strings.
单字符和多字符字符串值都用双引号（即“”）括起来。相比之下，单引号（即“”）用于强调关键字，而不是指字符或字符串。
In the text representation of decimal and hex numbers, digits to the left are more significant than digits to the right.
在十进制和十六进制数字的文本表示中，左边的数字比右边的数字更重要。
This section defined the meaning of the terms 'forward' and 'backward' as used in this document. This is specially applicable to parameters that have a specific direction associated with them.
本节定义了本文件中使用的术语“向前”和“向后”的含义。这特别适用于具有特定方向的参数。
In this document, 'forward' refers to the direction away from the ATM node under consideration, while 'backward' refers to the direction towards the ATM node. This convention must be used in all SDP-based session descriptions regardless of whether underlying bearer is an SVC, a dynamically allocated PVC/SPVC or a dynamically allocated CID. This is regardless of which side originates the service connection. If ATM SVC or AAL2 Q.2630.1 signaling is used, the directionality convention is independent of which side originates the SVC or AAL2 connection.
在本文件中，“向前”指远离所考虑的ATM节点的方向，“向后”指朝向ATM节点的方向。无论底层承载是SVC、动态分配的PVC/SPVC还是动态分配的CID，都必须在所有基于SDP的会话描述中使用此约定。这与哪一方发起服务连接无关。如果使用ATM SVC或AAL2 Q.2630.1信令，则方向性约定与SVC或AAL2连接的发起方无关。
This provides a simple way of identifying the direction in which a parameter is applicable, in a manner that is independent of the underlying ATM or AAL2 bearer. This simplicity comes at a price, described below.
这提供了一种以独立于底层ATM或AAL2承载的方式识别参数适用方向的简单方法。这种简单性是有代价的，如下所述。
The convention used by all ATM/AAL2 signaling specifications (e.g., Q.2931 Section 1.3.3 and Q.2630.1) mandates that forward direction is from the end initiating setup/establishment via bearer signaling towards the end receiving the setup/establishment request. The backward direction is in the opposite direction. In some cases, the 'forward' and 'backward' directions of the ATM signaling convention
所有ATM/AAL2信令规范（例如，Q.2931第1.3.3节和Q.2630.1节）使用的约定规定，前向是从通过承载信令发起设置/建立的端到接收设置/建立请求的端。向后的方向是相反的方向。在某些情况下，ATM信令约定的“向前”和“向后”方向
might be the exact opposite of the SDP convention described above, requiring the media gateway to perform the necessary translation. An example case in which this is needed is described below.
可能与上述SDP约定完全相反，要求媒体网关执行必要的翻译。下面描述了需要这样做的示例情况。
Consider an SDP description sent by a media gateway controller to the gateway originating a service-level call. In the backward SVC call set-up model, this gateway terminates (rather than originates) an SVC call. The media gateway refers to the traffic descriptor (and hence the PCR) in the direction away from this gateway as the forward traffic descriptor and forward PCR. Clearly, this is at odds with ATM SVC signaling which refers to this very PCR as the backward PCR. The gateway needs to be able to perform the required swap of directions. In this example, the media gateway terminating the service level call (and hence originating the SVC call) does not need to perform this swap.
考虑由媒体网关控制器向源于服务级别呼叫的网关发送的SDP描述。在反向SVC调用设置模型中，此网关终止（而不是发起）SVC调用。媒体网关将远离该网关方向上的流量描述符（以及PCR）称为前向流量描述符和前向PCR。显然，这与ATM SVC信令不一致，后者将这种PCR称为反向PCR。网关需要能够执行所需的方向交换。在此示例中，媒体网关终止服务级别调用（并因此发起SVC调用）不需要执行此交换。
Certain parameters within attributes are defined exclusively for the forward or backward directions. Examples for the forward direction are the <fsssar> subparameter within the 'aal2sscs3661unassured' media attribute line, the <fsssar>, <fsscopsdu> and <fsscopuu> subparameters within the 'aal2sscs3661assured' media attribute line, the <fsscopsdu> and <fsscopuu> subparameters within the 'aal5sscop' media attribute line, and the <fmaxFrame> parameter within the 'aal2sscs3662' media attribute line. Examples for the backward direction are the <bsssar> subparameter within the 'aal2sscs3661unassured' media attribute line, the <bsssar>, <bsscopsdu> and <bsscopuu> subparameters within the 'aal2sscs3661assured' media attribute line, the <bsscopsdu> and <bsscopuu> subparameters within the 'aal5sscop' media attribute line, and the <bmaxFrame> parameter within the 'aal2sscs3662' media attribute line.
属性中的某些参数专门为前进或后退方向定义。前进方向的示例包括“aal2sscs3661unassured”媒体属性行中的<fsssar>子参数、“aal2sscs3661assured”媒体属性行中的<fsssar>、<fsscopsdu>和<fsscopu>子参数、“aal5sscop”媒体属性行中的<fsscopsdu>和<fsscopu>子参数，以及“aal2sscs3662”媒体属性行中的<fmaxFrame>参数。后退方向的示例包括“aal2sscs3661unassured”媒体属性行中的<bsssar>子参数、“aal2sscs3661assured”媒体属性行中的<bsssar>、<BSSCPSDU>和<BSSCPUU>子参数、“aal5sscop”媒体属性行中的<BSSCPSDU>和<BSSCPUU>子参数，以及“aal2sscs3662”媒体属性行中的<bmaxFrame>参数。
As defined in RFC 2327 [1], SDP syntax is case-sensitive. Since these ATM conventions conform strictly with SDP syntax, they are case-sensitive. SDP line types (e.g., "c", "m", "o", "a") and fields in the SDP lines should be built according to the case conventions in [1] and in this document. It is suggested, but not required, that SDP parsers for ATM applications be case-tolerant where ignoring case does not result in ambiguity. Encoding names, which are defined outside the SDP protocol, are case-insensitive.
如RFC 2327[1]中所定义，SDP语法区分大小写。由于这些ATM约定严格符合SDP语法，因此它们区分大小写。SDP行类型（例如，“c”、“m”、“o”、“a”）和SDP行中的字段应根据[1]和本文档中的案例约定构建。建议（但不是必需的）ATM应用程序的SDP解析器应具有大小写容错性，忽略大小写不会导致歧义。在SDP协议之外定义的编码名称不区分大小写。
In general, RFC 2327-conformant string values of SDP parameters [1] do not include special characters that are neither alphabets nor digits. An exception is the "/" character used in the value "RTP/AVP" of transport sub-field of the 'm' line.
通常，SDP参数[1]的RFC 2327一致字符串值不包括既不是字母也不是数字的特殊字符。“m”行传输子字段的值“RTP/AVP”中使用的“/”字符是一个例外。
String values used in SDP descriptions of ATM connections retain this convention, while allowing the use of the special character "/" in a manner commensurate with [1]. In addition, the special characters "$" and "-" are used in the following manner. A "$" value is a wildcard that allows the recipient of the SDP description to select any permitted value of the parameter. A "-" value indicates that it is not necessary to specify the value of the parameter in the SDP description because this parameter is irrelevant for this application, or because its value can be known from another source such as provisioning, defaults, another protocol, another SDP descriptor or another part of the same SDP descriptor. If the use of these special characters is construed as a violation of RFC 2327 [1] syntax, then reserved string values can be used. The string "CHOOSE" can be used in lieu of "$". The string "OMIT" can be used in lieu of "-" for an omitted parameter.
ATM连接的SDP描述中使用的字符串值保留此约定，同时允许以与[1]相称的方式使用特殊字符“/”。此外，特殊字符“$”和“-”的使用方式如下。“$”值是一个通配符，它允许SDP描述的接收者选择参数的任何允许值。“-”值表示无需在SDP描述中指定参数的值，因为此参数与此应用程序无关，或者因为其值可以从其他来源（如供应、默认值、另一协议、另一SDP描述符或同一SDP描述符的另一部分）得知。如果使用这些特殊字符被解释为违反RFC 2327[1]语法，则可以使用保留字符串值。字符串“CHOOSE”可以用来代替“$”。对于省略的参数，可以使用字符串“OMIT”代替“-”。
To support the applications listed in section 1, the SDP conventions in this document provide the following session control capabilities:
为了支持第1节中列出的应用程序，本文档中的SDP约定提供了以下会话控制功能：
* Identification of the underlying bearer network type as ATM.
* 将底层承载网络类型标识为ATM。
* Identification by an ATM network element of its own address, in one of several possible formats. A connection peer can initiate SVC set-up to this address. A call agent or connection peer can select an pre-established bearer path to this address.
* ATM网元以几种可能的格式之一识别其自身地址。连接对等方可以为此地址启动SVC设置。呼叫代理或连接对等方可以选择到该地址的预先建立的承载路径。
* Identification of the ATM bearer connection that is to be bound to the service-level connection. Depending on the application, this is either a VCC or a subchannel (identified by a CID) within a VCC.
* 要绑定到服务级别连接的ATM承载连接的标识。根据应用，这是VCC或VCC内的子信道（由CID标识）。
* Identification of media type: audio, video, data.
* 媒体类型标识：音频、视频、数据。
* In AAL1/AAL5 applications, declaration of a set of payload types that can be bound to the ATM bearer connection. The encoding names and payload types defined for use in the RTP context [31] are re-used for AAL1 and AAL5, if applicable.
* 在AAL1/AAL5应用程序中，可绑定到ATM承载连接的一组有效负载类型的声明。为在RTP上下文[31]中使用而定义的编码名称和有效负载类型将重新用于AAL1和AAL5（如果适用）。
* In AAL2 applications, declaration of a set of profiles that can be bound to the ATM bearer connection. A mechanism for dynamically defining custom profiles within the SDP session description is included. This allows the use of custom profiles for connections that span multi-network interfaces.
* 在AAL2应用程序中，可绑定到ATM承载连接的一组配置文件的声明。包括用于在SDP会话描述中动态定义自定义配置文件的机制。这允许对跨多个网络接口的连接使用自定义配置文件。
* A means of correlating service-level connections with underlying ATM bearer connections. The backbone network connection identifier or bnc-id specified in ITU Q.1901 [36] standardization work is used for this purpose. In order to provide a common SDP base for applications based on Q.1901 and SIP/SIP+, the neutral term 'eecid' is used in lieu of 'bnc-id' in the SDP session descriptor.
* 将服务级别连接与底层ATM承载连接关联起来的一种方法。ITU Q.1901[36]标准化工作中规定的主干网连接标识符或bnc id用于此目的。为了为基于Q.1901和SIP/SIP+的应用程序提供公共SDP基础，在SDP会话描述符中使用中性术语“eecid”代替“bnc id”。
* A means of mapping codec types and packetization periods into service types (voice, voiceband data and facsimile). This is useful in determining the encoding to use when the connection is upspeeded in response to modem or facsimile tones.
* 将编解码器类型和打包周期映射为服务类型（语音、声带数据和传真）的一种方法。当连接响应调制解调器或传真音而提速时，这有助于确定要使用的编码。
* A means of describing the adaptation type, QoS class, ATM transfer capability/service category, broadband bearer class, traffic parameters, CPS parameters and SSCS parameters related the underlying bearer connection.
* 描述与基础承载连接相关的适配类型、QoS等级、ATM传输能力/服务类别、宽带承载等级、业务参数、CPS参数和SSCS参数的方法。
* Means for enabling or describing special functions such as leaf- initiated-join, anycast and SVC caching.
* 用于启用或描述特殊功能的方法，如叶启动的联接、选播和SVC缓存。
* For H.323 Annex C applications, a means of specifying the IP address and port number on which the node will receive RTCP messages.
* 对于H.323附录C应用程序，一种指定节点将在其上接收RTCP消息的IP地址和端口号的方法。
* A means of chaining consecutive SDP descriptors so that they refer to different layers of the same connection.
* 一种链接连续SDP描述符的方法，以便它们引用同一连接的不同层。
The sequence of lines in the session descriptions in this document conforms to RFC 2327 [1]. In general, a session description consists of a session-level part followed by zero or more media-level parts. ATM session descriptions consist of a session-level part followed by one or two media-level parts. The only two media applicable are the ATM bearer medium and RTCP control (where applicable).
本文件中会话描述中的行顺序符合RFC 2327[1]。通常，会话描述由会话级部分和零个或多个媒体级部分组成。ATM会话描述由会话级部分和一个或两个媒体级部分组成。唯一适用的两种介质是ATM承载介质和RTCP控制（如适用）。
The session level part consists of the following lines:
会话级部分由以下行组成：
v= (protocol version, zero or one line)
o= (origin, zero or one line)
s= (session name, zero or one line)
v= (protocol version, zero or one line)
o= (origin, zero or one line)
s= (session name, zero or one line)
c= (connection information, one line)
b= (bandwidth, zero or more lines)
t= (timestamp, zero or one line)
k= (encryption key, zero or one line)
c= (connection information, one line)
b= (bandwidth, zero or more lines)
t= (timestamp, zero or one line)
k= (encryption key, zero or one line)
In ATM session descriptions, there are no media attribute lines in the session level part. These are present in the media-level parts.
在ATM会话描述中，会话级别部分中没有媒体属性行。这些都存在于媒体级部件中。
The media-level part for the ATM bearer consists of the following lines:
ATM承载的媒体级部分由以下行组成：
m= (media information and transport address, one line)
b= (bandwidth, zero or more lines)
k= (encryption key, zero or more lines)
a= (media attribute, zero or more lines)
m= (media information and transport address, one line)
b= (bandwidth, zero or more lines)
k= (encryption key, zero or more lines)
a= (media attribute, zero or more lines)
The media-level part for RTCP control consists of the following lines:
RTCP控制的媒体级部件由以下几行组成：
m= (media information and transport address, one line)
c= (connection information for control only, one line)
m= (media information and transport address, one line)
c= (connection information for control only, one line)
In general, the 'v', 'o', 's', and 't' lines are mandatory. However, in the Megaco [26] context, these lines have been made optional. The 'o', 's', and 't' lines are omitted in most MGCP [25] applications.
通常，“v”、“o”、“s”和“t”行是强制性的。但是，在Megaco[26]上下文中，这些行是可选的。在大多数MGCP[25]应用中，省略了“o”、“s”和“t”行。
Note that SDP session descriptors for ATM can contain bandwidth (b=) and encryption key (k=) lines. Like all other lines, these lines should strictly conform to the SDP standard [1].
请注意，ATM的SDP会话描述符可以包含带宽（b=）和加密密钥（k=）行。与所有其他线路一样，这些线路应严格符合SDP标准[1]。
The bandwidth (b=) line is not necessarily redundant in the ATM context since, in some applications, it can be used to convey application-level information which does not map directly into the atmTrfcDesc media attribute line. For instance, the 'b' line can be used in SDP descriptors in RTSP commands to describe content bandwidth.
带宽（b=）线在ATM上下文中不一定是冗余的，因为在某些应用程序中，它可用于传输应用程序级信息，而这些信息不会直接映射到atmTrfcDesc媒体属性线。例如，可以在RTSP命令的SDP描述符中使用“b”行来描述内容带宽。
The encryption key line (k=) can be used to indicate an encryption key for the bearer, and a method to obtain the key. At present, the encryption of ATM and AAL2 bearers has not been conventionalized, unlike the encryption of RTP payloads. Nor has the authentication or encryption of ATM or AAL2 bearer signaling. In the ATM and AAL2 contexts, the term 'bearer' can include 'bearer signaling' as well as 'bearer payloads'.
加密密钥行（k=）可用于指示承载的加密密钥以及获取密钥的方法。目前，与RTP有效负载加密不同，ATM和AAL2承载的加密尚未实现常规化。ATM或AAL2承载信令的身份验证或加密也没有。在ATM和AAL2上下文中，术语“承载”可以包括“承载信令”以及“承载有效负载”。
The order of lines in an ATM session description is exactly in the RFC 2327-conformant order depicted above. However, there is no order of the media attribute ('a') lines with respect to other 'a' lines.
ATM会话描述中的行顺序与上面描述的RFC 2327一致。但是，媒体属性（“a”）行相对于其他“a”行没有顺序。
The SDP protocol version for session descriptions using these conventions is 0. In conformance with standard SDP, it is strongly recommended that the 'v' line be included at the beginning of each SDP session description. In some contexts such as Megaco, the 'v' line is optional and may be omitted unless several session descriptions are provided in sequence, in which case the 'v' line serves as a delimiter. Depending on the application, sequences of session descriptions might refer to:
使用这些约定的会话描述的SDP协议版本为0。根据标准SDP，强烈建议在每个SDP会话描述的开头包含“v”行。在某些上下文（如Megaco）中，“v”行是可选的，可以省略，除非按顺序提供多个会话描述，在这种情况下，“v”行用作分隔符。根据应用程序的不同，会话描述的顺序可能指：
- Different connections or sessions. - Alternate ways of realizing the same connection or session. - Different layers of the same session (section 5.6.4.1).
- 不同的连接或会话。-实现相同连接或会话的替代方法。-同一会话的不同层（第5.6.4.1节）。
The 'o', 's' and 't' lines are included for strict conformance with RFC 2327. It is possible that these lines might not carry useful information in some ATM-based applications. Therefore, some applications might omit these lines, although it is recommended that they not do so. For maximum interoperability, it is preferable that SDP parsers not reject session descriptions that do not contain these lines.
包括“o”、“s”和“t”行，以严格符合RFC 2327。在一些基于ATM的应用程序中，这些线路可能不携带有用的信息。因此，有些应用程序可能会忽略这些行，但建议不要这样做。为了实现最大的互操作性，SDP解析器最好不要拒绝不包含这些行的会话描述。
The origin line for an ATM-based session is structured as follows:
基于ATM的会话的起始线结构如下：
o=<username> <sessionID> <version> <networkType>
<addressType> <address>
o=<username> <sessionID> <version> <networkType>
<addressType> <address>
The <username> is set to "-".
<username>设置为“-”。
The <sessionID> can be set to one of the following:
<sessionID>可以设置为以下选项之一：
* an NTP timestamp referring to the moment when the SDP session descriptor was created. * a Call ID, connection ID or context ID that uniquely identifies the session within the scope of the ATM node. Since calls can comprise multiple connections (sessions), call IDs are generally not suitable for this purpose.
* NTP时间戳，表示创建SDP会话描述符的时刻。*在ATM节点范围内唯一标识会话的呼叫ID、连接ID或上下文ID。由于呼叫可以包含多个连接（会话），因此呼叫ID通常不适合此用途。
NTP time stamps can be represented as decimal or hex integers. The part of the NTP timestamp that refers to an integer number of seconds is sufficient. This is a 32-bit field
NTP时间戳可以表示为十进制或十六进制整数。NTP时间戳中引用整数秒数的部分就足够了。这是一个32位字段
On the other hand, call IDs, connection IDs and context IDs can be can be 32 hex digits long.
另一方面，调用ID、连接ID和上下文ID的长度可以是32个十六进制数字。
The <sessionID> field is represented as a decimal or hex number of up to 32 digits. A "0x" prefix is used before the hex representation. The <version> refers to the version of the SDP session descriptor (not that of the SDP protocol). This is can be set to one of the following:
<sessionID>字段表示为最多32位的十进制或十六进制数。十六进制表示法之前使用“0x”前缀。<version>指的是SDP会话描述符的版本（不是SDP协议的版本）。这可以设置为以下选项之一：
* 0. * an NTP timestamp referring to the moment when the SDP session descriptor was modified. If the SDP session descriptor has not been modified by an intermediate entity (such as an MGC), then the <version> timestamp will be the same as the <sessionId> timestamp, if any. As with the <sessionId>, only the integer part of the NTP timestamp is used.
* 0. * NTP时间戳，表示修改SDP会话描述符的时刻。如果中间实体（如MGC）未修改SDP会话描述符，则<version>时间戳将与<sessionId>时间戳相同（如果有）。与<sessionId>一样，只使用NTP时间戳的整数部分。
When equated to the integer part of an NTP timestamp, the <version> field is 10 digits wide. This is more restricted than [1], which allows unlimited size. As in [1], the most significant digit is non-zero when an NTP timestamp is used.
当等同于NTP时间戳的整数部分时，<version>字段的宽度为10位。这比[1]更受限制，后者允许无限大小。如[1]中所述，当使用NTP时间戳时，最高有效位为非零。
The <networkType> in SDP session descriptions for ATM applications should be assigned the string value "ATM" or wildcarded to a "$" or "-".
ATM应用程序SDP会话描述中的<networkType>应分配字符串值“ATM”或通配符给“$”或“-”。
The <addressType> and <address> parameters are identical to those for the connection information ('c') line (Section 5.3). Each of these parameters can be wildcarded per the conventions described for the 'c' line in Section 5.3. These parameters should not me omitted since this would violate SDP syntax [1].
<addressType>和<address>参数与连接信息（“c”）行的参数相同（第5.3节）。这些参数中的每一个都可以按照第5.3节中“c”行所述的约定进行通配符。不应忽略这些参数，因为这将违反SDP语法[1]。
As with the 'c' line, SDP parsers are not expected to check the consistency of <networkType> with <addressType>, <address> pairs. The <addressType> and <address> need to be consistent with each other.
与“c”行一样，SDP解析器不需要检查<networkType>与<addressType>，<address>对的一致性。<addressType>和<address>需要彼此一致。
In general, the session name line is structured as follows:
通常，会话名称行的结构如下所示：
s=<sessionName>
s=<sessionName>
For ATM-based sessions, the <sessionName> parameter is set to a "-". The resulting line is:
对于基于ATM的会话，<sessionName>参数设置为“-”。结果行是：
s=-
=-
In general, the connection information line [1] is structured as follows:
通常，连接信息行[1]的结构如下：
c=<networkType> <addressType> <address>
c=<networkType> <addressType> <address>
For ATM networks, additional values of <networkType>, <addressType> and <address> are defined, over and above those listed in [1]. The ABNF syntax (Section 9) for ATM SDP does not limit the ways in which <networkType> can be combined with <addressType>, <address> pairs. However, some combinations will not be valid in certain applications, while others will never be valid. Invalid combinations should be rejected by application-specific functions, and not by generic parsers. The ABNF syntax does limit the ways in which <addressType> and <address> can be paired.
对于ATM网络，除了[1]中列出的值之外，还定义了<networkType>、<addressType>和<address>的附加值。ATM SDP的ABNF语法（第9节）不限制<networkType>与<addressType>，<address>对组合的方式。但是，某些组合在某些应用程序中无效，而其他组合则永远无效。无效的组合应该被特定于应用程序的函数拒绝，而不是被通用解析器拒绝。ABNF语法限制了<addressType>和<address>的配对方式。
For ATM networks, the value of <networkType> should be set to "ATM". Further, this may be wildcarded to "$" or "-". If this is done, an node using ATM as the basic transport mechanism will select a value of "ATM". A node that interfaces with multiple network types ("IN", "ATM" etc.) that include ATM can also choose a value of "ATM".
对于ATM网络，<networkType>的值应设置为“ATM”。此外，这可以通配符为“$”或“-”。如果这样做，使用ATM作为基本传输机制的节点将选择“ATM”值。与包括ATM的多种网络类型（“IN”、“ATM”等）接口的节点也可以选择“ATM”值。
When the SDP description is built by a node such as a media gateway, the <address> refers to the address of the node building the SDP description. When this description is forwarded to another node, it still contains the original node's address. When the media gateway controller builds part or all of the SDP description, the local descriptor contains the address of the local node, while the remote descriptor contains the address of the remote node. If the <address> and/or <addressType> are irrelevant or are known by other means, they can be set to a "$" or a "-", as described below.
当SDP描述由节点（如媒体网关）构建时，<address>指构建SDP描述的节点的地址。当此描述转发到另一个节点时，它仍然包含原始节点的地址。当媒体网关控制器构建部分或全部SDP描述时，本地描述符包含本地节点的地址，而远程描述符包含远程节点的地址。如果<address>和/或<addressType>不相关或通过其他方式已知，则可将其设置为“$”或“-”，如下所述。
Additionally, in all contexts, the 'm' line can have an ATM address in the <virtualConnectionId> subparameter which, if present, is the remote address if the 'c' line address is local, and vice versa.
此外，在所有上下文中，“m”行可以在<virtualConnectionId>子参数中有一个ATM地址，如果“c”行地址是本地的，则该子参数是远程地址，反之亦然。
For ATM networks, the <addressType> can be NSAP, E164 or GWID (ALIAS). For ATM networks, the <address> syntax depends on the syntax of the <addressType>. SDP parsers should check the consistency of <addressType> with <address>.
对于ATM网络，<addressType>可以是NSAP、E164或GWID（别名）。对于ATM网络，<address>语法取决于<addressType>的语法。SDP解析器应该检查<addressType>与<address>的一致性。
NSAP: If the addressType is NSAP, the address is expressed in the standard dotted hex form. This is a string of 40 hex digits, with dots after the 2nd, 6th, 10th, 14th, 18th, 22nd, 26th, 30th, 34th and 38th digits. The last octet of the NSAP address is the 'selector' field that is available for non-standard use. An example of a line with an NSAP address is:
NSAP：如果addressType为NSAP，则地址以标准点十六进制形式表示。这是一个由40位十六进制数字组成的字符串，在第2位、第6位、第10位、第14位、第18位、第22位、第26位、第30位、第34位和第38位后面有点。NSAP地址的最后八位字节是可供非标准使用的“选择器”字段。具有NSAP地址的线路示例如下：
c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
A "0x" prefix shall not be used in this case since this is always in hexadecimal format.
在这种情况下，不应使用“0x”前缀，因为它始终是十六进制格式。
E164: If the addressType is E164, the address is expressed as a decimal number with up to 15 digits. For example:
E164：如果地址类型为E164，则地址表示为最多15位的十进制数。例如：
c=ATM E164 9738294382
c=ATM E164 9738294382
The use of E.164 numbers in the B-ISDN context is defined in ITU E.191. There is a disparity between the ATM forum and the ITU in the use of E.164 numbers for ATM addressing. The ATM forum (e.g., UNI Signaling 4.0) allows only International Format E.164 numbers, while the ITU (e.g., Q.2931) allows private numbering plans. Since the goal of this SDP specification is to interoperate with all bearer signaling protocols, it allows the use of numbers that do not conform to the E.164 International Format. However, to maximize overall consistency, network administrators can restrict the provisioning of numbers to the E.164 International Format.
在B-ISDN环境中使用E.164号码的定义见ITU E.191。ATM论坛和ITU在使用E.164号码进行ATM寻址方面存在差异。ATM论坛（如UNI信令4.0）只允许国际格式，如164号，而ITU（如Q.2931）允许私人编号计划。由于本SDP规范的目标是与所有承载信令协议互操作，因此允许使用不符合E.164国际格式的号码。但是，为了最大限度地提高整体一致性，网络管理员可以将数字的设置限制为E.164国际格式。
GWID (ALIAS): If the addressType is GWID, it means that the address is a Gateway Identifier or Node Alias. This may or may not be globally unique. In this format, the address is expressed as an alphanumeric string ("A"-"Z", "a"-"z", "0" - "9",".","-","_"). For example:
GWID（别名）：如果addressType为GWID，则表示该地址是网关标识符或节点别名。这可能是唯一的，也可能不是唯一的。在这种格式中，地址表示为字母数字字符串（“A”-“Z”、“A”-“Z”、“0”-“9”、“、”、“-”和“”）。例如：
c=ATM GWID officeABCmgx101vism12
c=ATM GWID办公室BCMGX101VIS12
Since these SDP conventions can be used for more than gateways, the string "ALIAS" can be used instead of "GWID" in the 'c' line. Thus, the example above is equivalent to:
由于这些SDP约定可用于多个网关，因此可以在“c”行中使用字符串“ALIAS”代替“GWID”。因此，上述示例相当于：
c=ATM ALIAS officeABCmgx101vism12
c=ATM别名办公室BCMGX101VISM12
An example of a GWID (ALIAS)is the CLLI code used for telecom equipment. For all practical purposes, it should be adequate for the GWID (ALIAS) to be a variable length string with a maximum size of 32 characters.
GWID（别名）的一个示例是用于电信设备的CLLI代码。出于所有实际目的，GWID（别名）应该是最大长度为32个字符的可变长度字符串。
The connection information line is always present in an SDP session descriptor. However, each of the parameters on this line can be wildcarded to a "$" or a "-", independently of whether other parameters on this line are wildcarded or not. Not all syntactically legal wildcard combinations are meaningful in a particular application.
连接信息行始终存在于SDP会话描述符中。但是，此行上的每个参数都可以通配符为“$”或“-”，这与此行上的其他参数是否通配符无关。并非所有语法合法的通配符组合在特定应用程序中都有意义。
Examples of meaningful wildcard combinations in the ATM context are:
ATM上下文中有意义的通配符组合示例如下：
c=- - -
c=$ $ $
c=ATM - -
c=ATM $ $
c=ATM <addressType> -
c=ATM <addressType> $
c=- - -
c=$ $ $
c=ATM - -
c=ATM $ $
c=ATM <addressType> -
c=ATM <addressType> $
Specifying the ATM address type without specifying the ATM address is useful when the recipient is asked to select an ATM address of a certain type (NSAP, E.164 etc.).
当要求收件人选择某一类型的ATM地址（NSAP，E.164等）时，指定ATM地址类型而不指定ATM地址非常有用。
Examples of syntactically legal wildcard combinations of dubious utility are:
可疑实用程序的语法合法通配符组合示例如下：
c=- $ -
c=- $ $
c=- <addressType> -
c=$ <addressType> $
c=- <addressType> <address>
c=$ <addressType> <address>
c=- $ -
c=- $ $
c=- <addressType> -
c=$ <addressType> $
c=- <addressType> <address>
c=$ <addressType> <address>
Note that <addressType> and/or <address> should not omitted without being set to a "-" or "$" since this would violate basic SDP syntax [1].
请注意，<addressType>和/或<address>不应在未设置为“-”或“$”的情况下省略，因为这将违反基本SDP语法[1]。
The timestamp line for an SDP session descriptor is structured as follows:
SDP会话描述符的时间戳行的结构如下：
t= <startTime> <stopTime>
t= <startTime> <stopTime>
Per Ref. [49], NTP time stamps use a 32 bit unsigned representation of seconds, and a 32 bit unsigned representation of fractional seconds. For ATM-based sessions, the <startTime>parameter can be made equal to the NTP timestamp referring to the moment when the SDP session descriptor was created. It can also be set to 0 indicating its irrelevance. If it made equal to the NTP timestamp in seconds, the fractional part of the NTP timestamp is omitted. When equated to the integer part of an NTP timestamp, the <startTime> field is 10 digits wide. This is more restricted than [1], which allows unlimited size. As in [1], the most significant digit is non-zero when an NTP timestamp is used.
根据参考文献[49]，NTP时间戳使用秒的32位无符号表示，以及分数秒的32位无符号表示。对于基于ATM的会话，<startTime>参数可以设置为等于NTP时间戳，表示创建SDP会话描述符的时刻。也可以将其设置为0，表示其不相关。如果以秒为单位使其等于NTP时间戳，则忽略NTP时间戳的小数部分。当等同于NTP时间戳的整数部分时，<startTime>字段的宽度为10位。这比[1]更受限制，后者允许无限大小。如[1]中所述，当使用NTP时间戳时，最高有效位为非零。
The <stopTime> parameter is set to 0 for ATM-based SDP descriptors.
对于基于ATM的SDP描述符，<stopTime>参数设置为0。
The general format of the media information line adapted for AAL1 and AAL5 applications is:
适用于AAL1和AAL5应用的媒体信息行的一般格式为：
m=<media> <virtualConnectionId> <transport> <format list>
m=<media> <virtualConnectionId> <transport> <format list>
The general format of the media information line adapted for AAL2 applications is:
适用于AAL2应用的媒体信息行的一般格式为：
m=<media> <virtualConnectionId> <transport#1> <format list#1>
<transport#2> <format list#2> ... <transport#M> <format list#M>
m=<media> <virtualConnectionId> <transport#1> <format list#1>
<transport#2> <format list#2> ... <transport#M> <format list#M>
Note that <virtualConnectionId> is equivalent to <port> in [1].
请注意，<virtualConnectionId>相当于[1]中的<port>。
The subparameter <media> can take on all the values defined in [1]. These are: "audio", "video", "application", "data" and "control".
子参数<media>可以接受[1]中定义的所有值。这些是：“音频”、“视频”、“应用”、“数据”和“控制”。
When the <transport> parameter has more than one value in the 'm' line, the <transport> <format list> pairs can be arranged in preferential order.
当<transport>参数在“m”行中有多个值时，<transport><format list>对可以按优先顺序排列。
In applications in which the media-level part of a session descriptor is bound to an ATM virtual circuit, the <virtualConnectionId> can be in one of the following formats:
在会话描述符的媒体级部分绑定到ATM虚拟电路的应用中，<virtualConnectionId>可以采用以下格式之一：
* <ex_vcci>
* <addressType>-<address>/<ex_vcci>
* <address>/<ex_vcci>
* <ex_bcg>/<ex_vcci>
* <ex_portId>/<ex_vpi>/<ex_vci>
* <ex_bcg>/<ex_vpi>/<ex_vci>
* <ex_vpci>/<ex_vci>
* <addressType>-<address>/<ex_vpci>/<ex_vci>
* <address>/<ex_vpci>/<ex_vci>
* <ex_vcci>
* <addressType>-<address>/<ex_vcci>
* <address>/<ex_vcci>
* <ex_bcg>/<ex_vcci>
* <ex_portId>/<ex_vpi>/<ex_vci>
* <ex_bcg>/<ex_vpi>/<ex_vci>
* <ex_vpci>/<ex_vci>
* <addressType>-<address>/<ex_vpci>/<ex_vci>
* <address>/<ex_vpci>/<ex_vci>
In applications in which the media-level part of a session descriptor is bound to a subchannel within an ATM virtual circuit, the <virtualConnectionId> can be in one of the following formats:
在会话描述符的媒体级部分绑定到ATM虚拟电路内的子信道的应用中，<virtualConnectionId>可以采用以下格式之一：
* <ex_vcci>/<ex_cid>
* <addressType>-<address>/<ex_vcci>/<ex_cid>
* <address>/<ex_vcci>/<ex_cid>
* <ex_bcg>/<ex_vcci>/<ex_cid>
* <ex_portId>/<ex_vpi>/<ex_vci>/<ex_cid>
* <ex_bcg>/<ex_vpi>/<ex_vci>/<ex_cid>
* <ex_vcci>/<ex_cid>
* <addressType>-<address>/<ex_vcci>/<ex_cid>
* <address>/<ex_vcci>/<ex_cid>
* <ex_bcg>/<ex_vcci>/<ex_cid>
* <ex_portId>/<ex_vpi>/<ex_vci>/<ex_cid>
* <ex_bcg>/<ex_vpi>/<ex_vci>/<ex_cid>
* <ex_vpci>/<ex_vci>/<ex_cid>
* <addressType>-<address>/<ex_vpci>/<ex_vci>/<ex_cid>
* <address>/<ex_vpci>/<ex_vci>/<ex_cid>
* <ex_vpci>/<ex_vci>/<ex_cid>
* <addressType>-<address>/<ex_vpci>/<ex_vci>/<ex_cid>
* <address>/<ex_vpci>/<ex_vci>/<ex_cid>
Here,
在这里
<ex_vcci> = VCCI-<vcci>
<ex_vpci> = VPCI-<vpci>
<ex_bcg> = BCG-<bcg>
<ex_portId> = PORT-<portId>
<ex_vpi> = VPI-<vpi>
<ex_vci> = VCI-<vci>
<ex_cid> = CID-<cid>
<ex_vcci> = VCCI-<vcci>
<ex_vpci> = VPCI-<vpci>
<ex_bcg> = BCG-<bcg>
<ex_portId> = PORT-<portId>
<ex_vpi> = VPI-<vpi>
<ex_vci> = VCI-<vci>
<ex_cid> = CID-<cid>
The <vcci>, <vpi>, <vci>, <vpci> and <cid> are decimal numbers or hexadecimal numbers. An "0x" prefix is used before their values when they are in the hex format.
<vcci>、<vpi>、<vci>、<vpci>和<cid>是十进制数或十六进制数。十六进制格式的值之前使用“0x”前缀。
The <portId> is always a hexadecimal number. An "0x" prefix is not used with it.
<portId>始终是十六进制数。“0x”前缀不与它一起使用。
The <addressType> and <address> are identical to their definitions above for the connection information line with the difference that this address refers to the remote peer in the media information line. Since the <virtualConnectionId>, as defined here, is meant for use in ATM networks, the values of <addressType> and <address> in the <virtualConnectionId> are limited to ATM-specific values.
<addressType>和<address>与上面对连接信息行的定义相同，不同之处在于此地址指的是媒体信息行中的远程对等方。由于此处定义的<virtualConnectionId>用于ATM网络，因此<virtualConnectionId>中的<addressType>和<address>值仅限于ATM特定值。
The <vpi>, <vci> and <cid> are the Virtual Path Identifier, Virtual Circuit Identifier and Channel Identifier respectively. The <vpi> is an 8 or 12 bit field. The <vci> is a 16-bit field. The <cid> is an 8-bit field ([8] and [11]). For AAL1 applications, it corresponds to the channel number defined in Annex C of [8].
<vpi>、<vci>和<cid>分别是虚拟路径标识符、虚拟电路标识符和通道标识符。<vpi>是一个8位或12位字段。<vci>是一个16位字段。<cid>是一个8位字段（[8]和[11]）。对于AAL1应用，其对应于[8]附录C中定义的信道编号。
The <vpci> is a 16-bit field defined in Section 4.5.16 of ITU Q.2931 [Ref. 15]. The <vpci> is similar to the <vpi>, except for its width and the fact that it retains its value across VP crossconnects. In some applications, the size of the <vpci> is the same as the size of the <vpi> (8 or 12 bits). In this case, the most significant 8 or 4 bits are ignored.
<vpci>是ITU Q.2931[参考文献15]第4.5.16节中定义的16位字段。<vpci>与<vpi>类似，不同之处在于它的宽度以及它在VP交叉连接中保持其值的事实。在某些应用中，<vpci>的大小与<vpi>的大小相同（8或12位）。在这种情况下，最高有效8位或4位被忽略。
The <vcci> is a 16-bit field defined in ITU Recommendation Q.2941.2 [32]. The <vcci> is similar to the <vci>, except for the fact that it retains its value across VC crossconnects.
<vcci>是ITU建议Q.2941.2[32]中定义的16位字段。<vcci>与<vci>类似，只是它在VC交叉连接中保持其值。
In general, <vpci> and <vcci> values are unique between a pair of nodes. When they are unique between a pair of nodes but not unique within a network, they need to be qualified, at any node, by the ATM
通常，<vpci>和<vcci>值在一对节点之间是唯一的。当它们在一对节点之间是唯一的，但在网络中不是唯一的时，它们需要在任何节点上通过ATM进行鉴定
address of the remote node. These parameters can be pre-provisioned or signaled. When signaled, the <vpci> is encapsulated in the connection identifier information element of SVC signaling messages. The <vcci> is encapsulated in the Generic Information Transport (GIT) information element of SVC signaling messages. In an ATM node pair, either node can assign <vcci> values and signal it to the other end via SVC signaling. A glare avoidance scheme is defined in [32] and [44]. This mechanism works in SVC applications. A different glare avoidance technique is needed when a pool of existing PVCs/SPVCs is dynamically assigned to calls. One such scheme for glare reduction is the assignment of <vcci> values from different ends of the <vcci> range, using the lowest or highest available value as applicable.
远程节点的地址。这些参数可以预先设置或发出信号。当发出信号时，<vpci>被封装在SVC信令消息的连接标识符信息元素中。<vcci>封装在SVC信令消息的通用信息传输（GIT）信息元素中。在ATM节点对中，任一节点都可以分配<vcci>值，并通过SVC信令将其发送给另一端。[32]和[44]中定义了眩光避免方案。此机制适用于SVC应用程序。当现有PVC/SPVC池被动态分配给呼叫时，需要一种不同的眩光避免技术。减少眩光的一种方案是使用适用的最低或最高可用值，从<vcci>范围的不同端分配<vcci>值。
When <vpci> and <vcci> values are pre-provisioned, administrations have the option of provisioning them uniquely in a network. In this case, the ATM address of the far end is not needed to qualify these parameters.
当预先设置<vpci>和<vcci>值时，管理部门可以选择在网络中唯一地设置它们。在这种情况下，不需要远端的ATM地址来限定这些参数。
In the AAL2 context, the definition of a VCC implies that there is no CID-level switching between its ends. If either end can assign <cid> values, then a glare reduction mechanism is needed. One such scheme for glare reduction is the assignment of <cid> values from different ends of the <cid> range, using the lowest or highest available value as applicable.
在AAL2上下文中，VCC的定义意味着其两端之间没有CID级别切换。如果任一端可以指定<cid>值，则需要眩光减少机制。减少眩光的一种方案是使用最低或最高可用值（如适用）从<cid>范围的不同端分配<cid>值。
The <portId> parameter is used to identify the physical trunk port on an ATM module. It can be represented as a hexadecimal number of up to 32 hex digits.
<portId>参数用于标识ATM模块上的物理中继端口。它可以表示为最多32个十六进制数字的十六进制数。
In some applications, it is meaningful to bundle a set of connections between a pair of ATM nodes into a bearer connection group. The <bcg> subparameter is an eight bit field that allows the bundling of up to 255 VPCs or VCCs.
在某些应用中，将一对ATM节点之间的一组连接捆绑到承载连接组中是有意义的。<bcg>子参数是一个8位字段，允许绑定多达255个VPC或VCC。
In some applications, it is necessary to wildcard the <virtualConnectionId> parameter, or some elements of this parameter. The "$" wildcard character can be substituted for the entire <virtualConnectionId> parameter, or some of its terms. In the latter case, the constant strings that qualify the terms in the <virtualConnectionId> are retained. The concatenation <addressType>-<address> can be wildcarded in the following ways:
在某些应用程序中，需要通配符<virtualConnectionId>参数或该参数的某些元素。“$”通配符可以替换整个<virtualConnectionId>参数或其某些术语。在后一种情况下，将保留限定<virtualConnectionId>中术语的常量字符串。级联<addressType>-<address>可以通过以下方式进行通配符：
* The entire concatenation, <addressType>-<address>, is replaced with a "$". * <address> is replaced with a "$", but <addressType> is not.
