Network Working Group M. Maher
Request for Comments: 2331 USC/ISI
Category: Standards Track April 1998
Network Working Group M. Maher
Request for Comments: 2331 USC/ISI
Category: Standards Track April 1998
ATM Signalling Support for IP over ATM - UNI Signalling 4.0 Update
ATM信令支持IP over ATM-UNI信令4.0更新
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 (1998). All Rights Reserved.
版权所有（C）互联网协会（1998年）。版权所有。
Abstract
摘要
This memo describes how to efficiently use the ATM call control signalling procedures defined in UNI Signalling 4.0 [SIG40] to support IP over ATM environments as described in RFC 2225 [LAUB98] and in RFC 2332 [LUC98]. Among the new features found in UNI Signalling 4.0 are Available Bit Rate signalling and traffic parameter negotiation. This memo highlights the features of UNI Signalling 4.0 that provide IP entities capabilities for requesting ATM service in sites with SVC support, whether it is private ATM or publicly provisioned ATM, in which case the SVC support is probably configured inside PVPs.
本备忘录描述了如何有效地使用UNI信令4.0[SIG40]中定义的ATM呼叫控制信令程序，以支持RFC 2225[LAUB98]和RFC 2332[LUC98]中所述的IP over ATM环境。UNI信令4.0中的新功能包括可用比特率信令和流量参数协商。本备忘录强调了UNI信令4.0的功能，该功能提供IP实体在支持SVC的站点中请求ATM服务的能力，无论是专用ATM还是公开配置的ATM，在这种情况下，SVC支持可能在PVPs内配置。
This document is only relevant to IP when used as the well known "best effort" connectionless service. In particular, this means that this document does not pertain to IP in the presence of implemented IP Integrated Services. The topic of IP with Integrated Services over ATM will be handled by a different specification or set of specifications being worked on in the ISSLL WG.
本文档仅在用作众所周知的“尽力而为”无连接服务时与IP相关。特别是，这意味着本文档不适用于存在已实现的IP集成服务的IP。通过ATM提供综合服务的IP主题将由ISSLL工作组正在制定的另一个规范或一组规范来处理。
This specification is a follow-on to RFC 1755, "ATM Signaling Support for IP over ATM", which is based on UNI 3.1 signalling [UNI95]. Readers are assumed to be familiar with RFC 1755.
本规范是RFC 1755“ATM上IP的ATM信令支持”的后续规范，该规范基于UNI 3.1信令[UNI95]。假定读者熟悉RFC1755。
Table of Contents
目录
1. Conventions ............................................... 2
2. Overview .................................................. 2
3. Use of Protocol Procedures ................................ 3
3.1 VC Teardown........................................... 3
4. Overview of Call Establishment Message Content ............ 3
5. Description of Information Elements ....................... 4
5.1 ATM Adaptation Layer Parameters ...................... 4
5.2 Broadband Low Layer Information ..................... 5
5.3 Traffic Management Issues and Related IEs............. 5
5.3.1 ATM Traffic Descriptor ........................ 6
5.3.1.1 Tagging vs. Dropping ................. 7
5.3.2 Traffic Parameter Negotiation .................. 7
5.3.3 Broadband Bearer Capability .................... 8
5.3.4 QoS Parameter .................................. 8
5.3.4.1 Signalling of Individual QoS Parameters 8
5.4 ATM Addressing Information ........................... 9
6. ABR Signalling In More Detail ............................ 9
7. Frame Discard Capability .................................. 10
8. Security Considerations ................................... 10
9. Acknowledgements........................................... 10
10. References ................................................ 10
11. Author's Address .......................................... 12
Appendix A Sample Signalling Messages ........................ 13
Appendix B ABR and nrt-VBR Signalling Guidelines for IP Routers 15
Appendix C Combinations of Traffic Related Parameters ........ 18
Full Copyright Statement ...................................... 26
1. Conventions ............................................... 2
2. Overview .................................................. 2
3. Use of Protocol Procedures ................................ 3
3.1 VC Teardown........................................... 3
4. Overview of Call Establishment Message Content ............ 3
5. Description of Information Elements ....................... 4
5.1 ATM Adaptation Layer Parameters ...................... 4
5.2 Broadband Low Layer Information ..................... 5
5.3 Traffic Management Issues and Related IEs............. 5
5.3.1 ATM Traffic Descriptor ........................ 6
5.3.1.1 Tagging vs. Dropping ................. 7
5.3.2 Traffic Parameter Negotiation .................. 7
5.3.3 Broadband Bearer Capability .................... 8
5.3.4 QoS Parameter .................................. 8
5.3.4.1 Signalling of Individual QoS Parameters 8
5.4 ATM Addressing Information ........................... 9
6. ABR Signalling In More Detail ............................ 9
7. Frame Discard Capability .................................. 10
8. Security Considerations ................................... 10
9. Acknowledgements........................................... 10
10. References ................................................ 10
11. Author's Address .......................................... 12
Appendix A Sample Signalling Messages ........................ 13
Appendix B ABR and nrt-VBR Signalling Guidelines for IP Routers 15
Appendix C Combinations of Traffic Related Parameters ........ 18
Full Copyright Statement ...................................... 26
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 [BRA97].
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[BRA97]中所述进行解释。
UNI Signalling version 4.0 (SIG 4.0) is the ATM Forum follow-on specification to UNI 3.1 signalling (UNI 3.1). Among the new features in SIG 4.0, those of particular interest to IP over ATM environments are:
UNI信令版本4.0（SIG 4.0）是UNI 3.1信令（UNI 3.1）的ATM论坛后续规范。在SIG 4.0中的新功能中，ATM上IP环境特别感兴趣的功能包括：
o Available Bit Rate (ABR) Signalling for Point-to-Point Calls o Traffic Parameter Negotiation o Frame Discard Support o Leaf Initiated Join (LIJ) Capability o ATM Anycast Capability o Switched Virtual Path (VP) Service
o 点到点呼叫的可用比特率（ABR）信令o流量参数协商o帧丢弃支持o叶发起加入（LIJ）功能o ATM选播功能o交换虚拟路径（VP）服务
This memo highlights the first three capabilities listed above. The last three capabilities are not discussed because models for their use in IP over ATM environments have not yet been defined. The ION WG is considering the applicability of LIJ and Group Addressing to the RFC2022 problem space. Furthermore, Anycast addressing is being explored as a technique for supporting server discovery in ATM networks.
此备忘录强调了上面列出的前三个功能。最后三种功能没有讨论，因为它们在IP over ATM环境中的使用模型尚未定义。ION WG正在考虑LIJ和组寻址对RFC2022问题空间的适用性。此外，选播寻址作为一种支持ATM网络中服务器发现的技术正在被探索中。
Section 3 in RFC 1755 introduces requirements of virtual circuit (VC) management intended to prevent VC thrashing, excessive VC consumption, and other related problems. This section updates RFC 1755's requirements related to VC teardown.
RFC 1755中的第3节介绍了虚拟电路（VC）管理的要求，旨在防止VC振荡、过度VC消耗和其他相关问题。本节更新了与VC拆卸相关的RFC 1755要求。
In environments running layer 3 (L3) signalling protocols, such as RSVP [RSVP], over ATM, data VCs might correspond to L3 reserved flows (even if the VC is a 'best effort' VC). In such environments it is beneficial for VCs to be torn down only when the L3 reservation has expired. In other words, it is more efficient for the sender of a L3 reserved flow to initiate VC tear-down when the receiver(s) has ceased refreshing the reservation. To support such L3 behavior, systems implementing a Public ATM UNI interface and serving as the _called_ party of a VCC MUST NOT use an inactivity timer on such a VCC by default. A system MAY use an inactivity timer on such a VCC if configured to do so.
在通过ATM运行第3层（L3）信令协议（如RSVP[RSVP]）的环境中，数据VCs可能对应于L3保留流（即使VC是“尽力”VC）。在这样的环境中，只有在L3保留过期时才拆除VCs是有益的。换言之，当接收方停止刷新保留时，L3保留流的发送方启动VC中断更有效。为支持此类L3行为，默认情况下，实现公共ATM UNI接口并充当VCC被叫方的系统不得在此类VCC上使用非活动计时器。如果配置为这样做，系统可以在这样的VCC上使用非活动计时器。
Signalling messages are structured to contain mandatory and optional variable length information elements (IEs). A SETUP message which establishes an ATM connection to be used for IP and multiprotocol interconnection calls MUST contain the following IEs:
信令消息的结构包含强制性和可选的可变长度信息元素（IE）。建立用于IP和多协议互连呼叫的ATM连接的设置消息必须包含以下IEs：
AAL Parameters ATM Traffic Descriptor Broadband Bearer Capability Broadband Low Layer Information QoS Parameter Called Party Number Calling Party Number
AAL参数ATM业务描述符宽带承载能力宽带低层信息QoS参数被叫方号码主叫方号码
and MAY, under certain circumstance contain the following IEs:
在某些情况下，可能包含以下信息：
Calling Party Subaddress Called Party Subaddress Transit Network Selection
主叫方子地址被叫方子地址中转网络选择
(New in SIG 4.0:) Minimum Acceptable ATM Traffic Descriptor Alternative ATM Traffic Descriptor ABR Setup Parameters ABR Additional Parameters Connection Scope Selection Extended QoS Parameters End-to-End Transit Delay
（SIG 4.0中新增：）最小可接受ATM业务描述符备选ATM业务描述符ABR设置参数ABR附加参数连接范围选择扩展QoS参数端到端传输延迟
In SIG 4.0, like UNI 3.1, the AAL Parameters and the Broadband Low Layer Information IEs are optional in a SETUP message. However, in support of IP over ATM these two IEs MUST be included. Appendix A shows a sample setup message.
