Network Working Group G. Hellstrom
Request for Comments: 4103 Omnitor AB
Obsoletes: 2793 P. Jones
Category: Standards Track Cisco Systems, Inc.
June 2005
Network Working Group G. Hellstrom
Request for Comments: 4103 Omnitor AB
Obsoletes: 2793 P. Jones
Category: Standards Track Cisco Systems, Inc.
June 2005
RTP Payload for Text Conversation
文本会话的RTP有效负载
Status of This Memo
关于下段备忘
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 (2005).
版权所有（C）互联网协会（2005年）。
Abstract
摘要
This memo obsoletes RFC 2793; it describes how to carry real-time text conversation session contents in RTP packets. Text conversation session contents are specified in ITU-T Recommendation T.140.
本备忘录废除RFC 2793；它描述了如何在RTP数据包中携带实时文本会话内容。ITU-T建议T.140中规定了文本对话会话内容。
One payload format is described for transmitting text on a separate RTP session dedicated for the transmission of text.
描述了一种有效载荷格式，用于在专用于文本传输的单独RTP会话上传输文本。
This RTP payload description recommends a method to include redundant text from already transmitted packets in order to reduce the risk of text loss caused by packet loss.
该RTP有效负载描述推荐了一种方法，以包括来自已经传输的分组的冗余文本，从而降低由分组丢失引起的文本丢失的风险。
Table of Contents
目录
1. Introduction ...................................................3
2. Conventions Used in This Document ..............................4
3. Usage of RTP ...................................................4
3.1. Motivations and Rationale .................................4
3.2. Payload Format for Transmission of text/t140 Data .........4
3.3. The "T140block" ...........................................5
3.4. Synchronization of Text with Other Media ..................5
3.5. RTP Packet Header .........................................5
4. Protection against Loss of Data ................................6
4.1. Payload Format When Using Redundancy ......................6
4.2. Using Redundancy with the text/t140 Format ................7
5. Recommended Procedure ..........................................8
5.1. Recommended Basic Procedure ...............................8
5.2. Transmission before and after "Idle Periods" ..............8
5.3. Detection of Lost Text Packets ............................9
5.4. Compensation for Packets Out of Order ....................10
6. Parameter for Character Transmission Rate .....................10
7. Examples ......................................................11
7.1. RTP Packetization Examples for the text/t140 Format ......11
7.2. SDP Examples .............................................13
8. Security Considerations .......................................14
8.1. Confidentiality ..........................................14
8.2. Integrity ................................................14
8.3. Source Authentication ....................................14
9. Congestion Considerations .....................................14
10. IANA Considerations ...........................................16
10.1. Registration of MIME Media Type text/t140 ...............16
10.2. SDP Mapping of MIME Parameters ..........................17
10.3. Offer/Answer Consideration ..............................17
11. Acknowledgements ..............................................18
12. Normative References ..........................................18
13. Informative References ........................................19
1. Introduction ...................................................3
2. Conventions Used in This Document ..............................4
3. Usage of RTP ...................................................4
3.1. Motivations and Rationale .................................4
3.2. Payload Format for Transmission of text/t140 Data .........4
3.3. The "T140block" ...........................................5
3.4. Synchronization of Text with Other Media ..................5
3.5. RTP Packet Header .........................................5
4. Protection against Loss of Data ................................6
4.1. Payload Format When Using Redundancy ......................6
4.2. Using Redundancy with the text/t140 Format ................7
5. Recommended Procedure ..........................................8
5.1. Recommended Basic Procedure ...............................8
5.2. Transmission before and after "Idle Periods" ..............8
5.3. Detection of Lost Text Packets ............................9
5.4. Compensation for Packets Out of Order ....................10
6. Parameter for Character Transmission Rate .....................10
7. Examples ......................................................11
7.1. RTP Packetization Examples for the text/t140 Format ......11
7.2. SDP Examples .............................................13
8. Security Considerations .......................................14
8.1. Confidentiality ..........................................14
8.2. Integrity ................................................14
8.3. Source Authentication ....................................14
9. Congestion Considerations .....................................14
10. IANA Considerations ...........................................16
10.1. Registration of MIME Media Type text/t140 ...............16
10.2. SDP Mapping of MIME Parameters ..........................17
10.3. Offer/Answer Consideration ..............................17
11. Acknowledgements ..............................................18
12. Normative References ..........................................18
13. Informative References ........................................19
This document defines a payload type for carrying text conversation session contents in RTP [2] packets. Text conversation session contents are specified in ITU-T Recommendation T.140 [1]. Text conversation is used alone or in connection with other conversational facilities, such as video and voice, to form multimedia conversation services. Text in multimedia conversation sessions is sent character-by-character as soon as it is available, or with a small delay for buffering.
本文档定义了在RTP[2]数据包中承载文本会话内容的有效负载类型。ITU-T建议T.140[1]中规定了文本对话会话内容。文本会话单独使用或与其他会话设施（如视频和语音）结合使用，以形成多媒体会话服务。多媒体对话会话中的文本在可用时会立即逐字符发送，或者会有一个小的缓冲延迟。
The text is intended to be entered by human users from a keyboard, handwriting recognition, voice recognition or any other input method. The rate of character entry is usually at a level of a few characters per second or less. In general, only one or a few new characters are expected to be transmitted with each packet. Small blocks of text may be prepared by the user and pasted into the user interface for transmission during the conversation, occasionally causing packets to carry more payload.
文本拟由人类用户通过键盘、手写识别、语音识别或任何其他输入方法输入。字符输入速率通常为每秒几个字符或更少。通常，每个数据包只需要传输一个或几个新字符。用户可以准备小的文本块，并将其粘贴到用户界面中以便在会话期间传输，偶尔会导致数据包携带更多的有效载荷。
T.140 specifies that text and other T.140 elements must be transmitted in ISO 10646-1 [5] code with UTF-8 [6] transformation. This makes it easy to implement internationally useful applications and to handle the text in modern information technology environments. The payload of an RTP packet that follows this specification consists of text encoded according to T.140, without any additional framing. A common case will be a single ISO 10646 character, UTF-8 encoded.
