Real-Time Transport Protocol (RTP) Payload for Text Conversation Interleaved in an Audio Stream
RFC 4351

• Status
• IESG evaluation record
• IESG writeups
• Email expansions
• History

• Versions
• 00

Network Working Group                                       G. Hellstrom
Request for Comments: 4351                                    Omnitor AB
Category: Historic                                              P. Jones
                                                     Cisco Systems, Inc.
                                                            January 2006

             Real-Time Transport Protocol (RTP) Payload for
           Text Conversation Interleaved in an Audio Stream

Status of This Memo

   This memo defines a Historic Document for the Internet community.  It
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This memo 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.

   One payload format is described for transmitting audio and text data
   within a single RTP session.

   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.

Hellstrom & Jones               Historic                        [Page 1]
RFC 4351        RTP Payload for Text in an Audio Stream     January 2006

Table of Contents

   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 audio/t140c Data ........4
      3.3. The "T140block" ............................................5
      3.4. Synchronization of Text with Other Media ...................5
      3.5. Synchronization Considerations for the audio/t140c Format ..5
      3.6. RTP Packet Header ..........................................6
   4. Protection against Loss of Data .................................7
      4.1. Payload Format When Using Redundancy .......................7
      4.2. Using Redundancy with the audio/t140c Format ...............8
   5. Recommended Procedure ...........................................8
      5.1. Recommended Basic Procedure ................................8
      5.2. Transmission before and after "Idle Periods" ...............9
      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 audio/t140c Format .....11
      7.2. SDP Examples ..............................................12
   8. Security Considerations ........................................13
      8.1. Confidentiality ...........................................13
      8.2. Integrity .................................................13
      8.3. Source Authentication .....................................13
   9. Congestion Considerations ......................................14
   10. IANA Considerations ...........................................15
      10.1. Registration of MIME Media Type audio/t140c ..............15
      10.2. SDP Mapping of MIME Parameters ...........................16
      10.3. Offer/Answer Consideration ...............................17
   11. Acknowledgements ..............................................17
   12. Normative References ..........................................17
   13. Informative References ........................................18

Hellstrom & Jones               Historic                        [Page 2]
RFC 4351        RTP Payload for Text in an Audio Stream     January 2006

1.  Introduction

   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 to 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.

   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