* 整个连接，<addressType>-<address>，被替换为“$”*<地址>替换为“$”，但<addressType>不是。
Examples of wildcarding the <virtualConnectionId> in the AAL1 and AAL5 contexts are: $, VCCI-$, BCG-100/VPI-20/VCI-$. Examples of wildcarding the <virtualConnectionId> in the AAL2 context are: $, VCCI-40/CID-$, BCG-100/VPI-20/VCI-120/CID-$, NSAP-$/VCCI-$/CID-$, $/VCCI-$/CID-$.
在AAL1和AAL5上下文中通配符<virtualConnectionId>的示例有：$、VCCI-$、BCG-100/VPI-20/VCI-$。在AAL2上下文中通配符<virtualConnectionId>的示例有：$、VCCI-40/CID-$、BCG-100/VPI-20/VCI-120/CID-$、NSAP-$/VCCI-$/CID-$、$/VCCI-$/CID-$。
It is also permissible to set the entire <virtualConnectionId> parameter to a "-" indicating its irrelevance.
还允许将整个<virtualConnectionId>参数设置为“-”，表示其不相关。
The <transport> parameter indicates the method used to encapsulate the service payload. These methods are not defined in this document, which refers to existing ATMF and ITU-T standards, which, in turn, might refer to other standards. For ATM applications, the following <transport> values are defined:
<transport>参数表示用于封装服务有效负载的方法。这些方法未在本文件中定义，本文件引用了现有的ATMF和ITU-T标准，而这些标准又可能引用其他标准。对于ATM应用，定义了以下<transport>值：
Table 1: List of Transport Parameter values used in SDP in the ATM context
表1:ATM上下文中SDP中使用的传输参数值列表
+---------------------------------------------------------------------+
| | Controlling Document for |
| Transport | Encapsulation of Service Payload |
+------------------------+--------------------------------------------+
| AAL1/ATMF | af-vtoa-0078.000 [7] |
+------------------------+--------------------------------------------+
| AAL1/ITU | ITU-T H.222.1 [51] |
+------------------------+--------------------------------------------+
| AAL5/ATMF | af-vtoa-0083.000 [46] |
+------------------------+--------------------------------------------+
| AAL5/ITU | ITU-T H.222.1 [51] |
+------------------------+--------------------------------------------+
| AAL2/ATMF | af-vtoa-0113.000 [44] and |
| | af-vmoa-0145.000 [52] |
+------------------------+--------------------------------------------+
| AAL2/ITU | ITU-T I.366.2 [13] |
+------------------------+--------------------------------------------+
| AAL1/custom | Corporate document or |
| AAL2/custom | application-specific interoperability |
| AAL5/custom | statement. |
+------------------------+--------------------------------------------+
| AAL1/<corporateName> | |
| AAL2/<corporateName> | |
| AAL5/<corporateName> | |
| AAL1/IEEE:<oui> | Corporate document |
| AAL2/IEEE:<oui> | |
| AAL5/IEEE:<oui> | |
+------------------------+--------------------------------------------+
| RTP/AVP | Annex C of H.323 [45] |
+------------------------+--------------------------------------------+
+---------------------------------------------------------------------+
| | Controlling Document for |
| Transport | Encapsulation of Service Payload |
+------------------------+--------------------------------------------+
| AAL1/ATMF | af-vtoa-0078.000 [7] |
+------------------------+--------------------------------------------+
| AAL1/ITU | ITU-T H.222.1 [51] |
+------------------------+--------------------------------------------+
| AAL5/ATMF | af-vtoa-0083.000 [46] |
+------------------------+--------------------------------------------+
| AAL5/ITU | ITU-T H.222.1 [51] |
+------------------------+--------------------------------------------+
| AAL2/ATMF | af-vtoa-0113.000 [44] and |
| | af-vmoa-0145.000 [52] |
+------------------------+--------------------------------------------+
| AAL2/ITU | ITU-T I.366.2 [13] |
+------------------------+--------------------------------------------+
| AAL1/custom | Corporate document or |
| AAL2/custom | application-specific interoperability |
| AAL5/custom | statement. |
+------------------------+--------------------------------------------+
| AAL1/<corporateName> | |
| AAL2/<corporateName> | |
| AAL5/<corporateName> | |
| AAL1/IEEE:<oui> | Corporate document |
| AAL2/IEEE:<oui> | |
| AAL5/IEEE:<oui> | |
+------------------------+--------------------------------------------+
| RTP/AVP | Annex C of H.323 [45] |
+------------------------+--------------------------------------------+
In H.323 Annex C applications [45], the <transport> parameter has a value of "RTP/AVP". This is because these applications use the RTP protocol [2] and audio/video profile [3]. The fact that RTP is carried directly over AAL5 per [45] can be indicated explicitly via the aalApp media attribute.
在H.323附录C应用[45]中，<transport>参数的值为“RTP/AVP”。这是因为这些应用程序使用RTP协议[2]和音频/视频配置文件[3]。根据[45]，RTP直接通过AAL5传输的事实可以通过aalApp媒体属性明确表示。
A value of "AAL1/custom", "AAL2/custom" or "AAL5/custom" for the <transport> parameter can indicate non-standard or semi-standard encapsulation schemes defined by a corporation or a multi-vendor agreement. Since there is no standard administration of this convention, care should be taken to preclude inconsistencies within the scope of a deployment.
<transport>参数的值“AAL1/custom”、“AAL2/custom”或“AAL5/custom”可以表示公司或多供应商协议定义的非标准或半标准封装方案。由于本公约没有标准管理，应注意防止部署范围内的不一致。
The use of <transport> values "AAL1/<corporateName>", "AAL2/<corporateName>", "AAL5/<corporateName>", "AAL1/IEEE:<oui>", "AAL2/IEEE:<oui>" and "AAL5/IEEE:<oui>" is similar. These indicate non-standard transport mechanisms or AAL2 profiles which should be used consistently within the scope of an application or deployment. The parameter <corporateName> is the registered, globally unique name of a corporation (e.g., Cisco, Telcordia etc.). The parameter <oui> is the hex representation of a three-octet field identical to the OUI maintained by the IEEE. Since this is always represented in hex, the "0x" prefix shall not be used. Leading zeros can be omitted. For example, "IEEE:00000C" and "IEEE:C" both refer to Cisco Systems, Inc.
<transport>值“AAL1/<corporateName>”、“AAL2/<corporateName>”、“AAL5/<corporateName>”、“AAL1/IEEE:<oui>”、“AAL2/IEEE:<oui>”和“AAL5/IEEE:<oui>”的使用类似。这些表示应在应用程序或部署范围内一致使用的非标准传输机制或AAL2配置文件。参数<corporateName>是公司（如Cisco、Telcordia等）的注册的、全球唯一的名称。参数<oui>是三个八位组字段的十六进制表示，与IEEE维护的oui相同。由于这始终以十六进制表示，因此不应使用“0x”前缀。前导零可以省略。例如，“IEEE:00000C”和“IEEE:C”都指思科系统公司。
In the AAL1 and AAL5 contexts, the <format list> is a list of payload types:
在AAL1和AAL5上下文中，<格式列表>是有效负载类型的列表：
<payloadType#1> <payloadType#2>...<payloadType#n>
<payloadType#1> <payloadType#2>...<payloadType#n>
In most AAL1 and AAL5 applications, the ordering of payload types implies a preference (preferred payload types before less favored ones). The payload type can be statically assigned or dynamically mapped. Although the transport is not the same, SDP in the ATM context leverages the encoding names and payload types registered with IANA [31] for RTP. Encoding names not listed in [31] use a "X-" prefix. Encodings that are not statically mapped to payload types in [31] are to be dynamically mapped at the time of connection establishment to payload types in the decimal range 96-127. The SDP 'atmmap' attribute (similar to 'rtpmap') is used for this purpose.
在大多数AAL1和AAL5应用中，有效负载类型的排序意味着偏好（首选有效负载类型优先于不太受欢迎的类型）。有效负载类型可以静态分配或动态映射。虽然传输方式不同，但ATM上下文中的SDP为RTP利用了IANA[31]注册的编码名称和有效负载类型。[31]中未列出的编码名称使用“X-”前缀。[31]中未静态映射到有效负载类型的编码将在建立连接时动态映射到十进制范围96-127中的有效负载类型。SDP“atmmap”属性（类似于“rtpmap”）用于此目的。
In addition to listing the IANA-registered encoding names and payload types found in [31], Table 2 defines a few non-standard encoding names(with "X-" prefixes).
除了在[31]中列出IANA注册的编码名称和有效负载类型外，表2还定义了一些非标准编码名称（带有“X-”前缀）。
In the AAL2 context, the <format list> is a list of AAL2 profile types:
在AAL2上下文中，<format list>是AAL2配置文件类型的列表：
<profile#1> <profile#2>...<profile#n>
<profile#1> <profile#2>...<profile#n>
In most applications, the ordering of profiles implies a preference (preferred profiles before less favored ones). The <profile> parameter is expressed as a decimal number in the range 1-255.
在大多数应用中，配置文件的顺序意味着偏好（优先配置文件优先于不太受欢迎的配置文件）。<profile>参数表示为1-255范围内的十进制数。
Using the parameter definitions above, the 'm' for AAL1-based audio media can be constructed as follows:
使用上述参数定义，基于AAL1的音频媒体的“m”可以如下构造：
m=audio <virtualConnectionId> AAL1/ATMF <payloadType#1>
<payloadType#2>...<payloadType #n>
m=audio <virtualConnectionId> AAL1/ATMF <payloadType#1>
<payloadType#2>...<payloadType #n>
Note that only those payload types, whether statically mapped or dynamically assigned, that are consistent with af-vtoa-78 [7] can be used in this construction.
请注意，只有符合af-vtoa-78[7]的静态映射或动态分配的有效负载类型才能用于此构造。
Backwards compatibility note: The transport value "AAL1/AVP" used in previous versions of this document should be considered equivalent to the value "AAL1/ATMF" defined above. "AAL1/AVP" is unsuitable because the AVP profile is closely tied to RTP.
向后兼容性说明：本文件先前版本中使用的传输值“AAL1/AVP”应视为等同于上述定义的值“AAL1/ATMF”。“AAL1/AVP”不合适，因为AVP配置文件与RTP密切相关。
An example 'm' line use for audio media over AAL1 is:
AAL1上音频媒体的“m”线使用示例如下：
m=audio VCCI-27 AAL1/ATMF 0
m=音频VCCI-27 AAL1/ATMF 0
This indicates the use of an AAL1 VCC with VCCI=24 to carry PCMU audio that is encapsulated according to ATMF's af-vtoa-78 [7].
这表明使用VCCI=24的AAL1 VCC来携带根据ATMF的af-vtoa-78[7]封装的PCMU音频。
Another example of the use of the 'm' line use for audio media over AAL1 is:
AAL1上音频媒体使用“m”线的另一个例子是：
m=audio $ AAL1/ATMF 0 8
m=音频$AAL1/ATMF 0 8
This indicates that any AAL1 VCC may be used. If it exists already, then its selection is subject to glare rules. The audio media on this VCC is encapsulated according to ATMF's af-vtoa-78 [7]. The encodings to be used are either PCMU or PCMA, in preferential order.
这表明可以使用任何AAL1 VCC。如果它已经存在，则其选择受眩光规则的约束。此VCC上的音频媒体根据ATMF的af-vtoa-78[7]进行封装。要使用的编码是PCMU或PCMA，按优先顺序排列。
The 'm' for AAL5-based audio media can be constructed as follows:
基于AAL5的音频媒体的“m”可以按如下方式构造：
m=audio <virtualConnectionId> AAL5/ATMF <payloadType#1>
<payloadType#2>...<payloadType #n>
m=audio <virtualConnectionId> AAL5/ATMF <payloadType#1>
<payloadType#2>...<payloadType #n>
An example 'm' line use for audio media over AAL5 is:
AAL5上音频媒体的“m”线使用示例如下：
m=audio PORT-2/VPI-6/$ AAL5/ITU 9 15
m=audio PORT-2/VPI-6/$ AAL5/ITU 9 15
implies that any VCI on VPI= 6 of trunk port #2 may be used. The identities of the terms in the virtual connection ID are implicit in the application context. The audio media on this VCC is encapsulated according to ITU-T H.222.1 [51]. The encodings to be used are either ITU-T G.722 or ITU-T G.728 (LD-CELP), in preferential order.
表示可以使用中继端口#2的VPI=6上的任何VCI。虚拟连接ID中术语的标识在应用程序上下文中是隐式的。此VCC上的音频媒体根据ITU-T H.222.1[51]进行封装。要使用的编码是ITU-T G.722或ITU-T G.728（LD-CELP），按优先顺序排列。
The 'm' for AAL5-based H.323 Annex C audio [45] can be constructed as follows:
基于AAL5的H.323附录C音频[45]的“m”可以如下构造：
m=audio <virtualConnectionId> RTP/AVP <payloadType#1>
<payloadType#2>...<payloadType #n>
m=audio <virtualConnectionId> RTP/AVP <payloadType#1>
<payloadType#2>...<payloadType #n>
For example:
例如：
m=audio PORT-9/VPI-3/VCI-$ RTP/AVP 2 96
a=rtpmap:96 X-G727-32
a=aalType:AAL5
a=aalApp:itu_h323c - -
m=audio PORT-9/VPI-3/VCI-$ RTP/AVP 2 96
a=rtpmap:96 X-G727-32
a=aalType:AAL5
a=aalApp:itu_h323c - -
implies that any VCI on VPI= 3 of trunk port #9 may be used. This VC encapsulates RTP packets directly on AAL5 per [45]. The 'rtpmap' (rather than the 'atmmap') attribute is used to dynamically map the payload type of 96 into the codec name X-G727-32 (Table 2). This name represents 32 kbps EADPCM.
意味着可以使用中继端口#9的VPI=3上的任何VCI。此VC根据[45]将RTP数据包直接封装在AAL5上。“rtpmap”（而不是“atmmap”）属性用于将96的有效负载类型动态映射到编解码器名称X-G727-32（表2）。此名称表示32 kbps EADPCM。
The 'm' line for AAL5-based video media can be constructed as follows:
基于AAL5的视频媒体的“m”线可按如下方式构造：
m=video <virtualConnectionId> AAL5/ITU <payloadType#1>
<payloadType#2>...<payloadType #n>
m=video <virtualConnectionId> AAL5/ITU <payloadType#1>
<payloadType#2>...<payloadType #n>
In this case, the use of AAL5/ITU as the transport points to H.222.1 as the controlling standard [51]. An example 'm' line use for video media is:
在这种情况下，使用AAL5/ITU作为传输点，将H.222.1作为控制标准[51]。视频媒体使用的“m”行示例如下：
m=video PORT-9/VPI-3/VCI-$ AAL5/ITU 33
m=video PORT-9/VPI-3/VCI-$ AAL5/ITU 33
This indicates that any VCI on VPI= 3 of trunk port #9 may be used. The video media on this VCC is encapsulated according to ITU-T H.222.1 [51]. The encoding scheme is an MPEG 2 transport stream ("MP2T" in Table 1). This is statically mapped per [31] to a payload type of 33.
这表示可以使用中继端口#9的VPI=3上的任何VCI。此VCC上的视频媒体根据ITU-T H.222.1[51]进行封装。编码方案是MPEG 2传输流（表1中的“MP2T”）。根据[31]将其静态映射为有效负载类型33。
Using the parameter definitions in the previous subsections, the media information line for AAL2-based audio media can be constructed as follows:
使用前面小节中的参数定义，基于AAL2的音频媒体的媒体信息行可以按如下方式构造：
m=<media> <virtualConnectionId> <transport#1> <format list#1>
<transport#2> <format list#2> ... <transport#M> <format list#M>
m=<media> <virtualConnectionId> <transport#1> <format list#1>
<transport#2> <format list#2> ... <transport#M> <format list#M>
where <format list#i> has the form <profile#i_1>...<profile#i_N>
Unlike the 'm' line for AAL1 or AAL5 applications, the 'm' line for
AAL2 applications can have multiple <transport> parameters, each
followed by a <format list>. This is because it is possible to
where <format list#i> has the form <profile#i_1>...<profile#i_N>
Unlike the 'm' line for AAL1 or AAL5 applications, the 'm' line for
AAL2 applications can have multiple <transport> parameters, each
followed by a <format list>. This is because it is possible to
consider definitions from multiple sources (ATMF, ITU and non-standard documents) when selecting AAL2 profile to be bound to a connection.
在选择绑定到连接的AAL2配置文件时，考虑来自多个源（ATMF、ITU和非标准文档）的定义。
In most applications, the ordering of profiles implies a preference (preferred profiles before less favored ones). Therefore, there can be multiple instances of the same <transport> value in the same 'm' line.
在大多数应用中，配置文件的顺序意味着偏好（优先配置文件优先于不太受欢迎的配置文件）。因此，同一“m”行中可能存在相同<transport>值的多个实例。
An example 'm' line use for audio media over AAL2 is:
AAL2上音频媒体的“m”线使用示例如下：
m=audio VCCI-27/CID-19 AAL2/ITU 7 AAL2/custom 100 AAL2/ITU 1
m=audio VCCI-27/CID-19 AAL2/ITU 7 AAL2/custom 100 AAL2/ITU 1
This indicates the use of CID #19 on VCCI #27 to carry audio. It provides a preferential list of profiles for this connection: profile AAL2/ITU 7 defined in [13], AAL2/custom 100 defined in an application-specific or interoperability document and profile AAL2/ITU 1 defined in [13].
这表示使用VCCI#27上的CID#19来传输音频。它提供了此连接的首选配置文件列表：在[13]中定义的配置文件AAL2/ITU 7、在特定应用程序或互操作性文档中定义的AAL2/custom 100以及在[13]中定义的配置文件AAL2/ITU 1。
Another example of the use of the 'm' line use for audio media over AAL2 is:
AAL2上音频媒体使用“m”线的另一个例子是：
m=audio VCCI-$/CID-$ AAL2/ATMF 6 8
m=audio VCCI-$/CID-$ AAL2/ATMF 6 8
This indicates that any AAL2 CID may be used, subject to any applicable glare avoidance/reduction rules. The profiles that can be bound to this connection are AAL2/ATMF 6 defined in af-vtoa-0113.000 [44] and AAL2/ATMF 8 defined in af-vmoa-0145.000 [52]. These sources use non-overlapping profile number ranges. The profiles they define fall under the <transport> category "AAL2/ATMF". This application does not order profiles preferentially. This rule is known a priori. It is not embedded in the 'm' line.
这表明根据任何适用的眩光避免/减少规则，可以使用任何AAL2 CID。可绑定到此连接的配置文件是af-vtoa-0113.000[44]中定义的AAL2/ATMF 6和af-vmoa-0145.000[52]中定义的AAL2/ATMF 8。这些源使用非重叠的配置文件编号范围。他们定义的配置文件属于<transport>类别“AAL2/ATMF”。此应用程序不优先订购配置文件。这个规则是先验的。它不嵌入“m”行中。
Another example of the use of the 'm' line use for audio media over AAL2 is:
AAL2上音频媒体使用“m”线的另一个例子是：
m=audio VCCI-20/CID-$ AAL2/xyzCorporation 11
m=audio VCCI-20/CID-$ AAL2/xyzCorporation 11
AAL2 VCCs in this application are single-CID VCCs. Therefore, it is possible to wildcard the CID. The single-CID VCC with VCCI=20 is selected. The AAL2 profile to be used is AAL2/xyzCorporation 11 defined by xyzCorporation.
本应用中的AAL2 VCC为单CID VCC。因此，可以通配符CID。选择VCCI=20的单个CID VCC。要使用的AAL2配置文件是由XYZ公司定义的AAL2/XYZ公司11。
In some applications, an "-" can be used in lieu of:
在某些应用中，可以使用“-”来代替：
- <format list>
- <transport> and <format list>
- <format list>
- <transport> and <format list>
This implies that these parameters are irrelevant or are known by other means (such as defaults). For example:
这意味着这些参数是无关的，或者通过其他方式（例如默认值）已知。例如：
m=audio VCCI-234 - -
a=aalType:AAL1
m=audio VCCI-234 - -
a=aalType:AAL1
indicates the use of VCCI=234 with AAL1 adaptation and unspecified encoding.
表示VCCI=234与AAL1自适应和未指定编码一起使用。
In another example application, the 'aal2sscs3662' attribute can indicate <faxDemod> = "on" and any other competing options as "off", and the <aalType> attribute can indicate AAL2. Thus:
在另一个示例应用中，“aal2sscs3662”属性可以指示<faxmdem>=“开”，任何其他竞争选项可以指示“关”，而<aalType>属性可以指示AAL2。因此：
m=audio VCCI-123/CID-5 - -
a=aalType:AAL2
a=aal2sscs3662:audio off off on off on off off off - - -
m=audio VCCI-123/CID-5 - -
a=aalType:AAL2
a=aal2sscs3662:audio off off on off on off off off - - -
Besides indicating an audio medium, a VCCI of 123 and a CID of 5, the 'm' line indicates an unspecified profile. The media attribute lines indicate an adaptation layer of AAL2, and the use of the audio SAP [13] to carry demodulated facsimile.
除了表示音频媒体、VCCI为123和CID为5外，“m”行还表示未指定的配置文件。媒体属性行指示AAL2的适配层，以及使用音频SAP[13]来携带解调的传真。
The media information line for "data" media has one of the following the following formats:
“数据”介质的介质信息行具有以下格式之一：
m=data <virtualConnectionId> - -
m=data - - -
m=data <virtualConnectionId> - -
m=data - - -
The data could be circuit emulation data carried over AAL1 or AAL2, or packet data carried over AAL5. Media attribute lines, rather than the 'm' line, are used to indicate the adaptation type for the data media. Examples of the representation of data media are listed below.
数据可以是通过AAL1或AAL2承载的电路仿真数据，或者通过AAL5承载的分组数据。媒体属性行（而不是“m”行）用于指示数据媒体的适配类型。下面列出了数据媒体表示的示例。
m=data PORT-7/VPI-6/VCI-$ - -
a=aalApp:AAL5_SSCOP- -
m=data PORT-7/VPI-6/VCI-$ - -
a=aalApp:AAL5_SSCOP- -
implies that any VCI on VPI= 6 of trunk port #7 may be used. This VC uses SSCOP on AAL5 to transport data.
意味着可以使用中继端口#7的VPI=6上的任何VCI。此VC使用AAL5上的SSCOP传输数据。
m=data PORT-7/VPI-6/VCI-50 - -
a=aalType:AAL1_SDT
a=sbc:6
m=data PORT-7/VPI-6/VCI-50 - -
a=aalType:AAL1_SDT
a=sbc:6
implies that VCI 50 on VPI 6 on port 7 uses structured AAL1 to transfer 6 x 64 kbps circuit emulation data. This may be alternately represented as:
意味着端口7上VPI 6上的VCI 50使用结构化AAL1传输6 x 64 kbps电路仿真数据。这可以交替地表示为：
m=data PORT-7/VPI-6/VCI-50 - -
b=AS:384
a=aalType:AAL1_SDT
m=data PORT-7/VPI-6/VCI-50 - -
b=AS:384
a=aalType:AAL1_SDT
The following lines:
以下几行：
m=data VCCI-123/CID-5 - -
a=aalType:AAL2
a=sbc:2
m=data VCCI-123/CID-5 - -
a=aalType:AAL2
a=sbc:2
imply that CID 5 of VCCI 123 is used to transfer 2 x 64 kbps circuit emulation data.
表示VCCI 123的CID 5用于传输2 x 64 kbps电路仿真数据。
In the AAL1 context, it is also permissible to represent circuit mode data as an "audio" codec. If this is done, the codec types used are X-CCD or X-CCD-CAS. These encoding names are dynamically mapped into payload types through the 'atmmap' attribute. For example:
在AAL1上下文中，还允许将电路模式数据表示为“音频”编解码器。如果这样做，则使用的编解码器类型为X-CCD或X-CCD-CAS。这些编码名称通过“atmmap”属性动态映射到有效负载类型。例如：
m=audio VCCI-27 AAL1/AVP 98
a=atmmap:98 X-CCD
a=sbc:6
m=audio VCCI-27 AAL1/AVP 98
a=atmmap:98 X-CCD
a=sbc:6
implies that AAL1 VCCI=27 is used for 6 x 64 transmission.
表示AAL1 VCCI=27用于6 x 64传输。
In the AAL2 context, the X-CCD codec can be assigned a profile type and number. Even though it is not possible to construct a profile table as described in ITU I.366.2 for this "codec", it is preferable to adopt the common AAL2 profile convention in its case. An example AAL2 profile mapping for the X-CCD codec could be as follows:
在AAL2上下文中，可以为X-CCD编解码器分配配置文件类型和编号。尽管无法为该“编解码器”构建ITU I.366.2中所述的配置文件表，但最好在其情况下采用通用AAL2配置文件约定。X-CCD编解码器的AAL2配置文件映射示例如下：
PROFILE TYPE PROFILE NUMBER "CODEC" (ONLY ONE) "custom" 200 X-CCD
配置文件类型配置文件编号“编解码器”（仅一个）“自定义”200 X-CCD
The profile does not identify the number of subchannels ('n' in nx64). This is known by other means such as the 'sbc' media attribute line.
配置文件未标识子通道的数量（nx64中为“n”）。这是通过其他方式知道的，例如“sbc”媒体属性行。
For example, the media information line:
例如，媒体信息行：
m=audio $ AAL2/custom 200
a=sbc:6
m=audio $ AAL2/custom 200
a=sbc:6
implies 384 kbps circuit emulation using AAL2 adaptation.
意味着使用AAL2自适应进行384 kbps电路仿真。
It is not necessary to define a profile with the X-CCD-CAS codec, since this method of CAS transport [7] is not used in AAL2 applications.
无需使用X-CCD-CAS编解码器定义配置文件，因为这种CAS传输方法[7]不用于AAL2应用程序。
In an SDP line sequence, the media information line 'm' is followed by one or more media attribute or 'a' lines. Media attribute lines are per the format below:
在SDP行序列中，媒体信息行“m”后面跟着一个或多个媒体属性或“a”行。媒体属性行的格式如下：
a=<attribute>:<value>
a=<attribute>:<value>
or
或
a=<value>
a=<value>
In general, media attribute lines are optional except when needed to qualify the media information line. This qualification is necessary when the "m" line for an AAL1 or AAL5 session specifies a payload type that needs to be dynamically mapped. The 'atmmap' media attribute line defined below is used for this purpose.
通常，介质属性行是可选的，除非需要限定介质信息行。当AAL1或AAL5会话的“m”行指定需要动态映射的有效负载类型时，此限定是必要的。下面定义的“atmmap”媒体属性行用于此目的。
In attribute lines, subparameters that are meant to be left unspecified are set to a "-". These are generally inapplicable or, if applicable, are known by other means such as provisioning. In some cases, a media attribute line with all parameters set to "-" carries no information and should be preferably omitted. In other cases, such as the 'lij' media attribute line, the very presence of the media attribute line conveys meaning.
在属性行中，未指定的子参数设置为“-”。这些通常不适用，或者，如果适用，通过其他方式（如供应）已知。在某些情况下，所有参数都设置为“-”的媒体属性行不携带任何信息，最好省略。在其他情况下，例如“lij”媒体属性行，媒体属性行的存在本身就传达了意义。
There are no restrictions placed by RFC 2327 [1] regarding the order of 'a' lines with respect to other 'a' lines. However, these lines must not contradict each other or the other SDP lines. Inconsistencies are not to be ignored and should be flagged as errors. Repeated media attribute lines can carry additional information. These should not be inconsistent with each other.
RFC 2327[1]对“a”行相对于其他“a”行的顺序没有任何限制。但是，这些线不得相互矛盾或与其他SDP线冲突。不一致性不可忽略，应标记为错误。重复的媒体属性行可以携带附加信息。这些不应相互矛盾。
Applications will selectively use the optional media attribute lines listed below. This is meant to be an exhaustive list for describing the general attributes of ATM bearer networks.
应用程序将有选择地使用下面列出的可选媒体属性行。这是一个详尽的列表，用于描述ATM承载网络的一般属性。
The base specification for SDP, RFC 2327 [1], allows the definition f new attributes. In keeping with this spirit, some of the attributes defined in this document can also be used in SDP descriptions of IP nd other non-ATM sessions. For example, the 'vsel', 'dsel' and 'fsel' attributes defined below refer generically to codec-s. These can be bed for service-specific codec negotiation and assignment in non-ATM s well as ATM applications.
SDP的基本规范RFC 2327[1]允许定义新属性。本着这种精神，本文中定义的一些属性也可用于IP和其他非ATM会话的SDP描述中。例如，下面定义的“vsel”、“dsel”和“fsel”属性通常指编解码器。在非ATM s以及ATM应用中，这些可作为特定于服务的编解码器协商和分配的基础。
SDP media attributes defined in this document for use in the ATM context are classified as:
本文档中定义的用于ATM上下文的SDP媒体属性分类如下：
* ATM bearer connection attributes (Section 5.6.1) * AAL attributes (Section 5.6.2) * Service attributes (Section 5.6.3). * Miscellaneous media attributes, that cannot be classified as ATM, AAL or service attributes (Section 5.6.4).
* ATM承载连接属性（第5.6.1节）*AAL属性（第5.6.2节）*服务属性（第5.6.3节）。*杂项媒体属性，不能归类为ATM、AAL或服务属性（第5.6.4节）。
In addition to these, the SDP attributes defined in [1] can also be used in the ATM context. Examples are:
除此之外，[1]中定义的SDP属性也可用于ATM上下文。例如：
* The attributes defined in RFC 2327 which allow indication of the direction in which a session is active. These are a=sendonly, a=recvonly, a=sendrecv, a=inactive.
* RFC 2327中定义的属性，允许指示会话活动的方向。它们是a=sendonly、a=RecVoOnly、a=sendrecv、a=inactive。
* The 'Ptime' attribute defined in RFC 2327. It indicates the packet period. It is not recommended that this attribute be used in ATM applications since packet period information is provided with other parameters (e.g., the profile type and number in the 'm' line, and the 'vsel', 'dsel' and 'fsel' attributes). Also, for AAL1 applications, 'ptime' is not applicable and should be flagged as an error. If used in AAL2 and AAL5 applications, 'ptime' should be consistent with the rest of the SDP description.
* RFC 2327中定义的“Ptime”属性。它表示数据包周期。不建议在ATM应用程序中使用此属性，因为包周期信息与其他参数一起提供（例如，“m”行中的配置文件类型和编号，以及“vsel”、“dsel”和“fsel”属性）。此外，对于AAL1应用程序，“ptime”不适用，应标记为错误。如果在AAL2和AAL5应用程序中使用，“ptime”应与SDP说明的其余部分一致。
* The 'fmtp' attribute used to designate format-specific parameters.
* “fmtp”属性用于指定特定于格式的参数。
The following is a summary list of the SDP media attributes that can be used to describe ATM bearer connections. These are detailed in subsequent subsections.
以下是可用于描述ATM承载连接的SDP媒体属性的摘要列表。这些将在后面的小节中详细说明。
* The 'eecid' attribute. This stands for 'end-to-end connection identifier'. It provides a means of correlating service-level connections with underlying ATM bearer connections. In the Q.1901 [36] context, the eecid is synonymous with the bnc-id (backbone network connection identifier).
* “eecid”属性。这表示“端到端连接标识符”。它提供了一种将服务级别连接与底层ATM承载连接关联起来的方法。在Q.1901[36]中，eecid与bnc id（主干网络连接标识符）同义。
* The 'aalType' attribute. This is used to indicate the nature of the ATM adaptation layer (AAL).
* “aalType”属性。这用于指示ATM适配层（AAL）的性质。
* The 'capability' attribute, which indicates the ATM transfer capability (ITU nomenclature), synonymous with the ATM Service Category (ATMF nomenclature).
* “能力”属性，表示ATM传输能力（ITU术语），与ATM服务类别（ATMF术语）同义。
* The 'qosClass' attribute, which indicates the QoS class of the ATM bearer connection.
* “qosClass”属性，指示ATM承载连接的QoS级别。
* The 'bcob' attribute, which indicates the broadband connection oriented bearer class, and whether end-to-end timing is required.
* “bcob”属性，指示面向宽带连接的承载类，以及是否需要端到端定时。
* The 'stc' attribute, which indicates susceptibility to clipping.
* “stc”属性，表示剪切的敏感性。
* The 'upcc' attribute, which indicates the user plane connection configuration.
* “upcc”属性，指示用户平面连接配置。
* The 'atmQOSparms' attribute, which is used to describe certain key ATM QoS parameters.
* “atmQOSparms”属性，用于描述某些关键ATM QoS参数。
* The 'atmTrfcDesc' attribute, which is used to describe ATM traffic descriptor parameters.
* “atmTrfcDesc”属性，用于描述ATM流量描述符参数。
* The 'abrParms' attribute, which is used to describe ABR-specific parameters. These parameters are per the UNI 4.0 signaling specification [5].
* “abrParms”属性，用于描述ABR特定参数。这些参数符合UNI 4.0信令规范[5]。
* The 'abrSetup' attribute, which is used to indicate the ABR parameters needed during call/connection establishment.
* “abrSetup”属性，用于指示呼叫/连接建立期间所需的ABR参数。
* The 'bearerType' attribute, which is used to indicate whether the underlying bearer is an ATM PVC/SPVC, an ATM SVC, or a subchannel within an existing ATM SVC/PVC/SPVC.
* “bearerType”属性，用于指示基础承载是ATM PVC/SPVC、ATM SVC还是现有ATM SVC/PVC/SPVC中的子信道。
* The 'lij' attribute, which is used to indicate the presence of a connection that uses the Leaf-initiated-join capability described in UNI 4.0 [5], and to optionally describe parameters associated with this capability.
* “lij”属性，用于指示存在使用UNI 4.0[5]中描述的叶启动连接功能的连接，并可选地描述与此功能相关的参数。
* The 'anycast' attribute, which is used to indicate the applicability of the anycast function described in UNI 4.0 [5], and to optionally qualify it with certain parameters.
* “选播”属性，用于指示UNI 4.0[5]中描述的选播函数的适用性，并可选择使用某些参数对其进行限定。
* The 'cache' attribute, which is used to enable SVC caching and to specify an inactivity timer for SVC release.
* “cache”属性，用于启用SVC缓存并为SVC释放指定非活动计时器。
* The 'bearerSigIE' attribute, which can be used to represent ITU Q-series information elements in bit-map form. This is useful in describing parameters that are not closely coupled to the ATM and AAL layers. Examples are the B-HLI and B-LLI IEs specified in ITU Q.2931 [15], and the user-to-user information element described in ITU Q.2957 [48].
* “BearSigie”属性，可用于以位图形式表示ITU Q系列信息元素。这在描述与ATM和AAL层不紧密耦合的参数时非常有用。例如，ITU Q.2931[15]中规定的B-HLI和B-LLI IEs，以及ITU Q.2957[48]中描述的用户对用户信息元素。
The 'eecid' attribute is synonymous with the 4-byte 'bnc-id' parameter used by T1SI, the ATM forum and the ITU (Q.1901) standardization effort. The term 'eecid' stands for 'end-to-end connection identifier', while 'bnc-id' stands for 'backbone network connection identifier'. The name "backbone" is slightly misleading since it refers to the entire ATM network including the ATM edge and ATM core networks. In Q.1901 terminology, an ATM "backbone" connects TDM or analog edges.
“eecid”属性与T1SI、ATM论坛和ITU（Q.1901）标准化工作使用的4字节“bnc id”参数同义。术语“eecid”表示“端到端连接标识符”，而“bnc id”表示“骨干网络连接标识符”。“主干网”这个名称有点误导，因为它指的是整个ATM网络，包括ATM边缘网和ATM核心网。在Q.1901术语中，ATM“主干网”连接TDM或模拟边缘。
While the term 'bnc-id' might be used in the bearer signaling plane and in an ISUP (Q.1901) call control plane, SDP session descriptors use the neutral term 'eecid'. This provides a common SDP baseline for applications that use ISUP (Q.1901) and applications that use SIP/SIP+.
虽然术语“bnc id”可在承载信令平面和ISUP（Q.1901）呼叫控制平面中使用，但SDP会话描述符使用中性术语“eecid”。这为使用ISUP（Q.1901）的应用程序和使用SIP/SIP+的应用程序提供了公共SDP基线。
Section 5.6.6 depicts the use of the eecid in call establishment procedures. In these procedures, the eecid is used to correlate service-level calls with SVC set-up requests.
第5.6.6节描述了eecid在呼叫建立程序中的使用。在这些过程中，eecid用于将服务级别调用与SVC设置请求关联起来。
In the forward SVC establishment model, the call-terminating gateway selects an eecid and transmits it via SDP to the call-originating gateway. The call originating gateway transmits this eecid to the call terminating gateway via the bearer set-up message (SVC set-up or Q.2630.1 establish request).
在前向SVC建立模型中，呼叫终止网关选择eecid，并通过SDP将其传输到呼叫发起网关。呼叫发起网关通过承载设置消息（SVC设置或Q.2630.1建立请求）将该eecid传输至呼叫终止网关。
In the backward SVC establishment model, the call-originating gateway selects an eecid and transmits it via SDP to the call-terminating gateway. The call terminating gateway transmits this eecid to the call originating gateway via the bearer set-up message (SVC set-up or Q.2630.1 establish request).
在反向SVC建立模型中，呼叫发起网关选择eecid，并通过SDP将其传输到呼叫终止网关。呼叫终止网关通过承载设置消息（SVC设置或Q.2630.1建立请求）将该eecid传输至呼叫发起网关。
The value of the eecid attribute values needs to be unique within the node terminating the SVC set-up but not across multiple nodes. Hence, the SVC-terminating gateway has complete control over using and releasing values of this parameter. The eecid attribute is used to correlate, one-to-one, received bearer set-up requests with service-level call control signaling.
eecid属性值的值在终止SVC设置的节点内必须是唯一的，但不能跨多个节点。因此，SVC终端网关可以完全控制此参数值的使用和释放。eecid属性用于将接收到的承载设置请求与服务级别呼叫控制信令一一关联。
Within an SDP session description, the eecid attribute is used as follows:
在SDP会话描述中，eecid属性使用如下：
a=eecid:<eecid>
a=eecid:<eecid>
where <eecid> consists of up to 8 hex digits (equivalent to 4 octets). Since this is always represented in hex, the "0x" prefix shall not be used.
其中，<eecid>最多由8个十六进制数字组成（相当于4个八位字节）。由于这始终以十六进制表示，因此不应使用“0x”前缀。
Within the text representation of the <eecid> parameter, hex digits to the left are more significant than hex digits to the right (Section 2.2).
在<eecid>参数的文本表示中，左侧的十六进制数字比右侧的十六进制数字更重要（第2.2节）。
This SDP document does not specify how the eecid (synonymous with bnc-id) is to be communicated through bearer signaling (Q.931, UNI, PNNI, AINI, IISP, proprietary signaling equivalent, Q.2630.1). This is a task of these bearer signaling protocols. However, the following informative statements are made to convey a sense of the interoperability that is a goal of current standardization efforts:
本SDP文件未规定eecid（与bnc id同义）如何通过承载信令（Q.931、UNI、PNNI、AINI、IISP、专有信令等效物，Q.2630.1）进行通信。这是这些承载信令协议的任务。但是，以下信息性陈述旨在传达互操作性的含义，这是当前标准化工作的目标：
- ITU Q.2941.3 and the ATMF each recommend the use of the GIT IE for carrying the eecid (synonymous with bnc-id) in the set-up message of ATM signaling protocols (Q.2931, UNI 4.0, PNNI, AINI, IISP). The coding for carrying the eecid (bnc-id) in the GIT IE is defined in ITU Q.2941.3 and accepted by the ATM forum.
- ITU Q.2941.3和ATMF均建议在ATM信令协议（Q.2931、UNI 4.0、PNNI、AINI、IISP）的设置消息中使用GIT IE来承载eecid（与bnc id同义）。在GIT IE中携带eecid（bnc id）的编码在ITU Q.2941.3中定义，并被ATM论坛接受。
- Another alternate method is to use the called party subaddress IE. In some networks, this might be considered a protocol violation and is not the recommended means of carrying the eecid (bnc-id). The GIT IE is the preferred method of transporting the eecid (bnc-id) in ATM signaling messages.
- 另一种替代方法是使用被叫方子地址IE。在某些网络中，这可能被视为违反协议，并且不是建议的携带eecid（bnc id）的方法。GIT IE是在ATM信令消息中传输eecid（bnc id）的首选方法。
- The establish request (ERQ) message of the Q.2630.1 [37] signaling protocol can use the SUGR (Served User Generated Reference) IE to transport the eecid (bnc-id).
- Q.2630.1[37]信令协议的建立请求（ERQ）消息可以使用SUGR（服务用户生成参考）IE传输eecid（bnc id）。
The node assigning the eecid can release and re-use it when it receives a Q.2931 [15] set-up message or a Q.2630.1 [37] establish request message containing the eecid.
分配eecid的节点可以在收到包含eecid的Q.2931[15]设置消息或Q.2630.1[37]建立请求消息时释放并重新使用eecid。
However, in both cases (backward and forward models), it is recommended that this eecid be retained until the connection terminates. Since the eecid space is large enough, it is not necessary to release it as soon as possible.
但是，在这两种情况下（向后和向前模式），建议保留此eecid，直到连接终止。由于eecid空间足够大，因此无需尽快释放它。
When present, the 'aalType' attribute is used to indicate the ATM adaptation layer. If this information is redundant with the 'm' line, it can be omitted. The format of the 'aalType' media attribute line is as follows:
存在时，“aalType”属性用于指示ATM适配层。如果此信息与“m”行冗余，则可以省略。“aalType”媒体属性行的格式如下：
a=aalType: <aalType>
a=aalType: <aalType>
Here, <aalType> can take on the following string values: "AAL1", "AAL1_SDT", "AAL1_UDT", "AAL2", "AAL3/4", "AAL5" and "USER_DEFINED_AAL". Note that "AAL3/4" and "USER DEFINED AAL" are not addressed in this document.
这里，<aalType>可以采用以下字符串值：“AAL1”、“AAL1\u SDT”、“AAL1\u UDT”、“AAL2”、“AAL3/4”、“AAL5”和“用户定义的\u AAL”。请注意，“AAL3/4”和“用户定义的AAL”在本文件中未提及。
When present, the 'capability' attribute indicates the ATM Transfer Capability described in ITU I.371 [28], equivalent to the ATM Service Category described in the UNI 4.1 Traffic Management specification [6].