在SIG 4.0中，与UNI 3.1一样，AAL参数和宽带低层信息IEs在设置消息中是可选的。然而，为了支持ATM上的IP，必须包括这两个IEs。附录A显示了一个示例设置消息。
This section describes the coding of, and procedures surrounding, information elements in SETUP and CONNECT messages. The first two IEs described, ATM Adaptation Layer Parameters and Broadband Low Layer Information, are categorized as having significance only to the end-points of an ATM call supporting IP. That is, the network does not process these IEs.
本节介绍设置和连接消息中信息元素的编码和相关过程。所描述的前两个ie，ATM适配层参数和宽带低层信息，被分类为仅对支持IP的ATM呼叫的端点有意义。也就是说，网络不处理这些IEs。
The AAL Parameters IE carries information about the ATM adaptation layer to be used on the connection. The parameters specified in this IE are the same as specified in [PER95].
AAL参数IE携带有关要在连接上使用的ATM适配层的信息。本IE中规定的参数与[PER95]中规定的参数相同。
Format and field values of AAL Parameters IE
AAL参数IE的格式和字段值
----------------------------------------------------------
| aal_parameters |
----------------------------------------------------------
| aal_type 5 (AAL 5) |
| fwd_max_sdu_size_identifier 140 |
| fwd_max_sdu_size 65,535 (desired IP MTU) |
| bkw_max_sdu_size_identifier 129 |
| bkw_max_sdu_size 65,535 (desired IP MTU) |
| sscs_type identifier 132 |
| sscs_type 0 (null SSCS) |
----------------------------------------------------------
----------------------------------------------------------
| aal_parameters |
----------------------------------------------------------
| aal_type 5 (AAL 5) |
| fwd_max_sdu_size_identifier 140 |
| fwd_max_sdu_size 65,535 (desired IP MTU) |
| bkw_max_sdu_size_identifier 129 |
| bkw_max_sdu_size 65,535 (desired IP MTU) |
| sscs_type identifier 132 |
| sscs_type 0 (null SSCS) |
----------------------------------------------------------
This shows maximum size MTUs. In practice, most sites have used 9180 IP MTUs for ATM [RFC1626].
这显示了最大大小的MTU。实际上，大多数站点都将9180 IP MTU用于ATM[RFC1626]。
Selection of an encapsulation to support IP over an ATM VCC is done using the Broadband Low Layer Information (B-LLI) IE, along with the AAL Parameters IE, and the B-LLI negotiation procedure. B-LLI negotiation is described in [PER95] in Appendix D. The procedures remain the same for this SIG 4.0 based specification.
使用宽带低层信息（B-LLI）IE、AAL参数IE和B-LLI协商过程来选择支持ATM VCC上IP的封装。附录D中的[PER95]中描述了B-LLI协商。基于SIG 4.0的规范的程序保持不变。
Format of B-LLI IE indicating LLC/SNAP encapsulation
指示LLC/SNAP封装的B-LLI IE格式
----------------------------------------------------------
| bb_low_layer_information |
----------------------------------------------------------
| layer_2_id 2 |
| user_information_layer 12 (lan_llc - ISO 8802/2) |
----------------------------------------------------------
----------------------------------------------------------
| bb_low_layer_information |
----------------------------------------------------------
| layer_2_id 2 |
| user_information_layer 12 (lan_llc - ISO 8802/2) |
----------------------------------------------------------
The ATM Forum Traffic Management Sub-working group has completed version 4.0 of their specification [TMGT40]. This latest version focuses primarily on the definition of the ABR service category. As opposed to the Unspecified Bit Rate (UBR) traffic class, ABR uses a rate-based flow control mechanism to assure certain traffic guarantees (bandwidth and delay). There has been much debate on whether IP benefits from ABR, and if so, how IP should use ABR. The IP Integrated Services (IIS) and RSVP models in IP add complexity to this issue because mapping IIS traffic classes to ATM traffic classes is not straightforward.
ATM论坛流量管理子工作组已完成其规范[TMGT40]的4.0版。最新版本主要关注ABR服务类别的定义。与未指定比特率（UBR）业务类别不同，ABR使用基于速率的流量控制机制来确保特定的业务保证（带宽和延迟）。关于知识产权是否受益于ABR，以及如果受益于ABR，知识产权应如何使用ABR，一直存在很多争论。IP中的IP集成服务（IIS）和RSVP模型增加了这个问题的复杂性，因为将IIS流量类映射到ATM流量类并不简单。
This document attempts only to present the required IP to ATM signaling interface for IP over ATM systems that do not support IIS as yet. It is an attempt to cause IP over ATM vendors to support enough options for signalling the traffic characteristics of VCs serving non-IIS IP datagrams. This specification also aims to give guidance to ATM system administrators so that they can configure their IP over ATM entities to conform to the varied services that their ATM provider may have sold to them. By definition, IP without IIS cannot be expected to provide a signalling interface that is flexible and allows application specific traffic descriptors. The topic of IP over ATM signalling for IP _with_ IIS is to be presented in other specifications being produced by the ISSLL WG of the IETF.
本文档仅尝试为不支持IIS的IP over ATM系统提供所需的IP到ATM信令接口。这是一种试图使IP over ATM供应商支持足够的选项，用于向服务于非IIS IP数据报的VCs的流量特性发送信号。本规范还旨在为ATM系统管理员提供指导，以便他们能够配置其IP over ATM实体，以符合其ATM提供商可能向其出售的各种服务。根据定义，没有IIS的IP不能提供灵活的信令接口，并允许特定于应用程序的流量描述符。IETF的ISSLL工作组正在制定的其他规范中介绍了针对IP_和IIS的IP over ATM信令的主题。
An IP over ATM interface may be configured to support all the defined ATM Service Categories (ASC). They are:
IP over ATM接口可配置为支持所有定义的ATM服务类别（ASC）。他们是：
- CBR - CBR with CLR specified (loss-permitting CBR) - ABR - UBR - real time VBR - non-real time VBR
- CBR-指定CLR的CBR（损耗允许CBR）-ABR-UBR-实时VBR-非实时VBR
The ATM Traffic Descriptor IE, Broadband Bearer Capability IE, and the QoS Parameter IE together define the signalling view of ATM traffic management. Additionally, the Extended QoS parameters IE and the End-to-end Transit Delay IE may be used to provide more specifics about traffic requirements, however this note does not provide explicit recommendations on their use. Annex 9 of [SIG40] describes a set of allowable combinations of traffic and QoS related paramenters defined for SIG 4.0. This set includes all forms of non-IIS IP signaling configurations that MUST be implemented in ATM endsystems to accommodate varied sites' needs. The principle is that IP over ATM service may be available in different sites by different types of procured ATM service; for one site, a CBR PVP might be cost-effective and then the SVCs that IP over ATM without IIS must establish must be CBR. Similarly, VBR or ABR PVPs could be provisioned. The intent of this document is to specify the use of the most sensible parameters within this non-IIS configuration. For instance, for non-IIS VBR, the SCR value may need to be hand-configured for IP users, or for ABR, the PCR value may be link-rate with a 0 MCR.
ATM业务描述符IE、宽带承载能力IE和QoS参数IE共同定义了ATM业务管理的信令视图。此外，扩展QoS参数IE和端到端传输延迟IE可用于提供更多关于流量要求的细节，但本说明未提供关于其使用的明确建议。[SIG40]的附录9描述了为SIG 4.0定义的一组允许的流量和QoS相关参数组合。这一组包括必须在ATM终端系统中实现的所有形式的非IIS IP信令配置，以适应不同站点的需求。其原则是，通过不同类型的ATM服务，可以在不同的站点提供IP over ATM服务；对于一个站点，CBR PVP可能是经济高效的，然后不带IIS的IP over ATM必须建立的SVC必须是CBR。类似地，可以提供VBR或ABR PVP。本文档旨在指定此非IIS配置中最合理参数的使用。例如，对于非IIS VBR，可能需要为IP用户手动配置SCR值，或者对于ABR，PCR值可能是具有0 MCR的链路速率。
For the reader's convenience, we have replicated the tables found in Annex 9 of [SIG40] in Appendix C of this document. Ideally this document could recommend specific values for the various table parameters that would offer the most sensible IP over ATM service. Nevertheless, it is not possible to mandate specific values given the varied scenarios of procured ATM service.
为方便读者，我们复制了本文件附录C中[SIG40]附件9中的表格。理想情况下，本文档可以为各种表参数推荐特定值，以提供最合理的IP over ATM服务。然而，鉴于采购的ATM服务的不同场景，不可能强制规定特定值。
Even with the newly defined ABR ASC, the most convenient model for supporting IP still corresponds to the best effort capability, the UBR ASC. The rationale for this assertion stems from the fact that a non-IIS IP service has no notion of the performance requirements of the higher layers it supports. Therefore, if a site's configuration allows use of UBR, users SHOULD signal for it using the IE's and parameters pertaining to the UBR ATC. See Appendix C for the list of those IE's and parameters.