T.140规定文本和其他T.140元素必须通过UTF-8[6]转换以ISO10646-1[5]代码传输。这使得实现国际上有用的应用程序和在现代信息技术环境中处理文本变得容易。遵循本规范的RTP数据包的有效载荷由根据T.140编码的文本组成，没有任何额外的帧。常见的情况是单个ISO10646字符，UTF-8编码。
T.140 requires the transport channel to provide characters without duplication and in original order. Text conversation users expect that text will be delivered with no, or a low level, of lost information.
T.140要求传输通道以原始顺序提供不重复的字符。文本对话用户希望文本不会丢失信息，或者信息丢失程度较低。
Therefore, a mechanism based on RTP is specified here. It gives text arrival in correct order, without duplication, and with detection and indication of loss. It also includes an optional possibility to repeat data for redundancy in order to lower the risk of loss. Because packet overhead is usually much larger than the T.140 contents, the increase in bandwidth, with the use of redundancy, is minimal.
因此，这里指定了一种基于RTP的机制。它使文本以正确的顺序到达，没有重复，并带有丢失检测和指示。它还包括重复数据以实现冗余的可选可能性，以降低丢失风险。由于数据包开销通常比T.140内容大得多，使用冗余时带宽的增加是最小的。
By using RTP for text transmission in a multimedia conversation application, uniform handling of text and other media can be achieved in, for example, conferencing systems, firewalls, and network translation devices. This, in turn, eases the design and increases the possibility for prompt and proper media delivery.
通过在多媒体会话应用程序中使用RTP进行文本传输，可以在例如会议系统、防火墙和网络翻译设备中实现文本和其他媒体的统一处理。这反过来又简化了设计，并增加了及时和正确交付媒体的可能性。
This document obsoletes RFC 2793 [16]. The text clarifies ambiguities in RFC 2793, improves on the specific implementation requirements learned through development experience and gives explicit usage examples.
本文件废除了RFC 2793[16]。本文澄清了RFC 2793中的歧义，改进了通过开发经验学习到的具体实现需求，并给出了明确的使用示例。
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 [4].
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[4]中所述进行解释。
The payload format for real-time text transmission with RTP [2] described in this memo is intended for general text conversation use and is called text/t140 after its MIME registration.
本备忘录中描述的RTP[2]实时文本传输的有效负载格式用于一般文本对话，在MIME注册后称为text/t140。
The text/t140 format is intended to be used for text transmitted on a separate RTP session, dedicated for the transmission of text, and not shared with other media.
text/t140格式用于在单独RTP会话上传输的文本，专用于传输文本，不与其他媒体共享。
The text/t140 format MAY be used for any non-gateway application, as well as in gateways. It MAY be used simultaneously with other media streams, transmitted as a separate RTP session, as required in real time multimedia applications.
text/t140格式可用于任何非网关应用程序以及网关中。根据实时多媒体应用的需要，它可以与其他媒体流同时使用，作为单独的RTP会话传输。
The text/t140 format specified in this memo is compatible with its earlier definition in RFC 2793. It has been refined, with the main intention to minimize interoperability problems and encourage good reliability and functionality.
本备忘录中指定的文本/t140格式与RFC 2793中的早期定义兼容。它经过了改进，主要目的是尽量减少互操作性问题，并鼓励良好的可靠性和功能性。
By specifying text transmission as a text medium, many good effects are gained. Routing, device selection, invocation of transcoding, selection of quality of service parameters, and other high and low level functions depend on each medium being explicitly specified.
通过将文本传输指定为文本媒介，可以获得许多良好的效果。路由、设备选择、代码转换调用、服务质量参数选择以及其他高级和低级功能取决于明确指定的每个介质。
A text/t140 conversation RTP payload format consists of one, and only one, block of T.140 data, referred to as a "T140block" (see Section 3.3). There are no additional headers specific to this payload format. The fields in the RTP header are set as defined in Section 3.5, carried in network byte order (see RFC 791 [12]).
text/t140对话RTP有效载荷格式由一个且仅一个T.140数据块组成，称为“t140块”（见第3.3节）。没有特定于此有效负载格式的附加标头。RTP报头中的字段按照第3.5节的定义进行设置，以网络字节顺序进行（见RFC 791[12]）。
T.140 text is UTF-8 coded, as specified in T.140, with no extra framing. The T140block contains one or more T.140 code elements as specified in [1]. Most T.140 code elements are single ISO 10646 [5] characters, but some are multiple character sequences. Each character is UTF-8 encoded [6] into one or more octets. Each block MUST contain an integral number of UTF-8 encoded characters regardless of the number of octets per character. Any composite character sequence (CCS) SHOULD be placed within one block.
按照T.140的规定，T.140文本采用UTF-8编码，没有额外的框架。T140块包含[1]中规定的一个或多个T.140代码元素。大多数T.140代码元素是单个ISO10646[5]字符，但有些是多字符序列。每个字符都经过UTF-8编码[6]为一个或多个八位字节。每个块必须包含整数个UTF-8编码字符，而不考虑每个字符的八位字节数。任何复合字符序列（CCS）都应放在一个块内。
Usually, each medium in a session utilizes a separate RTP stream. As such, if synchronization of the text and other media packets is important, the streams MUST be associated when the sessions are established and the streams MUST share the same reference clock (refer to the description of the timestamp field as it relates to synchronization in Section 5.1 of RFC 3550 [2]). Association of RTP streams can be done through the CNAME field of RTCP SDES function. It is dependent on the particular application and is outside the scope of this document.
通常，会话中的每个媒体都使用单独的RTP流。因此，如果文本和其他媒体分组的同步很重要，则在建立会话时必须关联流，并且流必须共享相同的参考时钟（参考RFC 3550[2]第5.1节中与同步相关的时间戳字段的描述）。RTP流的关联可以通过RTCP SDES函数的CNAME字段完成。它取决于特定的应用，不在本文件的范围内。
Each RTP packet starts with a fixed RTP header. The following fields of the RTP fixed header are specified for T.140 text streams:
每个RTP数据包都以一个固定的RTP报头开始。为T.140文本流指定RTP固定标题的以下字段：
Payload Type (PT): The assignment of an RTP payload type is specific to the RTP profile under which the payload format is used. For profiles that use dynamic payload type number assignment, this payload format can be identified by the MIME type "text/t140" (see Section 10). If redundancy is used per RFC 2198, another payload type number needs to be provided for the redundancy format. The MIME type for identifying RFC 2198 is available in RFC 4102 [9].