当存在时，“能力”属性表示ITU I.371[28]中描述的ATM传输能力，相当于UNI 4.1流量管理规范[6]中描述的ATM服务类别。
The 'capability' media attribute line is structured in one of the following ways:
“能力”媒体属性行的结构如下所示：
a=capability:<asc> <subtype>
a=capability:<asc> <subtype>
a=capability:<atc> <subtype>
a=capability:<atc> <subtype>
Possible values of the <asc> are enumerated below:
<asc>的可能值列举如下：
"CBR", "nrt-VBR", "rt-VBR", "UBR", "ABR", "GFR"
“CBR”、“nrt VBR”、“rt VBR”、“UBR”、“ABR”、“GFR”
Possible values of the <atc> are enumerated below:
<atc>的可能值列举如下：
"DBR","SBR","ABT/IT","ABT/DT","ABR"
“DBR”、“SBR”、“ABT/IT”、“ABT/DT”、“ABR”
Some applications might use non-standard <atc> and <asc> values not listed above. Equipment designers will need to agree on the meaning and implications of non-standard transfer capabilities / service capabilities.
某些应用程序可能使用上面未列出的非标准<atc>和<asc>值。设备设计师需要就非标准传输能力/服务能力的含义和影响达成一致。
The <subtype> field essentially serves as a subscript to the <asc> and <atc> fields. In general, it can take on any integer value, or the "-" value indicating that it does not apply or that the underlying data is to be known by other means, such as provisioning.
<subtype>字段基本上用作<asc>和<atc>字段的下标。一般来说，它可以采用任何整数值，或“-”值，表示它不适用，或通过其他方式（如资源调配）知道基础数据。
For an <asc> value of CBR and an <atc> value of DBR, the <subtype> field can be assigned values from Table 4-6 of ITU Q.2931 [15]. These are:
对于CBR的<asc>值和DBR的<atc>值，<subtype>字段可以从ITU Q.2931的表4-6中分配值[15]。这些是：
<asc>/<atc> <subtype> Meaning
<asc>/<atc> <subtype> Meaning
"CBR"/"DBR" 1 Voiceband signal transport (ITU G.711, G.722, I.363) "CBR"/"DBR" 2 Circuit transport (ITU I.363) "CBR"/"DBR" 4 High-quality audio signal transport (ITU I.363) "CBR"/"DBR" 5 Video signal transport (ITU I.363)
“CBR”/“DBR”1语音带信号传输（ITU G.711、G.722、I.363）“CBR”/“DBR”2电路传输（ITU I.363）“CBR”/“DBR”4高质量音频信号传输（ITU I.363）“CBR”/“DBR”5视频信号传输（ITU I.363）
Note that [15] does not define a <subtype> value of 3.
请注意，[15]没有定义<subtype>值3。
For other values of the <asc> and <atc> parameters, the following values can be assigned to the <subtype> field, based on [6] and [28].
对于<asc>和<atc>参数的其他值，可以根据[6]和[28]将以下值分配给<subtype>字段。
<asc>/<atc> <subtype> Meaning
<asc>/<atc> <subtype> Meaning
nrt-VBR 1 nrt-VBR.1 nrt-VBR 2 nrt-VBR.2 nrt-VBR 3 nrt-VBR.3 rt-VBR 1 rt-VBR.1 rt-VBR 2 rt-VBR.2 rt-VBR 3 rt-VBR.3 UBR 1 UBR.1 UBR 2 UBR.2 GFR 1 GFR.1 GFR 2 GRR.2 SBR 1 SBR1 SBR 2 SBR2 SBR 3 SBR3
nrt VBR 1 nrt VBR.1 nrt VBR 2 nrt VBR.2 nrt VBR 3 nrt VBR.3 rt VBR 1 rt VBR.1 rt VBR.2 rt VBR.3 UBR 1 UBR.1 UBR 2 UBR.2 GFR 1 GFR.1 GFR 2 GRR.2 SBR 1 SBR 1 SBR 2 SBR 3 SBR
It is beyond the scope of this specification to examine the equivalence of some of the ATMF and ITU definitions. These need to be recognized from the ATMF and ITU source specifications and exploited, as much as possible, to simplify ATM node design.
检查某些ATMF和ITU定义的等效性超出了本规范的范围。这些需要从ATMF和ITU源规范中识别，并尽可能地加以利用，以简化ATM节点设计。
When the bearer connection is a single AAL2 CID connection within a multiplexed AAL2 VC, the 'capability' attribute does not apply.
当承载连接是多路复用AAL2 VC中的单个AAL2 CID连接时，“能力”属性不适用。
When present, the 'qosClass' attribute indicates the QoS class specified in ITU I.2965.1 [34].
当存在时，“qosClass”属性表示ITU I.2965.1[34]中指定的QoS等级。
The 'qosClass' media attribute line is structured as follows:
“qosClass”媒体属性行的结构如下：
a=qosClass:<qosClass>
a=qosClass:<qosClass>
Here, <qosClass> is an integer in the range 0 - 5.
这里，<qosClass>是一个范围为0-5的整数。
<qosClass> Meaning
<qosClass>意义
0 Default QoS 1 Stringent 2 Tolerant 3 Bi-level 4 Unbounded 5 Stringent bi-level
0默认QoS 1严格2容忍3 Bi级别4无界5严格Bi级别
When present, the 'bcob' attribute represents the broadband connection oriented bearer class defined in [5], [15] and [33]. It can also be used to indicate whether end-to-end timing is required.
存在时，“bcob”属性表示[5]、[15]和[33]中定义的面向宽带连接的承载类。它还可用于指示是否需要端到端定时。
The 'bcob' media attribute line is structured as follows:
“bcob”媒体属性行的结构如下：
a=bcob:<bcob> <eetim>
a=bcob:<bcob> <eetim>
Here, <bcob> is the decimal or hex representation of a 5-bit field. The following values are currently defined:
这里，<bcob>是5位字段的十进制或十六进制表示形式。当前定义了以下值：
<bcob> Meaning
<bcob>意义
0x01 BCOB-A 0x03 BCOB-C 0x05 Frame relaying bearer service 0x10 BCOB-X 0x18 BCOB-VP (transparent VP service)
0x01 BCOB-A 0x03 BCOB-C 0x05帧中继承载业务0x10 BCOB-X 0x18 BCOB-VP（透明VP业务）
The <eetim> parameter can be assigned a value of "on" or "off" depending on whether end-to-end timing is required or not (Table 4-8 of [15]).
根据是否需要端到端定时，<eetim>参数可以指定一个“开”或“关”的值（见[15]表4-8]）。
Either of these parameters can be left unspecified by setting it to a "-". A 'bcob' media attribute line with all parameters set to "-" carries no information and should be omitted.
将这些参数中的任何一个设置为“-”都可以不指定。所有参数均设置为“-”的“bcob”媒体属性行不包含任何信息，应省略。
When present, the 'stc' attribute represents susceptibility to clipping. The 'stc' media attribute line is structured as follows:
当存在时，“stc”属性表示剪切的易感性。“stc”媒体属性行的结构如下：
a=stc:<stc>
a=stc:<stc>
Here, <stc> is the decimal equivalent of a 2-bit field. Currently, all values are unused and reserved with the following exceptions:
这里，<stc>是2位字段的十进制等价物。目前，所有值均未使用并保留，但以下情况除外：
<stc> value Binary Equivalent Meaning
<stc>值二进制等价意义
0 00 Not susceptible to clipping 1 01 Susceptible to clipping
0 00不受剪裁影响1 01受剪裁影响
When present, the 'upcc' attribute represents the user plane connection configuration. The 'upcc' media attribute line is structured as follows:
存在时，“upcc”属性表示用户平面连接配置。“upcc”媒体属性行的结构如下所示：
a=upcc:<upcc>
a=upcc:<upcc>
Here, <upcc> is the decimal equivalent of a 2-bit field. Currently, all values are unused and reserved with the following exceptions:
这里，<upcc>是2位字段的十进制等价物。目前，所有值均未使用并保留，但以下情况除外：
<upcc> value Binary Equivalent Meaning
<upcc>值二进制等价含义
0 00 Point to point 1 01 Point to multipoint
0 00点对点1 01点对多点
When present, the 'atmQOSparms' attribute is used to describe certain key ATM QoS parameters.
存在时，“atmQOSparms”属性用于描述某些关键ATM QoS参数。
The 'atmQOSparms' media attribute line is structured as follows:
“atmQOSparms”媒体属性行的结构如下：
a=atmQOSparms:<directionFlag><cdvType><acdv><ccdv><eetd><cmtd><aclr>
a=atmQOSparms:<directionFlag><cdvType><acdv><ccdv><eetd><cmtd><aclr>
The <directionFlag> can be assigned the following string values: "f", "b" and "fb". "f" and "b" indicate the forward and backward directions respectively. "fb" refers to both directions (forward and backward). Conventions for the forward and backward directions are per section 2.3.
<directionFlag>可以指定以下字符串值：“f”、“b”和“fb”。“f”和“b”分别表示向前和向后方向。“fb”指两个方向（向前和向后）。前进方向和后退方向的约定见第2.3节。
The <cdvType> parameter can take on the string values of "PP" and "2P". These refer to the peak-to-peak and two-point CDV as defined in UNI 4.0 [5] and ITU Q.2965.2 [35] respectively.
<cdvType>参数可以采用字符串值“PP”和“2P”。这些分别指UNI 4.0[5]和ITU Q.2965.2[35]中定义的峰间和两点CDV。
The CDV parameters, <acdv> and <ccdv>, refer to the acceptable and cumulative CDVs respectively. These are expressed in units of microseconds and represented as the decimal equivalent of a 24-bit field. These use the cell loss ratio, <aclr>, as the "alpha" quantiles defined in the ATMF TM 4.1 specification [6] and in ITU I.356 [47].
CDV参数<acdv>和<ccdv>分别指可接受和累积CDV。它们以微秒为单位表示，并表示为24位字段的十进制等效值。它们使用小区丢失率<aclr>作为ATMF TM 4.1规范[6]和ITU I.356[47]中定义的“α”分位数。
The transit delay parameters, <eetd> and <cmtd>, refer to the end-to-end and cumulative transit delays respectively in milliseconds. These are represented as the decimal equivalents of 16-bit fields. These parameters are defined in Q.2965.2 [35], UNI 4.0 [5] and Q.2931 [15].
传输延迟参数<eetd>和<cmtd>分别指以毫秒为单位的端到端传输延迟和累积传输延迟。这些字段表示为16位字段的十进制等效值。这些参数在Q.2965.2[35]、UNI 4.0[5]和Q.2931[15]中定义。
The <aclr> parameter refers to forward and backward acceptable cell loss ratios. This is the ratio between the number of cells lost and the number of cells transmitted. It is expressed as the decimal equivalent of an 8-bit field. This field expresses an order of magnitude n, where n is an integer in the range 1-15. The Cell Loss Ratio takes on the value 10 raised to the power of minus n.
<aclr>参数指向前和向后可接受的信元丢失率。这是丢失的小区数与传输的小区数之间的比率。它表示为8位字段的十进制等效值。该字段表示一个数量级n，其中n是范围为1-15的整数。电池损耗率的值为10，增加到负n的幂次方。
The <directionFlag> is always specified. Except for the <directionFlag>, the remaining parameters can be set to "-" to indicate that they are not specified, inapplicable or implied. However, there must be some specified parameters for the line to be useful in an SDP description.
始终指定<directionFlag>。除了<directionFlag>，其余参数可以设置为“-”，以表示未指定、不适用或隐含这些参数。但是，必须有一些指定的参数才能使该行在SDP描述中有用。
There can be several 'atmQOSparms' lines in an SDP description.
SDP描述中可能有多行“atmQOSparms”。
An example use of these attributes for an rt-VBR, single-CID AAL2 voice VC is:
rt VBR、单CID AAL2语音VC使用这些属性的示例如下：
a=atmQOSparms:f PP 8125 3455 32000 - 11
a=atmQOSparms:b PP 4675 2155 18000 - 12
a=atmQOSparms:f PP 8125 3455 32000 - 11
a=atmQOSparms:b PP 4675 2155 18000 - 12
This implies a forward acceptable peak-to-peak CDV of 8.125 ms, a backward acceptable peak-to-peak CDV of 4.675 ms, forward cumulative peak-to-peak CDV of 3.455 ms, a backward cumulative peak-to-peak CDV of 2.155 ms, a forward end-to-end transit delay of 32 ms, a backward end-to-end transit delay of 18 ms, an unspecified forward cumulative transit delay, an unspecified backward cumulative transit delay, a forward cell loss ratio of 10 raised to minus 11 and a backward cell loss ratio of 10 to the minus 12.
这意味着前向可接受的峰间CDV为8.125 ms，后向可接受的峰间CDV为4.675 ms，前向累积峰间CDV为3.455 ms，后向累积峰间CDV为2.155 ms，前向端到端传输延迟为32 ms，后向端到端传输延迟为18 ms，未指定的前向累积传输延迟、未指定的后向累积传输延迟、前向信元丢失率10提高到-11、后向信元丢失率10提高到-12。
An example of specifying the same parameters for the forward and backward directions is:
为前进和后退方向指定相同参数的示例如下：
a=atmQOSparms:fb PP 8125 3455 32000 - 11
a=atmQOSparms:fb PP 8125 3455 32000 - 11
This implies a forward and backward acceptable peak-to-peak CDV of 8.125 ms, a forward and backward cumulative peak-to-peak CDV of 3.455 ms, a forward and backward end-to-end transit delay of 32 ms, an unspecified cumulative transit delay in the forward and backward directions, and a cell loss ratio of 10 raised to minus 11 in the forward and backward directions.
这意味着向前和向后可接受的峰间CDV为8.125 ms，向前和向后累积的峰间CDV为3.455 ms，向前和向后的端到端传输延迟为32 ms，向前和向后方向上未指定的累积传输延迟，在前进和后退方向上，细胞损失率从10提高到-11。
When present, the 'atmTrfcDesc' attribute is used to indicate ATM traffic descriptor parameters. There can be several 'atmTrfcDesc' lines in an SDP description.
存在时，“atmTrfcDesc”属性用于指示ATM流量描述符参数。SDP描述中可能有多行“atmTrfcDesc”。
The 'atmTrfcDesc' media attribute line is structured as follows:
“atmTrfcDesc”媒体属性行的结构如下：
a=atmTrfcDesc:<directionFlag><clpLvl>
<pcr><scr><mbs><cdvt><mcr><mfs><fd><te>
a=atmTrfcDesc:<directionFlag><clpLvl>
<pcr><scr><mbs><cdvt><mcr><mfs><fd><te>
The <directionFlag> can be assigned the following string values: "f", "b" and "fb". "f" and "b" indicate the forward and backward directions respectively. "fb" refers to both directions (forward and backward). Conventions for the forward and backward directions are per section 2.3.
<directionFlag>可以指定以下字符串值：“f”、“b”和“fb”。“f”和“b”分别表示向前和向后方向。“fb”指两个方向（向前和向后）。前进方向和后退方向的约定见第2.3节。
The <directionFlag> is always specified. Except for the <directionFlag>, the remaining parameters can be set to "-" to indicate that they are not specified, inapplicable or implied. However, there must be some specified parameters for the line to be useful in an SDP description.
始终指定<directionFlag>。除了<directionFlag>，其余参数可以设置为“-”，以表示未指定、不适用或隐含这些参数。但是，必须有一些指定的参数才能使该行在SDP描述中有用。
The <clpLvl> (CLP level) parameter indicates whether the rates and bursts described in these media attribute lines apply to CLP values of 0 or (0+1). It can take on the following string values: "0", "0+1" and "-". If rates and bursts for both <clpLvl> values are to be described, then it is necessary to use two separate media attribute lines for each direction in the same session descriptor. If the <clpLvl> parameter is set to "-", then it implies that the CLP parameter is known by other means such as default, MIB provisioning etc.
<clpLvl>（CLP级别）参数指示这些媒体属性行中描述的速率和突发是否适用于0或（0+1）的CLP值。它可以采用以下字符串值：“0”、“0+1”和“-”。如果要描述两个<clpLvl>值的速率和突发，则有必要在同一会话描述符中为每个方向使用两个单独的媒体属性行。如果<clpLvl>参数设置为“-”，则表示CLP参数通过其他方式（如默认、MIB设置等）已知。
The meaning, units and applicability of the remaining parameters are per [6] and [28]:
其余参数的含义、单位和适用性见[6]和[28]：
PARAMETER MEANING UNITS APPLICABILITY
参数含义单位适用性
<pcr> PCR Cells/ CBR, rt-VBR, nrt-VBR,
second ABR, UBR, GFR;
CLP=0,0+1
<pcr> PCR Cells/ CBR, rt-VBR, nrt-VBR,
second ABR, UBR, GFR;
CLP=0,0+1
<scr> SCR Cells/ rt-VBR, nrt-VBR;
second CLP=0,0+1
<scr> SCR Cells/ rt-VBR, nrt-VBR;
second CLP=0,0+1
<mbs> MBS Cells rt-VBR, nrt-VBR,
GFR;
CLP=0,0+1
<mbs> MBS Cells rt-VBR, nrt-VBR,
GFR;
CLP=0,0+1
<cdvt> CDVT Microsec. CBR, rt-VBR, nrt-VBR,
ABR, UBR, GFR;
CLP=0,0+1
<cdvt> CDVT Microsec. CBR, rt-VBR, nrt-VBR,
ABR, UBR, GFR;
CLP=0,0+1
<mcr> MCR Cells/ ABR,GFR;
second CLP=0+1
<mcr> MCR Cells/ ABR,GFR;
second CLP=0+1
<mfs> MFS Cells GFR;
CLP=0,0+1
<mfs> MFS Cells GFR;
CLP=0,0+1
<fd> Frame "on"/"off" CBR, rt-VBR, nrt-VBR,
Discard ABR, UBR, GFR;
Allowed CLP=0+1
<fd> Frame "on"/"off" CBR, rt-VBR, nrt-VBR,
Discard ABR, UBR, GFR;
Allowed CLP=0+1
<te> CLP "on"/"off" CBR, rt-VBR, nrt-VBR,
tagging ABR, UBR, GFR;
Enabled CLP=0
<te> CLP "on"/"off" CBR, rt-VBR, nrt-VBR,
tagging ABR, UBR, GFR;
Enabled CLP=0
<fd> indicates that frame discard is permitted. It can take on the string values of "on" or "off". Note that, in the GFR case, frame discard is always enabled. Hence, this subparameter can be set to "-" in the case of GFR. Since the <fd> parameter is independent of CLP, it is meaningful in the case when <clpLvl> = "0+1". It should be set to "-" for the case when <clpLvl> = "0".
<fd>表示允许帧丢弃。它可以采用“开”或“关”的字符串值。请注意，在GFR情况下，帧丢弃始终处于启用状态。因此，在GFR的情况下，该子参数可以设置为“-”。由于<fd>参数独立于CLP，因此在<clpLvl>为“0+1”的情况下，它是有意义的。当<clpLvl>=“0”时，应将其设置为“-”。
<te> (tag enable) indicates that CLP tagging is allowed. These can take on the string values of "on" or "off". Since the <te> parameter applies only to cells with a CLP of 0, it is meaningful in the case when <clpLvl> = "0". It should be set to "-" for the case when <clpLvl> = "0+1".
<te>（标记启用）表示允许CLP标记。这些可以采用“开”或“关”的字符串值。由于<te>参数仅适用于CLP为0的单元，因此在<clpLvl>为“0”的情况下，它是有意义的。当<clpLvl>=“0+1”时，应将其设置为“-”。
An example use of these media attribute lines for an rt-VBR, single-CID AAL2 voice VC is:
这些媒体属性行用于rt VBR、单CID AAL2语音VC的示例如下：
a=atmTrfcDesc:f 0+1 200 100 20 - - - on -
a=atmTrfcDesc:f 0 200 80 15 - - - - off
a=atmTrfcDesc:b 0+1 200 100 20 - - - on -
a=atmTrfcDesc:b 0 200 80 15 - - - - off
a=atmTrfcDesc:f 0+1 200 100 20 - - - on -
a=atmTrfcDesc:f 0 200 80 15 - - - - off
a=atmTrfcDesc:b 0+1 200 100 20 - - - on -
a=atmTrfcDesc:b 0 200 80 15 - - - - off
This implies a forward and backward PCR of 200 cells per second all cells regardless of CLP, forward and backward PCR of 200 cells per second for cells with CLP=0, a forward and backward SCR of 100 cells per second for all cells regardless of CLP, a forward and backward SCR of 80 cells per second for cells with CLP=0, a forward and backward MBS of 20 cells for all cells regardless of CLP, a forward
这意味着向前和向后PCR为每秒200个细胞，不考虑CLP，向前和向后PCR为每秒200个细胞，CLP=0，向前和向后SCR为每秒100个细胞，不考虑CLP，向前和向后SCR为每秒80个细胞，CLP=0，a前向和后向MBS为20个小区，用于所有小区，不考虑CLP，a前向
and backward MBS of 15 cells for cells with CLP=0, an unspecified CDVT which can be known by other means, and an MCR and MFS which are unspecified because they are inapplicable. Frame discard is enabled in both the forward and backward directions. Tagging is not enabled in either direction.
对于CLP=0的小区，反向MBS为15个小区，未指定的CDVT可通过其他方式得知，MCR和MFS因不适用而未指定。帧丢弃在向前和向后方向都启用。两个方向均未启用标记。
The <pcr>, <scr>, <mbs>, <cdvt>, <mcr> and <mfs> are represented as decimal integers, with range as defined in Section 6. See section 2.2 regarding the omission of leading zeros in decimal representations.
<pcr>、<scr>、<mbs>、<cdvt>、<mcr>和<mfs>表示为十进制整数，其范围如第6节所定义。关于十进制表示法中前导零的省略，请参见第2.2节。
When present, the 'abrParms' attribute is used to indicate the ' additional' ABR parameters specified in the UNI 4.0 signaling specification [5]. There can be several 'abrParms' lines in an SDP description.
当存在时，“abrParms”属性用于指示UNI 4.0信令规范中指定的“附加”ABR参数[5]。SDP描述中可能有多行“abrParms”。
The 'abrParms' media attribute line is structured as follows:
“abrParms”媒体属性行的结构如下：
a=abrParms:<directionFlag><nrm><trm><cdf><adtf>
a=abrParms:<directionFlag><nrm><trm><cdf><adtf>
The <directionFlag> can be assigned the following string values: "f", "b" and "fb". "f" and "b" indicate the forward and backward directions respectively. "fb" refers to both directions (forward and backward). Conventions for the forward and backward directions are per section 2.3.
<directionFlag>可以指定以下字符串值：“f”、“b”和“fb”。“f”和“b”分别表示向前和向后方向。“fb”指两个方向（向前和向后）。前进方向和后退方向的约定见第2.3节。
The <directionFlag> is always specified. Except for the <directionFlag>, the remaining parameters can be set to "-" to indicate that they are not specified, inapplicable or implied. However, there must be some specified parameters for the line to be useful in an SDP description.
始终指定<directionFlag>。除了<directionFlag>，其余参数可以设置为“-”，以表示未指定、不适用或隐含这些参数。但是，必须有一些指定的参数才能使该行在SDP描述中有用。
These parameters are mapped into the ABR service parameters in [6] in the manner described below. These parameters can be represented in SDP as decimal integers, with fractions permitted for some. Details of the meaning, units and applicability of these parameters are in [5] and [6].
这些参数以下面描述的方式映射到[6]中的ABR服务参数中。这些参数可以在SDP中表示为十进制整数，有些参数允许分数。[5]和[6]中详细说明了这些参数的含义、单位和适用性。
In SDP, these parameters are represented as the decimal or hex equivalent of the binary fields mentioned below.
在SDP中，这些参数表示为下面提到的二进制字段的十进制或十六进制等效值。
+-----------+----------------------------------+-----------------------+
| PARAMETER | MEANING | FIELD SIZE |
+-----------+----------------------------------+-----------------------+
| <nrm> | Maximum number of cells per | 3 bits |
| | forward Resource Management cell | |
+-----------+----------------------------------+-----------------------+
| <trm> | Maximum time between | 3 bits |
| | forward Resource Management cells| |
+-----------+----------------------------------+-----------------------+
| <cdf> | Cutoff Decrease Factor | 3 bits |
+-----------+----------------------------------+-----------------------+
| <adtf> | Allowed Cell Rate Decrease | 10 bits |
| | Time Factor | |
+-----------+----------------------------------+-----------------------+
+-----------+----------------------------------+-----------------------+
| PARAMETER | MEANING | FIELD SIZE |
+-----------+----------------------------------+-----------------------+
| <nrm> | Maximum number of cells per | 3 bits |
| | forward Resource Management cell | |
+-----------+----------------------------------+-----------------------+
| <trm> | Maximum time between | 3 bits |
| | forward Resource Management cells| |
+-----------+----------------------------------+-----------------------+
| <cdf> | Cutoff Decrease Factor | 3 bits |
+-----------+----------------------------------+-----------------------+
| <adtf> | Allowed Cell Rate Decrease | 10 bits |
| | Time Factor | |
+-----------+----------------------------------+-----------------------+
When present, the 'abrSetup' attribute is used to indicate the ABR parameters needed during call/connection establishment (Section 10.1.2.2 of the UNI 4.0 signaling specification [5]). This line is structured as follows:
当存在时，“abrSetup”属性用于指示呼叫/连接建立期间所需的ABR参数（UNI 4.0信令规范第10.1.2.2节[5]）。该行的结构如下：
a=abrSetup:<ficr><bicr><ftbe><btbe><crmrtt><frif><brif><frdf><brdf>
a=abrSetup:<ficr><bicr><ftbe><btbe><crmrtt><frif><brif><frdf><brdf>
These parameters are defined as follows:
这些参数定义如下：
+-----------+----------------------------------+-----------------------+
| PARAMETER | MEANING | REPRESENTATION |
+-----------+----------------------------------+-----------------------+
| <ficr> | Forward Initial Cell Rate | Decimal equivalent |
| | (Cells per second) | of 24-bit field |
+-----------+----------------------------------+-----------------------+
| <bicr> | Backward Initial Cell Rate | Decimal equivalent |
| | (Cells per second) | of 24-bit field |
+-----------+----------------------------------+-----------------------+
| <ftbe> | Forward transient buffer | Decimal equivalent |
| | exposure (Cells) | of 24-bit field |
+-----------+----------------------------------+-----------------------+
| <btbe> | Backward transient buffer | Decimal equivalent |
| | exposure (Cells) | of 24-bit field |
+-----------+----------------------------------+-----------------------+
| <crmrtt> | Cumulative RM round-trip time | Decimal equivalent |
| | (Microseconds) | of 24-bit field |
+-----------+----------------------------------+-----------------------+
| <frif> | Forward rate increase factor | Decimal integer |
| | (used to derive cell count) | 0 -15 |
+-----------+----------------------------------+-----------------------+
| <brif> | Backward rate increase factor | Decimal integer |
| | (used to derive cell count) | 0 -15 |
+-----------+----------------------------------+-----------------------+
| <frdf> | Forward rate decrease factor | Decimal integer |
| | (used to derive cell count) | 0 -15 |
+-----------+----------------------------------+-----------------------+
| <brdf> | Backward rate decrease factor | Decimal integer |
| | (used to derive cell count) | 0 -15 |
+-----------+----------------------------------+-----------------------+
+-----------+----------------------------------+-----------------------+
| PARAMETER | MEANING | REPRESENTATION |
+-----------+----------------------------------+-----------------------+
| <ficr> | Forward Initial Cell Rate | Decimal equivalent |
| | (Cells per second) | of 24-bit field |
+-----------+----------------------------------+-----------------------+
| <bicr> | Backward Initial Cell Rate | Decimal equivalent |
| | (Cells per second) | of 24-bit field |
+-----------+----------------------------------+-----------------------+
| <ftbe> | Forward transient buffer | Decimal equivalent |
| | exposure (Cells) | of 24-bit field |
+-----------+----------------------------------+-----------------------+
| <btbe> | Backward transient buffer | Decimal equivalent |
| | exposure (Cells) | of 24-bit field |
+-----------+----------------------------------+-----------------------+
| <crmrtt> | Cumulative RM round-trip time | Decimal equivalent |
| | (Microseconds) | of 24-bit field |
+-----------+----------------------------------+-----------------------+
| <frif> | Forward rate increase factor | Decimal integer |
| | (used to derive cell count) | 0 -15 |
+-----------+----------------------------------+-----------------------+
| <brif> | Backward rate increase factor | Decimal integer |
| | (used to derive cell count) | 0 -15 |
+-----------+----------------------------------+-----------------------+
| <frdf> | Forward rate decrease factor | Decimal integer |
| | (used to derive cell count) | 0 -15 |
+-----------+----------------------------------+-----------------------+
| <brdf> | Backward rate decrease factor | Decimal integer |
| | (used to derive cell count) | 0 -15 |
+-----------+----------------------------------+-----------------------+
See Section 2.3 for a definition of the terms 'forward' and 'backward'.
有关术语“向前”和“向后”的定义，请参见第2.3节。
If any of these parameters in the 'abrSetup' media attribute line is not specified, is inapplicable or is implied, then it is set to h "- ".
如果“abrSetup”媒体属性行中的任何参数未指定、不适用或隐含，则将其设置为h“-”。
When present, the 'bearerType' attribute is used to indicate whether the underlying bearer is an ATM PVC/SPVC, an ATM SVC, or a subchannel within an existing ATM SVC/PVC/SPVC. Additionally, for ATM SVCs and AAL2 CID connections, the 'bearerType' attribute can be used to indicate whether the media gateway initiates connection set-up via bearer signaling (Q.2931-based or Q.2630.1 based). The format of the 'bearerType' media attribute line is as follows:
当存在时，“bearerType”属性用于指示基础承载是ATM PVC/SPVC、ATM SVC还是现有ATM SVC/PVC/SPVC中的子信道。此外，对于ATM SVC和AAL2 CID连接，“承载类型”属性可用于指示媒体网关是否通过承载信令（基于Q.2931或基于Q.2630.1）启动连接设置。“BearType”媒体属性行的格式如下：
a=bearerType: <bearerType> <localInitiation>
a=bearerType: <bearerType> <localInitiation>
The <bearerType> field can take on the following string values:
<bearerType>字段可以采用以下字符串值：
"PVC", "SVC", "CID", with semantics as defined above. Here, "PVC" includes both the PVC and SPVC cases.
“PVC”、“SVC”、“CID”，语义如上所述。此处，“PVC”包括PVC和SPVC外壳。
In the case when the underlying bearer is a PVC/SPVC, or a CID assigned by the MGC rather than through bearer signaling, the <localInitiation> flag can be omitted or set to "-". In the case when bearer signaling is used, this flag can be omitted when it is known by default or by other means whether the media gateway initiates the connection set-up via bearer signaling. Only when this is to be indicated explicitly that the <localInitiation> flag takes on the values of "on" or "off". An "on" value indicates that the media gateway is responsible for initiating connection set-up via bearer signaling (SVC signaling or Q.2630.1 signaling), an "off" value indicates otherwise.
在底层承载是PVC/SPVC或由MGC而不是通过承载信令分配的CID的情况下，<localinition>标志可以省略或设置为“-”。在使用承载信令的情况下，当默认情况下或通过其他方式知道媒体网关是否通过承载信令发起连接建立时，可以省略该标志。仅当明确指出<Localization>标志的值为“开”或“关”时。“on”值表示媒体网关负责通过承载信令（SVC信令或Q.2630.1信令）启动连接设置，“off”值表示其他情况。
When present, the 'lij' attribute is used to indicate the presence of a connection that uses the Leaf-initiated-join capability described in UNI 4.0 [5], and to optionally describe parameters associated with this capability. The format of the 'lij' media attribute line is as follows:
当存在时，“lij”属性用于指示存在使用UNI 4.0[5]中描述的叶启动连接功能的连接，并可选地描述与此功能相关的参数。“lij”媒体属性行的格式如下：
a=lij: <sci><lsn>
a=lij: <sci><lsn>
The <sci> (screening indication) is a 4-bit field expressed as a decimal or hex integer. It is defined in the UNI 4.0 signaling specification [5]. It is possible that the values of this field will be defined later by the ATMF and/or ITU. Currently, all values are reserved with the exception of 0, which indicates a 'Network Join without Root Notification'.
<sci>（屏蔽指示）是一个4位字段，表示为十进制或十六进制整数。它在UNI 4.0信令规范[5]中定义。该字段的值可能稍后由ATMF和/或ITU定义。目前，所有值均保留，但0除外，0表示“无根通知的网络连接”。
The <lsn> (leaf sequence number) is a 32-bit field expressed as a decimal or hex integer. Per the UNI 4.0 signaling specification [5], it is used by a joining leaf to associate messages and responses during LIJ (leaf initiated join) procedures.
<lsn>（叶序列号）是表示为十进制或十六进制整数的32位字段。根据UNI 4.0信令规范[5]，在LIJ（叶发起的连接）过程中，连接叶使用它来关联消息和响应。
Each of these fields can be set to a "-" when the intention is to not specify them in an SDP descriptor.
当目的是不在SDP描述符中指定这些字段时，可以将每个字段设置为“-”。
When present, the 'anycast' attribute line is used to indicate the applicability of the anycast function described in UNI 4.0 [5]. Optional parameters to qualify this function are provided. The format of the 'anycast' attribute is:
当存在时，“选播”属性行用于指示UNI 4.0[5]中描述的选播功能的适用性。提供了限定此函数的可选参数。“选播”属性的格式为：
a=anycast: <atmGroupAddress> <cdStd> <conScpTyp> <conScpSel>
a=anycast: <atmGroupAddress> <cdStd> <conScpTyp> <conScpSel>
The <atmGroupAddress> is per Annex 5 of UNI 4.0 [5]. Within an SDP descriptor, it can be represented in one of the formats (NSAP, E.164, GWID/ALIAS) described elsewhere in this document.
<atmGroupAddress>符合UNI 4.0[5]的附件5。在SDP描述符中，它可以用本文档其他地方描述的格式之一（NSAP，E.164，GWID/别名）表示。
The remaining subparameters mirror the connection scope selection information element in UNI 4.0 [5]. Their meaning and representation is as shown below:
其余子参数反映UNI 4.0[5]中的连接范围选择信息元素。其含义和表述如下所示：
PARAMETER MEANING REPRESENTATION
参数意义表示
<cdStd> Coding standard for the Decimal or hex connection scope selection IE equivalent of Definition: UNI 4.0 [5] 2 bits
十进制或十六进制连接范围选择的编码标准，即定义的等效值：UNI 4.0[5]2位
<conScpTyp> Type of connection scope Decimal or hex Definition: UNI 4.0 [5] equivalent of 4 bits
连接范围十进制或十六进制定义的类型：UNI 4.0[5]相当于4位
<conScpSel> Connection scope selection Decimal or hex Definition: UNI 4.0 [5] equivalent of 8 bits
连接范围选择十进制或十六进制定义：UNI 4.0[5]相当于8位
Currently, all values of <cdStd> and <conScpTyp> are reserved with the exception of <cdStd> = 3 (ATMF coding standard) and <conScpTyp> = 1 (connection scope type of 'organizational').
目前，<cdStd>和<conScpTyp>的所有值均保留，但<cdStd>=3（ATMF编码标准）和<conScpTyp>=1（连接范围类型为“组织”）除外。
Each of these fields can be set to a "-" when the intention is to not specify them in an SDP descriptor.
当目的是不在SDP描述符中指定这些字段时，可以将每个字段设置为“-”。
This attribute is used to enable SVC caching. This attribute has the following format:
此属性用于启用SVC缓存。此属性具有以下格式：
a=cache:<cacheEnable><cacheTimer>
a=cache:<cacheEnable><cacheTimer>
The <cacheEnable> flag indicates whether caching is enabled or not, corresponding to the string values of "on" and "off" respectively.
<cacheEnable>标志指示是否启用缓存，分别对应于字符串值“on”和“off”。
The <cacheTimer> indicates the period of inactivity following which the SVC is to be released by sending an SVC release message into the network. This is specified as the decimal or hex equivalent of a 32-bit field, indicating the timeout in seconds. As usual, leading zeros can be omitted. For instance,
<cacheTimer>表示不活动的时间段，之后通过向网络发送SVC释放消息来释放SVC。指定为32位字段的十进制或十六进制等效值，以秒为单位指示超时。通常，可以省略前导零。例如，
a=cache:on 7200
a=缓存：在7200上
implies that the cached SVC is to be deleted if it is idle for 2 hours.
表示如果缓存的SVC空闲2小时，将删除该SVC。
The <cacheTimer> can be set to "-" if it is inapplicable or implied.
如果<cacheTimer>不适用或隐含，则可以将其设置为“-”。
ATM signaling standards provide 'escape mechanisms' to represent, signal and negotiate higher-layer parameters. Examples are the B-HLI and B-LLI IEs specified in ITU Q.2931 [15], and the user-to-user information element described in ITU Q.2957 [48].
ATM信令标准提供了“转义机制”，用于表示、发送信号和协商更高层的参数。例如，ITU Q.2931[15]中规定的B-HLI和B-LLI IEs，以及ITU Q.2957[48]中描述的用户对用户信息元素。
The 'bearerSigIE'(bearer signaling information element) attribute is defined to allow a similar escape mechanism that can be used with these ATM SDP conventions. The format of this media attribute line is as follows:
“bearerSigIE”（承载信令信息元素）属性被定义为允许与这些ATM SDP约定一起使用的类似转义机制。此媒体属性行的格式如下：
a=bearerSigIE: <bearerSigIEType> <bearerSigIELng> <bearerSigIEVal>
a=bearerSigIE: <bearerSigIEType> <bearerSigIELng> <bearerSigIEVal>
When an 'bearerSigIE' media attribute line is present, all its subparameters are mandatory. The "0x" prefix is not used since these are always represented in hex.
当存在“BearSigie”媒体属性行时，其所有子参数都是必需的。不使用“0x”前缀，因为它们总是以十六进制表示。
The <bearerSigIEType> is represented as exactly 2 hex digits. It is the unique IE identifier as defined in the ITU Q-series standards. Leading zeros are not omitted. Some pertinent values are 7E (User-user IE per ITU Q.2957 [48]), 5F (B-LLI IE) and 5D (B-HLI IE). B-LLI and B-HLI, which stand for Broadband Low-layer Information and Broadband High-layer Information respectively, are defined in ITU Q.2931 [15]. Both of these refer to layers above the ATM adaptation layer.
<BearSiegeType>精确表示为2个十六进制数字。它是ITU Q系列标准中定义的唯一IE标识符。前导零不会被忽略。一些相关值为7E（根据ITU Q.2957[48]）、5F（B-LLI IE）和5D（B-HLI IE）。B-LLI和B-HLI分别代表宽带低层信息和宽带高层信息，定义见ITU Q.2931[15]。这两个层都指ATM适配层之上的层。
The <bearerSigIELng> consists of 1-4 hex digits. It is the length of the information element in octets. Leading zeros may be omitted.
<BearSiegeing>由1-4个十六进制数字组成。它是以八位字节为单位的信息元素的长度。前导零可以省略。
The <bearerSigIEVal> is the value of the information element, represented as a hexadecimal bit map. Although the size of this bit map is network/ service dependent, setting an upper bound of 256 octets (512 hex digits) is adequate. Since this a bit map, leading zeros should not be omitted. The number of hex digits in this bit map is even.
<BearSigeVal>是信息元素的值，表示为十六进制位图。尽管此位图的大小取决于网络/服务，但设置256个八位字节（512个十六进制数字）的上限已足够。由于这是一个位映射，所以不应忽略前导零。此位图中的十六进制数字为偶数。
The following is a summary list of the SDP media attributes that can be used to describe the ATM Adaptation Layer (AAL). These are detailed in subsequent subsections.
以下是可用于描述ATM适配层（AAL）的SDP媒体属性的摘要列表。这些将在后面的小节中详细说明。
* The 'aalApp' attribute, which is used to point to the controlling standard for an application layer above the ATM adaptation layer.
* “aalApp”属性，用于指向ATM适配层之上应用层的控制标准。
* The 'cbrRate' attribute, which represents the CBR rate octet defined in Table 4-6 of ITU Q.2931 [15].
* “cbrRate”属性，表示ITU Q.2931[15]表4-6中定义的CBR速率八位字节。
* The 'sbc' attribute, which denotes the subchannel count in the case of n x 64 clear channel communication.
* “sbc”属性，表示n x 64清晰信道通信情况下的子信道计数。
* The 'clkrec' attribute, which indicates the clock recovery method for AAL1 unstructured data transfer (UDT).
* “clkrec”属性，表示AAL1非结构化数据传输（UDT）的时钟恢复方法。
* The 'fec' attribute, which indicates the use of forward error correction.
* “fec”属性，指示使用前向纠错。
* The 'prtfl' attribute, which indicates indicate the fill level of partially filled cells.
* “prtfl”属性，指示部分填充单元格的填充级别。
* The 'structure' attribute, which is used to indicate the presence or absence of AAL1 structured data transfer (SDT), and the size of the SDT blocks.
* “structure”属性，用于指示是否存在AAL1结构化数据传输（SDT）以及SDT块的大小。
* The 'cpsSDUsize' attribute, which is used to indicate the maximum size of the CPCS SDU payload.
* “cpsSDUsize”属性，用于指示CPCS SDU有效负载的最大大小。
* The 'aal2CPS' attribute, which is used to indicate that an AAL2 CPS sublayer as defined in ITU I.363.2 [13] is associated with the VCC referred to in the 'm' line. Optionally, it can be used to indicate selected CPS options and parameter values for this VCC.
* “aal2CPS”属性，用于指示ITU I.363.2[13]中定义的AAL2 CPS子层与“m”行中提及的VCC相关联。可选地，它可用于指示此VCC的选定CPS选项和参数值。
* The 'aal2CPSSDUrate' attribute, which is used to place an upper bound on the SDU bit rate for an AAL2 CID.
* “aal2CPSSDUrate”属性，用于设置AAL2 CID的SDU比特率上限。
* The 'aal2sscs3661unassured' attribute, which is used to indicate the presence of an AAL2 SSCS sublayer with unassured transmission as defined in ITU I.366.1 [12]. Optionally, it can be used to indicate selected options and parameter values for this SSCS.