即使有了新定义的ABR ASC，支持IP的最方便的模型仍然对应于尽力而为的能力，即UBR ASC。此断言的基本原理源于这样一个事实，即非IIS IP服务不知道它所支持的更高层的性能要求。因此，如果站点的配置允许使用UBR，用户应使用IE和与UBR ATC相关的参数为其发送信号。有关这些IE和参数的列表，请参见附录C。
Although we consider the UBR ASC the most natural ASC for best-effort IP, ATM vendors that implement VBR and ABR services could possibly create hooks for convenient use of these services. If this is the
虽然我们认为UBR ASC是最优秀的IP ASP，但实现VBR和ABR服务的ATM供应商可能会创建用于方便使用这些服务的挂钩。如果这是
case, IP routers may perhaps have the most to gain from use of VBR or ABR services because of the large aggregated traffic volume they are required to forward. See Appendix B for detailed suggestions on VBR and ABR signalling for IP routers. We simply note here that, in support of ABR service, two new subfields have been added in SIG 4.0 to the Traffic Descriptor IE. These fields are the forward and backward 'Minimum Cell Rate' fields.
在这种情况下，IP路由器可能从VBR或ABR服务的使用中获益最多，因为它们需要转发大量的聚合流量。有关IP路由器的VBR和ABR信令的详细建议，请参见附录B。这里我们只需注意，为了支持ABR服务，在SIG 4.0中，在流量描述符IE中添加了两个新的子字段。这些字段是向前和向后的“最小信元速率”字段。
The Traffic Descriptor IE contains a 'tagging' subfield used for indicating whether the network is allowed to tag the source's data cells. Tagging in the network may occur during periods of congestion or when the source's traffic has violated the traffic contract for the connection. See Section 4 of [TMGT40] for an explanation of ATM connection conformance and the Usage Parameter Control (UPC) function.
流量描述符IE包含一个“标记”子字段，用于指示是否允许网络标记源的数据单元。网络中的标记可能发生在拥塞期间或源的流量违反连接的流量合同时。有关ATM连接一致性和使用参数控制（UPC）功能的说明，请参见[TMGT40]第4节。
SIG 4.0 and TMGT 4.0 define two modes of UBR, UBR.1 which disables tagging and UBR.2 which enables tagging (see Appendix C). In some network environments there is no potential for UBR traffic sources to violate the connection traffic contract because, either the user's terminal equipment supports traffic shaping, or the network does not enforce PCR. In such environments, the user SHOULD specify 'no tagging' in the SETUP message (UBR.1). Specifying 'no tagging' indicates to the network that cells should be dropped during periods of congestion instead of being randomly marked/tagged as low priority. Cells of packets that the source itself has marked as low priority are dropped first, thereby preserving the source's characterization of the traffic.
SIG 4.0和TMGT 4.0定义了两种UBR模式，UBR.1禁用标记，UBR.2启用标记（见附录C）。在某些网络环境中，由于用户的终端设备支持流量整形，或者网络不实施PCR，因此UBR流量源不可能违反连接流量契约。在这种环境中，用户应在设置消息（UBR.1）中指定“无标记”。指定“无标记”表示网络在拥塞期间应丢弃小区，而不是随机标记/标记为低优先级。首先丢弃源本身标记为低优先级的数据包单元，从而保留源的流量特征。
On the other hand, when the network applies PCR to the UPC function, meaning it enforces PCR, and traffic shaping is not enabled at the source, the source has the potential to violate the traffic contract and SHOULD therefore signal for tagging (UBR.2). Tagging allows the source's non-conforming cells to be tagged and forwarded instead of dropped.
另一方面，当网络将PCR应用于UPC功能时，这意味着它强制实施PCR，并且在源处未启用流量整形，源有可能违反流量合同，因此应发出标记信号（UBR.2）。标记允许对源的不一致单元格进行标记和转发，而不是丢弃。
SIG 4.0 allows certain traffic parameters to be negotiated during the call establishment phase Traffic parameters cannot be 'renegotiated' after the call is active. Two new IEs make negotiation possible:
SIG 4.0允许在呼叫建立阶段协商某些流量参数在呼叫激活后不能“重新协商”流量参数。两个新的IEs使谈判成为可能：
- the Minimum Acceptable ATM Traffic Descriptor IE allows negotiation of PCR parameters
- 最小可接受ATM流量描述符IE允许协商PCR参数
- the Alternative ATM Traffic Descriptor IE allows negotiation of other traffic parameters
- 备用ATM流量描述符IE允许协商其他流量参数
A SETUP or CONNECT message may include ONLY one of the above IEs. That is, the calling party may only offer an 'alternative' or 'minimum' to the requested traffic parameters. (See Section 8 of [SIG40].) IP over ATM entities SHOULD take advantage of this capability whenever possible. In order to do so, IP over ATM entities SHOULD specify PCR _equal_ to the link rate in the ATM Traffic Descriptor IE of the SETUP message and a minimum of zero PCR in the Minimum Acceptable ATM Traffic Descriptor IE.
设置或连接消息可能仅包括上述一个IEs。也就是说，呼叫方只能对请求的业务参数提供“替代”或“最小”。（见[SIG40]第8节）ATM上的IP实体应尽可能利用这一能力。为此，ATM上的IP实体应在设置消息的ATM流量描述符IE中指定等于链路速率的PCR，并在最小可接受ATM流量描述符IE中指定最小零PCR。
A new field in UNI signalling 4.0 called, 'ATM Transfer Capability' (ATC), has been defined in the Broadband Bearer Capability IE for the purpose of explicitly specifying the desired ATM traffic category. The figure below shows the allowable ATC values.
UNI信令4.0中的一个新字段称为“ATM传输能力”（ATC），已在宽带承载能力IE中定义，用于明确指定所需的ATM业务类别。下图显示了允许的ATC值。
Format and field values of Broadband Bearer Capability IE
宽带承载能力IE的格式和字段值
-------------------------------------------------------------
| bb_bearer_capability |
------------------------------------------------------------|
| spare 0 |
| bearer_class bcob-x,c,a or VP |
| transfer_capability cbr, rt-vbr, nrt-vbr, abr |
| susceptibility_to_clipping 0 (not suscept) |
| spare 0 |
| user_plane_configuration pt-to-pt, pt-to-mpt |
-------------------------------------------------------------
-------------------------------------------------------------
| bb_bearer_capability |
------------------------------------------------------------|
| spare 0 |
| bearer_class bcob-x,c,a or VP |
| transfer_capability cbr, rt-vbr, nrt-vbr, abr |
| susceptibility_to_clipping 0 (not suscept) |
| spare 0 |
| user_plane_configuration pt-to-pt, pt-to-mpt |
-------------------------------------------------------------
Inclusion of the QoS Parameter IE is not mandatory in SIG 4.0. It may be omitted from a SETUP message _if and only if_ the Extended QoS Parameters IE is included (see next section). This specification makes no explicit recommendation on the use of the QoS related IEs.
在SIG 4.0中不强制包含QoS参数IE。当且仅当包含扩展QoS参数IE时（见下一节），可从设置消息中省略该参数。本规范对QoS相关IEs的使用没有明确的建议。
SIG 4.0 allows for signalling of individual QoS parameters for the purpose of giving the the network and called party a more exact description of the desired delay and cell loss characteristics. The two individual QoS related IEs, Extended QoS Parameters IE and End-to-End Transit Delay IE, can be used in the SETUP and CONNECT signaling messages in place of the 'generic' QoS Parameter IE. Note that inclusion of these two IEs depends on the type of ATM service
SIG 4.0允许发送单个QoS参数的信号，以便为网络和被叫方提供所需延迟和信元丢失特性的更准确描述。两个单独的QoS相关IE（扩展QoS参数IE和端到端传输延迟IE）可用于设置和连接信令消息，以代替“通用”QoS参数IE。请注意，这两个IE的包含取决于ATM服务的类型
category requested (see Annex 9 in [SIG40]).
要求的类别（见[SIG40]中的附件9）。
ATM addressing information is carried in the Called Party Number, Calling Party Number, and, under certain circumstance, Called Party Subaddress, and Calling Party Subaddress IE. The ATM Forum ILMI Specification 4.0 [ILMI40] provides the procedure for an ATM endsystem to learn its own ATM address from the ATM network, for use in populating the Calling Party Number IE.
ATM寻址信息包含在被叫方号码、主叫方号码以及在某些情况下被叫方子地址和主叫方子地址中，即ATM论坛ILMI规范4.0[ILMI40]提供了ATM终端系统从ATM网络中学习其自身ATM地址的过程，用于填充主叫方号码，即。
Format and field values of Called Party Number IE
被叫方号码IE的格式和字段值
----------------------------------------------------------
| called_party_number |
----------------------------------------------------------
| type_of_number (international number / unknown) |
| addr_plan_ident (ISDN / ATM Endsystem Address) |
| addr_number (E.164 / ATM Endsystem Address) |
----------------------------------------------------------
----------------------------------------------------------
| called_party_number |
----------------------------------------------------------
| type_of_number (international number / unknown) |
| addr_plan_ident (ISDN / ATM Endsystem Address) |
| addr_number (E.164 / ATM Endsystem Address) |
----------------------------------------------------------
The IEs and procedures pertaining to ABR signalling are briefly described in this section. Nevertheless, this document makes no specific recommendation on when to use the ABR service category for IP VCCs or give suggestions on appropriate values for the various parameters in the ABR related IEs.