有效负载类型（PT）：RTP有效负载类型的分配特定于使用有效负载格式的RTP配置文件。对于使用动态有效负载类型编号分配的配置文件，可以通过MIME类型“text/t140”来标识此有效负载格式（请参阅第10节）。如果按照RFC 2198使用冗余，则需要为冗余格式提供另一个有效负载类型编号。RFC 4102[9]中提供了用于标识RFC 2198的MIME类型。
Sequence number: The definition of sequence numbers is available in RFC 3550 [2]. When transmitting text using the payload format for text/t140, it is used for detection of packet loss and out-of-order packets, and can be used in the process of retrieval of redundant text, reordering of text and marking missing text.
序列号：序列号的定义见RFC 3550[2]。当使用text/t140的有效负载格式传输文本时，它用于检测数据包丢失和无序数据包，并可用于检索冗余文本、重新排序文本和标记缺失文本的过程。
Timestamp: The RTP Timestamp encodes the approximate instance of entry of the primary text in the packet. A clock frequency of 1000 Hz MUST be used. Sequential packets MUST NOT use the same timestamp. Because packets do not represent any constant duration, the timestamp cannot be used to directly infer packet loss.
时间戳：RTP时间戳对数据包中主文本输入的近似实例进行编码。必须使用1000 Hz的时钟频率。连续数据包不得使用相同的时间戳。由于数据包不代表任何恒定的持续时间，时间戳不能用于直接推断数据包丢失。
M-bit: The M-bit MUST be included. The first packet in a session, and the first packet after an idle period, SHOULD be distinguished by setting the marker bit in the RTP data header to one. The marker bit in all other packets MUST be set to zero. The reception of the marker bit MAY be used for refined methods for detection of loss.
M位：必须包括M位。会话中的第一个数据包和空闲期后的第一个数据包应通过将RTP数据头中的标记位设置为1来区分。所有其他数据包中的标记位必须设置为零。标记比特的接收可用于检测丢失的改进方法。
Consideration must be devoted to keeping loss of text due to packet loss within acceptable limits. (See ITU-T F.703 [17])
必须考虑将由于数据包丢失而导致的文本丢失保持在可接受的范围内。（见ITU-T F.703[17]）
The default method that MUST be used, when no other method is explicitly selected, is redundancy in accordance with RFC 2198 [3]. When this method is used, the original text and two redundant generations SHOULD be transmitted if the application or end-to-end conditions do not call for other levels of redundancy to be used.
根据RFC 2198[3]，当没有明确选择其他方法时，必须使用的默认方法是冗余。使用此方法时，如果应用程序或端到端条件不要求使用其他冗余级别，则应传输原始文本和两个冗余生成。
Forward Error Correction mechanisms, as per RFC 2733 [8], or any other mechanism with the purpose of increasing the reliability of text transmission, MAY be used as an alternative or complement to redundancy. Text data MAY be sent without additional protection if end-to-end network conditions allow the text quality requirements, specified in ITU-T F.703 [17], to be met in all anticipated load conditions.
根据RFC 2733[8]，前向纠错机制或任何其他旨在提高文本传输可靠性的机制可作为冗余的替代或补充。如果端到端网络条件允许在所有预期负载条件下满足ITU-T F.703[17]中规定的文本质量要求，则可以发送文本数据而无需额外保护。
When using the payload format with redundant data, the transmitter may select a number of T140block generations to retransmit in each packet. A higher number introduces better protection against loss of text but marginally increases the data rate.
当使用具有冗余数据的有效载荷格式时，发射机可以选择在每个分组中重传的T140块生成数。数字越大，可以更好地防止文本丢失，但会略微提高数据速率。
The RTP header is followed by one or more redundant data block headers: one for each redundant data block to be included. Each of these headers provides the timestamp offset and length of the corresponding data block, in addition to a payload type number (indicating the payload format text/t140).
RTP头后面跟着一个或多个冗余数据块头：每个冗余数据块包含一个。除了有效负载类型号（指示有效负载格式text/t140）之外，这些报头中的每一个都提供了相应数据块的时间戳偏移量和长度。
The redundant data block headers are followed by the redundant data fields carrying T140blocks from previous packets. Finally, the new (primary) T140block for this packet follows.
冗余数据块头后面是冗余数据字段，该字段携带来自先前数据包的T140块。最后，该数据包的新（主）T140块如下。
Redundant data that would need a timestamp offset higher than 16383 (due to its age at transmission) MUST NOT be included in transmitted packets.
传输的数据包中不得包含需要大于16383的时间戳偏移量的冗余数据（由于其在传输时的使用年限）。
Because text is transmitted only when there is text to transmit, the timestamp is not used to identify a lost packet. Rather, missing sequence numbers are used to detect lost text packets at reception. Also, because sequence numbers are not provided in the redundant header, some additional rules must be followed to allow redundant data that corresponds to missing primary data to be properly merged into the stream of primary data T140blocks. They are:
因为只有当有文本要传输时才传输文本，所以时间戳不用于识别丢失的数据包。相反，丢失的序列号用于在接收时检测丢失的文本包。此外，由于冗余报头中未提供序列号，因此必须遵循一些附加规则，以允许与丢失的主数据相对应的冗余数据正确合并到主数据流T140块中。他们是：
- Each redundant data block MUST contain the same data as a T140block previously transmitted as primary data.
- 每个冗余数据块必须包含与先前作为主数据传输的T140块相同的数据。
- The redundant data MUST be placed in age order, with the most recent redundant T140block last in the redundancy area.
- 冗余数据必须按时间顺序放置，最新的冗余T140块最后位于冗余区域。
- All T140blocks, from the oldest desired generation up through the generation immediately preceding the new (primary) T140block, MUST be included.
- 必须包括所有T140块，从最旧的所需生成到新（主）T140块之前的生成。
These rules allow the sequence numbers for the redundant T140blocks to be inferred by counting backwards from the sequence number in the RTP header. The result will be that all the text in the payload will be contiguous and in order.
这些规则允许通过从RTP报头中的序列号向后计数来推断冗余T140块的序列号。结果将是有效负载中的所有文本都是连续的，并且是有序的。
If there is a gap in the received RTP sequence numbers, and redundant T140blocks are available in a subsequent packet, the sequence numbers for the redundant T140blocks should be inferred by counting backwards from the sequence number in the RTP header for that packet. If there are redundant T140blocks with sequence numbers matching those that are missing, the redundant T140blocks may be substituted for the missing T140blocks.