* “aal2sscs3661unassured”属性，用于指示存在具有ITU I.366.1[12]中定义的未保证传输的AAL2 SSCS子层。或者，它可用于指示该SSC的选定选项和参数值。
* The 'aal2sscs3661assured' attribute, which is used to indicate the presence of an AAL2 SSCS sublayer with assured transmission as defined in ITU I.366.1 [12]. Optionally, it can be used to indicate selected options and parameter values for this SSCS.
* “aal2sscs3661assured”属性，用于指示存在具有ITU I.366.1[12]中定义的可靠传输的AAL2 SSCS子层。或者，它可用于指示该SSC的选定选项和参数值。
* The 'aal2sscs3662' attribute, which is used to indicate the presence of an AAL2 SSCS sublayer as defined in ITU I.366.2. Optionally, it can be used to indicate selected options and parameter values for this SSCS.
* “aal2sscs3662”属性，用于指示是否存在ITU I.366.2中定义的AAL2 SSCS子层。或者，它可用于指示该SSC的选定选项和参数值。
* The 'aal5sscop' attribute, which is used to indicate the existence of an SSCOP protocol layer over an AAL5 CPS layer, and the parameters which pertain to this SSCOP layer.
* “aal5sscop”属性，用于指示AAL5 CPS层上是否存在SSCOP协议层，以及与此SSCOP层相关的参数。
When present, the 'aalApp' attribute is used to point to the controlling standard for an application layer above the ATM adaptation layer. The format of the 'aalApp' media attribute line is as follows:
当存在时，“aalApp”属性用于指向ATM适配层之上的应用层的控制标准。“aalApp”媒体属性行的格式如下：
a=aalApp: <appClass> <oui> <appId>
a=aalApp: <appClass> <oui> <appId>
If any of the subparameters, <appClass>, <oui> or <appId>, is meant to be left, unspecified, it is set to "-". However, an 'aalApp' attribute line with all subparameters set to "-" carries no information and should be omitted.
如果任何子参数，<appClass>、<oui>或<appId>都是未指定的左参数，则将其设置为“-”。但是，所有子参数都设置为“-”的“aalApp”属性行不包含任何信息，应该忽略。
The <appClass>, or application class, field can take on the string values listed below.
<appClass>或application class字段可以采用下面列出的字符串值。
This list is not exhaustive. An "X-" prefix should be used with <appClass> values not listed here.
这份清单并非详尽无遗。“X-”前缀应与此处未列出的<appClass>值一起使用。
<appClass> Meaning
<appClass>意义
"itu_h323c" Annex C of H.323 which specifies direct RTP on AAL5 [45].
H.323的“itu_h323c”附录C规定了AAL5上的直接RTP[45]。
"af83" af-vtoa-0083.001, which specifies variable size AAL5 PDUs with PCM voice and a null SSCS [46].
“af83”af-vtoa-0083.001，其中规定了具有PCM语音和空SSC的可变大小AAL5 PDU[46]。
"AAL5_SSCOP" SSCOP as defined in ITU Q.2110 [43] running over an AAL5 CPS [21]. No information is provided regarding any layers above SSCOP such as Service Specific Coordination Function (SSCF) layers.
“AAL5_SSCOP”指ITU Q.2110[43]中定义的在AAL5 CP上运行的SSCOP[21]。未提供有关SSCOP之上任何层的信息，如服务特定协调功能（SSCF）层。
"itu_i3661_unassured" SSCS with unassured transmission, per ITU I.366.1 [12].
根据itu I.366.1[12]，具有未保证传输的“itu_i3661_未保证”SSC。
"itu_i3661_assured" SSCS with assured transmission, per ITU I.366.1 [12]. This uses SSCOP [43].
按照itu I.366.1[12]，具有保证传输的“itu_i3661_保证”SSC。这使用SSCOP[43]。
"itu_i3662" SSCS per ITU I.366.2 [13].
根据itu I.366.2[13]的“itu_i3662”SSC。
"itu_i3651" Frame relay SSCS per ITU I.365.1 [39].
“itu_i3651”帧中继SSC符合itu I.365.1[39]。
"itu_i3652" Service-specific coordination function, as defined in ITU I.365.2, for Connection Oriented Network Service (SSCF-CONS) [40]. This uses SSCOP [43].
“itu_i3652”特定于服务的协调功能，如itu I.365.2中所定义，用于面向连接的网络服务（SSCF-CONS）[40]。这使用SSCOP[43]。
"itu_i3653" Service-specific coordination function, as defined in ITU I.365.3, for Connection Oriented Transport Service (SSCF-COTS) [41]. This uses SSCOP [43].
“itu_i3653”特定于服务的协调功能，如itu I.365.3中所定义，用于面向连接的传输服务（SSCF-COTS）[41]。这使用SSCOP[43]。
"itu_i3654" HDLC Service-specific coordination function, as defined in ITU I.365.4 [42].
“itu_i3654”特定于HDLC服务的协调功能，如itu I.365.4[42]所定义。
"FRF5" Use of the FRF.5 frame relay standard [53], which references ITU I.365.1 [39].
“FRF5”使用参考ITU I.365.1[39]的FRF.5帧中继标准[53]。
"FRF8" Use of the FRF.8.1 frame relay standard [54]. This implies a null SSCS and the mapping of the frame relay header into the ATM header.
“FRF8”使用FRF.8.1帧中继标准[54]。这意味着空SSC和帧中继报头到ATM报头的映射。
"FRF11" Use of the FRF.11 frame relay standard [55].
“FRF11”使用FRF.11帧中继标准[55]。
"itu_h2221" Use of the ITU standard H.222.1 for audiovisual communication over AAL5 [51].
“itu_h2221”将itu标准H.222.1用于AAL5上的视听通信[51]。
The <oui>, or Organizationally Unique Identifier, refers to the organization responsible for defining the <appId>, or Application Identifier. The <oui> is maintained by the IEEE. One of its uses is in 802 MAC addresses. It is a three-octet field represented as one to six hex digits. Since this is always represented in hex, the "0x" prefix is not used. Leading zeros may be omitted.
<oui>或组织唯一标识符指负责定义<appId>或应用程序标识符的组织。<oui>由IEEE维护。它的用途之一是802 MAC地址。它是一个三个八位字节的字段，表示为一到六个十六进制数字。因为它总是用十六进制表示，所以不使用“0x”前缀。前导零可以省略。
The <appId> subparameter refers to the application ID, a hex number consisting of up to 8 digits. Leading zeros may be omitted. The "0x" prefix is not used, since the representation is always hexadecimal. Currently, the only organization that has defined application identifiers is the ATM forum. These have been defined in the context of AAL2 ([44], [52], Section 5 of [61]). Within SDP, these can be used with <appClass> = itu_i3662. The <oui> value for the ATM forum is 0x00A03E.
<appId>子参数指的是应用程序ID，一个最多由8位数字组成的十六进制数。前导零可以省略。不使用“0x”前缀，因为表示形式始终为十六进制。目前，唯一定义了应用程序标识符的组织是ATM论坛。这些已在AAL2（[44]、[52]、[61]第5节）的上下文中定义。在SDP中，这些可与<appClass>=itu_i3662一起使用。ATM论坛的<oui>值为0x00A03E。
In the following example, the aalApp media attribute line is used to indicate 'Loop Emulation Service using CAS (POTS only) without the Emulated Loop Control Protocol (ELCP) [52]. The Application ID is defined by the ATM forum [61]. The SSCS used is per ITU I.366.2 [13].
在以下示例中，aalApp媒体属性行用于指示“使用CAS（仅限POTS）的环路仿真服务，而不使用仿真环路控制协议（ELCP）[52]。应用程序ID由ATM论坛定义[61]。所使用的SSC符合ITU I.366.2[13]。
a=aalApp:itu_i3662 A03E A
a=aalApp:itu_i3662 A03E a
If leading zeros are not dropped, this can be represented as:
如果未删除前导零，则可以表示为：
a=aalApp:itu_i3662 00A03E 0000000A
a=aalApp:itu_i3662 00A03E 0000000 a
Since application identifiers have been specified only in the context of the AAL2 SSCS defined in ITU I.366.2 [13],the <appClass> can be set to '-' without ambiguity. The aalApp media attribute line can be reduced to:
由于仅在ITU I.366.2[13]中定义的AAL2 SSC的上下文中指定了应用标识符，<appClass>可以设置为“-”，而不会产生歧义。aalApp媒体属性行可以减少为：
a=aalApp:- A03E A
a=aalApp:-A03E a
or
或
a=aalApp:- 00A03E 0000000A
a=aalApp:-00A03E 0000000 a
When present, the 'cbrRate' attribute is used to represent the CBR rate octet defined in Table 4-6 of ITU Q.2931 [15]. The format of this media attribute line is:
当存在时，“cbrRate”属性用于表示ITU Q.2931[15]表4-6中定义的CBR速率八位字节。此媒体属性行的格式为：
a=cbrRate: <cbrRate>
a=cbrRate: <cbrRate>
Here, <cbrRate> is represented as exactly two hex digits. The "0x" prefix is omitted since this parameter is always represented in hex. Values currently defined by the ITU are:
这里，<cbrRate>表示为两个十六进制数字。省略“0x”前缀，因为此参数始终以十六进制表示。国际电联目前定义的数值为：
+------------+-----------------------------------------------+
| VALUE | MEANING |
| (hex) | |
+------------+-----------------------------------------------+
| 01 | 64 kbps |
+------------+-----------------------------------------------+
| 04 | 1544 kbps |
+------------+-----------------------------------------------+
| 05 | 6312 kbps |
+------------+-----------------------------------------------+
| 06 | 32064 kbps |
+------------+-----------------------------------------------+
| 07 | 44736 kbps |
+------------+-----------------------------------------------+
| 08 | 97728 kbps |
+------------+-----------------------------------------------+
| 10 | 2048 kbps |
+------------+-----------------------------------------------+
| 11 | 8448 kbps |
+------------+-----------------------------------------------+
| 12 | 34368 kbps |
+------------+-----------------------------------------------+
| 13 | 139264 kbps |
+------------+-----------------------------------------------+
| 40 | n x 64 kbps |
+------------+-----------------------------------------------+
| 41 | n x 8 kbps |
+------------+-----------------------------------------------+
+------------+-----------------------------------------------+
| VALUE | MEANING |
| (hex) | |
+------------+-----------------------------------------------+
| 01 | 64 kbps |
+------------+-----------------------------------------------+
| 04 | 1544 kbps |
+------------+-----------------------------------------------+
| 05 | 6312 kbps |
+------------+-----------------------------------------------+
| 06 | 32064 kbps |
+------------+-----------------------------------------------+
| 07 | 44736 kbps |
+------------+-----------------------------------------------+
| 08 | 97728 kbps |
+------------+-----------------------------------------------+
| 10 | 2048 kbps |
+------------+-----------------------------------------------+
| 11 | 8448 kbps |
+------------+-----------------------------------------------+
| 12 | 34368 kbps |
+------------+-----------------------------------------------+
| 13 | 139264 kbps |
+------------+-----------------------------------------------+
| 40 | n x 64 kbps |
+------------+-----------------------------------------------+
| 41 | n x 8 kbps |
+------------+-----------------------------------------------+
It is preferable that the cbrRate attribute be omitted rather than set to an unspecified value of "-", since it conveys no information in the latter case.
最好省略cbrRate属性，而不是将其设置为未指定的值“-”，因为在后一种情况下，cbrRate属性不传递任何信息。
The 'sbc' media attribute line denotes the subchannel count and is meaningful only in the case of n x 64 clear channel communication. A clear n x 64 channel can use AAL1 (ATM forum af-vtoa-78) or AAL2 adaptation (ITU I.366.2). Although no such standard definition exists, it is also possible to use AAL5 for this purpose. An n x 64 clear channel is represented by the encoding names of "X-CCD" and "X-CCD-CAS" in Table 2.
“sbc”媒体属性行表示子信道计数，仅在n x 64清晰信道通信的情况下才有意义。清晰的n x 64通道可以使用AAL1（ATM论坛af-vtoa-78）或AAL2适配（ITU I.366.2）。尽管不存在此类标准定义，但也可以为此目的使用AAL5。表2中“x-CCD”和“x-CCD-CAS”的编码名称表示n x 64清晰通道。
The format of the 'sbc' media attribute line is as follows:
“sbc”媒体属性行的格式如下：
a=sbc:<sbc>
a=sbc:<sbc>
Here, <sbc> can be expressed as a decimal or hex integer. This attribute indicates the number of DS0s in a T1 or E1 frame that are aggregated for transmitting clear channel data. For T1-based applications, it can take on integral values in the inclusive range [1...24]. For E1-based applications, it can take on integral values in the inclusive range [1...31]. When omitted, other means are to be used to determine the subchannel count.
这里，<sbc>可以表示为十进制或十六进制整数。此属性表示T1或E1帧中为传输清晰通道数据而聚合的DS0数。对于基于T1的应用程序，它可以采用包含范围[1…24]内的整数值。对于基于E1的应用，它可以采用包含范围[1…31]内的整数值。省略时，将使用其他方法来确定子信道计数。
Use of the 'sbc' attribute provides a direct way to indicate the number of 64 kbps subchannels bundled into an n x 64 clear channel. An alternate mechanism to indicate this exists within the SDP bandwidth information, or 'b', line [1]. In this case, instead of specifying the number of subchannels, the aggregate bandwidth in kbps is specified. The syntax of the 'b' line, copied verbatim from [1], is as follows:
使用“sbc”属性可以直接指示捆绑到n x 64 clear通道中的64 kbps子通道的数量。SDP带宽信息或“b”行[1]中存在指示此情况的替代机制。在这种情况下，不指定子信道的数量，而是指定以kbps为单位的聚合带宽。逐字复制自[1]的“b”行的语法如下：
b=<modifier>:<bandwidth-value>
b=<modifier>:<bandwidth-value>
In the case of n x 64 clear channels, the <modifier> is assigned a text string value of "AS", indicating that the 'b' line is application-specific. The <bandwidth-value> parameter, which is a decimal number indicating the bandwidth in kbps, is limited to one of the following values in the n x 64 clear channel application context:
对于n x 64个清除通道，<modifier>被指定一个文本字符串值“AS”，表示“b”行是特定于应用程序的。<bandwidth value>参数是一个十进制数字，表示以kbps为单位的带宽，在n x 64 clear channel应用程序上下文中，该参数被限制为以下值之一：
64, 128, 192, 256, 320, 384, 448, 512, 576, 640, 704, 768, 832, 896, 960, 1024, 1088, 1152, 1216, 1280, 1344, 1408, 1472, 1600, 1664, 1728, 1792, 1856, 1920, 1984
64, 128, 192, 256, 320, 384, 448, 512, 576, 640, 704, 768, 832, 896, 960, 1024, 1088, 1152, 1216, 1280, 1344, 1408, 1472, 1600, 1664, 1728, 1792, 1856, 1920, 1984
Thus, for n x 64 circuit mode data service,
因此，对于n x 64电路模式数据服务，
a=sbc:6
a=sbc:6
is equivalent to
相当于
b=AS:384
b=AS:384
The media attribute line
媒体属性行
a=sbc:2
a=sbc:2
is equivalent to
相当于
b=AS:128
b=AS:128
When present, the 'clkrec' attribute is used to indicate the clock recovery method. This attribute is meaningful in the case of AAL1 unstructured data transfer (UDT). The format of the 'clkrec' media attribute line is as follows:
存在时，“clkrec”属性用于指示时钟恢复方法。此属性在AAL1非结构化数据传输（UDT）的情况下有意义。“clkrec”媒体属性行的格式如下：
a=clkrec:<clkrec>
a=clkrec:<clkrec>
The <clkrec> field can take on the following string values: "NULL", "SRTS" or "ADAPTIVE". SRTS and adaptive clock recovery are defined in ITU I.363.1 [10]. "NULL" indicates that the stream (e.g., T1/E1) encapsulated in ATM is synchronous to the ATM network or is retimed, before AAL1 encapsulation, via slip buffers.
<clkrec>字段可以采用以下字符串值：“NULL”、“SRTS”或“ADAPTIVE”。SRT和自适应时钟恢复在ITU I.363.1[10]中定义。“NULL”表示封装在ATM中的流（例如T1/E1）与ATM网络同步，或者在AAL1封装之前通过滑动缓冲器重新定时。
When present, the 'fec' attribute is used to indicate the use of forward error correction. Currently, there exists a forward error correction method defined for AAL1 in ITU I.363.1 [10]. The format of the 'fec' media attribute line is as follows:
存在时，“fec”属性用于指示使用前向纠错。目前，在ITU I.363.1[10]中存在一种针对AAL1定义的前向纠错方法。“fec”媒体属性行的格式如下：
a=fec:<fecEnable>
a=fec:<fecEnable>
The <fecEnable> flag indicates the presence of absence of Forward Error Correction. It can take on the string values of "NULL", "LOSS_SENSITIVE" and "DELAY_SENSITIVE". An "NULL" value implies disabling this capability. FEC can be enabled differently for delay-sensitive and loss-sensitive connections.
<feceenable>标志指示是否存在前向纠错。它可以采用字符串值“NULL”、“LOSS\u SENSITIVE”和“DELAY\u SENSITIVE”。“NULL”值表示禁用此功能。对于延迟敏感和丢失敏感的连接，FEC可以以不同的方式启用。
When present, the 'prtfl' attribute is used to indicate the fill level of cells. When this attribute is absent, then other means (such as provisionable defaults) are used to determine the presence and level of partial fill.
存在时，“prtfl”属性用于指示单元格的填充级别。如果缺少此属性，则使用其他方法（例如可设置的默认值）来确定部分填充的存在和级别。
This attribute indicates the number of non-pad payload octets, not including any AAL SAR or convergence sublayer octets. For example, in some AAL1 applications that use partially filled cells with padding at the end, this attribute indicates the number of leading payload octets not including any AAL overhead.
此属性表示非pad有效负载八位字节的数量，不包括任何AAL SAR或聚合子层八位字节。例如，在某些AAL1应用程序中，该属性表示不包括任何AAL开销的前导有效负载八位字节的数量，这些应用程序在末尾使用部分填充的单元格和填充。
The format of the 'prtfl' media attribute line is as follows:
“prtfl”媒体属性行的格式如下所示：
a=prtfl:<partialFill>
a=prtfl:<partialFill>
Here, <partialFill> can be expressed as a decimal or a hex integer.
这里，<partialFill>可以表示为十进制或十六进制整数。
In general, permitted values are integers in the range 1 - 48 inclusive. However, this upper bound is different for different adaptations since the AAL overhead, if any, is different. If the specified partial fill is greater than or equal to the maximum fill, then complete fill is used. Using a 'partial' fill of 48 always disables partial fill.
通常，允许值是范围为1-48（含1-48）的整数。然而，由于AAL开销（如果有的话）不同，因此对于不同的适应，该上限是不同的。如果指定的部分填充大于或等于最大填充，则使用完全填充。使用48的“部分”填充始终禁用部分填充。
In the AAL1 context, this media attribute line applies uniformly to both P and non-P cells. In AAL1 applications that do not distinguish between P and non-P cells, a value of 47 indicates complete fill (i.e., the absence of partial fill). In AAL1 applications that distinguish between P and non-P cells, a value of 46 indicates no padding in P-cells and a padding of one in non-P cells.
在AAL1上下文中，此媒体属性行统一应用于P和非P单元格。在不区分P和非P单元格的AAL1应用中，值47表示完全填充（即不存在部分填充）。在区分P和非P单元格的AAL1应用程序中，值46表示P单元格中没有填充，而非P单元格中的填充为1。
If partial fill is enabled (i.e there is padding in at least some cells), then AAL1 structures must not be split across cell boundaries. These shall fit in any cell. Hence, their size shall be less than or equal to the partial fill size. Further, the partial fill size is preferably an integer multiple of the structure size. If not, then the partial fill size stated in the SDP description shall be truncated to an integer multiple (e.g., a partial fill size of 40 is truncated to 36 to support six 6 x 64 channels).
如果启用了部分填充（即至少在某些单元格中存在填充），则AAL1结构不得跨单元格边界拆分。这些应适用于任何单元。因此，其尺寸应小于或等于部分填充尺寸。此外，部分填充尺寸优选为结构尺寸的整数倍。如果不是，则SDP说明中规定的部分填充大小应被截断为整数倍（例如，40的部分填充大小被截断为36，以支持六个6 x 64通道）。
This attribute applies to AAL1 connections only. When present, the ' structure' attribute is used to indicate the presence or absence of structured data transfer (SDT), and the size in octets of the SDT blocks. The format of the 'structure' media attribute line is as follows:
此属性仅适用于AAL1连接。存在时，“structure”属性用于指示是否存在结构化数据传输（SDT），以及SDT块的大小（以八位字节为单位）。“结构”媒体属性行的格式如下：
a=structure: <structureEnable> <blksz>
a=structure: <structureEnable> <blksz>
where the <structureEnable> flag indicates the presence of absence of SDT. It can take on the values of "on" or "off". An "on" value implies AAL1 structured data transfer (SDT), while an "off" value implies AAL1 unstructured data transfer (UDT).
其中，<structureEnable>标志表示存在或不存在SDT。它可以采用“开”或“关”的值。“开”表示AAL1结构化数据传输（SDT），而“关”表示AAL1非结构化数据传输（UDT）。
The block size field, <blksz>, is an optional 16-bit field [15] that can be represented in decimal or hex. It is set to a "-" when not applicable, as in the case of unstructured data transfer (UDT). For SDT, it can be set to a "-" when <blksz> is known by other means. For instance, af-vtoa-78 [7] fixes the structure size for n x 64 service, with or without CAS. The theoretical maximum value of <blksz> is 65,535, although most services use much less.
块大小字段<blksz>是可选的16位字段[15]，可以用十进制或十六进制表示。不适用时，将其设置为“-”，如非结构化数据传输（UDT）。对于SDT，当通过其他方式知道<blksz>时，可以将其设置为“-”。例如，af-vtoa-78[7]固定了n x 64服务的结构大小，包括或不包括CAS。<blksz>的理论最大值为65535，尽管大多数服务使用的数据要少得多。
When present, the 'cpsSDUsize' attribute is used to indicate the maximum size of the CPCS SDU payload. There can be several ' cpsSDUsize' lines in an SDP description.
存在时，“cpsSDUsize”属性用于指示CPCS SDU有效负载的最大大小。SDP描述中可以有多行“cpsSDUsize”。
The format of this media attribute line is as follows:
此媒体属性行的格式如下：
a=cpsSDUsize:<directionFlag><cpcs>
a=cpsSDUsize:<directionFlag><cpcs>
The <directionFlag> can be assigned the following string values: "f", "b" and "fb". "f" and "b" indicate the forward and backward directions respectively. "fb" refers to both directions (forward and backward). Conventions for the forward and backward directions are per section 2.3.
<directionFlag>可以指定以下字符串值：“f”、“b”和“fb”。“f”和“b”分别表示向前和向后方向。“fb”指两个方向（向前和向后）。前进方向和后退方向的约定见第2.3节。
The <cpcs> fields is a 16-bit integer that can be represented in decimal or in hex. The meaning and values of these fields are as follows:
<cpcs>字段是一个16位整数，可以用十进制或十六进制表示。这些字段的含义和值如下：
Application Field Meaning Values
Application Field Meaning Valuestranslate error, please retry
AAL5 <cpcs> Maximum CPCS-SDU size 1- 65,535
AAL5<cpcs>最大cpcs-SDU尺寸1-65535
AAL2 <cpcs> Maximum CPCS-SDU size 45 or 64
AAL2<cpcs>最大cpcs-SDU尺寸45或64
When present, the 'aal2CPS' attribute is used to describe parameters associated with the AAL2 CPS layer.
存在时，“aal2CPS”属性用于描述与AAL2 CPS层关联的参数。
The format of the 'aal2CPS' media attribute line is as follows:
a=aal2CPS:<cidLowerLimit><cidUpperLimit><timerCU> <simplifiedCPS>
The format of the 'aal2CPS' media attribute line is as follows:
a=aal2CPS:<cidLowerLimit><cidUpperLimit><timerCU> <simplifiedCPS>
Each of these fields can be set to a "-" when the intention is to not specify them in an SDP descriptor.
当目的是不在SDP描述符中指定这些字段时，可以将每个字段设置为“-”。
The <cidLowerLimit> and <cidUpperLimit> can be assigned integer values between 8 and 255 [11], with the limitation that <cidUpperLimit> be greater than or equal to <cidLowerLimit>. For instance, for POTS applications based on [52], <cidLowerLimit> and <cidUpperLimit> can have values of 16 and 223 respectively.
可以为<cidLowerLimit>和<cidLowerLimit>分配介于8和255[11]之间的整数值，限制为<cidLowerLimit>大于或等于<cidLowerLimit>。例如，对于基于[52]的POTS应用程序，<cidLowerLimit>和<cidUpperLimit>的值分别为16和223。
The <timerCU> integer represents the "combined use" timerCU defined in ITU I.363.2. This timer is represented as an integer number of microseconds. It is represented as the decimal integer equivalent of 32 bits.
<timerCU>整数表示ITU I.363.2中定义的“组合使用”timerCU。此计时器表示为微秒的整数。它表示为相当于32位的十进制整数。
The <simplifiedCPS> parameter can be assigned the values "on" or "off". When it is "on", the AAL2 CPS simplification described in [52] is adopted. Under this simplification, each ATM cell contains exactly on AAL2 packet. If necessary, octets at the end of the cell are padded with zeros. Since the <timerCU> value in this context is always 0, it can be set to "-".
<simplifiedCPS>参数可以指定值“开”或“关”。当“开启”时，采用[52]中描述的AAL2 CPS简化。在这种简化下，每个ATM信元正好包含一个AAL2数据包。如有必要，单元格末尾的八位字节用零填充。由于此上下文中的<timerCU>值始终为0，因此可以将其设置为“-”。
When present, the 'aal2CPSSDUrate' attribute is used to place an upper bound on the SDU bit rate for an AAL2 CID. This is useful for limiting the bandwidth used by a CID, specially if the CID is used for frame mode data defined in [13], or with the SSSAR defined in [12]. The format of this media attribute line is as follows:
存在时，“aal2CPSSDUrate”属性用于设置AAL2 CID的SDU比特率上限。这有助于限制CID使用的带宽，特别是当CID用于[13]中定义的帧模式数据或[12]中定义的SSSAR时。此媒体属性行的格式如下：
a=aal2CPSSDUrate: <fSDUrate><bSDUrate>
a=aal2CPSSDUrate: <fSDUrate><bSDUrate>
The fSDUrate and bSDUrate are the maximum forward and backward SDU rates in bits/second. These are represented as decimal integers, with range as defined in Section 6. If any of these parameters in these media attribute lines is not specified, is inapplicable or is implied, then it is set to "-".
fSDUrate和bSDUrate是以位/秒为单位的最大向前和向后SDU速率。它们表示为十进制整数，其范围如第6节所定义。如果这些媒体属性行中的任何参数未指定、不适用或隐含，则将其设置为“-”。
When present, the 'aal2sscs3661unassured' attribute is used to indicate the options that pertain to the unassured transmission SSCS defined in ITU I.366.1 [12]. This SSCS can be selected via the aalApp attribute defined below, or by virtue of the presence of the ' aal2sscs3661unassured' attribute. The format of this media attribute line is as follows:
存在时，“aal2sscs3661unassured”属性用于指示与ITU I.366.1[12]中定义的未保证传输SSC相关的选项。该SSC可通过以下定义的aalApp属性选择，或通过存在“aal2sscs3661unassured”属性选择。此媒体属性行的格式如下：
a=aal2sscs3661unassured: <ted> <rastimer> <fsssar> <bsssar>
a=aal2sscs3661unassured: <ted> <rastimer> <fsssar> <bsssar>
Each of these fields can be set to a "-" when the intention is to not specify them in an SDP descriptor.
当目的是不在SDP描述符中指定这些字段时，可以将每个字段设置为“-”。
The <ted> flag indicates the presence or absence of transmission error detection as defined in I.366.1. It can be assigned the values of "on" or "off". An "on" value indicates presence of the capability.
<ted>标志表示存在或不存在I.366.1中定义的传输错误检测。可以为其指定“开”或“关”的值。“开”值表示存在该能力。
The <rastimer> subparameter indicates the SSSAR reassembly timer in microseconds. It is represented as the decimal equivalent of 32 bits.
<rastimer>子参数以微秒为单位指示SSSAR重新组装计时器。它表示为相当于32位的十进制数。
The <fsssar> and <bsssar> fields are 24-bit integers that can be represented in decimal or in hex. The meaning and values of the <fsssar> and <bsssar> fields are as follows:
<fsssar>和<bsssar>字段是24位整数，可以用十进制或十六进制表示。<fsssar>和<bsssar>字段的含义和值如下：
Field Meaning Values
字段意义值
<fsssar> Maximum SSSAR-SDU size 1- 65,568 forward direction
<fsssar>最大SSSAR-SDU尺寸1-65568正向
<bsssar> Maximum SSSAR-SDU size 1- 65,568 backward direction
<bsssar>最大SSSAR-SDU尺寸1-65568反向
If present, the SSTED (Service-Specific Transmission Error Detection) sublayer is above the SSSAR (Service-Specific Segmentation and Reassembly) sublayer [12]. Since the maximum size of the SSTED-SDUs can be derived from the maximum SSSAR-SDU size, it need not be specified separately.
如果存在，SSTED（特定于服务的传输错误检测）子层位于SSSAR（特定于服务的分段和重新组装）子层之上[12]。由于SSTED SDU的最大大小可以从SSSAR-SDU的最大大小导出，因此无需单独指定。
When present, the 'aal2sscs3661assured' attribute is used to indicate the options that pertain to the assured transmission SSCS defined in ITU I.366.1 [12] on the basis of ITU Q.2110 [43]. This SSCS can be selected via the aalApp attribute defined below, or by virtue of the presence of the 'aal2sscs3661assured' attribute. The format of this media attribute line is as follows:
当存在时，“aal2sscs3661assured”属性用于指示与ITU I.366.1[12]中基于ITU Q.2110[43]定义的保证传输SSC相关的选项。该SSC可通过以下定义的aalApp属性选择，或通过存在“aal2sscs3661assured”属性选择。此媒体属性行的格式如下：
a=aal2sscs3661assured: <rastimer> <fsssar> <bsssar> <fsscopsdu>
<bsscopsdu><fsscopuu> <bsscopuu>
a=aal2sscs3661assured: <rastimer> <fsssar> <bsssar> <fsscopsdu>
<bsscopsdu><fsscopuu> <bsscopuu>
Each of these fields can be set to a "-" when the intention is to not specify them in an SDP descriptor.
当目的是不在SDP描述符中指定这些字段时，可以将每个字段设置为“-”。
The <rastimer> subparameter indicates the SSSAR reassembly timer in microseconds. It is represented as the decimal equivalent of 32 bits.
<rastimer>子参数以微秒为单位指示SSSAR重新组装计时器。它表示为相当于32位的十进制数。
The <fsssar> and <bsssar> fields are 24-bit integers that can be represented in decimal or in hex. The <fsscopsdu>, <bsscopsdu>, <fsscopuu> and <bsscopuu> fields are 16-bit integers that can be represented in decimal or in hex. The meaning and values of these fields is as follows:
<fsssar>和<bsssar>字段是24位整数，可以用十进制或十六进制表示。<fsscopsdu>、<bsscopsdu>、<fsscopu>和<bsscopu>字段是16位整数，可以用十进制或十六进制表示。这些字段的含义和值如下：
Field Meaning Values
字段意义值
<fsssar> Maximum SSSAR-SDU size 1- 65,568 forward direction
<fsssar>最大SSSAR-SDU尺寸1-65568正向
<bsssar> Maximum SSSAR-SDU size 1- 65,568 backward direction
<bsssar>最大SSSAR-SDU尺寸1-65568反向
<fsscopsdu> Maximum SSCOP-SDU size 1- 65,528 forward direction
<fsscopsdu>最大SSCOP-SDU尺寸1-65528正向
<bsscopsdu> Maximum SSCOP-SDU size 1- 65,528 backward direction
<bsscopsdu>最大SSCOP-SDU尺寸1-65528反向
<fsscopuu> Maximum SSCOP-UU field 1- 65,524 size, forward direction
<fsscopuu>最大SSCOP-UU字段1-65524大小，正向
<bsscopuu> Maximum SSCOP-UU field 1- 65,524 size, backward direction
<bsscopuu>最大SSCOP-UU字段1-65524大小，反向
The SSTED (Service-Specific Transmission Error Detection) sublayer is above the SSSAR (Service-Specific Segmentation and Reassembly) sublayer [12]. The SSADT (Service-Specific Assured Data Transfer) sublayer is above the SSTED sublayer. Since the maximum size of the SSTED-SDUs and SSADT-SDUs can be derived from the maximum SSSAR-SDU size, they need not be specified separately.
SSTED（特定于服务的传输错误检测）子层位于SSSAR（特定于服务的分段和重组）子层之上[12]。SSADT（特定服务保证数据传输）子层位于SSTED子层之上。由于SSTED SDU和SSADT SDU的最大大小可以从SSSAR-SDU的最大大小推导而来，因此无需单独指定。
The SSCOP protocol defined in [43] is used by the Assured Data Transfer service defined in [12]. In the context of the ITU I.366.1 SSCS, it is possible to use the 'aal2sscs3661assured' attribute to limit the maximum sizes of the SSCOP SDUs and UU (user-to-user) fields in either direction. Note that it is necessary for the parameters on the 'aal2sscs3661assured' media attribute line to be consistent with each other.
[43]中定义的SSCOP协议由[12]中定义的有保证数据传输服务使用。在ITU I.366.1 SSC的上下文中，可以使用“aal2sscs3661assured”属性限制SSCOP SDU和UU（用户对用户）字段在任一方向上的最大大小。请注意，“aal2sscs3661assured”媒体属性行上的参数必须相互一致。
When present, the 'aal2sscs3662' attribute is used to indicate the options that pertain to the SSCS defined in ITU I.366.2 [13]. This SSCS can be selected via the aalApp attribute defined below, or by the presence of the 'aal2sscs3662' attribute.
当存在时，“aal2sscs3662”属性用于指示与ITU I.366.2[13]中定义的SSC相关的选项。该SSC可通过以下定义的aalApp属性或“aal2sscs3662”属性进行选择。
The format of this media attribute line is as follows:
此媒体属性行的格式如下：
a=aal2sscs3662: <sap> <circuitMode> <frameMode> <faxDemod>
<cas> <dtmf> <mfall> <mfr1> <mfr2>
<PCMencoding> <fmaxFrame> <bmaxFrame>
a=aal2sscs3662: <sap> <circuitMode> <frameMode> <faxDemod>
<cas> <dtmf> <mfall> <mfr1> <mfr2>
<PCMencoding> <fmaxFrame> <bmaxFrame>
Each of these fields can be set to a "-" when the intention is to not specify them in an SDP descriptor. Additionally, the values of these fields need to be consistent with each other. Inconsistencies should be flagged as errors.
当目的是不在SDP描述符中指定这些字段时，可以将每个字段设置为“-”。此外，这些字段的值需要彼此一致。不一致应标记为错误。
The <sap> field can take on the following string values: "AUDIO" and "MULTIRATE". These correspond to the audio and multirate Service Access Points (SAPs) defined in ITU I.366.2.
<sap>字段可以采用以下字符串值：“音频”和“多速率”。这些对应于ITU I.366.2中定义的音频和多速率服务接入点（SAP）。
For the multirate SAP, the following parameters on the aal2sscs3662 attribute line do not apply: <faxDemod>,<cas>, <dtmf>, <mfall>, <mfr1>, <mfr2> and <PCMencoding>. These are set to "-" for the multirate SAP.
对于多速率SAP，aal2sscs3662属性行上的以下参数不适用：<FaxDerm>、<cas>、<dtmf>、<mfall>、<mfr1>、<mfr2>和<PCMencoding>。对于多速率SAP，这些设置为“-”。
The <circuitMode> flag indicates whether the transport of circuit mode data is enabled or disabled, corresponding to the string values of "on" and "off" respectively. For the multirate SAP, it cannot have a value of "off". For the audio SAP, it can be assigned a value of "on", "off" or "-". Note that the <sbc> attribute, defined elsewhere in this document, can be used to specify the number of 64 kbps subchannels bundled into a circuit mode data channel.
<circuitMode>标志指示电路模式数据的传输是启用还是禁用，分别对应于字符串值“on”和“off”。对于多速率SAP，其值不能为“off”。对于音频SAP，可以为其指定“开”、“关”或“-”的值。请注意，本文档其他地方定义的<sbc>属性可用于指定捆绑到电路模式数据通道中的64 kbps子通道的数量。
The <frameMode> flag indicates whether the transport of frame mode data is enabled or disabled, corresponding to the string values of "on" and "off" respectively.
<frameMode>标志指示帧模式数据的传输是启用还是禁用，分别对应于字符串值“on”和“off”。
The <faxDemod> flag indicates whether facsimile demodulation and remodulation are enabled or disabled, corresponding to the string values of "on" and "off" respectively.
<FaxDerm>标志指示是启用还是禁用传真解调和重新调制，分别对应于字符串值“开”和“关”。
The <cas> flag indicates whether the transport of Channel Associated Signaling (CAS) bits in AAL2 type 3 packets is enabled or disabled, corresponding to the string values of "on" and "off" respectively.
<cas>标志指示AAL2类型3数据包中信道相关信令（cas）位的传输是启用还是禁用，分别对应于字符串值“开”和“关”。
The <dtmf> flag indicates whether the transport of DTMF dialled digits in AAL2 type 3 packets is enabled or disabled, corresponding to the string values of "on" and "off" respectively.
<dtmf>标志指示AAL2类型3数据包中dtmf拨号数字的传输是启用还是禁用，分别对应于字符串值“开”和“关”。
The <mfall> flag indicates whether the transport of MF dialled digits in AAL2 type 3 packets is enabled or disabled, corresponding to the string values of "on" and "off" respectively. This flag enables MF dialled digits in a generic manner, without specifying type (e.g., R1, R2 etc.).
<mfall>标志指示AAL2类型3数据包中MF拨号数字的传输是启用还是禁用，分别对应于字符串值“开”和“关”。此标志以通用方式启用MF拨号数字，而不指定类型（例如R1、R2等）。
The <mfr1> flag indicates whether the transport, in AAL2 type 3 packets, of MF dialled digits for signaling system R1 is enabled or disabled, corresponding to the string values of "on" and "off" respectively.
<mfr1>标志指示在AAL2类型3数据包中，信号系统R1的MF拨号数字传输是启用还是禁用，分别对应于字符串值“开”和“关”。
The <mfr2> flag indicates whether the transport, in AAL2 type 3 packets, of MF dialled digits for signaling system R2 is enabled or disabled, corresponding to the string values of "on" and "off" respectively.
<mfr2>标志指示在AAL2类型3数据包中，信号系统R2的MF拨号数字传输是启用还是禁用，分别对应于字符串值“开”和“关”。
The <PCMencoding> field indicates whether PCM encoding, if used, is based on the A-law or the Mu-law. This can be used to qualify the ' generic PCM' codec stated in some of the AAL2 profiles. The <PCMencoding> field can take on the string values of "PCMA" and "PCMU".
<PCMencoding>字段指示PCM编码（如果使用）是基于A法则还是基于Mu法则。这可用于限定某些AAL2配置文件中所述的“通用PCM”编解码器。<PCMencoding>字段可以采用字符串值“PCMA”和“PCMU”。
The <fmaxFrame> and <bmaxFrame> fields are 16-bit integers that can be represented in decimal or in hex. The meaning and values of the <fmaxFrame> and <bmaxFrame> fields are as follows:
<fmaxFrame>和<bmaxFrame>字段是16位整数，可以用十进制或十六进制表示。<fmaxFrame>和<bmaxFrame>字段的含义和值如下：
Field Meaning Values
字段意义值
<fmaxFrame> Maximum length of a 1- 65,535 frame mode data unit, forward direction
<fmaxFrame>正向1-65535帧模式数据单元的最大长度
<bmaxFrame> Maximum length of a 1- 65,535 frame mode data unit, backward direction
<bmaxFrame>1-65535帧模式数据单元的最大长度，反向
When present, the 'aal5sscop' attribute is used to indicate the existence of an SSCOP [43] protocol layer over an AAL5 CPS layer [21], and the parameters which pertain to this SSCOP layer. SSCOP over AAL5 can also be selected via the aalApp attribute defined below. The format of the 'aal5sscop' media attribute line is as follows:
存在时，“aal5sscop”属性用于指示AAL5 CPS层[21]上存在SSCOP[43]协议层，以及与该SSCOP层相关的参数。也可以通过下面定义的aalApp属性选择AAL5上的SSCOP。“aal5sscop”媒体属性行的格式如下：
a=aal5sscop: <fsscopsdu> <bsscopsdu> <fsscopuu> <bsscopuu>
a=aal5sscop: <fsscopsdu> <bsscopsdu> <fsscopuu> <bsscopuu>
Each of these fields can be set to a "-" when the intention is to not specify them in an SDP descriptor.
当目的是不在SDP描述符中指定这些字段时，可以将每个字段设置为“-”。
The representation, meaning and values of the <fsscopsdu>, <bsscopsdu>, <fsscopuu> and <bsscopuu> fields are identical to those for the 'aal2sscs3661assured' media attribute line (Section 5.6.2.12). Note that it is necessary for the parameters on the ' aal5sscop' media attribute line to be consistent with each other.
<fsscopsdu>、<bsscopsdu>、<fsscopu>和<bsscopu>字段的表示、含义和值与“aal2sscs3661assured”媒体属性行的表示、含义和值相同（第5.6.2.12节）。请注意，“aal5sscop”介质属性行上的参数必须相互一致。
The following is a summary list of the SDP media attributes that can be used to describe the services that use the ATM Adaptation Layer (AAL). These attributes are detailed in subsequent subsections.
以下是SDP媒体属性的摘要列表，可用于描述使用ATM适配层（AAL）的服务。这些属性将在后续小节中详细介绍。
* The 'atmmap' attribute. In the AAL1 and AAL5 contexts, this is used to dynamically map payload types into codec strings.