本节简要描述了与ABR信令有关的IEs和程序。然而，本文件未就何时将ABR服务类别用于IP VCC提出具体建议，也未就ABR相关IEs中各种参数的适当值提出建议。
Two new IEs have been defined for ABR signaling:
为ABR信令定义了两个新的IEs：
o ABR Setup Parameters o ABR Additional Parameters
o ABR设置参数o ABR附加参数
These IEs may be optionally included in a SETUP or CONNECT message. The ABR Setup Parameters IE contains the following subfields:
这些IEs可以选择性地包含在设置或连接消息中。ABR设置参数IE包含以下子字段：
- Forward/Backward ABR Initial Cell Rate - Forward/Backward ABR Transient Buffer Exposure - Cumulative RM Fixed Round Trip Time - Forward/Backward Rate Increment Factor - Forward/Backward Rate Decrease Factor
- 前向/后向ABR初始信元速率-前向/后向ABR瞬态缓冲暴露-累积RM固定往返时间-前向/后向速率增量因子-前向/后向速率递减因子
The ABR Additional Parameters IE contains one subfield:
ABR附加参数IE包含一个子字段：
- Forward/Backward Additional Parameters Record
- 正向/反向附加参数记录
The Additional Parameters Record value is a compressed encoding of a set of ABR parameters (see [SIG40] and [ABRS]).
附加参数记录值是一组ABR参数的压缩编码（参见[SIG40]和[ABR]）。
The frame discard capability in SIG 4.0 is primarily based on the 'Partial and Early Packet Discard' strategy [ROM94]. Its use is defined for any of the ATM services, except for loss-less CBR. Frame discard signaling MUST be supported by all IP over ATM entities and it is RECOMMENDED that frame discard be signaled for all IP SVCs because it has been proven to increase throughput under network congestion. Signaling for frame discard is done by setting the frame discard bit in the 'Traffic Management Options' subfield in the Traffic Descriptor IE. It is possible that not all network entities in the SVC path support frame discard, but it is required that they all forward the signaling.
SIG 4.0中的帧丢弃功能主要基于“部分和早期数据包丢弃”策略[ROM94]。其用途定义为任何ATM服务，但无损耗CBR除外。帧丢弃信令必须由所有IP over ATM实体支持，并且建议为所有IP SVC发送帧丢弃信令，因为已经证明它可以在网络拥塞情况下提高吞吐量。帧丢弃的信令是通过在流量描述符IE中的“流量管理选项”子字段中设置帧丢弃位来完成的。SVC路径中的所有网络实体可能都不支持帧丢弃，但要求它们都转发信令。
The ATM Forum Security sub-working group is currently defining security mechanisms in ATM. The group has yet to produce a specification, therefore it is premature to begin defining IP over ATM signalling's use of ATM security. The ATM Forum is working on authentication mechanisms for signalling and on mechanisms for providing data integrity and confidentiality (e.g encryption). Lack of these ATM security mechanisms prevents the authentication of the originator of signalling messages, such as, connection setup request or connection teardown request. IP Security (RFC1825) can be applied to IP datagrams over ATM VCs to overcome the lack of security at the ATM layer.
ATM论坛安全分工作组目前正在定义ATM中的安全机制。该组织尚未制定规范，因此现在就开始定义IP over ATM信令对ATM安全性的使用还为时过早。ATM论坛正在研究信令的认证机制以及提供数据完整性和机密性（例如加密）的机制。由于缺乏这些ATM安全机制，无法对信令消息（如连接设置请求或连接断开请求）的发起人进行身份验证。IP安全性（RFC1825）可应用于ATM VCs上的IP数据报，以克服ATM层的安全性不足。
The authors would like to thank the members of the ION working group for their input. Special thanks to K.K. Ramakrishnan and Kerry Fendick who contributed Appendix B of this document.
作者要感谢离子工作组成员的投入。特别感谢K.K.Ramakrishnan和Kerry Fendick提供了本文件附录B。
REFERENCES
参考资料
[ABRS] ATM Forum, "Addendum to UNI Signalling v4.0 for ABR Parameter Negotiation", af-sig-0076.000; available at ftp://ftp.atmforum.com/pub.
[ABRS]ATM论坛，“ABR参数协商用UNI信令v4.0补遗”，af-sig-0076.000；可在ftp://ftp.atmforum.com/pub.
[ABRT] ATM Forum, "Addendum to Traffic Management v4.0 for ABR Parameter Negotiation", af-tm-0077.000; available at ftp://ftp.atmforum.com/pub.
[ABRT]ATM论坛，“ABR参数协商交通管理v4.0补遗”，af-tm-0077.000；可在ftp://ftp.atmforum.com/pub.
[RFC1122] Braden, R., Editor, "Requirements for Internet Hosts -- Communication Layers", STD 3, RFC 1122, October 1989.
[RFC1122]Braden，R.，编辑，“互联网主机的要求——通信层”，STD 3，RFC 1122，1989年10月。
[RFC1633] Braden, R., Clark, D., and S. Shenker, "Integrated Service in the Internet Architecture: An Overview", RFC 1633, June 1994.
[RFC1633]Braden，R.，Clark，D.，和S.Shenker，“互联网体系结构中的综合服务：概述”，RFC 16331994年6月。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2119]Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[RFC1483] Heinanen, J., "Multiprotocol Encapsulation over ATM Adaptation Layer 5", RFC 1483, July 1993.
[RFC1483]Heinanen，J.，“ATM适配层5上的多协议封装”，RFC 1483，1993年7月。
[ILMI40] ATM Forum, "Integrated Local Management Interface (ILMI) Specification Version 4.0", af-ilmi-0065.000, finalized September 1996; available at ftp://ftp.atmforum.com/pub.
[ILMI40]ATM论坛，“集成本地管理接口（ILMI）规范版本4.0”，af-ILMI-0065.000，1996年9月定稿；可在ftp://ftp.atmforum.com/pub.
[ISO8473] ISO/IEC 8473, Information processing systems - Data communications - Protocol for providing the connectionless-mode network service, 1988.
[ISO8473]ISO/IEC 8473，信息处理系统-数据通信-提供无连接模式网络服务的协议，1988年。
[ISO9577] Information Technology - Telecommunication and information exchange between systems - Protocol identification in the network layer ISO/IEC TR9577 (International Standards Organization: Geneva, 1990)
[ISO9577]信息技术-系统间远程通信和信息交换-网络层协议识别ISO/IEC TR9577（国际标准组织：日内瓦，1990）
[LAUB98] Laubach, M., and J. Halpern, "Classical IP and ARP over ATM", RFC 2225, April 1998.
[LAUB98]Laubach，M.和J.Halpern，“ATM上的经典IP和ARP”，RFC 2225，1998年4月。
[LUC98] Luciani, J., Katz, D., Piscitello, D., Cole, B., and N. Doraswamy, "NBMA Next Hop Resolution Protocol (NHRP)", RFC 2332, April 1998.
[LUC98]Luciani，J.，Katz，D.，Piscitello，D.，Cole，B.，和N.Doraswamy，“NBMA下一跳解析协议（NHRP）”，RFC 2332，1998年4月。
[RFC1755] Perez*, M., et. al., "ATM Signaling Support for IP over ATM", RFC 1755, February 1995. (* see author's information below)
[RFC1755]Perez*，M.，等，“ATM上IP的ATM信令支持”，RFC 17551995年2月。（*见下文作者信息）
[ROM94] Romanow, A., and Floyd, S., Dynamics of TCP Traffic over ATM Networks. IEEE JSAC, V. 13 N. 4, May 1995, p. 633-641. Abstract. An earlier version appeared in SIGCOMM '94, August 1994, pp. 79-88.
[ROM94]Romanow，A.，和Floyd，S.，ATM网络上TCP流量的动力学。IEEE JSAC，第13卷第4页，1995年5月，第。633-641. 摘要早期版本出现在SIGCOMM'941994年8月，第79-88页。
[RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S., and S. Jamin, "Resource ReSerVation Protocol (RSVP) - Version 1 Functional Specification", RFC 2205, September 1997.
[RFC2205]Braden，R.，Zhang，L.，Berson，S.，Herzog，S.，和S.Jamin，“资源预留协议（RSVP）-第1版功能规范”，RFC 22052997年9月。
[SIG40] ATM Forum, "ATM User-Network Interface (UNI) Signalling Specification Version 4.0", af-sig-0061.000, finalized July 1996; available at ftp://ftp.atmforum.com/pub.
[SIG40]ATM论坛，“ATM用户网络接口（UNI）信令规范4.0版”，af-sig-0061.000，1996年7月定稿；可在ftp://ftp.atmforum.com/pub.
[TMGT40] ATM Forum, "Traffic Management Specification Version 4.0", af-tm-0056.000, finalized April 1996; available at ftp://ftp.atmforum.com/pub.
[TMGT40]ATM论坛，“交通管理规范4.0版”，af-tm-0056.000，1996年4月定稿；可在ftp://ftp.atmforum.com/pub.
[UNI95] ATM Forum, "ATM User-Network Interface Specification Version 3.1", Prentice Hall, Upper Saddle River, NJ, 1995.