如果接收到的RTP序列号中存在间隙，并且冗余T140块在后续数据包中可用，则应通过从该数据包的RTP报头中的序列号向后计数来推断冗余T140块的序列号。如果存在序列号与缺失序列号匹配的冗余T140块，则可以用冗余T140块替换缺失的T140块。
This section contains RECOMMENDED procedures for usage of the payload format. Based on the information in the received packets, the receiver can:
本节包含使用有效负载格式的建议步骤。基于所接收的分组中的信息，接收机可以：
- reorder text received out of order. - mark where text is missing because of packet loss. - compensate for lost packets by using redundant data.
- 按顺序重新排列收到的文本。-标记由于数据包丢失而丢失文本的位置。-通过使用冗余数据补偿丢失的数据包。
Packets are transmitted when there is valid T.140 data to transmit.
当有有效的T.140数据要传输时，数据包被传输。
T.140 specifies that T.140 data MAY be buffered for transmission with a maximum buffering time of 500 ms. A buffering time of 300 ms is RECOMMENDED when the application or end-to-end network conditions are not known to require another value.
T.140规定，T.140数据可缓冲传输，最大缓冲时间为500 ms。当应用或端到端网络条件未知时，建议缓冲时间为300 ms。
If no new data is available for a longer period than the buffering time, the transmission process is in an idle period.
如果在比缓冲时间更长的时间内没有新数据可用，则传输过程处于空闲期。
When new text is available for transmission after an idle period, it is RECOMMENDED to send it as soon as possible. After this transmission, it is RECOMMENDED to buffer T.140 data in buffering time intervals, until the next idle period. This is done in order to keep the maximum bit rate usage for text at a reasonable level. The buffering time MUST be selected so that text users will perceive a real-time text flow.
当新文本在空闲时间后可供传输时，建议尽快发送。在此传输之后，建议以缓冲时间间隔缓冲T.140数据，直到下一个空闲周期。这样做是为了将文本的最大比特率使用保持在合理水平。必须选择缓冲时间，以便文本用户能够感知实时文本流。
When valid T.140 data has been sent and no new T.140 data is available for transmission after the selected buffering time, an empty T140block SHOULD be transmitted. This situation is regarded as the beginning of an idle period. The procedure is recommended in order to more rapidly detect potentially missing text before an idle period.
当已发送有效的T.140数据且在选定的缓冲时间后没有新的T.140数据可用于传输时，应传输空的T140块。这种情况被视为闲置期的开始。建议使用此步骤，以便在空闲时间之前更快速地检测可能丢失的文本。
An empty T140block contains no data.
空T140块不包含任何数据。
When redundancy is used, transmission continues with a packet at every transmission timer expiration and insertion of an empty T.140block as primary, until the last non-empty T140block has been transmitted, as primary and as redundant data, with all intended generations of redundancy. The last packet before an idle period will contain only one non-empty T140block as redundant data, while the remainder of the redundancy packet will contain empty T140blocks.
当使用冗余时，传输将在每次传输计时器到期时继续进行，并插入一个空的T.140块作为主数据块，直到最后一个非空的T140块作为主数据块和冗余数据块被传输，并产生所有预期的冗余。空闲时段前的最后一个数据包将仅包含一个非空T140块作为冗余数据，而冗余数据包的其余部分将包含空T140块。
Any empty T140block sent as primary data MUST be included as redundant T140blocks in subsequent packets, just as normal text T140blocks would be, unless the empty T140block is too old to be transmitted. This is done so that sequence number inference for the redundant T140blocks will be correct, as explained in Section 4.2.
任何作为主数据发送的空T140块必须作为冗余T140块包含在后续数据包中，就像普通文本T140块一样，除非空T140块太旧而无法传输。这样做是为了使冗余T140块的序列号推断正确，如第4.2节所述。
After an idle period, the transmitter SHOULD set the M-bit to one in the first packet with new text.
空闲时间过后，发送器应在具有新文本的第一个数据包中将M位设置为1。
Packet loss for text/t140 packets MAY be detected by observing gaps in the sequence numbers of RTP packets received by the receiver.
文本/t140分组的分组丢失可以通过观察接收机接收的RTP分组的序列号中的间隔来检测。
With text/t140, the loss of packets is usually detected by comparison of the sequence of RTP packets as they arrive. Any discrepancy MAY be used to indicate loss. The highest RTP sequence number received may also be compared with that in RTCP reports, as an additional check for loss of the last packet before an idle period.
对于text/t140，通常通过比较RTP数据包到达时的序列来检测数据包丢失。任何差异都可以用来表示损失。还可以将接收到的最高RTP序列号与RTCP报告中的序列号进行比较，作为空闲期之前最后一个数据包丢失的额外检查。
Missing data SHOULD be marked by insertion of a missing text marker in the received stream for each missing T140block, as specified in ITU-T T.140 Addendum 1 [1].
根据ITU-T T.140附录1[1]的规定，对于每个缺失T140块，应通过在接收流中插入缺失文本标记来标记缺失数据。
Because empty T140blocks are transmitted in the beginning of an idle period, there is a slight risk of falsely marking loss of text, when only an empty T140block was lost. Procedures based on detection of the packet with the M-bit set to one MAY be used to reduce the risk of introducing false markers of loss.
由于空T140块是在空闲期开始时传输的，因此只有空T140块丢失时，存在错误标记文本丢失的轻微风险。基于M位设置为1的分组检测的过程可用于降低引入错误丢失标记的风险。
If redundancy is used with the text/t140 format, and a packet is received with fewer redundancy levels than normally in the session, it SHOULD be treated as if one empty T140block has been received for each excluded level in the received packet. This is because the only occasion when a T140block is excluded from transmission is when it is an empty T140block that has become too old to be transmitted.
如果冗余与text/t140格式一起使用，并且接收到的数据包的冗余级别低于会话中的正常冗余级别，则应将其视为接收到的数据包中每个排除级别都接收到一个空t140块。这是因为T140块被排除在传输之外的唯一情况是，它是一个空的T140块，已经太旧而无法传输。
If two successive packets have the same number of redundant generations, it SHOULD be treated as the general redundancy level for the session. Change of the general redundancy level SHOULD only be done after an idle period.