* “atmmap”属性。在AAL1和AAL5上下文中，这用于将有效负载类型动态映射到编解码器字符串中。
* The 'silenceSupp' attribute, used to indicate the use of of voice activity detection for silence suppression, and to optionally parameterize the silence suppression function.
* “沉默抑制”属性，用于指示将语音活动检测用于沉默抑制，并可选地参数化沉默抑制功能。
* The 'ecan' attribute, used to indicate the use of of echo cancellation, and to parameterize the this function.
* “ecan”属性，用于指示回声消除的使用，并用于参数化此函数。
* The 'gc' attribute, used to indicate the use of of gain control, and to parameterize the this function.
* “gc”属性，用于指示增益控制的使用，并参数化此函数。
* The 'profileDesc' attribute, which can be used to describe AAL2 profiles. Although any AAL2 profile can be so described, this attribute is useful for describing, at connection establishment time, custom profiles that might not be known to the far end. This attribute applies in the AAL2 context only.
* “profileDesc”属性，可用于描述AAL2配置文件。尽管任何AAL2配置文件都可以这样描述，但此属性在连接建立时用于描述远端可能不知道的自定义配置文件。此属性仅适用于AAL2上下文。
* The 'vsel' attribute, which indicates a prioritized list of 3- tuples for voice service. Each 3-tuple indicates a codec, an optional packet length and an optional packetization period. This complements the 'm' line information and should be consistent with it.
* “vsel”属性，表示语音服务的3元组的优先级列表。每个三元组表示一个编解码器、一个可选的数据包长度和一个可选的数据包化周期。这是对“m”行信息的补充，并应与之保持一致。
* The 'dsel' attribute, which indicates a prioritized list of 3- tuples for voiceband data service. Each 3-tuple indicates a codec, an optional packet length and an optional packetization period. This complements the 'm' line information and should be consistent with it.
* “dsel”属性，表示语音带数据服务的3元组的优先级列表。每个三元组表示一个编解码器、一个可选的数据包长度和一个可选的数据包化周期。这是对“m”行信息的补充，并应与之保持一致。
* The 'fsel' attribute, which indicates a prioritized list of 3- tuples for facsimile service. Each 3-tuple indicates a codec, an optional packet length and an optional packetization period. This complements the 'm' line information and should be consistent with it.
* “fsel”属性，表示传真服务的3元组的优先列表。每个三元组表示一个编解码器、一个可选的数据包长度和一个可选的数据包化周期。这是对“m”行信息的补充，并应与之保持一致。
* The 'onewaySel' attribute, which indicates a prioritized list of 3-tuples for one direction of an asymmetric connection. Each 3-tuple indicates a codec, an optional packet length and an optional packetization period. This complements the 'm' line information and should be consistent with it.
* “onewaySel”属性，表示非对称连接的一个方向的3元组的优先列表。每个三元组表示一个编解码器、一个可选的数据包长度和一个可选的数据包化周期。这是对“m”行信息的补充，并应与之保持一致。
* The 'codecconfig' attribute, which is used to represent the contents of the single codec information element (IE) defined in ITU Q.765.5 [57].
* “codeconfig”属性，用于表示ITU Q.765.5[57]中定义的单个编解码器信息元素（IE）的内容。
* The 'isup_usi' attribute which is used to represent the bearer capability information element defined in Section 4.5.5 of ITU Q.931 [59], and reiterated as the user service information element (IE) in Section 3.57 of ITU Q.763 [60].
* “isup_usi”属性，用于表示ITU Q.931[59]第4.5.5节中定义的承载能力信息元素，并在ITU Q.763[60]第3.57节中重申为用户服务信息元素（IE）。
* The 'uiLayer1_Prot' attribute, which is used to represent the ' User Information Layer 1 protocol' field within the bearer capability information element defined in Section 4.5.5 of ITU Q.931 [59].
* “uiLayer1_Prot”属性，用于表示ITU Q.931[59]第4.5.5节定义的承载能力信息元素中的“用户信息层1协议”字段。
The 'atmmap' attribute is defined on the basis of the 'rtpmap' attribute used in RFC 2327.
“atmmap”属性是根据RFC 2327中使用的“rtpmap”属性定义的。
a=atmmap:<payloadType> <encodingName>
a=atmmap:<payloadType> <encodingName>
The 'atmmap' attribute is used to dynamically map encoding names into payload types. This is necessary for those encoding names which have not been assigned a static payload type through IANA [31]. Payload types and encoding techniques that have been registered with IANA for RTP are retained for AAL1 and AAL5.
“atmmap”属性用于将编码名称动态映射到有效负载类型。这对于那些尚未通过IANA分配静态有效负载类型的编码名称是必要的[31]。已向IANA注册用于RTP的有效负载类型和编码技术保留用于AAL1和AAL5。
The range of statically defined payload types is in the range 0-95. All static assignments of payload types to codecs are listed in [31]. The range of payload types defined dynamically via the 'atmmap' attribute is 96-127.
静态定义的有效负载类型的范围在0-95之间。[31]中列出了编解码器有效负载类型的所有静态分配。通过“atmmap”属性动态定义的有效负载类型范围为96-127。
In addition to reiterating the payload types and encoding names in [31], Table 2 defines non-standard encoding names (with "X-" prefixes). Note that [31], rather than Table 2, is the authoritative list of standard codec names and payload types in the ATM context.
除了重申[31]中的有效负载类型和编码名称外，表2还定义了非标准编码名称（带有“X-”前缀）。请注意[31]，而不是表2，是ATM上下文中标准编解码器名称和有效负载类型的权威列表。
Table 2: Encoding Names and Payload Types
表2：编码名称和有效负载类型
|---------------------|--------------|---------------------------|
| Encoding Technique | Encoding Name| Payload type |
|---------------------|--------------|---------------------------|
| PCM - Mu law | "PCMU" | 0 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| 32 kbps ADPCM | "G726-32" | 2 (Statically Mapped) |
|---------------------|--------------|---------------------------|
|Dual rate 5.3/6.3kbps| "G723" | 4 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| PCM- A law | "PCMA" | 8 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| 7 KHz audio coding | "G722" | 9 (Statically Mapped) |
| within 64 kbps | | |
|---------------------|--------------|---------------------------|
| LD-CELP | "G728" | 15 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| CS-ACELP | "G729" | 18 (Statically Mapped) |
|(normal/low-complexity) | |
|---------------------|--------------|---------------------------|
| Encoding Technique | Encoding Name| Payload type |
|---------------------|--------------|---------------------------|
| PCM - Mu law | "PCMU" | 0 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| 32 kbps ADPCM | "G726-32" | 2 (Statically Mapped) |
|---------------------|--------------|---------------------------|
|Dual rate 5.3/6.3kbps| "G723" | 4 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| PCM- A law | "PCMA" | 8 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| 7 KHz audio coding | "G722" | 9 (Statically Mapped) |
| within 64 kbps | | |
|---------------------|--------------|---------------------------|
| LD-CELP | "G728" | 15 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| CS-ACELP | "G729" | 18 (Statically Mapped) |
|(normal/low-complexity) | |
|---------------------|--------------|---------------------------|
| Low-complexity | "X-G729a" | None, map dynamically |
| CS-ACELP | | |
|---------------------|--------------|---------------------------|
|Normal | "X-G729b" | None, map dynamically |
|CS-ACELP w/ ITU | | |
|defined silence | | |
|suppression | | |
+---------------------+--------------+---------------------------+
|Low-complexity | "X-G729ab" | None, map dynamically |
|CS-ACELP w/ ITU | | |
|defined silence | | |
|suppression | | |
|---------------------|--------------|---------------------------|
| 16 kbps ADPCM | "X-G726-16" | None, map dynamically |
|---------------------|--------------|---------------------------|
| 24 kbps ADPCM | "X-G726-24" | None, map dynamically |
|---------------------|--------------|---------------------------|
| 40 kbps ADPCM | "X-G726-40" | None, map dynamically |
|---------------------|--------------|---------------------------|
| Dual rate 5.3/6.3 |"X-G7231-H" | None, map dynamically |
| kbps - high rate | | |
|---------------------|--------------|---------------------------|
| Dual rate 5.3/6.3 |"X-G7231-L" | None, map dynamically |
| kbps - low rate | | |
|---------------------|--------------|---------------------------|
| Dual rate 5.3/6.3 |"X-G7231a-H" | None, map dynamically |
| kbps - high rate w/ | | |
| ITU-defined silence | | |
| suppression | | |
|----------------------------------------------------------------|
+---------------------+--------------+---------------------------+
| Dual rate 5.3/6.3 |"X-G7231a-L" | None, map dynamically |
| kbps - high rate w/ | | |
| ITU-defined silence | | |
| suppression | | |
|---------------------|--------------|---------------------------|
| 16 kbps EADPCM | "X-G727-16" | None, map dynamically |
|---------------------|--------------|---------------------------|
| 24 kbps EADPCM | "X-G727-24" | None, map dynamically |
|---------------------|--------------|---------------------------|
| 32 kbps EADPCM | "X-G727-32" | None, map dynamically |
|---------------------|--------------|---------------------------|
|n x 64 kbps Clear | "X-CCD" | None, map dynamically |
|Channel without CAS | | |
|per af-vtoa-78 [7] | | |
|---------------------|--------------|---------------------------|
|---------------------|--------------|---------------------------|
| Low-complexity | "X-G729a" | None, map dynamically |
| CS-ACELP | | |
|---------------------|--------------|---------------------------|
|Normal | "X-G729b" | None, map dynamically |
|CS-ACELP w/ ITU | | |
|defined silence | | |
|suppression | | |
+---------------------+--------------+---------------------------+
|Low-complexity | "X-G729ab" | None, map dynamically |
|CS-ACELP w/ ITU | | |
|defined silence | | |
|suppression | | |
|---------------------|--------------|---------------------------|
| 16 kbps ADPCM | "X-G726-16" | None, map dynamically |
|---------------------|--------------|---------------------------|
| 24 kbps ADPCM | "X-G726-24" | None, map dynamically |
|---------------------|--------------|---------------------------|
| 40 kbps ADPCM | "X-G726-40" | None, map dynamically |
|---------------------|--------------|---------------------------|
| Dual rate 5.3/6.3 |"X-G7231-H" | None, map dynamically |
| kbps - high rate | | |
|---------------------|--------------|---------------------------|
| Dual rate 5.3/6.3 |"X-G7231-L" | None, map dynamically |
| kbps - low rate | | |
|---------------------|--------------|---------------------------|
| Dual rate 5.3/6.3 |"X-G7231a-H" | None, map dynamically |
| kbps - high rate w/ | | |
| ITU-defined silence | | |
| suppression | | |
|----------------------------------------------------------------|
+---------------------+--------------+---------------------------+
| Dual rate 5.3/6.3 |"X-G7231a-L" | None, map dynamically |
| kbps - high rate w/ | | |
| ITU-defined silence | | |
| suppression | | |
|---------------------|--------------|---------------------------|
| 16 kbps EADPCM | "X-G727-16" | None, map dynamically |
|---------------------|--------------|---------------------------|
| 24 kbps EADPCM | "X-G727-24" | None, map dynamically |
|---------------------|--------------|---------------------------|
| 32 kbps EADPCM | "X-G727-32" | None, map dynamically |
|---------------------|--------------|---------------------------|
|n x 64 kbps Clear | "X-CCD" | None, map dynamically |
|Channel without CAS | | |
|per af-vtoa-78 [7] | | |
|---------------------|--------------|---------------------------|
|n x 64 kbps Clear | "X-CCD-CAS" | None, map dynamically |
|Channel with CAS | | |
|per af-vtoa-78 [7] | | |
|---------------------|--------------|---------------------------|
|GSM Full Rate | "GSM" | 3 (Statically Mapped) |
|---------------------|--------------|---------------------------|
|GSM Half Rate | "GSM-HR" | None, map dynamically |
|---------------------|--------------|---------------------------|
|GSM-Enhanced Full Rate "GSM-EFR" | None, map dynamically |
|---------------------|--------------|---------------------------|
|GSM-Enhanced Half Rate "GSM-EHR" | None, map dynamically |
|---------------------|--------------|---------------------------|
|Group 3 fax demod. | "X-FXDMOD-3" | None, map dynamically |
|---------------------|--------------|---------------------------|
| Federal Standard | "1016" | 1 (Statically Mapped) |
| FED-STD 1016 CELP | | |
|---------------------|--------------|---------------------------|
| DVI4, 8 KHz [3] | "DVI4" | 5 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| DVI4, 16 KHz [3] | "DVI4" | 6 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| LPC [3], Linear | "LPC" | 7 (Statically Mapped) |
| Predictive Coding | | |
|---------------------|--------------|---------------------------|
| L16 [3], Sixteen | "L16" | 10 (Statically Mapped) |
| Bit Linear PCM, | | |
| Double channel | | |
|---------------------|--------------|---------------------------|
| L16 [3], Sixteen | "L16" | 11 (Statically Mapped) |
| Bit Linear PCM, | | |
| Single channel | | |
|---------------------|--------------|---------------------------|
| QCELP [3] | "QCELP" | 12 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| MPEG1/MPEG2 audio | "MPA" | 14 (Statically Mapped) |
|---------------------|--------------|---------------------------|
+---------------------+--------------+---------------------------+
| DVI4, 11.025 KHz[3] | "DVI4" | 16 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| DVI4, 22.05 KHz [3] | "DVI4" | 17 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| MPEG1/MPEG2 video | "MPV" | 32 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| MPEG 2 audio/video | "MP2T" | 33 (Statically Mapped) |
| transport stream | | |
|---------------------|--------------|---------------------------|
| ITU H.261 video | "H261" | 31 (Statically Mapped) |
|---------------------|--------------|---------------------------|
|n x 64 kbps Clear | "X-CCD-CAS" | None, map dynamically |
|Channel with CAS | | |
|per af-vtoa-78 [7] | | |
|---------------------|--------------|---------------------------|
|GSM Full Rate | "GSM" | 3 (Statically Mapped) |
|---------------------|--------------|---------------------------|
|GSM Half Rate | "GSM-HR" | None, map dynamically |
|---------------------|--------------|---------------------------|
|GSM-Enhanced Full Rate "GSM-EFR" | None, map dynamically |
|---------------------|--------------|---------------------------|
|GSM-Enhanced Half Rate "GSM-EHR" | None, map dynamically |
|---------------------|--------------|---------------------------|
|Group 3 fax demod. | "X-FXDMOD-3" | None, map dynamically |
|---------------------|--------------|---------------------------|
| Federal Standard | "1016" | 1 (Statically Mapped) |
| FED-STD 1016 CELP | | |
|---------------------|--------------|---------------------------|
| DVI4, 8 KHz [3] | "DVI4" | 5 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| DVI4, 16 KHz [3] | "DVI4" | 6 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| LPC [3], Linear | "LPC" | 7 (Statically Mapped) |
| Predictive Coding | | |
|---------------------|--------------|---------------------------|
| L16 [3], Sixteen | "L16" | 10 (Statically Mapped) |
| Bit Linear PCM, | | |
| Double channel | | |
|---------------------|--------------|---------------------------|
| L16 [3], Sixteen | "L16" | 11 (Statically Mapped) |
| Bit Linear PCM, | | |
| Single channel | | |
|---------------------|--------------|---------------------------|
| QCELP [3] | "QCELP" | 12 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| MPEG1/MPEG2 audio | "MPA" | 14 (Statically Mapped) |
|---------------------|--------------|---------------------------|
+---------------------+--------------+---------------------------+
| DVI4, 11.025 KHz[3] | "DVI4" | 16 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| DVI4, 22.05 KHz [3] | "DVI4" | 17 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| MPEG1/MPEG2 video | "MPV" | 32 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| MPEG 2 audio/video | "MP2T" | 33 (Statically Mapped) |
| transport stream | | |
|---------------------|--------------|---------------------------|
| ITU H.261 video | "H261" | 31 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| ITU H.263 video | "H263" | 33 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| ITU H.263 video |"H263-1998" | None, map dynamically |
| 1998 version | | |
|---------------------|--------------|---------------------------|
|MPEG 1 system stream | "MP1S" | None, map dynamically |
|---------------------|--------------|---------------------------|
|MPEG 2 program stream| "MP2P" | None, map dynamically |
|---------------------|--------------|---------------------------|
|Redundancy | "RED" | None, map dynamically |
|---------------------|--------------|---------------------------|
|Variable rate DVI4 | "VDVI" | None, map dynamically |
|---------------------|--------------|---------------------------|
|Cell-B | "CelB" | 25 |
|---------------------|--------------|---------------------------|
|JPEG | "JPEG" | 26 |
|---------------------|--------------|---------------------------|
|nv | "nv" | 28 |
|---------------------|--------------|---------------------------|
|L8, Eight Bit Linear | "L8" | None, map dynamically |
|PCM | | |
|---------------------|--------------|---------------------------|
| ITU-R Recommendation| "BT656" | None, map dynamically |
| BT.656-3 for | | |
| digital video | | |
|---------------------|--------------|---------------------------|
| Adaptive Multirate | "FR-AMR" | None, map dynamically |
|-Full Rate (3GPP)[58]| | |
|---------------------|--------------|---------------------------|
| Adaptive Multirate | "HR-AMR" | None, map dynamically |
|-Half Rate (3GPP)[58]| | |
|---------------------|--------------|---------------------------|
| Adaptive Multirate | "UMTS-AMR" | None, map dynamically |
|- UMTS(3GPP) [58] | | |
|---------------------|--------------|---------------------------|
| Adaptive Multirate | "AMR" | None, map dynamically |
|- Generic [58] | | |
|---------------------|--------------|---------------------------|
| ITU H.263 video | "H263" | 33 (Statically Mapped) |
|---------------------|--------------|---------------------------|
| ITU H.263 video |"H263-1998" | None, map dynamically |
| 1998 version | | |
|---------------------|--------------|---------------------------|
|MPEG 1 system stream | "MP1S" | None, map dynamically |
|---------------------|--------------|---------------------------|
|MPEG 2 program stream| "MP2P" | None, map dynamically |
|---------------------|--------------|---------------------------|
|Redundancy | "RED" | None, map dynamically |
|---------------------|--------------|---------------------------|
|Variable rate DVI4 | "VDVI" | None, map dynamically |
|---------------------|--------------|---------------------------|
|Cell-B | "CelB" | 25 |
|---------------------|--------------|---------------------------|
|JPEG | "JPEG" | 26 |
|---------------------|--------------|---------------------------|
|nv | "nv" | 28 |
|---------------------|--------------|---------------------------|
|L8, Eight Bit Linear | "L8" | None, map dynamically |
|PCM | | |
|---------------------|--------------|---------------------------|
| ITU-R Recommendation| "BT656" | None, map dynamically |
| BT.656-3 for | | |
| digital video | | |
|---------------------|--------------|---------------------------|
| Adaptive Multirate | "FR-AMR" | None, map dynamically |
|-Full Rate (3GPP)[58]| | |
|---------------------|--------------|---------------------------|
| Adaptive Multirate | "HR-AMR" | None, map dynamically |
|-Half Rate (3GPP)[58]| | |
|---------------------|--------------|---------------------------|
| Adaptive Multirate | "UMTS-AMR" | None, map dynamically |
|- UMTS(3GPP) [58] | | |
|---------------------|--------------|---------------------------|
| Adaptive Multirate | "AMR" | None, map dynamically |
|- Generic [58] | | |
|---------------------|--------------|---------------------------|
When present, the 'silenceSupp' attribute is used to indicate the use or non-use of silence suppression. The format of the 'silenceSupp' media attribute line is as follows:
存在时，“沉默抑制”属性用于指示使用或不使用沉默抑制。“沉默支持”媒体属性行的格式如下：
a=silenceSupp: <silenceSuppEnable> <silenceTimer> <suppPref> <sidUse>
<fxnslevel>
a=silenceSupp: <silenceSuppEnable> <silenceTimer> <suppPref> <sidUse>
<fxnslevel>
If any of the parameters in the silenceSupp media attribute line is not specified, is inapplicable or is implied, then it is set to "-".
如果沉默支持媒体属性行中的任何参数未指定、不适用或隐含，则将其设置为“-”。
The <silenceSuppEnable> can take on values of "on" or "off". If it is "on", then silence suppression is enabled.
<SilenceSuppleEnable>可以采用“开”或“关”的值。如果为“开”，则静音抑制启用。
The <silenceTimer> is a 16-bit field which can be represented in decimal or hex. Each increment (tick) of this timer represents a millisecond. The maximum value of this timer is between 1 and 3 minutes. This timer represents the time-lag before silence suppression kicks in. Even though this can, theoretically, be as low as 1 ms, most DSP algorithms take more than that to detect silence. Setting <silenceTimer> to a large value (say 1 minute> is equivalent to disabling silence suppression within a call. However, idle channel suppression between calls on the basis of silence suppression is still operative in non-switched, trunking applications if <silenceSuppEnable> = "on" and <silenceTimer> is a large value.
<silenetimer>是一个16位字段，可以用十进制或十六进制表示。此计时器的每个增量（滴答）表示一毫秒。此计时器的最大值在1到3分钟之间。此计时器表示静音抑制开始前的时间延迟。尽管理论上这可能低至1ms，但大多数DSP算法需要更多的时间来检测静默。将<silenetimer>设置为较大的值（例如1分钟>）相当于禁用呼叫内的静音抑制。但是，如果<silenesuppenable>=“on”和<silenetimer>是较大的值，则基于静音抑制的呼叫之间的空闲信道抑制在非交换中继应用程序中仍然有效。
The <suppPref> specifies the preferred silence suppression method that is preferred or already selected. It can take on the string values of "standard" and "custom". If its value is "standard", then a standard method (e.g., ITU-defined) is preferred to custom methods if such a standard is defined. Otherwise, a custom method may be used. If <suppPref> is set to "custom", then a custom method, if available, is preferred to the standard method.
<suppref>指定首选或已选择的首选静音抑制方法。它可以接受“标准”和“自定义”的字符串值。如果其值为“标准”，则如果定义了标准，则标准方法（例如，ITU定义的）优于自定义方法。否则，可以使用自定义方法。如果<suppref>设置为“自定义”，则自定义方法（如果可用）优于标准方法。
The <sidUse> indicates whether SIDs (Silence Insertion Descriptors) are to be used, and whether they use fixed comfort noise or sampled background noise. It can take on the string values of "No SID", "Fixed Noise", "Sampled Noise".
<sidUse>指示是否要使用SIDs（静音插入描述符），以及它们是使用固定舒适噪声还是采样背景噪声。它可以采用字符串值“无SID”、“固定噪声”、“采样噪声”。
If the value of <sidUse> is "Fixed Noise", then <fxnslevel> provides its level. It can take on integer values in the range 0-127, as follows:
如果<sidUse>的值为“固定噪音”，则<fxnslevel>提供其音量。它可以采用0-127范围内的整数值，如下所示：
+-----------------------+---------------------+
| <fxnslevel> value | Meaning |
+-----------------------+---------------------+
| 0-29 | Reserved |
| 30 | -30 dBm0 |
| 31 | -31 dBm0 |
| . . . | . . . |
| 77 | -77 dBm0 |
| 78 | -78 dBm0 |
| 79-126 | reserved |
| 127 | Idle Code (no noise)|
+-----------------------+---------------------+
+-----------------------+---------------------+
| <fxnslevel> value | Meaning |
+-----------------------+---------------------+
| 0-29 | Reserved |
| 30 | -30 dBm0 |
| 31 | -31 dBm0 |
| . . . | . . . |
| 77 | -77 dBm0 |
| 78 | -78 dBm0 |
| 79-126 | reserved |
| 127 | Idle Code (no noise)|
+-----------------------+---------------------+
In addition to the decimal representation of <fxnslevel>, a hex representation, preceded by a "0x" prefix, is also allowed.
除了<fxnslevel>的十进制表示法外，还允许使用十六进制表示法，前缀为“0x”。
When present, the 'ecan' attribute s is used to indicate the use or non-use of echo cancellation. There can be several 'ecan' lines in an SDP description.
存在时，“ecan”属性用于指示是否使用回音消除。SDP描述中可能有多行“ecan”。
The format of the 'ecan' media attribute line is as follows:
“ecan”媒体属性行的格式如下：
a=ecan:<directionFlag><ecanEnable><ecanType>
a=ecan:<directionFlag><ecanEnable><ecanType>
The <directionFlag> can be assigned the following string values: "f", "b" and "fb". "f" and "b" indicate the forward and backward directions respectively. "fb" refers to both directions (forward and backward). Conventions for the forward and backward directions are per section 2.3.
<directionFlag>可以指定以下字符串值：“f”、“b”和“fb”。“f”和“b”分别表示向前和向后方向。“fb”指两个方向（向前和向后）。前进方向和后退方向的约定见第2.3节。
The <directionFlag> is always specified. Except for the <directionFlag>, the remaining parameters can be set to "-" to indicate that they are not specified, inapplicable or implied. However, there must be some specified parameters for the line to be useful in an SDP description.
始终指定<directionFlag>。除了<directionFlag>，其余参数可以设置为“-”，以表示未指定、不适用或隐含这些参数。但是，必须有一些指定的参数才能使该行在SDP描述中有用。
If the 'ecan' media attribute lines is not present, then means other than the SDP descriptor must be used to determine the applicability and nature of echo cancellation for a connection direction. Examples of such means are MIB provisioning, the local connection options structure in MGCP etc.
如果“ecan”媒体属性行不存在，则必须使用SDP描述符以外的方法来确定连接方向回声消除的适用性和性质。此类方法的示例包括MIB配置、MGCP中的本地连接选项结构等。
The <ecanEnable> parameter can take on values of "on" or "off". If it is "on", then echo cancellation is enabled. If it is "off", then echo cancellation is disabled.
<ecanEnable>参数可以采用“开”或“关”的值。如果为“开”，则启用回声消除。如果为“关闭”，则回声消除被禁用。
The <ecanType> parameter can take on the string values "G165" and "G168" respectively.
<ecanType>参数可以分别采用字符串值“G165”和“G168”。
When SDP is used with some media gateway control protocols such as MGCP and Megaco [26], there exist means outside SDP descriptions to specify the echo cancellation properties of a connection. Nevertheless, this media attribute line is included for completeness. As a result, the SDP can be used for describing echo cancellation in applications where alternate means for this are unavailable.
当SDP与某些媒体网关控制协议（如MGCP和Megaco[26]）一起使用时，SDP描述之外存在指定连接的回音消除属性的方法。然而，为了完整起见，包含此媒体属性行。因此，SDP可用于在无法使用替代方法的应用中描述回声消除。
When present, the 'gc' attribute is used to indicate the use or non-use of gain control. There can be several 'gc' lines in an SDP description.
存在时，“gc”属性用于指示使用或不使用增益控制。SDP描述中可能有多行“gc”。
The format of the 'gc' media attribute line is as follows:
“gc”媒体属性行的格式如下：
a=gc:<directionFlag><gcEnable><gcLvl>
a=gc:<directionFlag><gcEnable><gcLvl>
The <directionFlag> can be assigned the following string values: "f", "b" and "fb". "f" and "b" indicate the forward and backward directions respectively. "fb" refers to both directions (forward and backward). Conventions for the forward and backward directions are per section 2.3.
<directionFlag>可以指定以下字符串值：“f”、“b”和“fb”。“f”和“b”分别表示向前和向后方向。“fb”指两个方向（向前和向后）。前进方向和后退方向的约定见第2.3节。
The <directionFlag> is always specified. Except for the <directionFlag>, the remaining parameters can be set to "-" to indicate that they are not specified, inapplicable or implied. However, there must be some specified parameters for the line to be useful in an SDP description.
始终指定<directionFlag>。除了<directionFlag>，其余参数可以设置为“-”，以表示未指定、不适用或隐含这些参数。但是，必须有一些指定的参数才能使该行在SDP描述中有用。
If the 'gc' media attribute lines is not present, then means other than the SDP descriptor must be used to determine the applicability and nature of gain control for a connection direction. Examples of such means are MIB provisioning, the local connection options structure in MGCP etc.
如果“gc”媒体属性行不存在，则必须使用SDP描述符以外的方法来确定连接方向增益控制的适用性和性质。此类方法的示例包括MIB配置、MGCP中的本地连接选项结构等。
The <gcEnable> parameter can take on values of "on" or "off". If it is "on", then gain control is enabled. If it is "off", then gain control is disabled.
<gcEnable>参数可以采用“开”或“关”的值。如果为“开”，则增益控制启用。如果为“关闭”，则增益控制被禁用。
The <gcLvl> parameter is represented as the decimal or hex equivalent of a 16-bit binary field. A value of 0xFFFF implies automatic gain control. Otherwise, this number indicates the number of decibels of inserted loss. The upper bound, 65,535 dB (0xFFFE) of inserted loss, is a large number and is a carryover from Megaco [26]. In practical applications, the inserted loss is much lower.
<gcLvl>参数表示为16位二进制字段的十进制或十六进制等效值。0xFFFF值表示自动增益控制。否则，该数字表示插入损耗的分贝数。插入损耗的上限为65535 dB（0xFFFE），这是一个很大的数字，是Megaco的遗留物[26]。在实际应用中，插入损耗大大降低。
When SDP is used with some media gateway control protocols such as MGCP and Megaco [26], there exist means outside SDP descriptions to specify the gain control properties of a connection. Nevertheless, this media attribute line is included for completeness. As a result, the SDP can be used for describing gain control in applications where alternate means for this are unavailable.
当SDP与某些媒体网关控制协议（如MGCP和Megaco[26]）一起使用时，SDP描述之外存在指定连接增益控制属性的方法。然而，为了完整起见，包含此媒体属性行。因此，SDP可用于描述应用中的增益控制，其中替代方法不可用。
There is one 'profileDesc' media attribute line for each AAL2 profile that is intended to be described. The 'profileDesc' media attribute line is structured as follows:
每个要描述的AAL2配置文件都有一个“profileDesc”媒体属性行。“profileDesc”媒体属性行的结构如下：
a=profileDesc: <aal2transport> <profile> <uuiCodeRange#1>
<encodingName#1> <packetLength#1> <packetTime#1>
<uuiCodeRange#2> <encodingName#2> <packetLength#2>
<packetTime#2>... <uuiCodeRange#N> <encodingName#N>
<packetLength#N> <packetTime#N>
a=profileDesc: <aal2transport> <profile> <uuiCodeRange#1>
<encodingName#1> <packetLength#1> <packetTime#1>
<uuiCodeRange#2> <encodingName#2> <packetLength#2>
<packetTime#2>... <uuiCodeRange#N> <encodingName#N>
<packetLength#N> <packetTime#N>
Here, <aal2transport> can have those values of <transport> (Table 1) that pertain to AAL2. These are:
这里，<aal2transport>可以具有与AAL2相关的<transport>（表1）值。这些是：
AAL2/ATMF
AAL2/ITU
AAL2/custom
AAL2/<corporateName>
AAL2/IEEE:<oui>
AAL2/ATMF
AAL2/ITU
AAL2/custom
AAL2/<corporateName>
AAL2/IEEE:<oui>
The parameter <profile> is identical to its definition for the 'm' line (Section 5.5.4).
参数<profile>与“m”线的定义相同（第5.5.4节）。
The profile elements (rows in the profile tables of ITU I.366.2 or AF-VTOA-0113) are represented as four-tuples following the <profile> parameter in the 'profileDesc' media attribute line. If a member of one of these four-tuples is not specified or is implied, then it is set to "-".
配置文件元素（ITU I.366.2或AF-VTOA-0113配置文件表中的行）表示为“profileDesc”媒体属性行中<profile>参数后的四个元组。如果未指定或暗示这四个元组中的一个元组的成员，则将其设置为“-”。
The <uuiCodeRange> parameter is represented by D1-D2, where D1 and D2 are decimal integers in the range 0 through 15.
<uuicoraderange>参数由D1-D2表示，其中D1和D2是0到15范围内的十进制整数。
The <encodingName> parameter can take one of the values in column 2 of Table 2. Additionally, it can take on the following descriptor strings: "PCMG", "SIDG" and "SID729". These stand for generic PCM, generic SID and G.729 SID respectively.
<encodingName>参数可以采用表2第2列中的一个值。此外，它可以采用以下描述符字符串：“PCMG”、“SIDG”和“SID729”。这些分别代表通用PCM、通用SID和G.729 SID。
The <packetLength> is a decimal integer representation of the AAL2 packet length in octets.
<packetLength>是AAL2数据包长度的十进制整数表示，以八位字节为单位。
The <packetTime> is a decimal integer representation of the AAL2 packetization interval in microseconds.
<packetTime>是以微秒为单位的AAL2打包间隔的十进制整数表示。
For instance, the 'profileDesc' media attribute line below defines the AAL2/custom 100 profile. This profile is reproduced in the Table 3 below. For a description of the parameters in this profile such as M and the sequence number interval, see ITU I.366.2 [13].
例如，下面的“profileDesc”媒体属性行定义了AAL2/custom 100配置文件。下表3再现了这一概况。有关此配置文件中参数（如M和序列号间隔）的说明，请参见ITU I.366.2[13]。
a=profileDesc:AAL2/custom 100 0-7 PCMG 40 5000 0-7 SIDG 1 5000 8-15 G726-32 40 10000 8-15 SIDG 1 5000
a=profileDesc:AAL2/定制100 0-7 PCMG 40 5000 0-7 SIDG 1 5000 8-15 G726-32 40 10000 8-15 SIDG 1 5000
If the <packetTime> parameter is to be omitted or implied, then the same profile can be represented as follows:
如果要省略或暗示<packetTime>参数，则相同的配置文件可以表示为：
a=profileDesc:AAL2/custom 100 0-7 PCMG 40 - 0-7 SIDG 1 - 8-15
G726-32 40 - 8-15 SIDG 1 -
a=profileDesc:AAL2/custom 100 0-7 PCMG 40 - 0-7 SIDG 1 - 8-15
G726-32 40 - 8-15 SIDG 1 -
If a gateway has a provisioned or hard coded definition of a profile, then any definition provided via the 'profileDesc' line overrides it. The exception to this rule is with regard to standard profiles such as ITU-defined profiles and ATMF-defined profiles. In general, these should not be defined via a 'profileDesc' media attribute line. If they are, then the definition needs to be consistent with the standard definition else the SDP session descriptor should be rejected with an appropriate error code.
如果网关具有配置文件的已配置或硬编码定义，则通过“profileDesc”行提供的任何定义都将覆盖该配置文件。此规则的例外情况是关于标准配置文件，如ITU定义的配置文件和ATMF定义的配置文件。通常，不应通过“profileDesc”媒体属性行定义这些属性。如果是，则定义需要与标准定义一致，否则SDP会话描述符应被拒绝，并带有适当的错误代码。
Table 3: Example of a custom AAL2 profile
表3：自定义AAL2配置文件示例
|---------------------------------------------------------------|
| UUI | Packet |Encoding | | |Packet|Seq.No. |
| Code | Length |per ITU |Description of | M |Time |Interval|
|point |(octets)|I.366.2 | Algorithm | |(ms) |(ms) |
|Range | | 2/99 | | | | |
| | | version | | | | |
|---------------------------------------------------------------|
| 0-7 | 40 | Figure | PCM, G.711-64,| 1 | 5 | 5 |
| | | B-1 | generic | | | |
|------|--------|---------|---------------|-----|------|--------|
| 0-7 | 1 | Figure | Generic SID | 1 | 5 | 5 |
| | | I-1 | | | | |
|------|--------|---------|---------------|-----|------|--------|
| 8-15 | 40 | Figure | ADPCM, | 2 | 10 | 5 |
| | | E-2 | G.726-32 | | | |
|------|--------|---------|---------------|-----|------|--------|
| 8-15 | 1 | Figure | Generic SID | 1 | 5 | 5 |
| | | I-1 | | | | |
|------|--------|---------|---------------|-----|------|--------|
|---------------------------------------------------------------|
| UUI | Packet |Encoding | | |Packet|Seq.No. |
| Code | Length |per ITU |Description of | M |Time |Interval|
|point |(octets)|I.366.2 | Algorithm | |(ms) |(ms) |
|Range | | 2/99 | | | | |
| | | version | | | | |
|---------------------------------------------------------------|
| 0-7 | 40 | Figure | PCM, G.711-64,| 1 | 5 | 5 |
| | | B-1 | generic | | | |
|------|--------|---------|---------------|-----|------|--------|
| 0-7 | 1 | Figure | Generic SID | 1 | 5 | 5 |
| | | I-1 | | | | |
|------|--------|---------|---------------|-----|------|--------|
| 8-15 | 40 | Figure | ADPCM, | 2 | 10 | 5 |
| | | E-2 | G.726-32 | | | |
|------|--------|---------|---------------|-----|------|--------|
| 8-15 | 1 | Figure | Generic SID | 1 | 5 | 5 |
| | | I-1 | | | | |
|------|--------|---------|---------------|-----|------|--------|
The 'vsel' attribute indicates a prioritized list of one or more 3- tuples for voice service. Each 3-tuple indicates a codec, an optional packet length and an optional packetization period. This complements the 'm' line information and should be consistent with it.
“vsel”属性表示语音服务的一个或多个3元组的优先级列表。每个三元组表示一个编解码器、一个可选的数据包长度和一个可选的数据包化周期。这是对“m”行信息的补充，并应与之保持一致。
The 'vsel' attribute refers to all directions of a connection. For a bidirectional connection, these are the forward and backward directions. For a unidirectional connection, this can be either the backward or forward direction.
“vsel”属性表示连接的所有方向。对于双向连接，这些是向前和向后方向。对于单向连接，可以是向后或向前。
The 'vsel' attribute is not meant to be used with bidirectional connections that have asymmetric codec configurations described in a single SDP descriptor. For these, the 'onewaySel' attribute (section 5.6.3.9) should be used. See section 5.6.3.9 for the requirement to not use the 'vsel' and 'onewaySel' attributes in the same SDP descriptor.
“vsel”属性不适用于具有在单个SDP描述符中描述的不对称编解码器配置的双向连接。对于这些，应使用“单向选择”属性（第5.6.3.9节）。有关在同一SDP描述符中不使用“vsel”和“onewaySel”属性的要求，请参见第5.6.3.9节。
The 'vsel' line is structured as follows:
“vsel”行的结构如下所示：
a=vsel:<encodingName #1> <packetLength #1><packetTime #1>
<encodingName #2> <packetLength #2><packetTime #2>
...
<encodingName #N> <packetLength #N><packetTime #N>
a=vsel:<encodingName #1> <packetLength #1><packetTime #1>
<encodingName #2> <packetLength #2><packetTime #2>
...
<encodingName #N> <packetLength #N><packetTime #N>
where the <encodingName> parameter can take one of the values in column 2 of Table 2. The <packetLength> is a decimal integer representation of the packet length in octets. The <packetTime> is a decimal integer representation of the packetization interval in microseconds. The parameters <packetLength> and <packetTime> can be set to "-" when not needed. Also, the entire 'vsel' media attribute line can be omitted when not needed.
其中，<encodingName>参数可以采用表2第2列中的一个值。<packetLength>是以八位字节表示的数据包长度的十进制整数。<packetTime>是以微秒为单位的打包间隔的十进制整数表示。不需要时，可以将参数<packetLength>和<packetTime>设置为“-”。此外，在不需要时，可以省略整个“vsel”媒体属性行。
For example,
例如
a=vsel:G729 10 10000 G726-32 40 10000
a=vsel:G729 10 10000 G726-32 40 10000
indicates first preference of G.729 or G.729a (both are interoperable) as the voice encoding scheme. A packet length of 10 octets and a packetization interval of 10 ms are associated with this codec. G726-32 is the second preference stated in this line, with an associated packet length of 40 octets and a packetization interval of 10 ms. If the packet length and packetization interval are intended to be omitted, then this media attribute line becomes
表示G.729或G.729a（两者均可互操作）作为语音编码方案的首选项。10个八位字节的数据包长度和10毫秒的数据包化间隔与此编解码器相关联。G726-32是该行中规定的第二个首选项，相关数据包长度为40个八位字节，数据包化间隔为10毫秒。如果数据包长度和数据包化间隔有意省略，则该媒体属性行变为
a=vsel:G729 - - G726-32 - -
a=vsel:G729 - - G726-32 - -
The media attribute line
媒体属性行
a=vsel:G726-32 40 10000
a=vsel:G726-32 40 10000
indicates preference for or selection of 32 kbps ADPCM with a packet length of 40 octets and a packetization interval of 10 ms.
表示首选或选择32 kbps ADPCM，数据包长度为40个八位字节，数据包化间隔为10 ms。
This media attribute line can be used in ATM as well as non-ATM contexts. Within the ATM context, it can be applied to the AAL1, AAL2 and AAL5 adaptations. The <packetLength> and <packetTime> are not meaningful in the AAL1 case and should be set to "-". In the AAL2 case, this line determines the use of some or all of the rows in a given profile table. If multiple 3-tuples are present, they can indicate a hierarchical assignment of some rows in that profile to voice service (e.g., row A preferred to row B etc.). If multiple profiles are present on the 'm' line, the profile qualified by this attribute is the first profile. If a single profile that has been selected for a connection is indicated in the 'm' line, the 'vsel' attribute qualifies the use, for voice service, of codecs within that profile.
此媒体属性行可用于ATM以及非ATM上下文。在ATM上下文中，它可以应用于AAL1、AAL2和AAL5自适应。<packetLength>和<packetTime>在AAL1情况下没有意义，应设置为“-”。在AAL2的情况下，此行确定给定概要文件表中部分或全部行的使用。如果存在多个3元组，则它们可以表示该配置文件中某些行对语音服务的分层分配（例如，a行优先于B行等）。如果“m”行上存在多个配置文件，则此属性限定的配置文件是第一个配置文件。如果已为连接选择的单个配置文件在“m”行中指示，“vsel”属性限定该配置文件中的编解码器用于语音服务。
With most of the encoding names in Figure 2, the packet length and packetization period can be derived from each other. One of them can be set to "-" without a loss of information. There are some exceptions such as the IANA-registered encoding names G723, DVI4 and L16 for which this is not true. Therefore, there is a need to retain both the packet length and packetization period in the definition of the 'vsel' line.