[UNI95]ATM论坛，“ATM用户网络接口规范3.1版”，普伦蒂斯大厅，新泽西州上鞍河，1995年。
Author's Address
作者地址
Maryann P. Maher (formerly Maryann Perez) USC/ISI 4350 N. Fairfax Drive, Suite 620 Arlington VA 22203
Maryann P.Maher（前Maryann Perez）USC/ISI 4350北费尔法克斯大道620室弗吉尼亚州阿灵顿22203
EMail: maher@isi.edu
EMail: maher@isi.edu
+--------------------------------------------------------------------+
SETUP
+--------------------------------------------------------------------+
SETUP
Information Elements/
Fields Value/(Meaning)
-------------------- ---------------
Information Elements/
Fields Value/(Meaning)
-------------------- ---------------
aal_parameters aal_type 5 (AAL 5) fwd_max_sdu_size_ident 140 fwd_max_sdu_size (xmit IP MTU value) bkw_max_sdu_size_ident 129 bkw_max_sdu_size (recv IP MTU, 0 for disallowing return traffic) sscs_type identifier 132 sscs_type 0 (null SSCS)
aal_参数aal_类型5（aal 5）fwd_max_sdu_size_ident 140 fwd_max_sdu_size（xmit IP MTU值）bkw_max_sdu_size_ident 129 bkw_max_sdu_size（recv IP MTU，0表示不允许返回流量）S_类型标识符132 SSC类型0（空SSC）
traffic_descriptor fwd_peak_cell_rate_0_1_ident 132 fwd_peak_cell_rate_0_1 (link rate) bkw_peak_cell_rate_0_1_ident 133 bkw_peak_cell_rate_0_1 (link rate) traff_mngt_options_ident 191 fwd_frame_discard 1 (on) bkw_frame_discard 1 (on if return traffic indicated) spare 0 tagging_bkw 1 (on) tagging_fwd 1 (on if return traffic indicated) best_effort_indication 190 (on)
流量描述符fwd_峰值_小区_速率_0_1_标识132 fwd_峰值_小区_0_1（链路速率）bkw_峰值_小区_速率_0_1标识133 bkw_峰值_小区_速率_0_1（链路速率）流量mngt选项_标识191 fwd_帧_丢弃1（打开）bkw_帧_丢弃1（如果指示返回流量，则打开）备用0_bkw 1（打开）标记如果指示返回流量（打开）最佳努力指示190（on）
minimum_acceptable_traffic_descriptor fwd_peak_cell_rate_0_1_ident 132 fwd_peak_cell_rate_0_1 0 bkw_peak_cell_rate_0_1_ident 133 bkw_peak_cell_rate_0_1 0
最小可接受通信量描述符fwd_峰值_小区_0_1_标识132 fwd_峰值_小区_0_1 0 bkw_峰值_小区_0_1_标识133 bkw_峰值_小区_0
bb_bearer_capability /* a coding for specifying UBR like service */
spare 0
bearer_class 16 (BCOC-X)
spare 0
atm_transfer_capability 10 (nrt-vbr)
susceptibility_to_clipping 0 (not susceptible to clipping)
spare 0
user_plane_configuration 0 (point_to_point)
bb_bearer_capability /* a coding for specifying UBR like service */
spare 0
bearer_class 16 (BCOC-X)
spare 0
atm_transfer_capability 10 (nrt-vbr)
susceptibility_to_clipping 0 (not susceptible to clipping)
spare 0
user_plane_configuration 0 (point_to_point)
bb_low_layer_information layer_2_id 2 user_information_layer 12 (lan_llc - ISO 8802/2)
bb_低_层_信息层_2_id 2用户信息层_12（lan_llc-ISO 8802/2）
qos_parameter qos_class_fwd 0 (class 0) qos_class_bkw 0 (class 0)
qos_参数qos_等级fwd 0（等级0）qos_等级bkw 0（等级0）
called_party_number type_of_number (international number / unknown) addr_plan_ident (ISDN / ATM Endsystem Address) number (E.164 / ATM Endsystem Address)
被叫方号码类型号码（国际号码/未知）地址计划标识（ISDN/ATM终端系统地址）号码（E.164/ATM终端系统地址）
calling_party_number type_of_number (international number / unknown) addr_plan_ident (ISDN / ATM Endsystem Address) presentation_indic (presentation allowed) spare 0 screening_indic (user_provided verified and passed) number (E.164 / ATM Endsystem Address)
主叫方号码类型号码（国际号码/未知）地址计划标识（ISDN/ATM终端系统地址）显示标识（允许显示）备用0屏蔽标识（用户提供的验证和通过）号码（E.164/ATM终端系统地址）
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
Figure 1. Sample contents of SETUP message
图1。设置消息的示例内容
When ATM is used to interconnect routers that are supporting a best effort service, the ATM connection typically carries an aggregation of IP flows, e.g., all best effort IP traffic between a pair of routers. With the efforts undertaken by ATM to be more "packet friendly" (e.g., frame discard), it is useful to examine ways that a VC can provide service comparable to or better than that of a dedicated or leased "link" in terms of performance and packet loss.
当ATM用于互连支持尽力而为服务的路由器时，ATM连接通常承载IP流的聚合，例如，一对路由器之间的所有尽力而为IP流量。随着ATM努力变得更“数据包友好”（例如，帧丢弃），研究VC在性能和数据包丢失方面可以提供与专用或租用“链路”相当或更好的服务的方法是有用的。
For ATM connections used to interconnect routers, a non-zero bandwidth reservation may be required to achieve consistently adequate performance for the aggregate set of flows. The support of bandwidth commitments for an ATM connection carrying IP traffic helps to assure that a certain fraction of each link's capacity is reserved for the total IP traffic between the routers. Reserving bandwidth for the aggregation of best-effort traffic between a pair of routers is analogous to provisioning a particular link bandwidth between the routers. There are at least 3 service classes defined in the ATM Traffic Management specification that provide varying degrees of capability that are suitable for interconnecting IP routers: UBR, ABR and VBR non-real-time. Although the use of best-effort service (UBR) at the ATM layer is the most straightforward and uncomplicated, it lacks the capability to enforce bandwidth commitments.
对于用于互连路由器的ATM连接，可能需要非零带宽预留，以实现聚合流集的一致充分性能。对承载IP流量的ATM连接的带宽承诺的支持有助于确保为路由器之间的总IP流量保留每个链路容量的某一部分。为一对路由器之间的尽力而为流量的聚合保留带宽类似于在路由器之间提供特定链路带宽。ATM流量管理规范中至少定义了3种服务类别，它们提供了不同程度的适用于互连IP路由器的能力：UBR、ABR和VBR非实时。尽管在ATM层使用尽力而为服务（UBR）是最直接和简单的，但它缺乏强制执行带宽承诺的能力。
Note that we are talking of providing a "virtual link" between routers, for the aggregate traffic. The provisioning is for the aggregate. It is therefore distinct from the per-flow bandwidth reservations that might be appropriate for Integrated Services.
注意，我们谈论的是在路由器之间提供一个“虚拟链路”，用于聚合流量。设置是针对聚合的。因此，它不同于可能适用于集成服务的每流带宽保留。
Even best-effort IP flows, when supported on an aggregate basis, have some broad service goals. The primary one is that of keeping packet loss rate reasonably small. A service class that strives to achieve this, keeping in mind the tradeoff between complexity and adequate service, is desirable. It has been recommended in this memo that UBR be the default service for this. UBR with (some form of) packet discard has the desirable goal of being simple in function, and it appears that vendors will be supporting it. However, when available, it may be quite worthwhile to consider ABR and VBR non-real-time service classes.
即使是尽力而为的IP流，在聚合基础上得到支持时，也有一些广泛的服务目标。主要的一个是保持数据包丢失率合理的小。一个致力于实现这一点的服务类是可取的，它需要考虑复杂性和适当服务之间的权衡。本备忘录中建议将UBR作为该项目的默认服务。具有（某种形式的）数据包丢弃的UBR具有功能简单的理想目标，而且供应商似乎将支持它。然而，当可用时，考虑ABR和VBR非实时服务类可能是非常值得的。
Because AAL5 frames with missing cells are discarded by the receiver, ATM bandwidth commitments are most useful if supported in the form of a committed rate of cell delivery in complete, non-errored AAL5 frames delivered to the receiver. In addition, it is desirable for the ATM connection to deliver additional complete frames, beyond this commitment, on a best-effort basis.
由于接收器丢弃丢失信元的AAL5帧，因此如果以信元交付速率的形式支持ATM带宽承诺，则在完整、无错误的AAL5帧中，ATM带宽承诺是最有用的。此外，ATM连接最好能在尽最大努力的基础上交付超出此承诺的额外完整帧。
These characteristics can be achieved through the ABR service category through the use of a Minimum Cell Rate, if the ABR service is supported by the ATM endpoints and if efficient frame discard is supported at the ABR source. The mechanisms put in place for the ABR service strive to keep loss quite low within the ATM network.
如果ATM端点支持ABR服务并且ABR源支持有效的帧丢弃，则可以通过使用最小信元速率通过ABR服务类别来实现这些特性。ABR服务的机制致力于在ATM网络中保持较低的损耗。
The parameters that should be specified by the end system are (i) the Peak Cell Rate (likely the link rate), (ii) the Minimum Cell Rate (the committed rate), and (iii) the Cumulative RM Fixed Round-Trip Time. The remaining parameter values, if left unspecified by the calling party, are selected by the network or are chosen from the default values specified in the ATM Forum Traffic Management specification.