如果两个连续数据包具有相同数量的冗余生成，则应将其视为会话的一般冗余级别。一般冗余级别的更改只能在空闲时间后进行。
The text/t140 format relies on use of the sequence number in the RTP packet header for detection of loss and, therefore, is not suitable for applications where it needs to be alternating with other payloads in the same RTP stream. It would be complicated and unreliable to
text/t140格式依赖于在RTP分组报头中使用序列号来检测丢失，因此，不适用于需要与同一RTP流中的其他有效负载交替的应用。这样做既复杂又不可靠
try to detect loss of data at the edges of the shifts between t140 text and other stream contents. Therefore, text/t140 is RECOMMENDED to be the only payload type in the RTP stream.
尝试检测t140文本和其他流内容之间移位边缘的数据丢失。因此，建议将text/t140作为RTP流中的唯一有效负载类型。
For protection against packets arriving out of order, the following procedure MAY be implemented in the receiver. If analysis of a received packet reveals a gap in the sequence and no redundant data is available to fill that gap, the received packet SHOULD be kept in a buffer to allow time for the missing packet(s) to arrive. It is RECOMMENDED that the waiting time be limited to 1 second.
为了防止分组无序到达，可以在接收机中实现以下过程。如果对接收到的数据包的分析显示序列中存在间隙，并且没有可用的冗余数据来填补该间隙，则应将接收到的数据包保存在缓冲器中，以留出时间让丢失的数据包到达。建议将等待时间限制为1秒。
If a packet with a T140block belonging to the gap arrives before the waiting time expires, this T140block is inserted into the gap and then consecutive T140blocks from the leading edge of the gap may be consumed. Any T140block that does not arrive before the time limit expires should be treated as lost and a missing text marker should be inserted (see Section 5.3).
如果具有属于该间隙的t140块的分组在等待时间到期之前到达，则将该t140块插入该间隙中，然后可以消耗该间隙前缘的连续t140块。任何未在时限到期前到达的T140块应视为丢失，并应插入缺失的文本标记（见第5.3节）。
In some cases, it is necessary to limit the rate at which characters are transmitted. For example, when a Public Switched Telephone Network (PSTN) gateway is interworking between an IP device and a PSTN textphone, it may be necessary to limit the character rate from the IP device in order to avoid throwing away characters (in case of buffer overflow at the PSTN gateway).
在某些情况下，有必要限制字符的传输速率。例如，当公共交换电话网（PSTN）网关在IP设备和PSTN文本电话之间互通时，可能需要限制来自IP设备的字符速率，以避免丢弃字符（在PSTN网关发生缓冲区溢出的情况下）。
To control the character transmission rate, the MIME parameter "cps" in the "fmtp" attribute [7] is defined (see Section 10 ). It is used in SDP with the following syntax:
为了控制字符传输速率，定义了“fmtp”属性[7]中的MIME参数“cps”（参见第10节）。它在SDP中使用，语法如下：
a=fmtp:<format> cps=<integer>
a=fmtp:<format> cps=<integer>
The <format> field is populated with the payload type that is used for text. The <integer> field contains an integer representing the maximum number of characters that may be received per second. The value shall be used as a mean value over any 10-second interval. The default value is 30.
<format>字段填充用于文本的有效负载类型。<integer>字段包含一个整数，表示每秒可接收的最大字符数。该值应作为任何10秒间隔的平均值。默认值为30。
Examples of use in SDP are found in Section 7.2.
SDP中的使用示例见第7.2节。
In receipt of this parameter, devices MUST adhere to the request by transmitting characters at a rate at or below the specified <integer> value. Note that this parameter was not defined in RFC 2793 [16]. Therefore implementations of the text/t140 format may be in use that do not recognize and act according to this parameter. Therefore,
在接收到该参数时，设备必须通过以等于或低于指定的<integer>值的速率传输字符来遵守请求。请注意，RFC 2793[16]中未定义此参数。因此，可能正在使用text/t140格式的实现，这些实现无法识别并根据此参数进行操作。因此
receivers of text/t140 MUST be designed so they can handle temporary reception of characters at a higher rate than this parameter specifies. As a result malfunction due to buffer overflow is avoided for text conversation with human input.
text/t140的接收器必须设计为能够以高于此参数指定的速率处理字符的临时接收。因此，对于人工输入的文本对话，避免了由于缓冲区溢出而导致的故障。
Below is an example of a text/t140 RTP packet without redundancy.
下面是没有冗余的text/t140 RTP数据包的示例。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC=0 |M| T140 PT | sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| timestamp (1000Hz) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T.140 encoded data |
+ +---------------+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC=0 |M| T140 PT | sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| timestamp (1000Hz) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T.140 encoded data |
+ +---------------+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Below is an example of a text/t140 RTP packet with one redundant T140block.
下面是带有一个冗余t140块的text/t140 RTP数据包的示例。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC=0 |M| "RED" PT | sequence number of primary |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| timestamp of primary encoding "P" |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| T140 PT | timestamp offset of "R" | "R" block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| T140 PT | "R" T.140 encoded redundant data |
+-+-+-+-+-+-+-+-+ +---------------+
+ | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+
| "P" T.140 encoded primary data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC=0 |M| "RED" PT | sequence number of primary |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| timestamp of primary encoding "P" |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| T140 PT | timestamp offset of "R" | "R" block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| T140 PT | "R" T.140 encoded redundant data |
+-+-+-+-+-+-+-+-+ +---------------+
+ | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+
| "P" T.140 encoded primary data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Below is an example of an RTP packet with one redundant T140block using text/t140 payload format. The primary data block is empty, which is the case when transmitting a packet for the sole purpose of forcing the redundant data to be transmitted in the absence of any new data.
下面是一个RTP包的示例，其中包含一个使用text/t140有效负载格式的冗余t140块。主数据块是空的，这是在没有任何新数据的情况下仅为了强制发送冗余数据而发送分组时的情况。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC=0 |M| "RED" PT | sequence number of primary |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| timestamp of primary encoding "P" |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| T140 PT | timestamp offset of "R" | "R" block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| T140 PT | "R" T.140 encoded redundant data |
+-+-+-+-+-+-+-+-+ +---------------+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC=0 |M| "RED" PT | sequence number of primary |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| timestamp of primary encoding "P" |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| T140 PT | timestamp offset of "R" | "R" block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| T140 PT | "R" T.140 encoded redundant data |
+-+-+-+-+-+-+-+-+ +---------------+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
As a follow-on to the previous example, the example below shows the next RTP packet in the sequence, which does contain a real T140block when using the text/t140 payload format. Note that the empty block is present in the redundant transmissions of the text/t140 payload format. This example shows two levels of redundancy and one primary data block. The value of the "R2 block length" would be set to zero in order to represent the empty T140block.