对于图2中的大多数编码名称，数据包长度和打包周期可以相互派生。其中一个可以设置为“-”，而不会丢失信息。有一些例外情况，例如IANA注册的编码名称G723、DVI4和L16，这些情况不适用。因此，需要在“vsel”行的定义中保留数据包长度和数据包化周期。
The 'dsel' attribute indicates a prioritized list of one or more 3- tuples for voiceband data service. The <fxIncl> flag indicates whether this definition of voiceband data includes fax ("on" value) or not ("off" value). If <fxIncl> is "on", then the 'dsel' line must be consistent with any 'fsel' line in the session description. In this case, an error event is generated in the case of inconsistency. Each 3-tuple indicates a codec, an optional packet length and an optional packetization period. This complements the 'm' line information and should be consistent with it.
“dsel”属性表示语音带数据服务的一个或多个3元组的优先级列表。<fxIncl>标志指示此声带数据定义是否包括传真（“开”值）或不包括传真（“关”值）。如果<fxIncl>为“开”，则“dsel”行必须与会话描述中的任何“fsel”行一致。在这种情况下，在不一致的情况下会生成一个错误事件。每个三元组表示一个编解码器、一个可选的数据包长度和一个可选的数据包化周期。这是对“m”行信息的补充，并应与之保持一致。
The 'dsel' attribute refers to all directions of a connection. For a bidirectional connection, these are the forward and backward directions. For a unidirectional connection, this can be either the backward or forward direction.
“dsel”属性表示连接的所有方向。对于双向连接，这些是向前和向后方向。对于单向连接，可以是向后或向前。
The 'dsel' attribute is not meant to be used with bidirectional connections that have asymmetric codec configurations described in a single SDP descriptor. For these, the 'onewaySel' attribute (section 5.6.3.9) should be used. See section 5.6.3.9 for the requirement to not use the 'dsel' and 'onewaySel' attributes in the same SDP descriptor.
“dsel”属性不适用于具有在单个SDP描述符中描述的不对称编解码器配置的双向连接。对于这些，应使用“单向选择”属性（第5.6.3.9节）。有关在同一SDP描述符中不使用“dsel”和“onewaySel”属性的要求，请参见第5.6.3.9节。
The 'dsel' line is structured as follows:
“dsel”行的结构如下所示：
a=dsel:<fxIncl> <encodingName #1> <packetLength #1><packetTime #1>
<encodingName #2> <packetLength #2><packetTime #2>
...
<encodingName #N> <packetLength #N><packetTime #N>
a=dsel:<fxIncl> <encodingName #1> <packetLength #1><packetTime #1>
<encodingName #2> <packetLength #2><packetTime #2>
...
<encodingName #N> <packetLength #N><packetTime #N>
where the <encodingName> parameter can take one of the values in column 2 of Table 2. The <packetLength> and <packetTime> parameters are per their definition, above, for the 'vsel' media attribute line. The parameters <packetLength> and <packetTime>) can be set to "-" when not needed. The <fxIncl> flag is presumed to be "off" if it is set to "-". Also, the entire 'dsel' media attribute line can be omitted when not needed.
其中，<encodingName>参数可以采用表2第2列中的一个值。<packetLength>和<packetTime>参数根据其定义，如上所述，用于“vsel”媒体属性行。不需要时，可以将参数<packetLength>和<packetTime>设置为“-”。如果<fxIncl>标志设置为“-”，则假定该标志为“关闭”。此外，在不需要时，可以省略整个“dsel”媒体属性行。
For example,
例如
a=dsel:- G726-32 20 5000 PCMU 40 5000
a=dsel:-G726-32 20 5000 PCMU 40 5000
indicates that this line does not address facsimile, and that the first preference for the voiceband data codes is 32 kbps ADPCM, while the second preference is PCMU. The packet length and the packetization interval associated with G726-32 are 20 octets and 5 ms respectively. For PCMU, they are 40 octets and 5 ms respectively.
表示该行不处理传真，并且语音带数据代码的第一个首选项为32 kbps ADPCM，而第二个首选项为PCMU。与G726-32相关的分组长度和分组间隔分别为20个八位字节和5ms。对于PCMU，它们分别为40个八位字节和5毫秒。
This media attribute line can be used in ATM as well as non-ATM contexts. Within the ATM context, it can be applied to the AAL1, AAL2 and AAL5 adaptations. The <packetLength> and <packetTime> are not meaningful in the AAL1 case and should be set to "-". In the AAL2 case, this line determines the use of some or all of the rows in a given profile table. If multiple 3-tuples are present, they can indicate a hierarchical assignment of some rows in that profile to voiceband data service (e.g., row A preferred to row B etc.) If multiple profiles are present on the 'm' line, the profile qualified by this attribute is the first profile. If a single profile that has been selected for a connection is indicated in the 'm' line, the ' dsel' attribute qualifies the use, for voiceband data service, of codecs within that profile.
此媒体属性行可用于ATM以及非ATM上下文。在ATM上下文中，它可以应用于AAL1、AAL2和AAL5自适应。<packetLength>和<packetTime>在AAL1情况下没有意义，应设置为“-”。在AAL2的情况下，此行确定给定概要文件表中部分或全部行的使用。如果存在多个3元组，则它们可以表示该配置文件中某些行对语音带数据服务的分层分配（例如，a行优先于B行等）。如果“m”行上存在多个配置文件，则由该属性限定的配置文件是第一个配置文件。如果在“m”行中指示已为连接选择的单个配置文件，“dsel”属性限定该配置文件中的编解码器用于声带数据服务。
With most of the encoding names in Figure 2, the packet length and packetization period can be derived from each other. One of them can be set to "-" without a loss of information. There are some exceptions such as the IANA-registered encoding names G723, DVI4 and L16 for which this is not true. Therefore, there is a need to retain both the packet length and packetization period in the definition of the 'dsel' line.
对于图2中的大多数编码名称，数据包长度和打包周期可以相互派生。其中一个可以设置为“-”，而不会丢失信息。有一些例外情况，例如IANA注册的编码名称G723、DVI4和L16，这些情况不适用。因此，在“dsel”行的定义中需要保留数据包长度和数据包化周期。
The 'fsel' attribute indicates a prioritized list of one or more 3- tuples for facsimile service. If an 'fsel' line is present, any ' dsel' line with <fxIncl> set to "on" in the session description must be consistent with it. In this case, an error event is generated in the case of inconsistency. Each 3-tuple indicates a codec, an optional packet length and an optional packetization period. This complements the 'm' line information and should be consistent with it.
“fsel”属性表示传真服务的一个或多个3元组的优先级列表。如果存在“fsel”行，则会话描述中<fxIncl>设置为“on”的任何“dsel”行必须与之一致。在这种情况下，在不一致的情况下会生成一个错误事件。每个三元组表示一个编解码器、一个可选的数据包长度和一个可选的数据包化周期。这是对“m”行信息的补充，并应与之保持一致。
The 'fsel' attribute refers to all directions of a connection. For a bidirectional connection, these are the forward and backward directions. For a unidirectional connection, this can be either the backward or forward direction.
“fsel”属性表示连接的所有方向。对于双向连接，这些是向前和向后方向。对于单向连接，可以是向后或向前。
The 'fsel' attribute is not meant to be used with bidirectional connections that have asymmetric codec configurations described in a --single SDP descriptor. For these, the 'onewaySel' attribute (section 5.6.3.9) should be used. See section 5.6.3.9 for the requirement to not use the 'fsel' and 'onewaySel' attributes in the same SDP descriptor.
“fsel”属性不适用于具有单SDP描述符中描述的不对称编解码器配置的双向连接。对于这些，应使用“单向选择”属性（第5.6.3.9节）。有关在同一SDP描述符中不使用“fsel”和“onewaySel”属性的要求，请参见第5.6.3.9节。
The 'fsel' line is structured as follows:
“fsel”行的结构如下所示：
a=fsel:<encodingName #1> <packetLength #1><packetTime #1>
<encodingName #2> <packetLength #2><packetTime #2>
...
<encodingName #N> <packetLength #N><packetTime #N>
a=fsel:<encodingName #1> <packetLength #1><packetTime #1>
<encodingName #2> <packetLength #2><packetTime #2>
...
<encodingName #N> <packetLength #N><packetTime #N>
where the <encodingName> parameter can take one of the values in column 2 of Table 2. The <packetLength> and <packetTime> parameters are per their definition, above, for the 'vsel' media attribute line. The parameters <packetLength> and <packetTime> can be set to "-" when not needed. Also, the entire 'fsel' media attribute line can be omitted when not needed.
其中，<encodingName>参数可以采用表2第2列中的一个值。<packetLength>和<packetTime>参数根据其定义，如上所述，用于“vsel”媒体属性行。不需要时，可以将参数<packetLength>和<packetTime>设置为“-”。此外，在不需要时，可以省略整个“fsel”媒体属性行。
For example,
例如
a=fsel:FXDMOD-3 - -
a=fsel:FXDMOD-3 - -
indicates demodulation and remodulation of ITU-T group 3 fax at the gateway.
表示网关上ITU-T第3组传真的解调和重新调制。
a=fsel:PCMU 40 5000 G726-32 20 5000
a=fsel:PCMU 40 5000 G726-32 20 5000
indicates a first and second preference of Mu-law PCM and 32 kbps ADPCM as the facsimile encoding scheme. The packet length and the packetization interval associated with G726-32 are 20 octets and 5 ms respectively. For PCMU, they are 40 octets and 5 ms respectively.
表示Mu-law PCM和32 kbps ADPCM作为传真编码方案的第一和第二首选项。与G726-32相关的分组长度和分组间隔分别为20个八位字节和5ms。对于PCMU，它们分别为40个八位字节和5毫秒。
This media attribute line can be used in ATM as well as non-ATM contexts. Within the ATM context, it can be applied to the AAL1, AAL2 and AAL5 adaptations. The <packetLength> and <packetTime> are not meaningful in the AAL1 case and should be set to "-". In the AAL2 case, this line determines the use of some or all of the rows in a given profile table. If multiple 3-tuples are present, they can indicate a hierarchical assignment of some rows in that profile to facsimile service (e.g., row A preferred to row B etc.). If multiple profiles are present on the 'm' line, the profile qualified by this attribute is the first profile. If a single profile that has been selected for a connection is indicated in the 'm' line, the 'fsel' attribute qualifies the use, for facsimile service, of codecs within that profile.
此媒体属性行可用于ATM以及非ATM上下文。在ATM上下文中，它可以应用于AAL1、AAL2和AAL5自适应。<packetLength>和<packetTime>在AAL1情况下没有意义，应设置为“-”。在AAL2的情况下，此行确定给定概要文件表中部分或全部行的使用。如果存在多个3元组，则它们可以指示将该配置文件中的某些行分层分配给传真服务（例如，a行优先于B行等）。如果“m”行上存在多个配置文件，则此属性限定的配置文件是第一个配置文件。如果已为连接选择的单个配置文件在“m”行中指示，“fsel”属性限定该配置文件中的编解码器用于传真服务。
With most of the encoding names in Figure 2, the packet length and packetization period can be derived from each other. One of them can be set to "-" without a loss of information. There are some exceptions such as the IANA-registered encoding names G723, DVI4 and L16 for which this is not true. Therefore, there is a need to retain both the packet length and packetization period in the definition of the 'fsel' line.
对于图2中的大多数编码名称，数据包长度和打包周期可以相互派生。其中一个可以设置为“-”，而不会丢失信息。有一些例外情况，例如IANA注册的编码名称G723、DVI4和L16，这些情况不适用。因此，在“fsel”行的定义中需要保留数据包长度和数据包化周期。
The 'onewaySel' (one way select) attribute can be used with connections that have asymmetric codec configurations. There can be several 'onewaySel' lines in an SDP description. The 'onewaySel' line is structured as follows:
“onewaySel”（单向选择）属性可用于具有非对称编解码器配置的连接。SDP描述中可能有多个“单向选择”行。“单向选择”行的结构如下所示：
a=onewaySel:<serviceType> <directionFlag>
<encodingName #1> <packetLength #1><packetTime #1>
<encodingName #2> <packetLength #2><packetTime #2>
...
<encodingName #N> <packetLength #N><packetTime #N>
a=onewaySel:<serviceType> <directionFlag>
<encodingName #1> <packetLength #1><packetTime #1>
<encodingName #2> <packetLength #2><packetTime #2>
...
<encodingName #N> <packetLength #N><packetTime #N>
The <serviceType> parameter can be assigned the following string values: "v", "d", "f", "df" and "all". These indicate voice, voiceband data (fax not included), fax, voiceband data (fax included) and all services respectively.
<serviceType>参数可以指定以下字符串值：“v”、“d”、“f”、“df”和“all”。这些分别表示语音、声带数据（不包括传真）、传真、声带数据（包括传真）和所有服务。
The <directionFlag> can be assigned the following string values: "f", "b" and "fb". "f" and "b" indicate the forward and backward directions respectively. "fb" refers to both directions (forward and
<directionFlag>可以指定以下字符串值：“f”、“b”和“fb”。“f”和“b”分别表示向前和向后方向。“fb”指两个方向（向前和向后）
backward) and shall not be used with the 'onewaySel' line. Conventions for the forward and backward directions are per section 2.3.
向后）且不得与“单向选择”线路一起使用。前进方向和后退方向的约定见第2.3节。
Following <directionFlag>, there is a prioritized list of one or more 3-tuples. Each 3-tuple indicates a codec, an optional packet length and an optional packetization period. This complements the 'm' line information and should be consistent with it.
在<directionFlag>之后，有一个或多个3元组的优先列表。每个三元组表示一个编解码器、一个可选的数据包长度和一个可选的数据包化周期。这是对“m”行信息的补充，并应与之保持一致。
Within each 3-tuple, the <encodingName> parameter can take one of the values in column 2 of Table 2. The <packetLength> is a decimal integer representation of the packet length in octets. The <packetTime> is a decimal integer representation of the packetization interval in microseconds.
在每个3元组中，<encodingName>参数可以采用表2第2列中的一个值。<packetLength>是以八位字节表示的数据包长度的十进制整数。<packetTime>是以微秒为单位的打包间隔的十进制整数表示。
The 'onewaySel' attribute must not be used in SDP descriptors that have one or more of the following attributes: 'vsel', 'dsel', 'fsel'. If it is present, then command containing the SDP description may be rejected. An alternate response to such an ill-formed SDP descriptor might the selective ignoring of some attributes, which must be coordinated via an application-wide policy.
具有以下一个或多个属性的SDP描述符中不得使用“onewaySel”属性：“vsel”、“dsel”、“fsel”。如果存在，则可能拒绝包含SDP说明的命令。对这种格式错误的SDP描述符的另一种响应可能是选择性地忽略某些属性，这些属性必须通过应用程序范围的策略进行协调。
The <serviceType>, <directionFlag> and <encodingName> parameters may not be set to "-". However, the parameters <packetLength> and <packetTime> can be set to "-" when not needed.
<serviceType>、<directionFlag>和<encodingName>参数不能设置为“-”。但是，参数<packetLength>和<packetTime>可以在不需要时设置为“-”。
For example,
例如
a=onewaySel:v f G729 10 10000
a=onewaySel:v b G726-32 40 10000
a=onewaySel:v f G729 10 10000
a=onewaySel:v b G726-32 40 10000
indicates that for voice service, the codec to be used in the forward direction is G.729 or G.729a (both are interoperable), and the codec to be used in the backward direction is G726-32. A packet length of 10 octets and a packetization interval of 10 ms are associated with the G.729/G.729a codec. A packet length of 40 octets and a packetization interval of 10 ms are associated with the G726-32 codec.
指示对于语音服务，正向使用的编解码器为G.729或G.729a（两者都可互操作），反向使用的编解码器为G726-32。G.729/G.729a编解码器具有10个八位字节的数据包长度和10毫秒的数据包化间隔。数据包长度为40个八位字节，数据包化间隔为10毫秒，与G726-32编解码器相关。
For example,
例如
a=onewaySel:d f G726-32 20 5000
a=onewaySel:d b PCMU 40 5000
a=onewaySel:d f G726-32 20 5000
a=onewaySel:d b PCMU 40 5000
indicates that for voiceband service (fax not included), the codec to be used in the forward direction is G726-32), and the codec to be used in the backward direction is PCMU. A packet length of 20 octets
表示对于语音带服务（不包括传真），正向使用的编解码器为G726-32），反向使用的编解码器为PCMU。20个八位字节的数据包长度
and a packetization interval of 5 ms are associated with the G726-32 codec. A packet length of 40 octets and a packetization interval of 5 ms are associated with the PCMU codec.
G726-32编解码器与5ms的打包间隔相关联。40个八位字节的数据包长度和5毫秒的数据包化间隔与PCMU编解码器相关联。
This media attribute line can be used in ATM as well as non-ATM contexts. Within the ATM context, it can be applied to the AAL1, AAL2 and AAL5 adaptations. The <packetLength> and <packetTime> are not meaningful in the AAL1 case and should be set to "-". In the AAL2 case, these lines determine the use of some or all of the rows in a given profile table. If multiple 3-tuples are present, they can indicate a hierarchical assignment of some rows in that profile to voice service (e.g., row A preferred to row B etc.). If multiple profiles are present on the 'm' line, the profile qualified by this attribute is the first profile.
此媒体属性行可用于ATM以及非ATM上下文。在ATM上下文中，它可以应用于AAL1、AAL2和AAL5自适应。<packetLength>和<packetTime>在AAL1情况下没有意义，应设置为“-”。在AAL2情况下，这些行决定了给定概要文件表中部分或全部行的使用。如果存在多个3元组，则它们可以表示该配置文件中某些行对语音服务的分层分配（例如，a行优先于B行等）。如果“m”行上存在多个配置文件，则此属性限定的配置文件是第一个配置文件。
With most of the encoding names in Figure 2, the packet length and packetization period can be derived from each other. One of them can be set to "-" without a loss of information. There are some exceptions such as the IANA-registered encoding names G723, DVI4 and L16 for which this is not true. Therefore, there is a need to retain both the packet length and packetization period in the definition of the 'onewaySel' line.
对于图2中的大多数编码名称，数据包长度和打包周期可以相互派生。其中一个可以设置为“-”，而不会丢失信息。有一些例外情况，例如IANA注册的编码名称G723、DVI4和L16，这些情况不适用。因此，在“单向选择”线路的定义中需要保留数据包长度和数据包化周期。
When present, the 'codecconfig' attribute is used to represent the contents of the single codec information element (IE) defined in [57]. The contents of this IE are: a single-octet Organizational Identifier (OID) field, followed by a single-octet Codec Type field, followed by zero or more octets of a codec configuration bit-map. The semantics of the codec configuration bit-map are specific to the organization [57, 58]. The 'codecconfig' attribute is represented as follows:
存在时，“codeconfig”属性用于表示[57]中定义的单个编解码器信息元素（IE）的内容。此IE的内容包括：单个八位字节组织标识符（OID）字段，后跟单个八位字节编解码器类型字段，后跟编解码器配置位图的零个或多个八位字节。编解码器配置位图的语义特定于组织[57,58]。“codeconfig”属性表示如下：
a=codecconfig:<q7655scc>
a=codecconfig:<q7655scc>
The <q7655scc> (Q.765.5 single codec IE contents) parameter is represented as a string of hex digits. The number of hex digits is even (range 4 -32). The "0x" prefix shall be omitted since this value is always hexadecimal. As with other hex values [Section 2.2], digits to the left are more significant than digits to the right. Leading zeros shall not be omitted.
<q7655scc>（Q.765.5单编解码器IE内容）参数表示为十六进制数字字符串。十六进制数字的数量为偶数（范围4-32）。应省略“0x”前缀，因为该值始终为十六进制。与其他十六进制值一样[第2.2节]，左边的数字比右边的数字更重要。前导零不得省略。
An example of the use of this media attribute is:
使用此媒体属性的示例如下：
a=codecconfig:01080C
a=codeconfig:01080C
The first octet indicates an Organizational Identifier of 0x01 (the ITU-T). Using ITU Q.765.5 [57], the second octet (0x08) indicates a codec type of G.726 (ADPCM). The last octet, 0x0C indicates that 16 kbps and 24 kbps rates are NOT supported, while the 32 kbps and 40 kbps rates ARE supported.
第一个八位组表示组织标识符0x01（ITU-T）。使用ITU Q.765.5[57]，第二个八位字节（0x08）表示编解码器类型为G.726（ADPCM）。最后一个八位字节0x0C表示不支持16 kbps和24 kbps速率，而支持32 kbps和40 kbps速率。
When present, the 'isup_usi' attribute is used to represent the bearer capability information element defined in Section 4.5.5 of ITU Q.931 [59] (excluding the information element identifier and length). This information element is reiterated as the user service information element (IE) in Section 3.57 of ITU Q.763 [60]. The ' isup_usi' attribute is represented as follows:
当存在时，“isup_usi”属性用于表示ITU Q.931[59]第4.5.5节中定义的承载能力信息元素（不包括信息元素标识符和长度）。在ITU Q.763[60]第3.57节中，该信息元素被重申为用户服务信息元素（IE）。“isup_usi”属性表示如下：
a=isup_usi:<isupUsi>
a=isup_usi:<isupUsi>
The <isupUsi> parameter is represented as a string of hex digits. The number of hex digits is even (allowed range 4 -24). The "0x" prefix shall be omitted since this value is always hexadecimal. As with other hex values [Section 2.2], digits to the left are more significant than digits to the right. Leading zeros shall not be omitted.
<isupUsi>参数表示为十六进制数字字符串。十六进制数字的数量为偶数（允许范围为4-24）。应省略“0x”前缀，因为该值始终为十六进制。与其他十六进制值一样[第2.2节]，左边的数字比右边的数字更重要。前导零不得省略。
When present, the 'uiLayer1_Prot' attribute is used to represent the 'User Information Layer 1 protocol' field within the bearer capability information element defined in Section 4.5.5 of [59], and reiterated as the user service information element (IE) in Section 3.57 of [60]. The 'User Information Layer 1 protocol' field consists of the five least significant bits of Octet 5 of this information element.
当存在时，“uiLayer1_Prot”属性用于表示[59]第4.5.5节中定义的承载能力信息元素内的“用户信息层1协议”字段，并在[60]第3.57节中重申为用户服务信息元素（IE）。“用户信息层1协议”字段由该信息元素的八位字节5的五个最低有效位组成。
Within SDP, the 'uiLayer1_Prot' attribute is represented as follows:
在SDP中，“uiLayer1_Prot”属性表示如下：
a='uiLayer1_Prot':<uiLayer1Prot>
a='uiLayer1_Prot':<uiLayer1Prot>
The <uiLayer1Prot> parameter is represented as a string of two hex digits. The "0x" prefix shall be omitted since this value is always hexadecimal. As with other hex values [Section 2.2], digits to the left are more significant than digits to the right. These hex digits are constructed from an octet with three leading '0' bits and last five bits equal to the 'User Information Layer 1 protocol' field described above. As specified in [59] and [26], bit 5 of this field is the most significant bit. The resulting values of the <uiLayer1Prot> parameter are as follows:
<uiLayer1Prot>参数表示为两个十六进制数字的字符串。应省略“0x”前缀，因为该值始终为十六进制。与其他十六进制值一样[第2.2节]，左边的数字比右边的数字更重要。这些十六进制数字由八位字节构成，八位字节有三个前导“0”位，最后五位等于上述“用户信息层1协议”字段。如[59]和[26]所述，该字段的第5位是最高有效位。<uiLayer1Prot>参数的结果值如下：
VALUE MEANING 0x01 CCITT standardized rate adaption V.110 and X.30 0x02 Recommendation G.711 Mu-law 0x03 Recommendation G.711 A-law 0x04 Recommendation G.721 32 kbps ADPCM and Recommendation I.460 0x05 Recommendations H.221 and H.242 0x06 Recommendation H.223 and H.245 0x07 Non-ITU-T standardized rate adaption 0x08 ITU-T standardized rate adaption V.120 0x09 CCITT standardized rate adaption X.31 HDLC flag stuffing
值含义0x01 CCITT标准化速率自适应V.110和X.30 0x02建议G.711 Mu法则0x03建议G.711 A法则0x04建议G.721 32 kbps ADPCM和建议I.460 0x05建议H.221和H.242 0x06建议H.223和H.245 0x07非ITU-T标准化速率自适应0x08 ITU-T标准化速率自适应V.120 0x09 CCITT标准化速率自适应X.31 HDLC标志填充
The 'chain' media attribute line, which is used to chain consecutive SDP descriptions, cannot be classified as an ATM, AAL or service attribute. It is detailed in the following subsection.
用于链接连续SDP描述的“链”媒体属性行不能归类为ATM、AAL或服务属性。下面的小节将对此进行详细说明。
The start of an SDP descriptor is marked by a 'v' line. In some applications, consecutive SDP descriptions are alternative descriptions of the same session. In others, these describe different layers of the same connection (e.g., IP, ATM, frame relay). This is useful when these connectivity at these layers are established at the same time (e.g., an IP-based session over an ATM SVC). To distinguish between the alternation and concatenation of SDP descriptions, a 'chain' attribute can be used in the case of concatenation.
SDP描述符的开头用“v”行标记。在某些应用程序中，连续SDP描述是同一会话的替代描述。在其他情况下，这些描述了相同连接的不同层（例如，IP、ATM、帧中继）。当这些层上的这些连接同时建立时（例如，通过ATM SVC的基于IP的会话），这非常有用。为了区分SDP描述的交替和串联，可以在串联的情况下使用“chain”属性。
When present, the 'chain' attribute binds an SDP description to the next or previous SDP description. The next or previous description is separated from the current one by a 'v' line. It is not necessary that this description also have a 'chain' media attribute line.
存在时，“链”属性将SDP描述绑定到下一个或上一个SDP描述。下一个或上一个描述与当前描述之间用“v”行分隔。此说明不必同时具有“链”媒体属性行。
Chaining averts the need to set up a single SDP description for a session that is simultaneously created at multiple layers. It allows the SDP descriptors for different layers to remain simple and clean. Chaining is not needed in the Megaco context, where it is possible to create separate terminations for the different layers of a connection.
链接避免了为在多个层上同时创建的会话设置单个SDP描述的需要。它允许不同层的SDP描述符保持简单和干净。在Megaco上下文中不需要链接，因为可以为连接的不同层创建单独的终端。
The 'chain' media attribute line has the following format:
“链”媒体属性行具有以下格式：
a=chain:<chainPointer>
a=chain:<chainPointer>
The <chainPointer> field can take on the following string values: "NEXT", "PREVIOUS" and "NULL". The value "NULL" is not equivalent to omitting the chain attribute from a description since it expressly
<chainPointer>字段可以采用以下字符串值：“NEXT”、“PREVIOUS”和“NULL”。值“NULL”并不等同于从描述中省略chain属性，因为它明确表示
precludes the possibility of chaining. If the 'chain' attribute is absent in an SDP description, chaining can still be realized by the presence of a chain media attribute line in the previous or next description.
排除了链接的可能性。如果SDP描述中没有“链”属性，则链仍然可以通过在上一个或下一个描述中存在链媒体属性行来实现。
Section 4 mentions that H.323 annex C applications have a second media level part for the ATM session description. This is used to convey information about the RTCP stream. Although the RTP stream is encapsulated in AAL5 with no intervening IP layer, the RTCP stream is sent to an IP address and RTCP port. This media-level part has the following format:
第4节提到H.323附录C应用程序有第二个媒体级部分用于ATM会话描述。这用于传递有关RTCP流的信息。尽管RTP流封装在AAL5中，没有中间的IP层，但RTCP流被发送到IP地址和RTCP端口。此媒体级部件具有以下格式：
m= control <rtcpPortNum> H323c -
c= IN IP4 <rtcpIPaddr>
m= control <rtcpPortNum> H323c -
c= IN IP4 <rtcpIPaddr>
Consistency with RFC 2327 is maintained in the location and format of these lines. The <fmt list> in the 'm' line is set to "-". The 'c' line in the second media-level part pertains to RTCP only.
这些行的位置和格式与RFC 2327保持一致。“m”行中的<fmt list>设置为“-”。第二媒体级部件中的“c”行仅与RTCP相关。
The <rtcpPortNum> and <rtcpIPaddr> subparameters indicate the port number and IP address on which the media gateway is prepared to receive RTCP packets.
<rtcpPortNum>和<rtcpIPaddr>子参数表示媒体网关准备接收RTCP数据包的端口号和IP地址。
Any of the subparameters on these lines can be set to "-" if they are known by other means.
如果通过其他方式知道这些行上的任何子参数，则可以将其设置为“-”。
The range and format of the <rtcpPortNum> and <rtcpIPaddr> subparameters is per [1]. The <rtcpPortNum> is a decimal number between 1024 and 65535. It is an odd number. If an even number in this range is specified, the next odd number is used. The <rtcpIPaddr> is expressed in the usual dotted decimal IP address representation, from 0.0.0.0 to 255.255.255.255.
<rtcpPortNum>和<rtcpIPaddr>子参数的范围和格式符合[1]。<rtcpPortNum>是介于1024和65535之间的十进制数。这是一个奇数。如果指定此范围内的偶数，则使用下一个奇数。<rtcpIPaddr>以通常的点十进制IP地址表示形式表示，从0.0.0.0到255.255.255.255。
5.6.6 Use of the eecid media attribute in call establishment procedures
5.6.6 在呼叫建立过程中使用eecid媒体属性
This informative section supplements the definition of the eecid attribute (Section 5.6.1.1) by describing example procedures for its use. These procedures assume a bearer-signaling mechanism for connection set-up that is independent of service-level call control. These procedures are independent of the media gateway control protocol (MGCP, Megaco, SIP etc.), the protocol used between media gateway controllers (ITU Q.1901, SIP etc.) and the protocol used for bearer connection set-up (Q.2931, UNI, PNNI, AINI, IISP, Q.2630.1 etc.).
本信息性章节通过描述eecid属性使用的示例程序补充了eecid属性的定义（第5.6.1.1节）。这些过程假定用于连接建立的承载信令机制独立于服务级别呼叫控制。这些程序独立于媒体网关控制协议（MGCP、Megaco、SIP等）、媒体网关控制器之间使用的协议（ITU Q.1901、SIP等）和用于承载连接设置的协议（Q.2931、UNI、PNNI、AINI、IISP、Q.2630.1等）。
Inter-MGC
+---------+ Protocol +---------+
| MGC |------------------| MGC |
+---------+ +---------+
| |
|Media Gateway |Media Gateway
|Control Protocol |Control Protocol
| |
+------------+ (ATM Network) +------------+
|Originating |------------------|Terminating |
|Media | Bearer Setup |Media |
|Gateway | Protocol |Gateway |
+------------+ +------------+
Inter-MGC
+---------+ Protocol +---------+
| MGC |------------------| MGC |
+---------+ +---------+
| |
|Media Gateway |Media Gateway
|Control Protocol |Control Protocol
| |
+------------+ (ATM Network) +------------+
|Originating |------------------|Terminating |
|Media | Bearer Setup |Media |
|Gateway | Protocol |Gateway |
+------------+ +------------+
In the diagram above, the originating media gateway originates the service-level call. The terminating media gateway terminates it. In the forward bearer connection set-up model, the originating media gateway initiates bearer connection set-up. In the backward bearer connection set-up model, the terminating gateway initiates bearer connection set-up.
在上图中，发起媒体网关发起服务级别调用。终止媒体网关终止它。在前向承载连接设置模型中，发起媒体网关启动承载连接设置。在反向承载连接建立模型中，终端网关启动承载连接建立。
Example use of the Backward Bearer Connection Set-up Model:
反向承载连接设置模型的示例使用：
(1) The originating media gateway controller (OMGC) initiates service-level call establishment by sending the appropriate control message to the originating media gateway (OMG).
(1) 发起媒体网关控制器（OMGC）通过向发起媒体网关（OMG）发送适当的控制消息来发起服务级别呼叫建立。
(2) The originating media gateway (OMG) provides its NSAP address and an eecid value to the OMGC, using the following SDP description:
(2) 原始媒体网关（OMG）使用以下SDP描述向OMGC提供其NSAP地址和eecid值：
v=0 o=- 2873397496 0 ATM NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00 s=- c=ATM NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00 t=0 0 m=audio $ AAL2/ITU 8 a=eecid:B3D58E32
v=0 o=-2873397496 0 ATM NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00 s=-c=ATM NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00 t=0 0 m=0音频$AAL2/ITU 8 a=eecid:B3D58E32
(3) The originating media gateway controller (OMGC) signals the terminating media gateway controller (TMGC) through the appropriate mechanism (ISUP with Q.1901 extensions, SIP etc.). It provides the TMGC with the NSAP address and the eecid provided by the OMG.
(3) 发起媒体网关控制器（OMGC）通过适当的机制（ISUP和Q.1901扩展、SIP等）向终端媒体网关控制器（TMGC）发送信号。它向TMGC提供NSAP地址和OMG提供的eecid。
(4) The TMGC sends the appropriate control message to the TMG. This includes the session descriptor received from the OMG. This descriptor contains the NSAP address of the OMG and the EECID assigned by the OMG. Additionally, the TMGC instructs the TMG to set up an SVC to the OMG. It also requests the TMG to notify the TMGC when SVC set-up is complete. Depending on the control protocol used, this can be done through a variety of means. In the Megaco context, the request to set-up an SVC (not the notification request for the SVC set-up event) can be made through the following local descriptor:
(4) TMGC向TMG发送适当的控制消息。这包括从OMG接收的会话描述符。该描述符包含OMG的NSAP地址和OMG分配的EECID。此外，TMGC指示TMG为OMG设置SVC。它还要求TMG在SVC设置完成时通知TMGC。根据所使用的控制协议，这可以通过多种方式实现。在Megaco上下文中，可以通过以下本地描述符发出设置SVC的请求（而不是SVC设置事件的通知请求）：
v=0
o=- 2873397497 0 ATM - -
s=-
c=ATM - -
t=0 0
m=audio $ - -
a=bearerType:SVC on
v=0
o=- 2873397497 0 ATM - -
s=-
c=ATM - -
t=0 0
m=audio $ - -
a=bearerType:SVC on
The 'bearerType' attribute indicates that an SVC is to be used and that the <localInitiation> flag is on i.e., the SVC is to be set up by the TMG.
“bearerType”属性表示要使用SVC，并且<Localization>标志处于打开状态，即SVC将由TMG设置。
(5) The TMG acknowledges the control message from the TMGC. It returns the following SDP descriptor with the acknowledge:
(5) TMG确认来自TMGC的控制消息。它返回以下带有应答的SDP描述符：
v=0 o=- 2873397498 0 ATM NSAP 47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00 s=- c=ATM NSAP 47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00 t=0 0 m=audio $ AAL2/ITU 8
v=0 o=-2873397498 0 ATM NSAP 47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00 s=-c=ATM NSAP 47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00 t=0 0 m=音频$AAL2/ITU 8
The NSAP address information provided in this descriptor is not needed. It can be omitted (by setting it to "- -").
不需要此描述符中提供的NSAP地址信息。可以省略（通过将其设置为“--”）。
(6) The TMG sends an SVC set-up message to the OMG. Within the GIT information element, it includes eecid (B3D58E32) received from the OMG.
(6) TMG向OMG发送SVC设置消息。在GIT信息元素中，它包括从OMG接收的eecid（B3D58E32）。
(7) The OMG uses the eecid to correlate the SVC set-up request with service-level control message received before from the OMGC.
(7) OMG使用eecid将SVC设置请求与之前从OMGC收到的服务级别控制消息关联起来。
(8) The OMG returns an SVC connect message to the TMG. On receiving this message, the TMG sends an event notification to the TMGC indicating successful SVC set-up.
(8) OMG向TMG返回SVC connect消息。收到此消息后，TMG向TMGC发送事件通知，指示SVC设置成功。
Note that, for this example, the "v=", "o=", "s=" and "t=" lines can be omitted in the Megaco context.
注意，在本例中，Megaco上下文中可以省略“v=”、“o=”、“s=”和“t=”行。
Example use of the Forward Bearer Connection Set-up Model:
前向承载连接设置模型的示例使用：
(1) The originating media gateway controller (OMGC) initiates service-level call establishment by sending the appropriate controlsmessage to the originating media gateway (OMG).
(1) 发起媒体网关控制器（OMGC）通过向发起媒体网关（OMG）发送适当的控制消息来发起服务级别呼叫建立。
(2) The originating media gateway (OMG) provides its NSAP address to the OMGC, using the following SDP description:
(2) 发起媒体网关（OMG）使用以下SDP描述向OMGC提供其NSAP地址：
v=0 o=- 2873397496 0 ATM NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00 s=- c=ATM NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00 t=0 0 m=audio $ AAL2/ITU 8
v=0 o=-2873397496 0 ATM NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00 s=-c=ATM NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00 t=0 m=0音频$AAL2/ITU 8
The NSAP address information provided in this descriptor is not needed. It can be omitted (by setting it to "- -").
不需要此描述符中提供的NSAP地址信息。可以省略（通过将其设置为“--”）。
(3) The originating media gateway controller (OMGC) signals the terminating media gateway controller (TMGC) through the appropriate mechanism (ISUP with Q.1901 extensions, SIP etc.). Although this is not necessary, it can provide the TMGC with the NSAP address provided by the OMG.
(3) 发起媒体网关控制器（OMGC）通过适当的机制（ISUP和Q.1901扩展、SIP等）向终端媒体网关控制器（TMGC）发送信号。尽管这不是必需的，但它可以向TMGC提供OMG提供的NSAP地址。
(4) The TMGC sends the appropriate control message to the TMG. This includes the session descriptor received from the OMG. This descriptor contains the NSAP address of the OMG.
(4) TMGC向TMG发送适当的控制消息。这包括从OMG接收的会话描述符。此描述符包含OMG的NSAP地址。
(5) The TMG acknowledges the control message from the TMGC. Along with the acknowledgement, it provides an SDP descriptor with a locally assigned eecid.
(5) TMG确认来自TMGC的控制消息。除了确认之外，它还提供了一个带有本地分配的eecid的SDP描述符。
v=0 o=- 2873397714 0 ATM NSAP 47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00 s=- c=ATM NSAP 47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00 t=0 0 m=audio $ AAL2/ITU 8 a=eecid:B3D58E32
v=0 o=-2873397714 0 ATM NSAP 47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00 s=-c=ATM NSAP 47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00 t=0 0 m=音频$AAL2/ITU 8 a=eecid:B3D58E32
(6) The terminating media gateway controller (TMGC) signals the originating media gateway controller (OMGC) through the appropriate mechanism (ISUP with Q.1901 extensions, SIP etc.). It provides the OMGC with the NSAP address and the eecid provided by the TMG.
(6) 终端媒体网关控制器（TMGC）通过适当的机制（ISUP和Q.1901扩展、SIP等）向发起媒体网关控制器（OMGC）发送信号。它向OMGC提供NSAP地址和TMG提供的eecid。
(7) The OMGC sends the appropriate control message to the OMG. This includes the session descriptor received from the TMG. This descriptor contains the NSAP address of the TMG and the EECID assigned by the TMG. Additionally, the OMGC instructs the OMG to set up an SVC to the TMG. It also requests the OMG to notify the OMGC when SVC set-up is complete. Depending on the control protocol used, this can be done through a variety of means. In the Megaco context, the request to set-up an SVC (not the notification request for the SVC set-up event) can be made through the following local descriptor:
(7) OMGC向OMG发送适当的控制消息。这包括从TMG接收的会话描述符。该描述符包含TMG的NSAP地址和TMG分配的EECID。此外，OMGC指示OMG为TMG设置SVC。它还要求OMG在SVC设置完成时通知OMGC。根据所使用的控制协议，这可以通过多种方式实现。在Megaco上下文中，可以通过以下本地描述符发出设置SVC的请求（而不是SVC设置事件的通知请求）：
v=0
o=- 2873397874 0 ATM - -
s=-
c=ATM - -
t=0 0
m=audio $ - -
a=bearerType:SVC on
v=0
o=- 2873397874 0 ATM - -
s=-
c=ATM - -
t=0 0
m=audio $ - -
a=bearerType:SVC on
The 'bearerType' attribute indicates that an SVC is to be used and that the <localInitiation> flag is on i.e., the SVC is to be set up by the TMG.
“bearerType”属性表示要使用SVC，并且<Localization>标志处于打开状态，即SVC将由TMG设置。
(8) The OMG acknowledges the control message from the OMGC.
(8) OMG确认来自OMGC的控制消息。
(9) The OMG sends an SVC set-up message to the TMG. Within the GIT information element, it includes eecid (B3D58E32) received from the TMG.
(9) OMG向TMG发送SVC设置消息。在GIT信息元素中，它包括从TMG接收的eecid（B3D58E32）。
(10) The TMG uses the eecid to correlate the SVC set-up request with the service-level control message received before from the TMGC.
（10） TMG使用eecid将SVC设置请求与之前从TMGC收到的服务级别控制消息关联起来。
(11) The TMG returns an SVC connect message to the OMG. On receiving this message, the OMG sends an event notification to the OMGC indicating successful SVC set-up.
（11） TMG向OMG返回SVC connect消息。收到此消息后，OMG向OMGC发送事件通知，指示SVC设置成功。
Note that, for this example, the "v=", "o=", "s=" and "t=" lines can be omitted in the Megaco context.
注意，在本例中，Megaco上下文中可以省略“v=”、“o=”、“s=”和“t=”行。
This section provides a list of the parameters used in this document, and the formats used to represent them in SDP descriptions. In general, a "-" value can be used for any field that is not specified, is inapplicable or is implied.