终端系统应指定的参数包括（i）峰值小区速率（可能是链路速率），（ii）最小小区速率（承诺速率），以及（iii）累积RM固定往返时间。如果主叫方未指定其余参数值，则由网络选择或从ATM论坛流量管理规范中指定的默认值中选择。
Parameters (i) and (ii) are contained in the mandatory Traffic Descriptor IE, whereas parameter (iii) is contained in the mandatory ABR Setup Parameters IE. Other paramenters in the ABR Setup Parameters IE may be omitted. (Note that the third IE which pertains to ABR signalling, the ABR Additional Parameters IE, is an optional IE and therefore need not be included.) Parameter (iii) is dependent on the hardware of the end system, so that the default value specified for that hardware should be used. In the absense of such a default, a value of zero MAY be specified by the end system. Entities using ABR connections for IP over ATM SHOULD take advantage of parameter negotiation by specifying Peak Cell Rate equal to the link rate in the ATM Traffic Descriptor IE of the SETUP message. The value selected for the Minimum Cell Rate is implementation specific. Note that the MCR also MAY be negotiated if an MCR parameter is included by the end system in the Minimum Acceptable ATM Traffic Descriptor IE. The use of MCR negotiation by the end system is implementation specific. Also, note that Frame Discard MAY be requested for ABR connections as well as for UBR connections. Although the ABR service attempts to minimize cell loss, the use of Frame Discard may improve throughput when cell loss is not eliminated.
参数（i）和（ii）包含在强制流量描述符IE中，而参数（iii）包含在强制ABR设置参数IE中。ABR设置参数IE中的其他参数可以省略。（注意，与ABR信令有关的第三个IE，即ABR附加参数IE，是可选IE，因此不需要包括在内。）参数（iii）取决于终端系统的硬件，因此应使用为该硬件指定的默认值。在没有此类默认值的情况下，终端系统可以指定零值。使用ABR连接进行IP over ATM的实体应通过在设置消息的ATM流量描述符IE中指定等于链路速率的峰值信元速率来利用参数协商。为最小信元速率选择的值是特定于实现的。注意，如果终端系统在最小可接受ATM流量描述符中包含MCR参数，也可以协商MCR。终端系统使用MCR协商是特定于实现的。另外，请注意，对于ABR连接以及UBR连接，可能会请求帧丢弃。尽管ABR服务试图最小化小区丢失，但在不消除小区丢失时，使用帧丢弃可以提高吞吐量。
ATM recognizes in addition to the service class (UBR, ABR, etc.), a notion of a QoS class. The QoS class specifies the type of guarantee requested of the network when the call is setup. This is distinct from the service class requested for the connection, and the specification of the traffic parameters (which specify what the source's traffic will look like). QoS class 0 is the "simplest", and is called the Unspecified QoS class. In the context of ABR (and VBR non-realtime below), we are only concerned with the QoS class providing an assurance of acceptable loss behavior for the connection.
ATM除了识别服务类别（UBR、ABR等）外，还识别QoS类别的概念。QoS类指定设置呼叫时请求的网络保证类型。这与为连接请求的服务类和流量参数的规范（指定源流量的样子）不同。QoS类0是“最简单的”，称为未指定的QoS类。在ABR（和下面的VBR非实时）的上下文中，我们只关心QoS类，它为连接提供可接受的丢失行为的保证。
The Unspecified QoS Class (QoS Class 0) MUST be requested for ABR connections. In this context, QoS Class 0 corresponds to a network-specific objective for the cell loss ratio. Networks in general are expected to support a low Cell Loss Ratio for ABR sources that adjust cell flow in response to control information.
必须为ABR连接请求未指定的QoS类（QoS类0）。在此上下文中，QoS等级0对应于小区丢失率的网络特定目标。一般来说，网络应支持ABR源的低信元丢失率，ABR源根据控制信息调整信元流量。
The VBR-nrt service category provides an alternate means of achieving these characteristics. These characteristics may be obtained with VBR-nrt connections for which (i) the VBR.3 conformance definition is used, (ii) a Sustainable Cell Rate (SCR) and Maximum Burst Size (MBS), and Peak Cell Rate (PCR) are specified, and (iii) both tagging and frame discard are requested. A request for tagging indicates that best-effort delivery is desired for traffic offered in excess of the SCR and MBS. A request for frame discard indicates to the network that the user desires allocations of committed and excess bandwidth to translate into corresponding throughputs at the frame level.
VBR nrt服务类别提供了实现这些特性的替代方法。这些特性可通过VBR nrt连接获得，其中（i）使用VBR.3合规性定义，（ii）规定了可持续信元速率（SCR）和最大突发大小（MBS）以及峰值信元速率（PCR），以及（iii）要求标记和帧丢弃。标记请求表明，对于超过SCR和MBS的流量，需要尽最大努力交付。帧丢弃请求向网络指示用户希望分配提交的和多余的带宽，以便在帧级别转换为相应的吞吐量。
As with UBR connections, entities using VBR-nrt connections for IP over ATM should take advantage of parameter negotiation by specifying PCR equal to the link rate in the ATM Traffic Descriptor IE of the SETUP message and PCR equal to SCR in the Minimum Acceptable Traffic descriptor. The selection of SCR, MBS, and CLR (cell loss ratio) should be implementation specific. However, for IP over ATM, an MBS value of N*(Maximum MTU) is RECOMMENDED, where N>=1 with a default of 2 and where Maximum MTU is equal to 192 cells (consistent with an IP MTU size of 9180 bytes [RFC1626]).
与UBR连接一样，使用VBR nrt连接进行IP over ATM的实体应通过指定PCR等于设置消息的ATM流量描述符IE中的链路速率和PCR等于最小可接受流量描述符中的SCR来利用参数协商。SCR、MBS和CLR（信元丢失率）的选择应根据具体实施而定。然而，对于ATM上的IP，建议MBS值为N*（最大MTU），其中N>=1，默认值为2，最大MTU等于192个信元（与9180字节的IP MTU大小一致[RFC1626]）。
This appendix contains a copy of the five tables found in Annex 9 of [SIG40] which show the allowable combinations of traffic and QoS related parameters in a SIG 4.0 SETUP message.
本附录包含[SIG40]附录9中五个表格的副本，其中显示了SIG 4.0设置消息中允许的流量和QoS相关参数组合。
+--------------------------------------------------------------------+
|ATM Service Category| CBR |
|--------------------|---------------|---------------|---------------|
| Conformance |CBR.1 (note 10)| (note 4) | (note 4) |
|--------------------|---------------|---------------|---------------|
| Bearer Capability | | | |
|--------------------|---------------|---------------|---------------|
| BB Bearer Class | A | X | VP | A | X | VP^| A | X | VP^|
|--------------------|---------------|----|-----|----|----|-----|----|
| ATM Transfer | | | 4,5,| | | 4,5,| |
| Capability (note 1)| 7 | abs| or 6| 5 | abs| or 6| 5 |
|--------------------|---------------|---------------|---------------|
| Traffic Descriptor | | | |
| for a given dir. | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0) | | | S |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0+1) | S | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0) | | | |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0+1) | | | |
|--------------------|---------------|---------------|---------------|
| Best Effort | | | |
|--------------------|---------------|---------------|---------------|
| Tagging | N | N | Y/N |
|--------------------|---------------|---------------|---------------|
| Frame Discard | Y/N | Y/N | Y/N |
|--------------------|---------------|---------------|---------------|
| QoS Classes | * | * | * |
|--------------------|---------------|---------------|---------------|
| Transit Delay | O | O | O |
|--------------------|---------------|---------------|---------------|
| Peak-to-Peak CDV | O | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0)~ | | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0+1)~ | O | | |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
|ATM Service Category| CBR |
|--------------------|---------------|---------------|---------------|
| Conformance |CBR.1 (note 10)| (note 4) | (note 4) |
|--------------------|---------------|---------------|---------------|
| Bearer Capability | | | |
|--------------------|---------------|---------------|---------------|
| BB Bearer Class | A | X | VP | A | X | VP^| A | X | VP^|
|--------------------|---------------|----|-----|----|----|-----|----|
| ATM Transfer | | | 4,5,| | | 4,5,| |
| Capability (note 1)| 7 | abs| or 6| 5 | abs| or 6| 5 |
|--------------------|---------------|---------------|---------------|
| Traffic Descriptor | | | |
| for a given dir. | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0) | | | S |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0+1) | S | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0) | | | |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0+1) | | | |
|--------------------|---------------|---------------|---------------|
| Best Effort | | | |
|--------------------|---------------|---------------|---------------|
| Tagging | N | N | Y/N |
|--------------------|---------------|---------------|---------------|
| Frame Discard | Y/N | Y/N | Y/N |
|--------------------|---------------|---------------|---------------|
| QoS Classes | * | * | * |
|--------------------|---------------|---------------|---------------|
| Transit Delay | O | O | O |
|--------------------|---------------|---------------|---------------|
| Peak-to-Peak CDV | O | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0)~ | | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0+1)~ | O | | |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
|ATM Service Category| Real Time VBR |
|--------------------|---------------|---------------|---------------|
| Conformance |VBR.1 (note 10)| VBR.2 | VBR.3 |
|--------------------|---------------|---------------|---------------|
| Bearer Capability | | | |
|--------------------|---------------|---------------|---------------|
| BB Bearer Class | C | X | VP | C | X | VP | C | X | VP |
|--------------------|---------------|----|-----|----|----|-----|----|
| ATM Transfer | | | 1 | | | 1 | |
| Capability | 19 | 9 | or 9| 9 | 9 | or 9| 9 |
|--------------------|---------------|---------------|---------------|
| Traffic Descriptor | | | |
| for a given dir. | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0) | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0+1) | S | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0) | | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0+1) | S | | |
|--------------------|---------------|---------------|---------------|
| Best Effort | | | |
|--------------------|---------------|---------------|---------------|
| Tagging | N | N | Y/N |
|--------------------|---------------|---------------|---------------|
| Frame Discard | Y/N | Y/N | Y/N |
|--------------------|---------------|---------------|---------------|
| QoS Classes | * | * | * |
|--------------------|---------------|---------------|---------------|
| Transit Delay(nt.2)| O | O | O |