作为上一示例的后续，下面的示例显示了序列中的下一个RTP数据包，当使用text/t140有效负载格式时，它确实包含一个真正的t140块。注意，文本/t140有效负载格式的冗余传输中存在空块。此示例显示了两个级别的冗余和一个主数据块。“R2块长度”的值将设置为零，以表示空T140块。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC=0 |M| "RED" PT | sequence number of primary |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| timestamp of primary encoding "P" |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| T140 PT | timestamp offset of "R2" | "R2" block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| T140 PT | timestamp offset of "R1" | "R1" block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| T140 PT | "R1" T.140 encoded redundant data |
+-+-+-+-+-+-+-+-+ +---------------+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+
| "P" T.140 encoded primary data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC=0 |M| "RED" PT | sequence number of primary |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| timestamp of primary encoding "P" |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| T140 PT | timestamp offset of "R2" | "R2" block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| T140 PT | timestamp offset of "R1" | "R1" block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| T140 PT | "R1" T.140 encoded redundant data |
+-+-+-+-+-+-+-+-+ +---------------+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+
| "P" T.140 encoded primary data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Below is an example of SDP, which describes RTP text transport on port 11000:
下面是SDP的一个示例，它描述了端口11000上的RTP文本传输：
m=text 11000 RTP/AVP 98
a=rtpmap:98 t140/1000
m=text 11000 RTP/AVP 98
a=rtpmap:98 t140/1000
Below is an example of SDP that is similar to the above example, but also utilizes RFC 2198 to provide the recommended two levels of redundancy for the text packets:
下面是与上述示例类似的SDP示例，但也利用RFC 2198为文本分组提供推荐的两个冗余级别：
m=text 11000 RTP/AVP 98 100
a=rtpmap:98 t140/1000
a=rtpmap:100 red/1000
a=fmtp:100 98/98/98
m=text 11000 RTP/AVP 98 100
a=rtpmap:98 t140/1000
a=rtpmap:100 red/1000
a=fmtp:100 98/98/98
Note: Although these examples utilize the RTP/AVP profile, it is not intended to limit the scope of this memo. Any appropriate profile may be used in conjunction with this memo.
注：尽管这些示例使用RTP/AVP配置文件，但并不打算限制本备忘录的范围。任何适当的档案均可与本备忘录一起使用。
All of the security considerations from Section 14 of RFC 3550 [2] apply.
RFC 3550[2]第14节中的所有安全注意事项均适用。
Because the intention of the described payload format is to carry text in a text conversation, security measures in the form of encryption are of importance. The amount of data in a text conversation session is low. Therefore, any encryption method MAY be selected and applied to T.140 session contents or to whole RTP packets. Secure Real-time Transport Protocol (SRTP) [14] provides a suitable method for ensuring confidentiality.
由于所述有效载荷格式的目的是在文本对话中携带文本，因此以加密形式的安全措施非常重要。文本对话会话中的数据量较低。因此，可以选择任何加密方法并将其应用于T.140会话内容或整个RTP分组。安全实时传输协议（SRTP）[14]为确保机密性提供了合适的方法。
It may be desirable to protect the text contents of an RTP stream against manipulation. SRTP [14] provides methods for providing integrity that MAY be applied.
可能希望保护RTP流的文本内容不受操纵。SRTP[14]提供了提供完整性的方法，这些方法可以应用。
There are several methods of making sure the source of the text is the intended one.
有几种方法可以确保文本的来源是预期的来源。
Text streams are usually used in a multimedia control environment. Security measures for authentication are available and SHOULD be applied in the registration and session establishment procedures, so that the identity of the sender of the text stream is reliably associated with the person or device setting up the session. Once established, SRTP [14] mechanisms MAY be applied to ascertain that the source is maintained the same during the session.
文本流通常用于多媒体控制环境。身份验证的安全措施可用，并应在注册和会话建立过程中应用，以便文本流发送者的身份与设置会话的人员或设备可靠关联。一旦建立，SRTP[14]机制可用于确定源在会话期间保持不变。
The congestion considerations from Section 10 of RFC 3550 [2], Section 6 of RFC 2198 [3], and any used profile (e.g., the section about congestion in chapter 2 of RFC 3551 [11]) apply with the following application-specific considerations.
RFC 3550[2]第10节、RFC 2198[3]第6节以及任何使用的配置文件（例如，RFC 3551[11]第2章中关于拥塞的部分）中的拥塞注意事项适用于以下特定于应用的注意事项。
Automated systems MUST NOT use this format to send large amounts of text at rates significantly above those a human user could enter.
自动化系统不得使用此格式发送大量文本，发送速率远远高于人类用户可以输入的速率。
Even if the network load from users of text conversation is usually very low, for best-effort networks an application MUST monitor the packet loss rate and take appropriate actions to reduce its sending rate (if this application sends at higher rate than what TCP would
即使文本会话用户的网络负载通常很低，对于尽力而为的网络，应用程序必须监控数据包丢失率，并采取适当的措施降低其发送速率（如果此应用程序的发送速率高于TCP的发送速率）
achieve over the same path). The reason for this is that this application, due to its recommended usage of two or more redundancy levels, is very robust against packet loss. At the same time, due to the low bit-rate of text conversations, if one considers the discussion in RFC 3714 [13], this application will experience very high packet loss rates before it needs to perform any reduction in the sending rate.
在同一条道路上实现）。这样做的原因是，由于推荐使用两个或更多冗余级别，该应用程序对数据包丢失非常鲁棒。同时，由于文本对话的低比特率，如果考虑RFC 3714[13]中的讨论，该应用程序在需要执行任何发送速率降低之前将经历非常高的丢包率。
If the application needs to reduce its sending rate, it SHOULD NOT reduce the number of redundancy levels below the default amount specified in Section 4. Instead, the following actions are RECOMMENDED in order of priority:
如果应用程序需要降低其发送速率，则不应将冗余级别的数量降低到第4节中指定的默认数量以下。相反，建议按优先顺序采取以下措施：
- Increase the shortest time between transmissions (described in Section 5.1) from the recommended 300 ms to 500 ms, which is the highest value allowed according to T.140.