本节提供了本文档中使用的参数列表，以及用于在SDP描述中表示这些参数的格式。通常，“-”值可用于任何未指定、不适用或隐含的字段。
PARAMETER MEANING REPRESENTATION
参数意义表示
<username> User name Constant "-"
<username>用户名常量“-”
<sessionID> Session ID Up to 32 decimal or hex digits
<sessionID>会话ID最多32位十进制或十六进制数字
<version> Version of "0" or 10 decimal digits SDP descriptor
“0”或10位十进制数字SDP描述符的版本
<networkType> Network type Constant "ATM" for ATM transport
<networkType>ATM传输的网络类型常量“ATM”
<addressType> Address type String values: "NSAP", "E164", "GWID", "ALIAS"
<addressType>地址类型字符串值：“NSAP”、“E164”、“GWID”、“别名”
<address> Address "NSAP": 40 hex digits, dotted
"E164": up to 15 decimal digits
"GWID": up to 32 characters
"ALIAS": up to 32 characters
<address> Address "NSAP": 40 hex digits, dotted
"E164": up to 15 decimal digits
"GWID": up to 32 characters
"ALIAS": up to 32 characters
<sessionName> Session name Constant "-"
<sessionName>会话名称常量“-”
<startTime> Session start "0" or 10 decimal digits time
<startTime>会话开始时间为“0”或10位小数
<stopTime> Session stop Constant "0" time
<stopTime>会话停止常量“0”时间
<vcci> Virtual Circuit Decimal or hex equivalent Connection of 16 bits Identifier
16位标识符的虚拟电路十进制或十六进制等效连接
<ex_vcci> Explicit "VCCI-" prefixed to <vcci>
representation
of <vcci>
<ex_vcci> Explicit "VCCI-" prefixed to <vcci>
representation
of <vcci>
<bcg> Bearer Connection Decimal or hex equivalent Group of 8 bits
<bcg>承载连接十进制或等效于十六进制的8位组
<ex_bcg> Explicit "BCG-" prefixed to <bcg>
representation
of <bcg>
<ex_bcg> Explicit "BCG-" prefixed to <bcg>
representation
of <bcg>
<portId> Port ID Hex number of up to 32 digits
<portId>端口ID十六进制数，最多32位
<ex_portId> Explicit "PORT-" prefixed to <portId>
representation
of <portId>
<ex_portId> Explicit "PORT-" prefixed to <portId>
representation
of <portId>
<vpi> Virtual Path Decimal or hex equivalent Identifier of 8 or 12 bits
<vpi>8位或12位的虚拟路径十进制或十六进制等效标识符
<ex_vpi> Explicit "VPI-" prefixed to <vpi>
representation
of <vpi>
<ex_vpi> Explicit "VPI-" prefixed to <vpi>
representation
of <vpi>
<vci> Virtual Circui t Decimal or hex equivalent Identifier of 16 bits
<vci>16位的十进制或十六进制等效虚拟电路标识符
<ex_vci> Explicit "VCI-" prefixed to <vci>
representation
of <vci>
<ex_vci> Explicit "VCI-" prefixed to <vci>
representation
of <vci>
<vpci> Virtual Path Decimal or hex equivalent Connection of 16 bits Identifier
<vpci>16位标识符的虚拟路径十进制或十六进制等效连接
<ex_vpci> Explicit "VPCI-" prefixed to <vpci>
representation
of <vpci>
<ex_vpci> Explicit "VPCI-" prefixed to <vpci>
representation
of <vpci>
<cid> Channel Decimal or hex equivalent Identifier of 8 bits
通道十进制或十六进制等效标识符，8位
<ex_cid> Explicit "CID-" prefixed to <cid>
representation
of <cid>
<ex_cid> Explicit "CID-" prefixed to <cid>
representation
of <cid>
<payloadType> Payload Decimal integer 0-127 Type
<payloadType>有效负载十进制整数0-127类型
<transport> Transport Values listed in Table 1.
<transport>表1中列出的传输值。
<profile> Profile Decimal integer 1-255
<profile>profile十进制整数1-255
<eecid> End-to-end Up to 8 hex digits Connection Identifier
<eecid>端到端最多8个十六进制数字的连接标识符
<aalType> AAL type String values: "AAL1","AAL1_SDT","AAL1_UDT", "AAL2", "AAL3/4", "AAL5", "USER_DEFINED_AAL"
AAL类型字符串值：“AAL1”、“AAL1\u SDT”、“AAL1\u UDT”、“AAL2”、“AAL3/4”、“AAL5”、“用户定义的\u AAL”
<asc> ATM service String values: category defined "CBR", "nrt-VBR", "rt-VBR", by the ATMF "UBR", "ABR", "GFR"
<asc>ATM服务字符串值：由ATMF“UBR”、“ABR”、“GFR”定义的类别“CBR”、“nrt VBR”、“rt VBR”
<atc> ATM transfer String values: capability "DBR","SBR","ABT/IT","ABT/DT", defined by the "ABR" ITU
<atc>ATM传输字符串值：能力“DBR”、“SBR”、“ABT/IT”、“ABT/DT”，由“ABR”ITU定义
<subtype> <asc>/<atc> Decimal integer 1-10
subtype
<subtype> <asc>/<atc> Decimal integer 1-10
subtype
<qosClass> QoS Class Decimal integer 0-5
<qosClass>QoS类十进制整数0-5
<bcob> Broadband Bearer Decimal or hex representation Class of 5-bit field
宽带承载十进制或十六进制表示类的5位字段
<eetim> End-to-end timing String values: "on", required "off".
<eetim>端到端定时字符串值：“开”，需要“关”。
<stc> Susceptibility Decimal equivalent of to clipping a 2-bit field
<stc>相当于剪裁2位字段
<upcc> User plane Decimal equivalent of connection a 2-bit field configuration
<upcc>连接的用户平面十进制等效于2位字段配置
<directionFlag> Direction Flag String values: "f", "b", "fb"
<directionFlag>方向标志字符串值：“f”、“b”、“fb”
<cdvType> CDV type String values: "PP", "2P"
CDV类型字符串值：“PP”、“2P”
<acdv> Acceptable CDV Decimal equivalent of 24-bit field
<acdv>24位字段的可接受CDV十进制等效值
<ccdv> Cumulative CDV Decimal equivalent of 24-bit field
24位字段的累积CDV十进制等效值
<eetd> End-to-end transit Decimal equivalent delay of 16-bit field
<eetd>16位字段的端到端传输十进制等效延迟
<cmtd> Cumulative transit Decimal equivalent delay of 16-bit field
<cmtd>16位字段的累积传输十进制等效延迟
<aclr> Acceptable Decimal equivalent Cell Loss Ratio of 8-bit field
<aclr>8位字段的可接受十进制等效单元丢失率
<clpLvl> CLP level String values:
"0", "0+1"
<clpLvl> CLP level String values:
"0", "0+1"
<pcr> Peak Decimal Cell Rate equivalent of a 24-bit field.
<pcr>峰值十进制单元速率相当于24位字段。
<scr> Sustained Decimal Cell Rate equivalent of a 24-bit field
<scr>24位字段的持续十进制单元速率
<mbs> Maximum Decimal Burst Size equivalent of 16-bit field
<mbs>16位字段的最大十进制突发大小
<cdvt> CDVT Decimal equivalent of 24-bit field.
<cdvt>cdvt十进制等效于24位字段。
<mcr> Minimum Decimal Cell Rate equivalent of a 24-bit field
<mcr>等效于24位字段的最小十进制单元速率
<mfs> Maximum Decimal Frame Size equivalent of a 16-bit field
<mfs>16位字段的最大十进制帧大小
<fd> Frame Discard String Values: Allowed "on", "off"
帧丢弃字符串值：允许“开”、“关”
<te> CLP tagging String Values: "on", "off"
<te>CLP标记字符串值：“开”、“关”
<nrm> NRM Decimal/hex equivalent of 3 bit field
<nrm>nrm十进制/十六进制等效3位字段
<trm> TRM -ditto-
<trm> TRM -ditto-
<cdf> CDF -ditto-
<cdf> CDF -ditto-
<adtf> ADTF Decimal/Hex equivalent of 10 bit field
10位字段的adtf十进制/十六进制等效值
<ficr> Forward Initial Decimal equivalent of Cell Rate 24-bit field
<ficr>前向初始十进制等效信元速率24位字段
<bicr> Backward Initial Decimal equivalent of Cell Rate 24-bit field
<bicr>单元速率24位字段的向后初始十进制等效值
<ftbe> Forward Transient Decimal equivalent of Buffer Exposure 24-bit field
缓冲区暴露24位字段的前向瞬态十进制等效值
<btbe> Backward Transient Decimal equivalent of Buffer Exposure 24-bit field
<btbe>缓冲区暴露24位字段的向后瞬态十进制等效值
<crmrtt> Cumulative RM Decimal equivalent of round-trip time 24-bit field (Microseconds)
往返时间24位字段的累积RM十进制等效值（微秒）
<frif> Forward rate Decimal integer increase factor 0 -15
远期汇率十进制整数增加系数0-15
<brif> Backward rate Decimal integer increase factor 0 -15
<brif>反向速率十进制整数增加系数0-15
<frdf> Forward rate Decimal integer decrease factor 0 -15
<frdf>远期汇率十进制整数递减系数0-15
<brdf> Backward rate Decimal integer decrease factor 0 -15
<brdf>反向速率十进制整数递减因子0-15
<bearerType> Bearer Type String Values: "PVC", "SVC", "CID"
<bearerType>承载类型字符串值：“PVC”、“SVC”、“CID”
<localInitiation> Local Initiation String values: "on", "off"
<LocationInitiation>本地启动字符串值：“开”、“关”
<sci> Screening Indication Decimal or hex equivalent of 4 bits.
<sci>屏蔽指示十进制或等效于4位的十六进制。
<lsn> Leaf Sequence Number Decimal or hex equivalent of 32 bits.
<lsn>叶序列号十进制或等效于32位的十六进制。
<cdStd> Coding standard for Decimal or hex connection scope equivalent of 2 bits. selection IE Definition: UNI 4.0 [5]
相当于2位的十进制或十六进制连接范围的编码标准。选择IE定义：UNI 4.0[5]
<conScpTyp> Type of connection scope Decimal or hex Definition: UNI 4.0 [5] equivalent of 4 bits
连接范围十进制或十六进制定义的类型：UNI 4.0[5]相当于4位
<conScpSel> Connection scope selection Decimal or hex Definition: UNI 4.0 [5] equivalent of 8 bits
连接范围选择十进制或十六进制定义：UNI 4.0[5]相当于8位
<cacheEnable> Enable SVC caching String values: "on", "off"
<cacheEnable>启用SVC缓存字符串值：“开”、“关”
<cacheTimer> Timer for cached SVC Decimal or hex equivalent deletion of 32-bit field
<cacheTimer>缓存SVC十进制或十六进制等效删除32位字段的计时器
<bearerSigIEType> Bearer Signaling IE Type 2 hex digits
<BearSiegeType>承载信令，即类型2十六进制数字
<bearerSigIELng> Bearer Signaling IE Length 1-4 hex digits
<bearersigeing>承载信令，即长度为1-4个十六进制数字
<bearerSigIEVal> Bearer Signaling IE Value Even number of hex digits, 2-512
<bearerSigIEVal>承载信令IE值十六进制数字的偶数，2-512
<appClass> Application String values: specification "itu_h323c","af83", "AAL5_SSCOP", "itu_i3661_unassured", "itu_i3661_assured", "itu_i3662", "itu_i3651", "itu_i3652", "itu_i3653", "itu_i3654", "FRF5", "FRF8","FRF11", "itu_h2221"
<appClass>应用程序字符串值：规范“itu_h323c”、“af83”、“AAL5_SSCOP”、“itu_i3661_未保证”、“itu_i3661_保证”、“itu_i3662”、“itu_i3651”、“itu_i3652”、“itu_i3653”、“itu_i3654”、“FRF5”、“FRF8”、“FRF11”、“itu_h2221”
<oui> Organizationally 1 to 6 hex digits Unique Identifier
<oui>组织上1到6个十六进制数字的唯一标识符
<appId> Application Identifier 1 to 8 digits
<appId>应用程序标识符1到8位
<cbrRate> CBR Rate Two hex digits.
<cbrRate>CBR Rate两个十六进制数字。
<sbc> Subchannel Count T1: Decimal integer 1-24 or hex equivalent E1: Decimal integer 1-31 or hex equivalent
<sbc>子通道计数T1：十进制整数1-24或十六进制等效值E1：十进制整数1-31或十六进制等效值
<clkrec> Clock Recovery String values: Method "NULL", "SRTS", "ADAPTIVE"
时钟恢复字符串值：方法“NULL”、“SRTS”、“自适应”
<fecEnable> Forward Error String values: Correction Enable "NULL", "LOSS_SENSITIVE" "DELAY_SENSITIVE"
<feceenable>转发错误字符串值：更正启用“NULL”、“丢失敏感”和“延迟敏感”
<partialFill> Partial Fill Decimal integer 1-48 or hex equivalent
<partialFill>部分填充十进制整数1-48或十六进制等效值
<structureEnable> Structure Present String values: "on", "off"
<structureEnable>结构显示字符串值：“开”、“关”
<blksz> Block Size Decimal or hexadecimal equivalent of 16 bits
块大小为十进制或16位的十六进制等效值
<cpcs> Maximum AAL5: Decimal or hex CPCS SDU size equivalent of 16 bits AAL2: 45 or 64, decimal or hex representation
<cpcs>最大AAL5：十进制或十六进制cpcs SDU大小等于16位AAL2:45或64，十进制或十六进制表示
<cidLowerLimit> AAL2 CID lower limit Decimal integer 8-255 or hex equivalent
<cidLowerLimit>AAL2 CID下限十进制整数8-255或十六进制等效值
<cidUpperLimit> AAL2 CID upper limit Decimal integer 8-255 or hex equivalent
<cidUpperLimit>AAL2 CID上限十进制整数8-255或十六进制等效值
<timerCU> Timer, combined use Integer decimal; range (microseconds) determined by application. Use decimal equivalent of 32 bits.
<timerCU>定时器，组合使用整数小数；范围（微秒）由应用程序确定。使用相当于32位的十进制数。
<simplifiedCPS> Simplified CPS [52] String values: "on", "off"
<simplifiedCPS>简化CPS[52]字符串值：“开”、“关”
<fSDUrate> Forward SDU rate Decimal equivalent of (bits per second) 24-bit field
<fSDUrate>前向SDU速率十进制等效值（位/秒）24位字段
<bSDUrate> Backward SDU rate Decimal equivalent of (bits per second) 24-bit field
<bSDUrate>向后SDU速率十进制等效值（位/秒）24位字段
<ted> Transmission Error String values: Detection Enable "on", "off"
传输错误字符串值：检测启用“开”、“关”
<rastimer> SSSAR reassembly Integer decimal, (microseconds) Range determined by application. Use decimal equivalent of 32 bits.
<rastimer>SSSAR重组整数十进制（微秒）范围由应用程序确定。使用相当于32位的十进制数。
<fsssar> Maximum SSSAR-SDU Decimal 1- 65568 size, forward or hex equivalent direction
<fsssar>最大SSSAR-SDU十进制1-65568尺寸，正向或十六进制等效方向
<bsssar> Maximum SSSAR-SDU Decimal 1- 65568 size, backward or hex equivalent direction
<bsssar>最大SSSAR-SDU十进制1-65568大小，向后或十六进制等效方向
<fsscopsdu> Maximum SSCOP-SDU Decimal 1- 65528 size, forward or hex equivalent direction
最大SSCOP-SDU十进制1-65528尺寸，正向或十六进制等效方向
<bsscopsdu> Maximum SSCOP-SDU Decimal 1- 65528 size, backward or hex equivalent direction
<bsscopsdu>最大SSCOP-SDU十进制1-65528大小，向后或十六进制等效方向
<fsscopuu> Maximum SSCOP-UU Decimal 1- 65524 field size, forward or hex equivalent direction
<fsscopuu>最大SSCOP-UU十进制1-65524字段大小，正向或十六进制等效方向
<bsscopuu> Maximum SSCOP-UU Decimal 1- 65524 field size, backward or hex equivalent direction
<bsscopuu>最大SSCOP-UU十进制1-65524字段大小，向后或十六进制等效方向
<sap> Service Access String values: Point "AUDIO", "MULTIRATE"
<sap>服务访问字符串值：点“音频”、“多速率”
<circuitMode> Circuit Mode String values: Enable "on", "off"
<circuitMode>电路模式字符串值：启用“开”、“关”
<frameMode> Frame Mode String values: Enable "on", "off"
<frameMode>帧模式字符串值：启用“开”、“关”
<faxDemod> Fax Demodulation String values: Enable "on", "off"
传真解调字符串值：启用“开”、“关”
<cas> Enable CAS transport String values: via Type 3 packets "on", "off"
<cas>启用cas传输字符串值：通过类型3数据包“开”、“关”
<dtmf> Enable DTMF transport String values: via Type 3 packets "on", "off"
<dtmf>启用dtmf传输字符串值：通过类型3数据包“开”、“关”
<mfall> Enable MF transport String values: via Type 3 packets "on", "off"
<mfall>启用MF传输字符串值：通过类型3数据包“开”、“关”
<mfr1> Enable MF (R1) String values: transport via "on", "off" Type 3 packets
<mfr1>启用MF（R1）字符串值：通过“开”、“关”类型3数据包传输
<mfr2> Enable MF (R2) String values: transport via "on", "off" Type 3 packets
<mfr2>启用MF（R2）字符串值：通过“开”、“关”类型3数据包传输
<PCMencoding> PCM encoding String values: "PCMA", "PCMU"
PCM编码字符串值：“PCMA”、“PCMU”
<fmaxFrame> Maximum length of a Decimal or hex frame mode data unit, equivalent of forward direction 16-bit field
<fmaxFrame>十进制或十六进制帧模式数据单元的最大长度，相当于正向16位字段
<bmaxFrame> Maximum length of a -ditto-frame mode data unit, backward direction
<bmaxFrame>a-同上帧模式数据单元的最大长度，向后
<silenceSuppEnable> Silence suppression String values: Enable "on", "off"
<silenceSuppEnable>静音抑制字符串值：启用“开”、“关”
<silenceTimer> Kick-in timer Decimal or hex representation for silence of 16-bit field suppression
<silenetimer>16位字段抑制静音的十进制或十六进制定时器表示法
<suppPref> Preferred Silence String values: Suppression Method "standard", "custom"
<suppref>首选静默字符串值：抑制方法“标准”、“自定义”
<sidUse> SID Use String values: Method "No SID", "Fixed Noise", "Sampled Noise"
<sidUse>SID使用字符串值：方法“无SID”、“固定噪声”、“采样噪声”
<fxnslevel> Fixed Noise Decimal or hex representation Level of a 7-bit field
<fxnslevel>固定了7位字段的十进制或十六进制噪声表示级别
<ecanEnable> Enable Echo String values: Cancellation "on", "off"
<ecanEnable>启用回显字符串值：取消“开”、“关”
<ecanType> Type of Echo String values: Cancellation "G165", "G168"
回声字符串值的类型：取消“G165”、“G168”
<gcEnable> Enable Gain String values: Control "on", "off"
<gcEnable>启用增益字符串值：控制“开”、“关”
<gcLvl> Level of inserted Decimal or hex equivalent Loss of 16-bit field
<gcLvl>16位字段的插入十进制或十六进制等效丢失的级别
<aal2transport> AAL2 transport Values listed in Table 1 that begin with the string "AAL2"
表1中列出的以字符串“AAL2”开头的AAL2传输值
<uuiCodeRange> UUI code range Decimal integer 0-15
<uuicoraderange>UUI代码范围十进制整数0-15
<encodingName> Encoding name String values: "PCMG", "SIDG", "SID729", any value from column 2 of Table 2
<encodingName>编码名称字符串值：“PCMG”、“SIDG”、“SID729”、表2第2列中的任何值
<packetLength> Packet length Decimal integer 0-45
<packetLength>数据包长度十进制整数0-45
<packetTime> Packetization Decimal integer 1-65,536 Interval in microsec.
<packetTime>Packetization十进制整数1-65536间隔（以微秒为单位）。
<fxIncl> Facsimile included String values: "on", "off"
<fxIncl> Facsimile included String values: "on", "off"
<serviceType> Service type String values: "v", "d", "f", "df", "all"
<serviceType>服务类型字符串值：“v”、“d”、“f”、“df”、“all”
<q7655scc> Contents of the Even number of hex Q.765.5 Single digits (4-32) Codec IE
<q7655scc>偶数十六进制Q.765.5位（4-32）编解码器IE的内容
<isupUsi> ISUP User Service Even number of hex digits Information (4-24)
<isupUsi>ISUP用户服务偶数十六进制数字信息（4-24）
<uiLayer1Prot> User Information Two hex digits Layer 1 Protocol
<uiLayer1Prot>用户信息两个十六进制数字第1层协议
<chainPointer> Chain pointer String values: "NEXT", "PREVIOUS", "NULL"
<chainPointer>链指针字符串值：“下一个”、“上一个”、“空”
<rtcpPortNum> RTCP port number for Odd decimal in range 1,024 to H.323 Annex C 65,535. applications Preferred: Odd number in the range 49,152 to 65,535
1024至H.323范围内奇数十进制的RTCP端口号附录C 65535。首选应用：奇数在49152到65535之间
<rtcpIPaddr> IP address for receipt Dotted decimal, 7-15 chars of RTCP packets
<rtcpIPaddr>接收点十进制数据包的IP地址，7-15个字符的RTCP数据包
An example of a complete AAL1 session description in SDP is:
SDP中完整的AAL1会话描述示例如下：
v=0 o=- A3C47F21456789F0 0 ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00 s=- c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00 t=0 0 m=audio $ AAL1/AVP 18 0 96 a=atmmap:96 X-G727-32 a=eecid:B3D58E32
v=0 o=-A3C47F21456789F00 ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00 s=-c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.00 t=0 0 m=audio$AAL1/AVP180 96 a=atmmap:96 X-G727-32 a=CID:B3D58E32
An example of a complete AAL2 session description in SDP is:
SDP中完整的AAL2会话描述示例如下：
v=0
o=- A3C47F21456789F0 0 ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
s=-
c=ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
t=0 0
m=audio $ AAL2/ITU 8 AAL2/custom 100 AAL2/ITU 1
a=eecid:B3E32
v=0
o=- A3C47F21456789F0 0 ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
s=-
c=ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
t=0 0
m=audio $ AAL2/ITU 8 AAL2/custom 100 AAL2/ITU 1
a=eecid:B3E32
The AAL2 session descriptor below is the same as the one above except that it states an explicit preference for a voice codec, a voiceband data codec and a voiceband fax codec. Further, it defines the profile AAL2/custom 100 rather than assume that the far-end is cognizant of the elements of this profile.
下面的AAL2会话描述符与上面的相同，只是它明确表示了语音编解码器、语音带数据编解码器和语音带传真编解码器的首选项。此外，它定义了概要文件AAL2/custom 100，而不是假设远端知道该概要文件的元素。
v=0
o=- A3C47F21456789F0 0 ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
s=-
c=ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
t=0 0
m=audio $ AAL2/ITU 8 AAL2/custom 100 AAL2/ITU 1
a=eecid:B3E32
a=profileDesc:AAL2/custom 100 0-7 PCMG 40 5000 0-7 SIDG 1
5000 8-15 G726-32 40 10000 8-15 SIDG 1 5000
a=vsel:G726-32 40 10000
a=dsel:off PCMU - -
a=fsel:G726-32 40 10000
v=0
o=- A3C47F21456789F0 0 ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
s=-
c=ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
t=0 0
m=audio $ AAL2/ITU 8 AAL2/custom 100 AAL2/ITU 1
a=eecid:B3E32
a=profileDesc:AAL2/custom 100 0-7 PCMG 40 5000 0-7 SIDG 1
5000 8-15 G726-32 40 10000 8-15 SIDG 1 5000
a=vsel:G726-32 40 10000
a=dsel:off PCMU - -
a=fsel:G726-32 40 10000
An example of an SDP session descriptor for an AAL5 switched virtual circuit for delivering MPEG-2 video:
用于传送MPEG-2视频的AAL5交换虚拟电路的SDP会话描述符的示例：
v=0
o=- A3C47F21456789F0 0 ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
s=-
c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
t=0 0
m=video $ AAL5/ITU 33
a=eecid:B3E32
a=aalType:AAL5
a=bearerType:SVC on
a=atmTrfcDesc:f 0+1 7816 - - - - - off -
a=atmTrfcDesc:b 0+1 0 - - - - - on -
a=cpsSDUsize:f 20680
a=aalApp:itu_h2221 - -
v=0
o=- A3C47F21456789F0 0 ATM NSAP
47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
s=-
c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00
t=0 0
m=video $ AAL5/ITU 33
a=eecid:B3E32
a=aalType:AAL5
a=bearerType:SVC on
a=atmTrfcDesc:f 0+1 7816 - - - - - off -
a=atmTrfcDesc:b 0+1 0 - - - - - on -
a=cpsSDUsize:f 20680
a=aalApp:itu_h2221 - -
An example of an SDP session descriptor for an AAL5 permanent virtual circuit for delivering MPEG-2 video:
用于传送MPEG-2视频的AAL5永久虚拟电路的SDP会话描述符的示例：
v=0
o=- A3C47F21456789F0 0 ATM - -
s=-
c=ATM - -
t=0 0
m=video PORT-$/VPI-0/VCI-$ AAL5/ITU 33
a=bearerType:PVC -
a=atmTrfcDesc:f 0+1 7816 - - - - - off -
a=atmTrfcDesc:b 0+1 0 - - - - - on -
a=cpsSDUsize:f 20680
a=aalApp:itu_h2221 - -
v=0
o=- A3C47F21456789F0 0 ATM - -
s=-
c=ATM - -
t=0 0
m=video PORT-$/VPI-0/VCI-$ AAL5/ITU 33
a=bearerType:PVC -
a=atmTrfcDesc:f 0+1 7816 - - - - - off -
a=atmTrfcDesc:b 0+1 0 - - - - - on -
a=cpsSDUsize:f 20680
a=aalApp:itu_h2221 - -
At present, standard means of encrypting ATM and AAL2 bearers are not conventionalized in the same manner as means of encrypting RTP payloads. Nor has the authentication of ATM or AAL2 bearer signaling.
目前，加密ATM和AAL2承载的标准方式与加密RTP有效负载的方式不同。ATM或AAL2承载信令的认证也没有。
The SDP encryption key line (k=) defined in RFC 2327 can be used to represent the encryption key and the method of obtaining the key. In the ATM and AAL2 contexts, the term 'bearer' can include 'bearer signaling' as well as 'bearer payloads'.
RFC 2327中定义的SDP加密密钥行（k=）可用于表示加密密钥和获取密钥的方法。在ATM和AAL2上下文中，术语“承载”可以包括“承载信令”以及“承载有效负载”。
The SDP session descriptions might originate in untrusted areas such as equipment owned by end-subscribers or located at end-subscriber premises. SDP relies on the security mechanisms of the encapsulating protocol or layers below the encapsulating protocol. Examples of encapsulating protocols are the Session Initiation Protocol (SIP), MGCP and Multimedia Gateway Control Protocol (MEGACO). No additional security mechanisms are needed. SIP, MGCP and MEGACO can use IPSec authentication as described in RFC 1826 [Ref. 27]. IPSec encryption can be optionally used with authentication to provide an additional, potentially more expensive level of security. IPSec security associations can be made between equipment located in untrusted areas and equipment located in trusted areas through configured shared secrets or the use of a certificate authority.
SDP会话描述可能起源于不受信任的区域，例如终端订户拥有的设备或位于终端订户场所的设备。SDP依赖于封装协议的安全机制或封装协议下的层。封装协议的示例包括会话启动协议（SIP）、MGCP和多媒体网关控制协议（MEGACO）。不需要额外的安全机制。SIP、MGCP和MEGACO可以使用RFC 1826中所述的IPSec身份验证[参考文献27]。IPSec加密可以选择性地与身份验证一起使用，以提供额外的、可能更昂贵的安全级别。通过配置共享机密或使用证书颁发机构，可以在位于不受信任区域的设备和位于受信任区域的设备之间建立IPSec安全关联。
This appendix provides an Augmented BNF (ABNF) grammar for the ATM conventions for SDP. ABNF is defined in rfc2234. This is not a complete ABNF description of SDP. Readers are referred to [1] for an ABNF description of the SDP base line protocol, and to rfc2848, rfc2543, rfc2045 and rfc2326 for application-specific conventions for SDP use. For case conventions, see section 2.4.
本附录提供了SDP ATM协议的扩充BNF（ABNF）语法。ABNF在rfc2234中定义。这不是对SDP的完整ABNF描述。读者可参考[1]了解SDP基线协议的ABNF说明，并参考rfc2848、rfc2543、rfc2045和rfc2326了解SDP使用的特定应用约定。有关案例惯例，请参见第2.4节。
; Constant definitions
; 恒定定义
safe = alpha-numeric / "'" / "-" / "." / "/" / ":" / "?" / DQUOTE /
"#" / "$" / "&" / "*" / ";" / "=" / "@" / "[" / "]" / "^" / "_" /
"`" / "{" / "|" / "}" / "+" / "~"
DQUOTE = %x22 ; double quote
alpha-numeric = ALPHA / DIGIT
ALPHA = "a" / "b" / "c" / "d" / "e" / "f" / "g" / "h" / "i" / "j" /
"k" / "l" / "m" / "n" / "o" / "p" / "q" / "r" / "s" / "t" /
"u" / "v" / "w" / "x" / "y" / "z" /
"A" / "B" / "C" / "D" / "E" / "F" / "G" / "H" / "I" / "J" /
"K" / "L" / "M" / "N" / "O" / "P" / "Q" / "R" / "S" / "T" /
"U" / "V" / "W" / "X" / "Y" / "Z"
DIGIT = "0" / POS-DIGIT
POS-DIGIT = "1" / "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9"
hex-prefix = "0" ("x" / "X")
HEXDIG = DIGIT / "a" / "b" / "c" / "d" / "e" / "f" /
"A" / "B" / "C" / "D" / "E" / "F"
space = %d32
EOL = (CR / LF / CRLF) ; as per Megaco RFC
CR = %d13
LF = %d10
safe = alpha-numeric / "'" / "-" / "." / "/" / ":" / "?" / DQUOTE /
"#" / "$" / "&" / "*" / ";" / "=" / "@" / "[" / "]" / "^" / "_" /
"`" / "{" / "|" / "}" / "+" / "~"
DQUOTE = %x22 ; double quote
alpha-numeric = ALPHA / DIGIT
ALPHA = "a" / "b" / "c" / "d" / "e" / "f" / "g" / "h" / "i" / "j" /
"k" / "l" / "m" / "n" / "o" / "p" / "q" / "r" / "s" / "t" /
"u" / "v" / "w" / "x" / "y" / "z" /
"A" / "B" / "C" / "D" / "E" / "F" / "G" / "H" / "I" / "J" /
"K" / "L" / "M" / "N" / "O" / "P" / "Q" / "R" / "S" / "T" /
"U" / "V" / "W" / "X" / "Y" / "Z"
DIGIT = "0" / POS-DIGIT
POS-DIGIT = "1" / "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9"
hex-prefix = "0" ("x" / "X")
HEXDIG = DIGIT / "a" / "b" / "c" / "d" / "e" / "f" /
"A" / "B" / "C" / "D" / "E" / "F"
space = %d32
EOL = (CR / LF / CRLF) ; as per Megaco RFC
CR = %d13
LF = %d10
decimal-uchar = DIGIT
/ POS-DIGIT DIGIT
/ ("1" 2*(DIGIT))
/ ("2" ("0"/"1"/"2"/"3"/"4") DIGIT)
/ ("2" "5" ("0"/"1"/"2"/"3"/"4"/"5"))
decimal-uchar = DIGIT
/ POS-DIGIT DIGIT
/ ("1" 2*(DIGIT))
/ ("2" ("0"/"1"/"2"/"3"/"4") DIGIT)
/ ("2" "5" ("0"/"1"/"2"/"3"/"4"/"5"))
generic-U8 = (hex-prefix hex-U8) / decimal-uchar
generic-U12 = (hex-prefix hex-U12) / 1*4 (DIGIT)
generic-U16 = (hex-prefix hex-U16) / 1*5(DIGIT)
generic-U24 = (hex-prefix hex-U24) / 1*8(DIGIT)
generic-U32 = (hex-prefix hex-U32) / 1*10(DIGIT)
hex-U8 = 1*2(HEXDIG)
hex-U12 = 1*3(HEXDIG)
hex-U16 = 1*4(HEXDIG)
hex-U24 = 1*6(HEXDIG)
hex-U32 = 1*8(HEXDIG)
generic-U8-or-null = generic-U8 / "-"
generic-U12-or-null = generic-U12 / "-"
generic-U16-or-null = generic-U16 / "-"
generic-U24-or-null = generic-U24 / "-"
generic-U32-or-null = generic-U32 / "-"
decimal-U8-or-null = decimal-uchar / "-"
decimal-U12-or-null = 1*4(DIGIT) / "-"
decimal-U16-or-null = 1*5(DIGIT) / "-"
decimal-U24-or-null = 1*8 (DIGIT) / "-"
decimal-U32-or-null = 1*10(DIGIT) / "-"
on-off-or-null = "on" / "off" / "-"
generic-U8 = (hex-prefix hex-U8) / decimal-uchar
generic-U12 = (hex-prefix hex-U12) / 1*4 (DIGIT)
generic-U16 = (hex-prefix hex-U16) / 1*5(DIGIT)
generic-U24 = (hex-prefix hex-U24) / 1*8(DIGIT)
generic-U32 = (hex-prefix hex-U32) / 1*10(DIGIT)
hex-U8 = 1*2(HEXDIG)
hex-U12 = 1*3(HEXDIG)
hex-U16 = 1*4(HEXDIG)
hex-U24 = 1*6(HEXDIG)
hex-U32 = 1*8(HEXDIG)
generic-U8-or-null = generic-U8 / "-"
generic-U12-or-null = generic-U12 / "-"
generic-U16-or-null = generic-U16 / "-"
generic-U24-or-null = generic-U24 / "-"
generic-U32-or-null = generic-U32 / "-"
decimal-U8-or-null = decimal-uchar / "-"
decimal-U12-or-null = 1*4(DIGIT) / "-"
decimal-U16-or-null = 1*5(DIGIT) / "-"
decimal-U24-or-null = 1*8 (DIGIT) / "-"
decimal-U32-or-null = 1*10(DIGIT) / "-"
on-off-or-null = "on" / "off" / "-"
; ABNF definition of SDP with ATM conventions
; 带ATM约定的SDP的ABNF定义
SDP-infoset = 1*(announcement)announcement = proto-version
origin-field session-name-field information-field uri-field
email-fields phone-fields connection-field bandwidth-fields
time-fields key-field attribute-fields media-descriptions
SDP-infoset = 1*(announcement)announcement = proto-version
origin-field session-name-field information-field uri-field
email-fields phone-fields connection-field bandwidth-fields
time-fields key-field attribute-fields media-descriptions
proto-version = ["v=" 1*4(DIGIT) EOL] ; use "v=0" for ATM SDP
proto-version = ["v=" 1*4(DIGIT) EOL] ; use "v=0" for ATM SDP
origin-field = ["o=" username space sess-id space sess-version space
net-type-addr EOL]
origin-field = ["o=" username space sess-id space sess-version space
net-type-addr EOL]
username = 1* safe ; for ATM use "-"
username = 1* safe ; for ATM use "-"
sess-id = (1*32 DIGIT) / (hex-prefix 1*32 HEXDIG)
sess-version = (1*10 DIGIT) / (hex-prefix 1*8 HEXDIG)
sess-id = (1*32 DIGIT) / (hex-prefix 1*32 HEXDIG)
sess-version = (1*10 DIGIT) / (hex-prefix 1*8 HEXDIG)
net-type-addr= nettype space addrtype-addr
net type addr=net type space addrtype addr
netttype = "ATM" / "IN" / "TN" / "-" / "$"
netttype = "ATM" / "IN" / "TN" / "-" / "$"
; Other nettype values may be defined in the future in other documents
; Validity of nettype and addrtype-addr combination to be checked at
; application level, not protocol syntax level
; Other nettype values may be defined in the future in other documents
; Validity of nettype and addrtype-addr combination to be checked at
; application level, not protocol syntax level
addrtype-addr = atm-addrtype-addr / ip-addrtype-addr / tn-addrtype-addr
; ip-addrtype-addr per rfc2327
; tn-addrtype-addr per rfc2848
addrtype-addr = atm-addrtype-addr / ip-addrtype-addr / tn-addrtype-addr
; ip-addrtype-addr per rfc2327
; tn-addrtype-addr per rfc2848
; ATM address definition
; ATM地址定义
atm-addrtype-addr = atm-nsap-addr / atm-e164-addr / atm-alias-addr
atm-addrtype-addr = atm-nsap-addr / atm-e164-addr / atm-alias-addr
atm-nsap-addr = ("NSAP" / "-" / "$") space (nsap-addr / "-" / "$")
atm-e164-addr = ("E164" / "-" / "$") space (e164-addr / "-" / "$")
atm-alias-addr = ("GWID" / "ALIAS" / "-" / "$") space (alias-addr /
"-" / "$")
atm-nsap-addr = ("NSAP" / "-" / "$") space (nsap-addr / "-" / "$")
atm-e164-addr = ("E164" / "-" / "$") space (e164-addr / "-" / "$")
atm-alias-addr = ("GWID" / "ALIAS" / "-" / "$") space (alias-addr /
"-" / "$")
nsap-addr = 2(HEXDIG) "." 9(4(HEXDIG) ".") 2(HEXDIG)
nsap-addr = 2(HEXDIG) "." 9(4(HEXDIG) ".") 2(HEXDIG)
e164-addr = 1*15 (DIGIT)
alias-addr = 1*32(alpha-numeric / "-" / "." / "_")
e164-addr = 1*15 (DIGIT)
alias-addr = 1*32(alpha-numeric / "-" / "." / "_")
session-name-field = ["s=" text EOL] ; for ATM use "s=-"
text = byte-string
byte-string = 1*(byte-string-char) ; definition per rfc2327
byte-string-char = %x01-09/ %x0B/ %x0C/ %x0E-FF ; all ASCII except
NUL, CR & LF
; Definitions of information-field, uri-field, email-fields,
; phone-fields per rfc2327. These fields are omitted in
; ATM SDP descriptions. If received, they are ignored in the ATM
; context
session-name-field = ["s=" text EOL] ; for ATM use "s=-"
text = byte-string
byte-string = 1*(byte-string-char) ; definition per rfc2327
byte-string-char = %x01-09/ %x0B/ %x0C/ %x0E-FF ; all ASCII except
NUL, CR & LF
; Definitions of information-field, uri-field, email-fields,
; phone-fields per rfc2327. These fields are omitted in
; ATM SDP descriptions. If received, they are ignored in the ATM
; context
connection-field = ["c=" c-net-type-addr]
connection-field = ["c=" c-net-type-addr]
; connection-field required, not optional, in ATM
; ATM中需要连接字段，非可选
c-net-type-addr = nettype space c-addrtype-addr c-addrtype-addr = atm-addrtype-addr / c-ip-addrtype-addr / tn-addrtype-addr
c-net-type-addr=nettype space c-addrtype-addr c-addrtype-addr=atm addrtype addr/c-ip-addrtype-addr/tn addrtype addr
; atm-addrtype-addr defined above
; 上面定义的atm addr类型addr
; c-ip-addrtype-addr per rfc2327 ; difference in address usage between 'o' and 'c' lines per rfc2327
; 根据rfc2327的c-ip-addrtype-addr；根据rfc2327，“o”和“c”行之间的地址使用差异
; tn-addrtype-addr per rfc2848
; tn addrtype addr符合rfc2848
bandwidth-fields = *("b=" bwtype ":" bandwidth EOL)
bandwidth-fields = *("b=" bwtype ":" bandwidth EOL)
bwtype = 1*(alpha-numeric)
bandwidth = 1*(DIGIT)
bwtype = 1*(alpha-numeric)
bandwidth = 1*(DIGIT)
time-fields = *( "t=" start-time space stop-time
*(EOL repeat-fields) EOL)
[zone-adjustments EOL]
start-time = time / "0"
stop-time = time / "0" ; always "0" in ATM
time = POS-DIGIT 9*(DIGIT) ; same as rfc2327
; repeat-fields and zone-adjustments per rfc2327, not used in ATM
time-fields = *( "t=" start-time space stop-time
*(EOL repeat-fields) EOL)
[zone-adjustments EOL]
start-time = time / "0"
stop-time = time / "0" ; always "0" in ATM
time = POS-DIGIT 9*(DIGIT) ; same as rfc2327
; repeat-fields and zone-adjustments per rfc2327, not used in ATM
; Definition of optional key-field per rfc2327 ;
; 根据rfc2327定义可选密钥字段；
attribute-fields = *("a=" attribute EOL)
attribute-fields = *("a=" attribute EOL)
; SDP descriptors for ATM do not have session-level media attribute ; lines. If these are provided, they should be ignored.
; ATM的SDP描述符没有会话级媒体属性；线如果提供了这些，则应忽略它们。
media-descriptions = *(media-description)
media-description = media-field information-field *(connection-field)
bandwidth-fields key-field attribute-fields
media-descriptions = *(media-description)
media-description = media-field information-field *(connection-field)
bandwidth-fields key-field attribute-fields
; Definitions of information-field per RFC 2327. These fields are
; omitted in ATM SDP descriptions. If received, they are ignored in
; the ATM context
;
; In ATM, the connection-field is used in media-description to indicate
; the IP address associated with the RTCP control protocol in H.323.C
; applications. In this case, the connection field is per the RFC 2327
; definition for IP v4-based connections. Otherwise, it is not used in
; media-description. If received as part of media-description,
; it is ignored.
;
; Definition of optional bandwidth-fields as above.
: Definition of optional key-field as in RFC 2327
; Definitions of information-field per RFC 2327. These fields are
; omitted in ATM SDP descriptions. If received, they are ignored in
; the ATM context
;
; In ATM, the connection-field is used in media-description to indicate
; the IP address associated with the RTCP control protocol in H.323.C
; applications. In this case, the connection field is per the RFC 2327
; definition for IP v4-based connections. Otherwise, it is not used in
; media-description. If received as part of media-description,
; it is ignored.
;
; Definition of optional bandwidth-fields as above.