|--------------------|---------------|---------------|---------------|
| Peak-to-Peak CDV | O | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0)~ | | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0+1)~ | O | | |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
|ATM Service Category| Real Time VBR |
|--------------------|---------------|---------------|---------------|
| Conformance |VBR.1 (note 10)| VBR.2 | VBR.3 |
|--------------------|---------------|---------------|---------------|
| Bearer Capability | | | |
|--------------------|---------------|---------------|---------------|
| BB Bearer Class | C | X | VP | C | X | VP | C | X | VP |
|--------------------|---------------|----|-----|----|----|-----|----|
| ATM Transfer | | | 1 | | | 1 | |
| Capability | 19 | 9 | or 9| 9 | 9 | or 9| 9 |
|--------------------|---------------|---------------|---------------|
| Traffic Descriptor | | | |
| for a given dir. | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0) | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0+1) | S | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0) | | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0+1) | S | | |
|--------------------|---------------|---------------|---------------|
| Best Effort | | | |
|--------------------|---------------|---------------|---------------|
| Tagging | N | N | Y/N |
|--------------------|---------------|---------------|---------------|
| Frame Discard | Y/N | Y/N | Y/N |
|--------------------|---------------|---------------|---------------|
| QoS Classes | * | * | * |
|--------------------|---------------|---------------|---------------|
| Transit Delay(nt.2)| O | O | O |
|--------------------|---------------|---------------|---------------|
| Peak-to-Peak CDV | O | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0)~ | | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0+1)~ | O | | |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
|ATM Service Category| Real Time VBR |
|--------------------|---------------|---------------|---------------|
| Conformance | (note 4,7) | (note 4,8) | (note 4) |
|--------------------|---------------|---------------|---------------|
| Bearer Capability | | | |
|--------------------|---------------|---------------|---------------|
| BB Bearer Class | X | X | X | C or VP^|
|--------------------|---------------|---------------|-----|---------|
| ATM Transfer | | | | |
| Capability | 1 or 9 | 1 or 9 | 1or9| 9 |
|--------------------|---------------|---------------|---------------|
| Traffic Descriptor | | | |
| for a given dir. | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0) | S | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0+1) | S | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0) | | | |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0+1) | | | S |
|--------------------|---------------|---------------|---------------|
| Best Effort | | | |
|--------------------|---------------|---------------|---------------|
| Tagging | Y/N | N | N |
|--------------------|---------------|---------------|---------------|
| Frame Discard | Y/N | Y/N | Y/N |
|--------------------|---------------|---------------|---------------|
| QoS Classes | * | * | * |
|--------------------|---------------|---------------|---------------|
| Transit Delay(nt.2)| O | O | O |
|--------------------|---------------|---------------|---------------|
| Peak-to-Peak CDV | O | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0)~ | O | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0+1)~ | | | |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
|ATM Service Category| Real Time VBR |
|--------------------|---------------|---------------|---------------|
| Conformance | (note 4,7) | (note 4,8) | (note 4) |
|--------------------|---------------|---------------|---------------|
| Bearer Capability | | | |
|--------------------|---------------|---------------|---------------|
| BB Bearer Class | X | X | X | C or VP^|
|--------------------|---------------|---------------|-----|---------|
| ATM Transfer | | | | |
| Capability | 1 or 9 | 1 or 9 | 1or9| 9 |
|--------------------|---------------|---------------|---------------|
| Traffic Descriptor | | | |
| for a given dir. | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0) | S | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0+1) | S | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0) | | | |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0+1) | | | S |
|--------------------|---------------|---------------|---------------|
| Best Effort | | | |
|--------------------|---------------|---------------|---------------|
| Tagging | Y/N | N | N |
|--------------------|---------------|---------------|---------------|
| Frame Discard | Y/N | Y/N | Y/N |
|--------------------|---------------|---------------|---------------|
| QoS Classes | * | * | * |
|--------------------|---------------|---------------|---------------|
| Transit Delay(nt.2)| O | O | O |
|--------------------|---------------|---------------|---------------|
| Peak-to-Peak CDV | O | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0)~ | O | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0+1)~ | | | |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
|ATM Service Category| Non-Real Time VBR |
|--------------------|---------------|---------------|---------------|
| Conformance |VBR.1 (note 10)| VBR.2 | VBR.3 |
|--------------------|---------------|---------------|---------------|
| Bearer Capability | | | |
|--------------------|---------------|---------------|---------------|
| BB Bearer Class | C | X | VP |C | X | VP|C | X | VP|
|--------------------|---------------|--|--------|---|--|--------|---|
| ATM Transfer | | |abs,0,2,|abs| |abs,0,2,|abs|
| Capability | 11 |ab| 8,10 |10 |ab| 8,10 |10 |
|--------------------|---------------|---------------|---------------|
| Traffic Descriptor | | | |
| for a given dir. | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0) | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0+1) | S | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0) | | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0+1) | S | | |
|--------------------|---------------|---------------|---------------|
| Best Effort | | | |
|--------------------|---------------|---------------|---------------|
| Tagging | N | N | Y |
|--------------------|---------------|---------------|---------------|
| Frame Discard | Y/N | Y/N | Y/N |
|--------------------|---------------|---------------|---------------|
| QoS Classes | * | * | * |
|--------------------|---------------|---------------|---------------|
| Transit Delay(nt.2)| (note 3) | (note 3) | (note 3) |
|--------------------|---------------|---------------|---------------|
| Peak-to-Peak CDV | | | |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0)~ | | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0+1)~ | O | | |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
|ATM Service Category| Non-Real Time VBR |
|--------------------|---------------|---------------|---------------|
| Conformance |VBR.1 (note 10)| VBR.2 | VBR.3 |
|--------------------|---------------|---------------|---------------|
| Bearer Capability | | | |
|--------------------|---------------|---------------|---------------|
| BB Bearer Class | C | X | VP |C | X | VP|C | X | VP|
|--------------------|---------------|--|--------|---|--|--------|---|
| ATM Transfer | | |abs,0,2,|abs| |abs,0,2,|abs|
| Capability | 11 |ab| 8,10 |10 |ab| 8,10 |10 |
|--------------------|---------------|---------------|---------------|
| Traffic Descriptor | | | |
| for a given dir. | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0) | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0+1) | S | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0) | | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0+1) | S | | |
|--------------------|---------------|---------------|---------------|
| Best Effort | | | |
|--------------------|---------------|---------------|---------------|
| Tagging | N | N | Y |
|--------------------|---------------|---------------|---------------|
| Frame Discard | Y/N | Y/N | Y/N |
|--------------------|---------------|---------------|---------------|
| QoS Classes | * | * | * |
|--------------------|---------------|---------------|---------------|
| Transit Delay(nt.2)| (note 3) | (note 3) | (note 3) |
|--------------------|---------------|---------------|---------------|
| Peak-to-Peak CDV | | | |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0)~ | | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0+1)~ | O | | |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
|ATM Service Category| Non-Real Time VBR |
|--------------------|---------------|---------------|---------------|
| Conformance | (note 4,7) | (note 4,8) | (note 4) |
|--------------------|---------------|---------------|---------------|
| Bearer Capability | | | |
|--------------------|---------------|---------------|---------------|
| BB Bearer Class | C | X | C | X |C | X |VP^|
|--------------------|-------|-------|-------|-------|--|--------|---|
| ATM Transfer | |abs,0,2| |abs,0,2| |abs,0,2,|abs|
| Capability | abs |8 or 10| |8 or 10|ab| 8 or10 |10 |
|--------------------|---------------|---------------|---------------|
| Traffic Descriptor | | | |
| for a given dir. | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0) | S | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0+1) | S | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0) | | | |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0+1) | | | S |
|--------------------|---------------|---------------|---------------|
| Best Effort | | | |
|--------------------|---------------|---------------|---------------|