- 将传输之间的最短时间（如第5.1节所述）从建议的300 ms增加到500 ms，这是根据T.140允许的最高值。
- Limit the maximum rate of characters transmitted.
- 限制传输字符的最大速率。
- Increase the shortest time between transmissions to a higher value, not higher than 5 seconds. This will cause unpleasant delays in transmission, beyond what is allowed according to T.140, but text will still be conveyed in the session with some usability.
- 将两次传输之间的最短时间增加到更高的值，不超过5秒。这将导致令人不快的传输延迟，超出T.140允许的范围，但文本仍将在会话中传输，具有一定的可用性。
- Exclude participants from the session.
- 将参与者排除在会话之外。
Please note that if the reduction in bit-rate achieved through the above measures is not sufficient, the only remaining action is to terminate the session.
请注意，如果通过上述措施实现的比特率降低还不够，唯一剩下的操作是终止会话。
As guidance, some load figures are provided here as examples based on use of IPv4, including the load from IP, UDP, and RTP headers without compression .
作为指导，这里提供了一些基于IPv4使用的负载数据作为示例，包括来自IP、UDP和RTP报头的负载（无压缩）。
- Experience tells that a common mean character transmission rate, during a complete PSTN text telephony session, is around two characters per second.
- 经验告诉我们，在一个完整的PSTN文本电话会话期间，一个普通的平均字符传输速率大约为每秒两个字符。
- A maximum performance of 20 characters per second is enough even for voice-to-text applications.
- 即使对于语音到文本应用程序，每秒最多20个字符的性能也足够了。
- With the (unusually high) load of 20 characters per second, in a language that makes use of three octets per UTF-8 character, two redundant levels, and 300 ms between transmissions, the maximum load of this application is 3300 bits/s.
- 在每秒20个字符（异常高）的负载情况下，在一种每UTF-8字符使用三个八位字节、两个冗余级别以及传输间隔为300毫秒的语言中，此应用程序的最大负载为3300位/秒。
- When the restrictions mentioned above are applied, limiting transmission to 10 characters per second, using 5 s between transmissions, the maximum load of this application, in a language that uses one octet per UTF-8 character, is 300 bits/s.
- 当应用上述限制时，将传输限制为每秒10个字符，在传输之间使用5秒，在每UTF-8字符使用一个八位字节的语言中，此应用程序的最大负载为300位/秒。
Note that this payload can be used in a congested situation as a last resort to maintain some contact when audio and video media need to be stopped. The availability of one low bit-rate stream for text in such adverse situations may be crucial for maintaining some communication in a critical situation.
请注意，在拥挤的情况下，当音频和视频媒体需要停止时，可以使用此有效负载作为最后手段来保持一些联系。在这种不利情况下，文本的一个低比特率流的可用性对于在危急情况下维持某些通信可能是至关重要的。
This document updates the RTP payload format named "t140" and the associated MIME type "text/t140", in the IANA RTP and Media Type registries.
本文档更新IANA RTP和媒体类型注册表中名为“t140”的RTP有效负载格式和相关MIME类型“text/t140”。
MIME media type name: text
MIME媒体类型名称：text
MIME subtype name: t140
MIME子类型名称：t140
Required parameters: rate: The RTP timestamp clock rate, which is equal to the sampling rate. The only valid value is 1000.
所需参数：速率：RTP时间戳时钟速率，等于采样速率。唯一有效的值是1000。
Optional parameters: cps: The maximum number of characters that may be received per second. The default value is 30.
可选参数：cps：每秒可接收的最大字符数。默认值为30。
Encoding considerations: T.140 text can be transmitted with RTP as specified in RFC 4103.
编码注意事项：T.140文本可以按照RFC 4103中的规定使用RTP传输。
Security considerations: See Section 8 of RFC 4103.
安全注意事项：见RFC 4103第8节。
Interoperability considerations: This format is the same as specified in RFC2793. For RFC2793 the "cps=" parameter was not defined. Therefore, there may be implementations that do not consider this parameter. Receivers need to take that into account.
互操作性注意事项：此格式与RFC2793中指定的格式相同。对于RFC2793，未定义“cps=”参数。因此，可能有不考虑此参数的实现。接收者需要考虑到这一点。
Published specification: ITU-T T.140 Recommendation. RFC 4103.
已发布规范：ITU-T.140建议。RFC4103。
Applications which use this media type: Text communication terminals and text conferencing tools.
使用此媒体类型的应用程序：文本通信终端和文本会议工具。
Additional information: This type is only defined for transfer via RTP.
附加信息：此类型仅为通过RTP传输而定义。
Magic number(s): None
幻数：无
File extension(s): None
Macintosh File Type Code(s): None
File extension(s): None
Macintosh File Type Code(s): None
Person & email address to contact for further information: Gunnar Hellstrom E-mail: gunnar.hellstrom@omnitor.se
联系人和电子邮件地址以获取更多信息：Gunnar Hellstrom电子邮件：Gunnar。hellstrom@omnitor.se
Intended usage: COMMON
预期用途：普通
Author / Change controller: Gunnar Hellstrom | IETF avt WG gunnar.hellstrom@omnitor.se |
作者/变更控制员：Gunnar Hellstrom | IETF avt WG Gunnar。hellstrom@omnitor.se |
The information carried in the MIME media type specification has a specific mapping to fields in the Session Description Protocol (SDP) [7], which is commonly used to describe RTP sessions. When SDP is used to specify sessions employing the text/t140 format, the mapping is as follows:
MIME媒体类型规范中包含的信息具有到会话描述协议（SDP）[7]中字段的特定映射，该协议通常用于描述RTP会话。当使用SDP指定采用text/t140格式的会话时，映射如下：
- The MIME type ("text") goes in SDP "m=" as the media name.
- MIME类型（“文本”）以SDP“m=”作为媒体名称。
- The MIME subtype (payload format name) goes in SDP "a=rtpmap" as the encoding name. The RTP clock rate in "a=rtpmap" MUST be 1000 for text/t140.