: Definition of optional key-field as in RFC 2327
media-field = rfc2327-media-field / rfc2848-media-field /
atm-media-field
; rfc2327-media-field and rfc2848-media-field defined in those rfc's
atm-media-field = "m=" media space vcId space transport-fmts EOL
; superset of rfc2327 definition
media-field = rfc2327-media-field / rfc2848-media-field /
atm-media-field
; rfc2327-media-field and rfc2848-media-field defined in those rfc's
atm-media-field = "m=" media space vcId space transport-fmts EOL
; superset of rfc2327 definition
media = "audio" / "video" / "data" / "application" / "control" /
1*(alpha-numeric)
media = "audio" / "video" / "data" / "application" / "control" /
1*(alpha-numeric)
vcId = "$" / "-" / ex-vcci / (ex-vcci "/" ex-cid) /
(atm-type-addr-m "/" ex-vcci) /
vcId = "$" / "-" / ex-vcci / (ex-vcci "/" ex-cid) /
(atm-type-addr-m "/" ex-vcci) /
(atm-type-addr-m "/" ex-vcci "/" ex-cid) /
(ex-bcg "/" ex-vcci) / (ex-bcg "/" ex-vcci "/" ex-cid)
(ex-portid "/" ex-vpi "/" ex-vci) /
(ex-portid "/" ex-vpi "/" ex-vci "/" ex-cid) /
(ex-bcg "/" ex-vpi "/" ex-vci) /
(ex-bcg "/" ex-vpi "/" ex-vci "/" ex-cid) /
(ex-vpci "/" ex-vci) /
(ex-vpci "/" ex-vci "/" ex-cid) /
(atm-type-addr-m "/" ex-vpci "/" ex-vci) /
(atm-type-addr-m "/" ex-vpci "/" ex-vci "/" ex-cid)
(atm-type-addr-m "/" ex-vcci "/" ex-cid) /
(ex-bcg "/" ex-vcci) / (ex-bcg "/" ex-vcci "/" ex-cid)
(ex-portid "/" ex-vpi "/" ex-vci) /
(ex-portid "/" ex-vpi "/" ex-vci "/" ex-cid) /
(ex-bcg "/" ex-vpi "/" ex-vci) /
(ex-bcg "/" ex-vpi "/" ex-vci "/" ex-cid) /
(ex-vpci "/" ex-vci) /
(ex-vpci "/" ex-vci "/" ex-cid) /
(atm-type-addr-m "/" ex-vpci "/" ex-vci) /
(atm-type-addr-m "/" ex-vpci "/" ex-vci "/" ex-cid)
atm-type-addr-m = atm-nsap-addr-m / atm-e164-addr-m / atm-alias-addr-m
atm-nsap-addr-m = ["NSAP-"] (nsap-addr / "$")
atm-e164-addr-m = ["E164-"] (e164-addr / "$")
atm-alias-addr-m = ["GWID-" / "ALIAS-"] (alias-addr / "$")
; The -m at the end indicates use in the media field
; Wildcarding rules different from ATM address on 'o' and 'c' lines
atm-type-addr-m = atm-nsap-addr-m / atm-e164-addr-m / atm-alias-addr-m
atm-nsap-addr-m = ["NSAP-"] (nsap-addr / "$")
atm-e164-addr-m = ["E164-"] (e164-addr / "$")
atm-alias-addr-m = ["GWID-" / "ALIAS-"] (alias-addr / "$")
; The -m at the end indicates use in the media field
; Wildcarding rules different from ATM address on 'o' and 'c' lines
ex-vcci = "VCCI-" vcci ex-cid = "CID-" cid ex-bcg = "BCG-" bcg ex-portid = "PORT-" portid ex-vpi = "VPI-" vpi ex-vci = "VCI-" vci ex-vpci = "VPCI-" vpci
ex vcci=“vcci-”vcci ex cid=“cid-”cid ex bcg=“bcg-”bcg ex portid=“PORT-”portid ex vpi=“vpi-”vpi ex vci=“vci-”vci ex vpci=“vpci-”vpci
vcci = generic-U16 cid = generic-U8 bcg = generic-U8 portid = 1*32 (HEXDIG) vpi = generic-U12 vci = generic-U16 vpci = generic-U16
vcci=generic-U16 cid=generic-U8 bcg=generic-U8 portid=1*32（HEXDIG）vpi=generic-U12 vci=generic-U16 vpci=generic-U16
transport-fmts = generic-transport-fmts / known-transport-fmts / "- -"
generic-transport-fmts = generic-transport 1*(space fmt)
generic-transport = 1*(alpha-numeric / "/")
fmt = 1*(alpha-numeric)
transport-fmts = generic-transport-fmts / known-transport-fmts / "- -"
generic-transport-fmts = generic-transport 1*(space fmt)
generic-transport = 1*(alpha-numeric / "/")
fmt = 1*(alpha-numeric)
known-transport-fmts = aal1-transport space aal1-fmt-list / aal2-transport space aal2-fmt-list *(space aal2-transport space aal2-fmt-list) / aal5-transport space aal5-fmt-list / rtp-transport space rtp-fmt-list / tn-proto space tn-fmt-list / h323c-proto "-" h323c-proto = "H323c"
已知传输fmt=aal1传输空间aal1 fmt列表/aal2传输空间aal2 fmt列表*（空间aal2传输空间aal2 fmt列表）/aal5传输空间aal5 fmt列表/rtp传输空间rtp fmt列表/tn协议空间tn fmt列表/h323c协议“-”h323c协议=“h323c”
; h323c-proto used for RTCP control ports in H.323 annex C ; applications. tn-proto and tn-fmt-list per rfc2848
; H.323附录C中用于RTCP控制端口的h323c协议；应用。根据rfc2848的tn协议和tn fmt列表
aal1-transport = "AAL1" "/" aal1-transport-list
aal1-transport-list = "ATMF" / "ITU" / "custom" / "IEEE:" oui /
corporate-name
corporate-name = 1*(safe)
aal2-transport = "AAL2" "/" aal2-transport-list
aal2-transport-list = aal1-transport-list
aal5-transport = "AAL5" "/" aal5-transport-list
aal5-transport-list = aal1-transport-list
rtp-transport = "RTP" "/" rtp-transport-list
rtp-transport-list = "AVP"
aal1-transport = "AAL1" "/" aal1-transport-list
aal1-transport-list = "ATMF" / "ITU" / "custom" / "IEEE:" oui /
corporate-name
corporate-name = 1*(safe)
aal2-transport = "AAL2" "/" aal2-transport-list
aal2-transport-list = aal1-transport-list
aal5-transport = "AAL5" "/" aal5-transport-list
aal5-transport-list = aal1-transport-list
rtp-transport = "RTP" "/" rtp-transport-list
rtp-transport-list = "AVP"
aal1-fmt-list = (payload-type *(space payload-type)) / "-"
payload-type = decimal-uchar
aal5-fmt-list = aal1-fmt-list
rtp-fmt-list = aal1-fmt-list
aal2-fmt-list = (profile *(space profile)) / "-"
profile = decimal-uchar
attribute-fields = *("a=" attribute EOL)
attribute = known-attribute / (generic-att-field ":" att-value) /
generic-att-field
generic-att-field = 1*(alpha-numeric)
att-value = byte-string
known-attribute = atm-attribute / PINT-attribute / rfc2327-attribute
; PINT-attribute as defined in rfc2848
; rfc2327 attribute as defined in that rfc
aal1-fmt-list = (payload-type *(space payload-type)) / "-"
payload-type = decimal-uchar
aal5-fmt-list = aal1-fmt-list
rtp-fmt-list = aal1-fmt-list
aal2-fmt-list = (profile *(space profile)) / "-"
profile = decimal-uchar
attribute-fields = *("a=" attribute EOL)
attribute = known-attribute / (generic-att-field ":" att-value) /
generic-att-field
generic-att-field = 1*(alpha-numeric)
att-value = byte-string
known-attribute = atm-attribute / PINT-attribute / rfc2327-attribute
; PINT-attribute as defined in rfc2848
; rfc2327 attribute as defined in that rfc
atm-attribute =
"eecid" ":" eecid /
"aalType" ":" aalType /
"capability" ":" (asc / atc) space subtype /
"qosclass" ":" qosclass /
"bcob" ":" bcob space eetim /
"stc" ":" stc /
"upcc" ":" upcc /
"atmQOSparms" ":" directionFlag space cdvType
space acdv space ccdv space eetd space cmtd
space aclr /
"atmTrfcDesc" ":" directionFlag space clpLvl
space pcr space scr space mbs space cdvt space
mcr space mfs space fd space te /
"abrParms" ":" directionFlag space nrm space trm space cdf
space adtf /
"abrSetup" ":" ficr space bicr space ftbe space btbe space
crmrtt space frif space brif space frdf space brdf /
"bearertype" ":" bearerType space localInitiation /
atm-attribute =
"eecid" ":" eecid /
"aalType" ":" aalType /
"capability" ":" (asc / atc) space subtype /
"qosclass" ":" qosclass /
"bcob" ":" bcob space eetim /
"stc" ":" stc /
"upcc" ":" upcc /
"atmQOSparms" ":" directionFlag space cdvType
space acdv space ccdv space eetd space cmtd
space aclr /
"atmTrfcDesc" ":" directionFlag space clpLvl
space pcr space scr space mbs space cdvt space
mcr space mfs space fd space te /
"abrParms" ":" directionFlag space nrm space trm space cdf
space adtf /
"abrSetup" ":" ficr space bicr space ftbe space btbe space
crmrtt space frif space brif space frdf space brdf /
"bearertype" ":" bearerType space localInitiation /
"lij" ":" sci space lsn /
"anycast" ":" atmGroupAddress space cdStd space
conScpTyp space conScpSel /
"cache" ":" cacheEnable space cacheTimer /
"bearerSigIE" ":" bearerSigIEType space
bearerSigIELng space bearerSigIEVal /
"aalApp" ":" appClass space oui space appId /
"cbrRate" ":" cbrRate /
"sbc" ":" sbc /
"clkrec" ":" clkrec /
"fec" ":" fecEnable /
"prtfl" ":" partialFill /
"structure" ":" structureEnable space blksz /
"cpsSDUsize" ":" directionFlag space cpcs /
"aal2CPS" ":" cidLowerLimit space cidUpperLimit space
timerCU space simplifiedCPS /
"aal2CPSSDUrate" ":" fSDUrate space bSDUrate /
"aal2sscs3661unassured" ":" ted space rastimer space fsssar
space bsssar /
"aal2sscs3661assured" ":" rastimer space fsssar space bsssar
space fsscopsdu space bsscopsdu space fsscopuu
space bsscopuu /
"aal2sscs3662" ":" sap space circuitMode space frameMode
space faxDemod space cas space dtmf space mfall space mfr1
space mfr2 space PCMencoding space fmaxFrame
space bmaxFrame /
"aal5sscop" ":" fsscopsdu space bsscopsdu space fsscopuu
space bsscopuu /
"atmmap" ":" payload-type space encoding-name /
"silenceSupp" ":" silenceSuppEnable space silenceTimer
space suppPref space sidUse space fxnslevel /
"ecan" ":" directionFlag space ecanEnable space ecanType /
"gc" ":" directionFlag space gcEnable space gcLvl /
"profileDesc" ":" aal2-transport space profile space
1*(profile-row) /
"vsel" ":" 1*(encoding-name space packet-length space
packet-time space) /
"dsel" ":" fxIncl space
1*(encoding-name space packet-length space
packet-time space) /
"fsel" ":" 1*(encoding-name space packet-length space
packet-time space) /
"onewaySel" ":" serviceType space directionFlag space
1*(encoding-name space packet-length space
packet-time space) /
"lij" ":" sci space lsn /
"anycast" ":" atmGroupAddress space cdStd space
conScpTyp space conScpSel /
"cache" ":" cacheEnable space cacheTimer /
"bearerSigIE" ":" bearerSigIEType space
bearerSigIELng space bearerSigIEVal /
"aalApp" ":" appClass space oui space appId /
"cbrRate" ":" cbrRate /
"sbc" ":" sbc /
"clkrec" ":" clkrec /
"fec" ":" fecEnable /
"prtfl" ":" partialFill /
"structure" ":" structureEnable space blksz /
"cpsSDUsize" ":" directionFlag space cpcs /
"aal2CPS" ":" cidLowerLimit space cidUpperLimit space
timerCU space simplifiedCPS /
"aal2CPSSDUrate" ":" fSDUrate space bSDUrate /
"aal2sscs3661unassured" ":" ted space rastimer space fsssar
space bsssar /
"aal2sscs3661assured" ":" rastimer space fsssar space bsssar
space fsscopsdu space bsscopsdu space fsscopuu
space bsscopuu /
"aal2sscs3662" ":" sap space circuitMode space frameMode
space faxDemod space cas space dtmf space mfall space mfr1
space mfr2 space PCMencoding space fmaxFrame
space bmaxFrame /
"aal5sscop" ":" fsscopsdu space bsscopsdu space fsscopuu
space bsscopuu /
"atmmap" ":" payload-type space encoding-name /
"silenceSupp" ":" silenceSuppEnable space silenceTimer
space suppPref space sidUse space fxnslevel /
"ecan" ":" directionFlag space ecanEnable space ecanType /
"gc" ":" directionFlag space gcEnable space gcLvl /
"profileDesc" ":" aal2-transport space profile space
1*(profile-row) /
"vsel" ":" 1*(encoding-name space packet-length space
packet-time space) /
"dsel" ":" fxIncl space
1*(encoding-name space packet-length space
packet-time space) /
"fsel" ":" 1*(encoding-name space packet-length space
packet-time space) /
"onewaySel" ":" serviceType space directionFlag space
1*(encoding-name space packet-length space
packet-time space) /
"codecconfig" ":" q7655scc /
"isup_usi" ":" isupUsi /
"codecconfig" ":" q7655scc /
"isup_usi" ":" isupUsi /
"uiLayer1_Prot" ":" uiLayer1Prot / "chain" ":" chainPointer
“uiLayer1_Prot”“：“uiLayer1 Prot/“chain”“：“chainPointer”
eecid = 8 (HEXDIG)
aalType = "AAL1" / "AAL2" / "AAL3/4" / "AAL5" / "USER_DEFINED_AAL"
asc = "CBR" / "nrt-VBR" / "rt-VBR" / "UBR" / "ABR" / "GFR"
atc = "DBR" / "SBR" / "ABT/IT" / "ABT/DT" / "ABR"
subtype = decimal-U8-or-null
qosclass = decimal-U8-or-null
bcob = generic-U8
eetim = on-off-or-null
stc = decimal-uchar
upcc = decimal-uchar
directionFlag = "f" / "b" / "fb"
cdvType = "PP" / "2P" / "-"
acdv = decimal-U32-or-null
ccdv = decimal-U32-or-null
eetd = decimal-U16-or-null
cmtd = decimal-U16-or-null
aclr = decimal-U8-or-null
clpLvl = "0" / "0+1" / "-"
pcr = decimal-U24-or-null
scr = decimal-U24-or-null
mbs = decimal-U16-or-null
cdvt = decimal-U24-or-null
mcr = decimal-U24-or-null
mfs = decimal-U16-or-null
fd = on-off-or-null
te = on-off-or-null
nrm = generic-U8-or-null
trm = generic-U8-or-null
cdf = generic-U8-or-null
adtf = generic-U16-or-null
ficr = decimal-U24-or-null
bicr = decimal-U24-or-null
ftbe = decimal-U24-or-null
btbe = decimal-U24-or-null
crmrtt = decimal-U24-or-null
frif = 1*2 (DIGIT)
brif = 1*2 (DIGIT)
frdf = 1*2 (DIGIT)
brdf = 1*2 (DIGIT)
bearerType = "PVC" / "SVC" / "CID"
localInitiation = on-off-or-null
sci = generic-U8-or-null
lsn = generic-U32-or-null
atmGroupAddress = atm-type-addr
cdStd = generic-U8-or-null
eecid = 8 (HEXDIG)
aalType = "AAL1" / "AAL2" / "AAL3/4" / "AAL5" / "USER_DEFINED_AAL"
asc = "CBR" / "nrt-VBR" / "rt-VBR" / "UBR" / "ABR" / "GFR"
atc = "DBR" / "SBR" / "ABT/IT" / "ABT/DT" / "ABR"
subtype = decimal-U8-or-null
qosclass = decimal-U8-or-null
bcob = generic-U8
eetim = on-off-or-null
stc = decimal-uchar
upcc = decimal-uchar
directionFlag = "f" / "b" / "fb"
cdvType = "PP" / "2P" / "-"
acdv = decimal-U32-or-null
ccdv = decimal-U32-or-null
eetd = decimal-U16-or-null
cmtd = decimal-U16-or-null
aclr = decimal-U8-or-null
clpLvl = "0" / "0+1" / "-"
pcr = decimal-U24-or-null
scr = decimal-U24-or-null
mbs = decimal-U16-or-null
cdvt = decimal-U24-or-null
mcr = decimal-U24-or-null
mfs = decimal-U16-or-null
fd = on-off-or-null
te = on-off-or-null
nrm = generic-U8-or-null
trm = generic-U8-or-null
cdf = generic-U8-or-null
adtf = generic-U16-or-null
ficr = decimal-U24-or-null
bicr = decimal-U24-or-null
ftbe = decimal-U24-or-null
btbe = decimal-U24-or-null
crmrtt = decimal-U24-or-null
frif = 1*2 (DIGIT)
brif = 1*2 (DIGIT)
frdf = 1*2 (DIGIT)
brdf = 1*2 (DIGIT)
bearerType = "PVC" / "SVC" / "CID"
localInitiation = on-off-or-null
sci = generic-U8-or-null
lsn = generic-U32-or-null
atmGroupAddress = atm-type-addr
cdStd = generic-U8-or-null
conScpTyp = generic-U8-or-null
conScpSel = generic-U8-or-null
cacheEnable = on-off-or-null
cacheTimer = generic-U32-or-null
bearerSigIEType = 2 * (HEXDIG)
bearerSigIELng = 1*4 (HEXDIG)
bearerSigIEVal = 2*512 (HEXDIG)
appClass = "-" /
"itu_h323c" / "af83" / "AAL5_SSCOP" / "itu_i3661_unassured" /
"itu_ i3661_assured"/ "itu_i3662"/ "itu_i3651" /
"itu_i3652" / "itu_i3653" / "itu_i3654" / "FRF11" / "FRF5" /
"FRF8" / "itu_h2221"
oui = "-" / 1*6 (HEXDIG)
appId = "-" / 1*8 (HEXDIG)
cbrRate = 2 (HEXDIG)
sbc = generic-U8
clkrec = "NULL" / "SRTS" / "ADAPTIVE"
fecEnable = "NULL" / "LOSS_SENSITIVE" / "DELAY_SENSITIVE"
partialFill = generic-U8
structureEnable = on-off-or-null
blksz = generic-U16-or-null
cpcs = generic-U16
cidLowerLimit = generic-U8-or-null
cidUpperLimit = generic-U8-or-null
timerCU = decimal-U32-or-null
simplifiedCPS = on-off-or-null
fSDUrate = decimal-U24-or-null
bSDUrate = decimal-U24-or-null
ted = on-off-or-null
rastimer = decimal-U32-or-null
fsssar = generic-U24-or-null
bsssar = generic-U24-or-null
fsscopsdu = generic-U16-or-null
bsscopsdu = generic-U16-or-null
fsscopuu = generic-U16-or-null
bsscopuu = generic-U16-or-null
sap = "AUDIO" / "MULTIRATE" / "-"
circuitMode = on-off-or-null
frameMode = on-off-or-null
faxDemod = on-off-or-null
cas = on-off-or-null
dtmf = on-off-or-null
mfall = on-off-or-null
mfr1 = on-off-or-null
mfr2 = on-off-or-null
PCMencoding = "PCMA" / "PCMU" / "-"
fmaxframe = generic-U16-or-null
bmaxframe = generic-U16-or-null
conScpTyp = generic-U8-or-null
conScpSel = generic-U8-or-null
cacheEnable = on-off-or-null
cacheTimer = generic-U32-or-null
bearerSigIEType = 2 * (HEXDIG)
bearerSigIELng = 1*4 (HEXDIG)
bearerSigIEVal = 2*512 (HEXDIG)
appClass = "-" /
"itu_h323c" / "af83" / "AAL5_SSCOP" / "itu_i3661_unassured" /
"itu_ i3661_assured"/ "itu_i3662"/ "itu_i3651" /
"itu_i3652" / "itu_i3653" / "itu_i3654" / "FRF11" / "FRF5" /
"FRF8" / "itu_h2221"
oui = "-" / 1*6 (HEXDIG)
appId = "-" / 1*8 (HEXDIG)
cbrRate = 2 (HEXDIG)
sbc = generic-U8
clkrec = "NULL" / "SRTS" / "ADAPTIVE"
fecEnable = "NULL" / "LOSS_SENSITIVE" / "DELAY_SENSITIVE"
partialFill = generic-U8
structureEnable = on-off-or-null
blksz = generic-U16-or-null
cpcs = generic-U16
cidLowerLimit = generic-U8-or-null
cidUpperLimit = generic-U8-or-null
timerCU = decimal-U32-or-null
simplifiedCPS = on-off-or-null
fSDUrate = decimal-U24-or-null
bSDUrate = decimal-U24-or-null
ted = on-off-or-null
rastimer = decimal-U32-or-null
fsssar = generic-U24-or-null
bsssar = generic-U24-or-null
fsscopsdu = generic-U16-or-null
bsscopsdu = generic-U16-or-null
fsscopuu = generic-U16-or-null
bsscopuu = generic-U16-or-null
sap = "AUDIO" / "MULTIRATE" / "-"
circuitMode = on-off-or-null
frameMode = on-off-or-null
faxDemod = on-off-or-null
cas = on-off-or-null
dtmf = on-off-or-null
mfall = on-off-or-null
mfr1 = on-off-or-null
mfr2 = on-off-or-null
PCMencoding = "PCMA" / "PCMU" / "-"
fmaxframe = generic-U16-or-null
bmaxframe = generic-U16-or-null
silenceSuppEnable = on-off-or-null
silenceTimer = generic-U16-or-null
suppPref = "standard" / "custom" / "-"
sidUse = "No SID" / "Fixed Noise" / "Sampled Noise" / "-"
fxnslevel = generic-U8-or-null
ecanEnable = on-off-or-null
ecanType = "G165" / "G168" / "-"
gcEnable = on-off-or-null
gcLvl = generic-U16-or-null
silenceSuppEnable = on-off-or-null
silenceTimer = generic-U16-or-null
suppPref = "standard" / "custom" / "-"
sidUse = "No SID" / "Fixed Noise" / "Sampled Noise" / "-"
fxnslevel = generic-U8-or-null
ecanEnable = on-off-or-null
ecanType = "G165" / "G168" / "-"
gcEnable = on-off-or-null
gcLvl = generic-U16-or-null
profile-row = uuiCodeRange space encoding-name space packet-length
space packet-time space
uuiCodeRange = decimal-uchar "-" decimal-uchar / "-"
encoding-name = "-" /
"PCMG" / "SIDG" / "SID729" /
"PCMU" / "G726-32" / "G723" / "PCMA" / "G722" / "G728" /
"G729" / "X-G729a" / "X-G729b" / "X-G729ab" /
"X-G726-16" / "X-G726-24" / "X-G726-40" / "X-G7231-H" /
"X-G7231-L" / "X-G7231a-H" / "X-G7231a-L" /
"X-G727-16" / "X-G727-24" / "X-G727-32" /
"X-CCD" / "X-CCD-CAS" / "GSM" / "GSM-HR" / "GSM-EFR" /
"GSM-EHR" / "X-FXDMOD-3" / "1016" / "DVI4" / "L16" /
"LPC" / "MPA" / "QCELP" / "H263" / "H263-1998" /
"JPEG" / "H261" / "MPV" / "MP2T" / "nv" / "RED" /
"CelB" / "L8" / "VDVI" / "MP1S" / "MP2P" / "BT656" /
"FR-AMR" / "HR-AMR" / "UMTS-AMR" / "AMR"
packet-length = decimal-U8-or-null
packet-time = decimal-U16-or-null
fxIncl = on-off-or-null
serviceType = "v" / "d" / "f" / "df" / "all"
q7655scc = 4*32 (HEXDIG)
isupUsi = 4*24 (HEXDIG)
uiLayer1Prot = 2 (HEXDIG)
profile-row = uuiCodeRange space encoding-name space packet-length
space packet-time space
uuiCodeRange = decimal-uchar "-" decimal-uchar / "-"
encoding-name = "-" /
"PCMG" / "SIDG" / "SID729" /
"PCMU" / "G726-32" / "G723" / "PCMA" / "G722" / "G728" /
"G729" / "X-G729a" / "X-G729b" / "X-G729ab" /
"X-G726-16" / "X-G726-24" / "X-G726-40" / "X-G7231-H" /
"X-G7231-L" / "X-G7231a-H" / "X-G7231a-L" /
"X-G727-16" / "X-G727-24" / "X-G727-32" /
"X-CCD" / "X-CCD-CAS" / "GSM" / "GSM-HR" / "GSM-EFR" /
"GSM-EHR" / "X-FXDMOD-3" / "1016" / "DVI4" / "L16" /
"LPC" / "MPA" / "QCELP" / "H263" / "H263-1998" /
"JPEG" / "H261" / "MPV" / "MP2T" / "nv" / "RED" /
"CelB" / "L8" / "VDVI" / "MP1S" / "MP2P" / "BT656" /
"FR-AMR" / "HR-AMR" / "UMTS-AMR" / "AMR"
packet-length = decimal-U8-or-null
packet-time = decimal-U16-or-null
fxIncl = on-off-or-null
serviceType = "v" / "d" / "f" / "df" / "all"
q7655scc = 4*32 (HEXDIG)
isupUsi = 4*24 (HEXDIG)
uiLayer1Prot = 2 (HEXDIG)
chainPointer = "NEXT" / "PREVIOUS" / "NULL"
chainPointer = "NEXT" / "PREVIOUS" / "NULL"
References
工具书类
[1] Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998.
[1] Handley，M.和V.Jacobson，“SDP：会话描述协议”，RFC 2327，1998年4月。
[2] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", RFC 1889, January 1996.
[2] Schulzrinne，H.，Casner，S.，Frederick，R.和V.Jacobson，“RTP：实时应用的传输协议”，RFC 1889，1996年1月。
RFC 1889 will be obsoleted, in a substantially backwards compatible manner, by a work in progress that will become an RFC.
RFC 1889将以基本向后兼容的方式，被将成为RFC的在制品淘汰。
[3] Schulzrinne, H., "RTP Profile for Audio and Video Conferences with Minimal Control", RFC 1890, January 1996.
[3] Schulzrinne，H.，“具有最小控制的音频和视频会议的RTP配置文件”，RFC 1890，1996年1月。
RFC 1890 will be obsoleted, in a fully backwards compatible manner, by a work in progress that will become an RFC.
RFC 1890将以完全向后兼容的方式被一个将成为RFC的在建工程淘汰。
[4] ATMF UNI 3.1 Specification, af-uni-0010.002. Of special interest for this document is Section 5.4.5.5, ATM Adaptation Layer Parameters.
[4] ATMF UNI 3.1规范，af-UNI-0010.002。本文件特别关注的是第5.4.5.5节，ATM适配层参数。
[5] ATMF UNI 4.0 Signaling Specification, af-sig-0061.000.
[5] ATMF UNI 4.0信令规范，af-sig-0061.000。
[6] ATMF Traffic Management Specification, Version 4.1, af-tm-0121.000.
[6] ATMF交通管理规范，版本4.1，af-tm-0121.000。
[7] ATMF Circuit Emulation Service (CES) Interoperability Specification, version 2.0, af-vtoa-0078.000, Jan. 97.
[7] ATMF电路仿真服务（CES）互操作性规范，版本2.0，af-vtoa-0078.000，1997年1月。
[8] ATMF Voice and Telephony over ATM - ATM Trunking using AAL1 for Narrowband Services, version 1.0, af-vtoa-0089.000, July 1997.
[8] ATM上的ATMF语音和电话-使用AAL1的窄带业务ATM中继，版本1.0，af-vtoa-0089.000，1997年7月。
[9] ATMF Specifications of (DBCES) Dynamic Bandwidth Utilization - in 64kbps Timeslot Trunking over ATM - using CES, af-vtoa-0085.000, July 1997.
[9] （DBCES）动态带宽利用的ATMF规范-在ATM上的64kbps时隙中继中-使用CES，af-vtoa-0085.000，1997年7月。
[10] ITU-T I.363.1, B-ISDN ATM Adaptation Layer Specification: Type 1 AAL, August 1996.
[10] ITU-T I.363.1，B-ISDN ATM适配层规范：类型1 AAL，1996年8月。
[11] ITU-T I.363.2, B-ISDN ATM Adaptation Layer Specification: Type 2 AAL, Sept. 1997.
[11] ITU-T I.363.2，B-ISDN ATM适配层规范：类型2 AAL，1997年9月。
[12] ITU-T I.366.1, Segmentation and Reassembly Service Specific Convergence Sublayer for AAL Type 2, June 1998.
[12] ITU-T I.366.1，AAL类型2的特定于服务的聚合子层的分段和重新组装，1998年6月。
[13] ITU-T I.366.2, AAL Type 2 Reassembly Service Specific Convergence Sublayer for Trunking, Feb. 99.
[13] ITU-T I.366.2，用于中继的AAL 2型重组服务特定汇聚子层，1999年2月。
[14] Petrack, S., "RTP payloads for Telephone Signal Events", Work in Progress.
[14] Petrack，S.，“电话信号事件的RTP有效载荷”，正在进行中。
[15] ITU-T Q.2931, B-ISDN Application Protocol for Access Signaling.
[15] ITU-T Q.2931，接入信令的B-ISDN应用协议。
[16] Amendment 1, 2, 3 and 4 to ITU-T Q.2931, B-ISDN Application Protocol for Access Signaling.
[16] ITU-T Q.2931《接入信令用B-ISDN应用协议》修正案1、2、3和4。
[17] Handley, M., Perkins C. and E. Whelan, "Session Announcement Protocol", RFC 2974, October 2000.
[17] Handley，M.，Perkins C.和E.Whelan，“会话公告协议”，RFC 29742000年10月。
[18] Handley, M., Schulzrinne, H., Schooler, E. and J. Rosenberg, "Session Initiation Protocol (SIP)", RFC 2543, March 1999.
[18] Handley，M.，Schulzrinne，H.，Schooler，E.和J.Rosenberg，“会话启动协议（SIP）”，RFC 25431999年3月。
[19] Almquist, P., "Type of Service in the Internet Protocol Suite", July 1992.
[19] Almquist，P.，“互联网协议套件中的服务类型”，1992年7月。
[20] Nichols, K., Blake, S., Baker, F. and D. Black, "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers", December 1998.
[20] Nichols，K.，Blake，S.，Baker，F.和D.Black，“IPv4和IPv6报头中区分服务字段（DS字段）的定义”，1998年12月。
[21] ITU-T I.363.5, B-ISDN ATM Adaptation Layer Specification: Type 5 AAL, Aug. 1996.
[21] ITU-T I.363.5，B-ISDN ATM适配层规范：5型AAL，1996年8月。
[22] ATMF PNNI 1.0, af-pnni-0055.000, March 1996.
[22] ATMF PNNI 1.0，af-PNNI-0055.000，1996年3月。
[23] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", Work in Progress.
[23] Schulzrinne，H.，Casner，S.，Frederick，R.和V.Jacobson，“RTP：实时应用的传输协议”，正在进行中。
[24] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video Conferences with Minimal Control", Work in Progress.
[24] Schulzrinne，H.和S.Casner，“具有最小控制的音频和视频会议的RTP配置文件”，正在进行中。
[25] Arango, M., Dugan, A., Elliott, I., Huitema, C. and S. Pickett, "Media Gateway Control Protocol (MGCP)", RFC 2705, October 1999.
[25] Arango，M.，Dugan，A.，Elliott，I.，Huitema，C.和S.Pickett，“媒体网关控制协议（MGCP）”，RFC 27052999年10月。
[26] Cuervo, F., Greene, N., Rayhan, A., Huitema, C., Rosen, B. and J. Segers, "Megaco Protocol Version 1.0", RFC 3015, November 2000.
[26] Cuervo，F.，Greene，N.，Rayhan，A.，Huitema，C.，Rosen，B.和J.Segers，“Megaco协议版本1.0”，RFC 30152000年11月。
[27] Atkinson, R., "IP Authentication Header", RFC 1826, August 1995.
[27] 阿特金森，R.，“IP认证头”，RFC 1826，1995年8月。
[28] ITU I.371, Traffic Control and Congestion Control in the BISDN.
[28] ITU I.371，BISDN中的流量控制和拥塞控制。
[29] ITU E.191, BISDN Numbering and Addressing.
[29] ITU E.191，BISDN编号和寻址。
[30] ATM Forum Addressing: Reference Guide, af-ra-0106.000.
[30] ATM论坛地址：参考指南，af-ra-0106.000。
[31] http://www.iana.org/assignments/rtp-parameters for a list of codecs with static payload types.
[31] http://www.iana.org/assignments/rtp-parameters 获取具有静态负载类型的编解码器列表。
[32] ITU Q.2941-2, Digital Subscriber Signalling System No. 2 (DSS 2): Generic identifier transport extensions.
[32] ITU Q.2941-2，第2号数字用户信令系统（DSS 2）：通用标识符传输扩展。
[33] ITU Q.2961, Digital subscriber signalling system no.2 (DSS 2) - additional traffic parameters. Also, Amendment 2 to Q.2961.
[33] ITU Q.2961，第2号数字用户信号系统（DSS 2）-附加业务参数。此外，Q.2961的修正案2。
[34] ITU Q. 2965.1, Digital subscriber signalling system no.2 (DSS 2) - Support of Quality of Service classes.
[34] ITU Q.2965.1，第2号数字用户信号发送系统（DSS 2）——对服务质量等级的支持。
[35] ITU Q. 2965.2, Digital subscriber signalling system no.2 (DSS 2) - Signalling of individual Quality of Service parameters.
[35] ITU Q.2965.2，第2号数字用户信号发送系统（DSS 2）-单个服务质量参数的信号发送。
[36] ITU Q.1901, Bearer Independent Call Control Protocol.
[36] ITU Q.1901，承载独立呼叫控制协议。
[37] ITU Q.2630.1, AAL type 2 signaling protocol - capability set 1.
[37] ITU Q.2630.1，AAL类型2信令协议-能力集1。
[38] ITU I.363.5, B-ISDN ATM Adaptation Layer specification: Type 5 AAL.
[38] ITU I.363.5，B-ISDN ATM适配层规范：类型5 AAL。
[39] I.365.1,Frame relaying service specific convergence sublayer (FR-SSCS).
[39] I.365.1，帧中继服务特定汇聚子层（FR-SSCS）。
[40] I.365.2, B-ISDN ATM adaptation layer sublayers: service specific coordination function to provide the connection oriented network service.
[40] I.365.2，B-ISDN ATM适配层子层：提供面向连接的网络服务的特定于服务的协调功能。
[41] I.365.3, B-ISDN ATM adaptation layer sublayers: service specific coordination function to provide the connection-oriented transport service.
[41] I.365.3，B-ISDN ATM适配层子层：提供面向连接的传输服务的特定于服务的协调功能。
[42] I.365.4, B-ISDN ATM adaptation layer sublayers: Service specific convergence sublayer for HDLC applications.
[42] I.365.4，B-ISDN ATM适配层子层：HDLC应用的特定于服务的汇聚子层。
[43] Q.2110, B-ISDN ATM adaptation layer - service specific connection oriented protocol (SSCOP).
[43] Q.2110，B-ISDN ATM适配层-特定于服务的面向连接协议（SSCOP）。
[44] af-vtoa-0113.000, ATM trunking using AAL2 for narrowband services.
[44] af-vtoa-0113.000，使用AAL2进行窄带服务的ATM中继。
[45] H.323-2, Packet-based multimedia communications systems.
[45] H.323-2，基于分组的多媒体通信系统。
[46] af-vtoa-0083.000, Voice and Telephony Over ATM to the Desktop.
[46] af-vtoa-0083.000，通过ATM到桌面的语音和电话。
[47] I.356, BISDN ATM layer cell transfer performance.
[47] I.356，BISDN ATM层信元传输性能。
[48] ITU Q.2957, Digital Subscriber Signaling System No. 2, User to user signaling.
[48] ITU Q.2957，第2号数字用户信令系统，用户对用户信令。
[49] Mills, D., "Network Time Protocol (Version 3) Specification, Implementation and Analysis", RFC 1305, March 1992.
[49] Mills，D.，“网络时间协议（第3版）规范、实施和分析”，RFC13051992年3月。
[50] TIA/EIA/IS-J-STD-025-A, Lawfully Authorized Electronic Surveillance, May 2000.
[50] TIA/EIA/IS-J-STD-025-A，合法授权的电子监控，2000年5月。
[51] ITU-T H.222.1, Multimedia multiplex and synchronization for audiovisual communication in ATM environments.
[51] ITU-T H.222.1，ATM环境中视听通信的多媒体多路复用和同步。
[52] af-vmoa-0145.000, Voice and Multimedia over ATM, Loop Emulation Service using AAL2.
[52] af-vmoa-0145.000，ATM上的语音和多媒体，使用AAL2的环路模拟服务。
[53] FRF.5, Frame Relay/ATM PVC Network Interworking Implementation Agreement.
[53] FRF.5，帧中继/ATM PVC网络互通实施协议。
[54] FRF.8.1, Frame Relay/ATM PVC Service Interworking Implementation Agreement.
[54] FRF.8.1，帧中继/ATM PVC业务互通实施协议。
[55] FRF.11, Voice over Frame Relay Implementation Agreement.
[55] FRF.11，语音帧中继实施协议。
[56] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997.
[56] Crocker，D.和P.Overell，“语法规范的扩充BNF:ABNF”，RFC 2234，1997年11月。
[57] ITU Q.765.5, Application Transport Mechanism - Bearer Independent Call Control.
[57] ITU Q.765.5，应用传输机制-承载独立呼叫控制。
[58] http://www.3gpp.org/ftp/Specs for specifications related to 3GPP, including AMR codecs.
[58] http://www.3gpp.org/ftp/Specs 有关3GPP的规范，包括AMR编解码器。
[59] ITU Q.931, Digital Subscriber Signaling System No. 1: Network Layer.
[59] ITU Q.931，数字用户信号系统第1号：网络层。
[60] ITU Q.763, SS7 - ISUP formats and codes.
[60] ITU Q.763，SS7-ISUP格式和代码。
[61] http://www.atmforum.com/atmforum/specs/specs.html, ATM Forum, Well-known addresses and assigned codes.
[61] http://www.atmforum.com/atmforum/specs/specs.html，ATM论坛，知名地址和指定代码。
[62] Bradner, S., "Keywords for use in RFCs to indicate requirement levels", BCP 14, RFC 2119, March 1997.
[62] Bradner，S.，“RFC中用于指示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
Acknowledgements
致谢
The authors wish to thank several colleagues at Cisco and in the industry who have contributed towards the development of these SDP conventions, and who have reviewed, implemented and tested these constructs. Valuable technical ideas that have been incorporated into this internet document have been provided by Hisham Abdelhamid, Flemming Andreasen, David Auerbach, Robert Biskner, Bruce Buffam, Steve Casner, Alex Clemm, Bill Foster, Snehal Karia, Raghu Thirumalai Rajan, Joe Stone, Bruce Thompson, Dan Wing and Ken Young of Cisco, Michael Brown, Rade Gvozdanovic, Graeme Gibbs, Tom-PT Taylor, Mark Watson and Sophia Scoggins of Nortel Networks, Brian Rosen, Tim Dwight and Michael Mackey of Marconi, Ed Guy and Petros Mouchtaris of Telcordia, Christian Groves of Ericsson, Charles Eckel of Vovida Networks, Tom Jepsen, Dal Chohan, Sagar Gordhan and Chris Gallon of Fujitsu, Mahamood Hussain of Hughes Software Systems and Sean Sheedy of nCUBE Corporation, Narendra Tulpule of Intel, Albrecht Schwarz of Alcatel, and Jonathan Rosenberg of Dynamicsoft. The authors also wish to thank the ISC device control group, and the MMUSIC and MEGACO subgroups of the IETF, especially Bill Foster, Joerg Ott, Sean Sheedy and Brian Rosen for their help in the preparation of this document. Finally, thanks are due to Narendra Tulpule of Intel whose ABNF grammar was adapted for this document.
作者希望感谢Cisco和业界的几位同事，他们为这些SDP约定的开发做出了贡献，并且审查、实施和测试了这些构造。Hisham Abdelhamid、Flemming Andreasen、David Auerbach、Robert Biskner、Bruce Buffam、Steve Casner、Alex Clemm、Bill Foster、Snehal Karia、Raghu Thirumalai Rajan、Joe Stone、Bruce Thompson、Dan Wing和Cisco的Ken Young、Michael Brown、，北电网络的格沃兹达诺维奇、格雷姆·吉布斯、汤姆·泰勒、马克·沃森和索菲亚·斯科金斯、马可尼的布赖恩·罗森、蒂姆·德怀特和迈克尔·麦基、特科迪亚的埃德·盖伊和彼得罗斯·穆赫塔里斯、爱立信的克里斯汀·格罗夫斯、沃维达网络的查尔斯·埃克尔、富士通的汤姆·杰普森、达尔·乔汉、萨加尔·戈尔丹和克里斯·加伦，休斯软件系统公司（Hughes Software Systems）的马哈茂德·侯赛因（Mahamood Hussain）和nCUBE公司的肖恩·希迪（Sean Sheedy）、英特尔公司（Intel）的纳伦德拉·图尔普勒（Narendra Tulpule）、阿尔卡特公司（Alcatel）的阿尔布雷希特·施瓦兹（Albrecht Schwarz）和。作者还希望感谢ISC设备控制小组以及IETF的MMUSIC和MEGACO小组，特别是Bill Foster、Joerg Ott、Sean Sheedy和Brian Rosen在编写本文件过程中提供的帮助。最后，感谢英特尔公司的Narendra Tulpule，其ABNF语法被改编用于本文档。
Authors' Addresses
作者地址
Rajesh Kumar Cisco Systems, Inc. M/S SJC01/3 170 West Tasman Drive San Jose, CA 95134-1706
Rajesh Kumar Cisco Systems，Inc.位于加利福尼亚州圣何塞市西塔斯曼大道170号SJC01/3，邮编95134-1706
Phone: 1-800-250-4800 EMail: rkumar@cisco.com
电话：1-800-250-4800电子邮件：rkumar@cisco.com
Mohamed Mostafa Cisco Systems, Inc. M/S SJC01/3 170 West Tasman Drive San Jose, CA 95134-1706
Mohamed Mostafa Cisco Systems，Inc.位于加利福尼亚州圣何塞市西塔斯曼大道170号SJC01/3，邮编95134-1706
Phone: 1-800-250-4800 EMail: mmostafa@cisco.com
电话：1-800-250-4800电子邮件：mmostafa@cisco.com
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Acknowledgement
确认
Funding for the RFC Editor function is currently provided by the Internet Society.
RFC编辑功能的资金目前由互联网协会提供。