| Tagging | Y/N | N | N |
|--------------------|---------------|---------------|---------------|
| Frame Discard | Y/N | Y/N | Y/N |
|--------------------|---------------|---------------|---------------|
| QoS Classes | * | * | * |
|--------------------|---------------|---------------|---------------|
| Transit Delay(nt.2)| (note 3) | (note 3) | (note 3) |
|--------------------|---------------|---------------|---------------|
| Peak-to-Peak CDV | | | |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0)~ | O | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0+1)~ | | | |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
|ATM Service Category| Non-Real Time VBR |
|--------------------|---------------|---------------|---------------|
| Conformance | (note 4,7) | (note 4,8) | (note 4) |
|--------------------|---------------|---------------|---------------|
| Bearer Capability | | | |
|--------------------|---------------|---------------|---------------|
| BB Bearer Class | C | X | C | X |C | X |VP^|
|--------------------|-------|-------|-------|-------|--|--------|---|
| ATM Transfer | |abs,0,2| |abs,0,2| |abs,0,2,|abs|
| Capability | abs |8 or 10| |8 or 10|ab| 8 or10 |10 |
|--------------------|---------------|---------------|---------------|
| Traffic Descriptor | | | |
| for a given dir. | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0) | S | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0+1) | S | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0) | | | |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0+1) | | | S |
|--------------------|---------------|---------------|---------------|
| Best Effort | | | |
|--------------------|---------------|---------------|---------------|
| Tagging | Y/N | N | N |
|--------------------|---------------|---------------|---------------|
| Frame Discard | Y/N | Y/N | Y/N |
|--------------------|---------------|---------------|---------------|
| QoS Classes | * | * | * |
|--------------------|---------------|---------------|---------------|
| Transit Delay(nt.2)| (note 3) | (note 3) | (note 3) |
|--------------------|---------------|---------------|---------------|
| Peak-to-Peak CDV | | | |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0)~ | O | O | O |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0+1)~ | | | |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
|ATM Service Category| ABR | UBR |
|--------------------|---------------|---------------|---------------|
| Conformance | ABR | UBR.1 | UBR.2 |
|--------------------|---------------|---------------|---------------|
| Bearer Capability | | | |
|--------------------|---------------|---------------|---------------|
| BB Bearer Class | C | X | VP |C | X | VP|C | X | VP|
|--------------------|---------------|--|--------|---|--|--------|---|
| ATM Transfer | | |abs,0,2,|abs| |abs,0,2,|abs|
| Capability | 12 |ab| 8,10 |10 |ab| 8,10 |10 |
|--------------------|---------------|---------------|---------------|
| Traffic Descriptor | | | |
| for a given dir. | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0) | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0+1) | S | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0) | | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0+1) | S | | |
|--------------------|---------------|---------------|---------------|
| ABR MCR | (note 6) | | |
|--------------------|---------------|---------------|---------------|
| Best Effort | | S (note 9) | S (note 9) |
|--------------------|---------------|---------------|---------------|
| Tagging | N | N | N |
|--------------------|---------------|---------------|---------------|
| Frame Discard | Y/N | Y/N | Y/N |
|--------------------|---------------|---------------|---------------|
| QoS Classes | 0 | 0 | 0 |
|--------------------|---------------|---------------|---------------|
| Transit Delay(nt.2)| | | |
|--------------------|---------------|---------------|---------------|
| Peak-to-Peak CDV | | | |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0)~ | | | |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0+1)~ | | | |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
|ATM Service Category| ABR | UBR |
|--------------------|---------------|---------------|---------------|
| Conformance | ABR | UBR.1 | UBR.2 |
|--------------------|---------------|---------------|---------------|
| Bearer Capability | | | |
|--------------------|---------------|---------------|---------------|
| BB Bearer Class | C | X | VP |C | X | VP|C | X | VP|
|--------------------|---------------|--|--------|---|--|--------|---|
| ATM Transfer | | |abs,0,2,|abs| |abs,0,2,|abs|
| Capability | 12 |ab| 8,10 |10 |ab| 8,10 |10 |
|--------------------|---------------|---------------|---------------|
| Traffic Descriptor | | | |
| for a given dir. | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0) | | | |
|--------------------|---------------|---------------|---------------|
| PCR (CLP=0+1) | S | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0) | | S | S |
|--------------------|---------------|---------------|---------------|
| SCR, MBS (CLP=0+1) | S | | |
|--------------------|---------------|---------------|---------------|
| ABR MCR | (note 6) | | |
|--------------------|---------------|---------------|---------------|
| Best Effort | | S (note 9) | S (note 9) |
|--------------------|---------------|---------------|---------------|
| Tagging | N | N | N |
|--------------------|---------------|---------------|---------------|
| Frame Discard | Y/N | Y/N | Y/N |
|--------------------|---------------|---------------|---------------|
| QoS Classes | 0 | 0 | 0 |
|--------------------|---------------|---------------|---------------|
| Transit Delay(nt.2)| | | |
|--------------------|---------------|---------------|---------------|
| Peak-to-Peak CDV | | | |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0)~ | | | |
|--------------------|---------------|---------------|---------------|
| CLR (CLP=0+1)~ | | | |
+--------------------------------------------------------------------+
ab, abs = absent.
ab，abs=缺席。
Y/N = either "Yes" or "No" is allowed.
是/否=允许“是”或“否”。
O = Optional. May be specified using:
O=可选。可使用以下方式指定：
- an additional QoS parameter encoded i the Extended QoS parameters information element or the end-to-end transit information element; or,
- 在扩展QoS参数信息元素或端到端传输信息元素中编码的附加QoS参数i；或
- objectives implied from the QoS class If an Extended QoS Parameters IE is not present in the message, then any value of this parameter is acceptable. If neither the parameter nor the Extended QoS Parameters IE is present, then the objective for this parameter is determined from the QoS class in the QoS Parameter IE.
- QoS类隐含的目标如果消息中不存在扩展QoS参数IE，则此参数的任何值都是可接受的。如果参数和扩展QoS参数IE均不存在，则该参数的目标由QoS参数IE中的QoS类确定。
S = Specified.
S=指定。
(blank) = Unspecified.
（空白）=未指定。
* = allowed QoS class values are a network option. Class 0 is always for alignment with ITU-T.
* =允许的QoS类值是网络选项。0级始终与ITU-T保持一致。
^ = (note 5).
^ = (note 5).
~ = (note 11).
~ = (note 11).
Note 1 - Values 0,1,2,4,6, and 8 are not used on transmission but shall be understood on reception.
注1-值0、1、2、4、6和8不用于传输，但应在接收时理解。
Note 2 - Maximum end-2-end transit delay objectives may only be specified for the forward direction.
注2-最大端-端运输延误目标只能针对正向指定。
Note 3 - Maximum end-2-end transit delay objectives may be specified for the ATM Service Category of Non-real Time VBR for reasons of backward compatibility with ITU-T Recommendations.
注3：出于与ITU-T建议向后兼容的原因，可为非实时VBR的ATM服务类别指定最大端2端传输延迟目标。
Note 4 - Included for reasons of backward compatibility with UNI 3.1and ITU-T Recommendations. With these conformance definitions, the CLR commitment is only for the CLP=0 traffic stream.
注4-包括的原因是与UNI 3.1和ITU-T建议向后兼容。使用这些一致性定义，CLR承诺仅适用于CLP=0流量流。
Note 5 - Included to allow switched virtual paths to use the UNI 3.1 conformance definitions.
注5-包括允许交换虚拟路径使用UNI 3.1一致性定义。
Note 6 - Optional in the user-to-network direction. Specified in the network-to-user direction.
注6-在用户到网络方向中为可选。在网络到用户方向中指定。
Note 7 - This combination should be treated as if the received PCR (CLP=0) parameter were a SCR (CLP=0) parameter and a MBS (CLP=0) parameter with a value of 1.
注7-应将此组合视为接收到的PCR（CLP=0）参数为SCR（CLP=0）参数和MBS（CLP=0）参数，其值为1。
Note 8 - This combination should be treated as if an additional SCR (CLP=0) parameter were received with the same value as a PCR (CLP=0+1) parameter and a MBS (CLP=0) parameter with a value of 1.
注8-应将此组合视为收到的附加SCR（CLP=0）参数的值与PCR（CLP=0+1）参数的值相同，MBS（CLP=0）参数的值为1。
Note 9 - The best effort parameter applies to both the forward and backward directions.
注9-最大努力参数适用于前进和后退方向。
Note 10 - This combination should only be used when the CLR commitment on CLP=0+1 is required versus CLR commitment on CLP=0 traffic, since these combinations are not supported by UNI 3.0/3.1 nor ITU-T Q.2931.
注10-仅当CLP=0+1需要CLR承诺而CLP=0流量需要CLR承诺时，才应使用此组合，因为UNI 3.0/3.1或ITU-T Q.2931不支持这些组合。
Note 11 - In this table the CLR commitment is shown as two entries to indicated explicitly whether the CLR commitment is for the CLP=0 or the CLP=0+1 cells.
注11-在本表中，CLR承诺显示为两个条目，明确指出CLR承诺是针对CLP=0还是CLP=0+1单元格。
Full Copyright Statement
完整版权声明
Copyright (C) The Internet Society (1998). All Rights Reserved.
版权所有（C）互联网协会（1998年）。版权所有。
This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.
本文件及其译本可复制并提供给他人，对其进行评论或解释或协助其实施的衍生作品可全部或部分编制、复制、出版和分发，不受任何限制，前提是上述版权声明和本段包含在所有此类副本和衍生作品中。但是，不得以任何方式修改本文件本身，例如删除版权通知或对互联网协会或其他互联网组织的引用，除非出于制定互联网标准的需要，在这种情况下，必须遵循互联网标准过程中定义的版权程序，或根据需要将其翻译成英语以外的其他语言。
The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.
上述授予的有限许可是永久性的，互联网协会或其继承人或受让人不会撤销。
This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
本文件和其中包含的信息是按“原样”提供的，互联网协会和互联网工程任务组否认所有明示或暗示的保证，包括但不限于任何保证，即使用本文中的信息不会侵犯任何权利，或对适销性或特定用途适用性的任何默示保证。