- MIME子类型（有效负载格式名称）以SDP“a=rtpmap”作为编码名称。对于text/t140，“a=rtpmap”中的RTP时钟频率必须为1000。
- The parameter "cps" goes in SDP "a=fmtp" attribute.
- 参数“cps”位于SDP“a=fmtp”属性中。
- When the payload type is used with redundancy according to RFC 2198, the level of redundancy is shown by the number of elements in the slash-separated payload type list in the "fmtp" parameter of the redundancy declaration as defined in RFC 4102 [9] and RFC 2198 [3].
- 根据RFC 2198，当有效负载类型与冗余一起使用时，冗余级别由RFC 4102[9]和RFC 2198[3]中定义的冗余声明的“fmtp”参数中以斜线分隔的有效负载类型列表中的元素数量表示。
In order to achieve interoperability within the framework of the offer/answer model [10], the following consideration should be made:
为了在提供/应答模型[10]的框架内实现互操作性，应考虑以下因素：
- The "cps" parameter is declarative. Both sides may provide a value, which is independent of the other side.
- “cps”参数是声明性的。双方都可以提供一个独立于另一方的值。
The authors want to thank Stephen Casner, Magnus Westerlund, and Colin Perkins for valuable support with reviews and advice on creation of this document, to Mickey Nasiri at Ericsson Mobile Communication for providing the development environment, Michele Mizarro for verification of the usability of the payload format for its intended purpose, and Andreas Piirimets for editing support and validation.
作者要感谢Stephen Casner、Magnus Westerlund和Colin Perkins对本文档创建的宝贵支持和建议，感谢爱立信移动通信公司的Mickey Nasiri提供开发环境，感谢Michele Mizarro验证有效载荷格式的可用性，Andreas Piirimets负责编辑支持和验证。
[1] ITU-T Recommendation T.140 (1998) - Text conversation protocol for multimedia application, with amendment 1, (2000).
[1] ITU-T建议T.140（1998）-多媒体应用的文本对话协议，修订件1，（2000年）。
[2] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", RFC 3550, July 2003.
[2] Schulzrinne，H.，Casner，S.，Frederick，R.和V.Jacobson，“RTP：实时应用的传输协议”，RFC 35502003年7月。
[3] Perkins, C., Kouvelas, I., Hodson, O., Hardman, V., Handley, M., Bolot, J., Vega-Garcia, A., and S. Fosse-Parisis, "RTP Payload for Redundant Audio Data", RFC 2198, September 1997.
[3] 帕金斯，C.，库维拉斯，I.，霍德森，O.，哈德曼，V.，汉德利，M.，博洛特，J.，维加·加西亚，A.，和S.福斯·帕里斯，“冗余音频数据的RTP有效载荷”，RFC 21981997年9月。
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[4] Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[5] ISO/IEC 10646-1: (1993), Universal Multiple Octet Coded Character Set.
[5] ISO/IEC 10646-1:（1993），通用多八位编码字符集。
[6] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003.
[6] Yergeau，F.，“UTF-8，ISO 10646的转换格式”，STD 63，RFC 3629，2003年11月。
[7] Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998.
[7] Handley，M.和V.Jacobson，“SDP：会话描述协议”，RFC 2327，1998年4月。
[8] Rosenberg, J. and H. Schulzrinne, "An RTP Payload Format for Generic Forward Error Correction", RFC 2733, December 1999.
[8] Rosenberg，J.和H.Schulzrinne，“通用前向纠错的RTP有效载荷格式”，RFC 2733，1999年12月。
[9] Jones, P., "Registration of the text/red MIME Sub-Type", RFC 4102, June 2005.
[9] Jones，P.，“文本/红色MIME子类型的注册”，RFC 4102，2005年6月。
[10] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with the Session Description Protocol (SDP)", RFC 3264, June 2002.
[10] Rosenberg，J.和H.Schulzrinne，“具有会话描述协议（SDP）的提供/应答模型”，RFC 3264，2002年6月。
[11] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video Conference with Minimal Control", STD 65, RFC 3551, July 2003.
[11] Schulzrinne，H.和S.Casner，“最小控制音频和视频会议的RTP配置文件”，STD 65，RFC 3551，2003年7月。
[12] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.
[12] Postel，J.，“互联网协议”，STD 5，RFC 7911981年9月。
[13] Floyd, S. and J. Kempf, "IAB Concerns Regarding Congestion Control for Voice Traffic in the Internet", RFC 3714, March 2004.
[13] Floyd，S.和J.Kempf，“IAB对互联网语音流量拥塞控制的关注”，RFC 3714，2004年3月。
[14] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004.
[14] Baugher，M.，McGrew，D.，Naslund，M.，Carrara，E.，和K.Norrman，“安全实时传输协议（SRTP）”，RFC 37112004年3月。
[15] Schulzrinne, H. and S. Petrack, "RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals", RFC 2833, May 2000.
[15] Schulzrinne，H.和S.Petrack，“DTMF数字、电话音和电话信号的RTP有效载荷”，RFC 28332000年5月。
[16] Hellstrom, G., "RTP Payload for Text Conversation", RFC 2793, May 2000.
[16] Hellstrom，G.，“文本对话的RTP有效载荷”，RFC 2793，2000年5月。
[17] ITU-T Recommendation F.703, Multimedia Conversational Services, November 2000.
[17] ITU-T建议F.703，多媒体会话服务，2000年11月。
Authors' Addresses
作者地址
Gunnar Hellstrom Omnitor AB Renathvagen 2 SE-121 37 Johanneshov Sweden
Gunnar Hellstrom Omnitor AB Renathvagen 2 SE-121 37瑞典约翰尼绍夫
Phone: +46 708 204 288 / +46 8 556 002 03
Fax: +46 8 556 002 06
EMail: gunnar.hellstrom@omnitor.se
Phone: +46 708 204 288 / +46 8 556 002 03
Fax: +46 8 556 002 06
EMail: gunnar.hellstrom@omnitor.se
Paul E. Jones Cisco Systems, Inc. 7025 Kit Creek Rd. Research Triangle Park, NC 27709 USA
Paul E.Jones Cisco Systems，Inc.美国北卡罗来纳州三角研究公园Kit Creek路7025号，邮编：27709
Phone: +1 919 392 6948
EMail: paulej@packetizer.com
Phone: +1 919 392 6948
EMail: paulej@packetizer.com
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