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RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV)
RFC 3558

Network Working Group                                              A. Li
Request for Comments: 3558                                          UCLA
Category: Standards Track                                      July 2003

      RTP Payload Format for Enhanced Variable Rate Codecs (EVRC)
                   and Selectable Mode Vocoders (SMV)

Status of this Memo

   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.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document describes the RTP payload format for Enhanced Variable
   Rate Codec (EVRC) Speech and Selectable Mode Vocoder (SMV) Speech.
   Two sub-formats are specified for different application scenarios.  A
   bundled/interleaved format is included to reduce the effect of packet
   loss on speech quality and amortize the overhead of the RTP header
   over more than one speech frame.  A non-bundled format is also
   supported for conversational applications.

Table of Contents

   1. Introduction ................................................... 2
   2. Background ..................................................... 2
   3. The Codecs Supported ........................................... 3
      3.1. EVRC ...................................................... 3
      3.2. SMV ....................................................... 3
      3.3. Other Frame-Based Vocoders ................................ 4
   4. RTP/Vocoder Packet Format ...................................... 4
      4.1. Interleaved/Bundled Packet Format ......................... 5
      4.2. Header-Free Packet Format ................................. 6
      4.3. Determining the Format of Packets ......................... 7
   5. Packet Table of Contents Entries and Codec Data Frame Format ... 7
      5.1. Packet Table of Contents entries .......................... 7
      5.2. Codec Data Frames ......................................... 8
   6. Interleaving Codec Data Frames ................................. 9
   7. Bundling Codec Data Frames .................................... 12
   8. Handling Missing Codec Data Frames ............................ 12

Li                          Standards Track                     [Page 1]
RFC 3558          RTP Payload Format for EVRC and SMV          July 2003

   9. Implementation Issues ......................................... 12
      9.1. Interleaving Length .......................................12
      9.2. Validation of Received Packets ............................13
      9.3. Processing the Late Packets ...............................13
   10. Mode Request ................................................. 13
   11. Storage Format ............................................... 14
   12. IANA Considerations .......................................... 15
      12.1. Registration of Media Type EVRC ..........................15
      12.2. Registration of Media Type EVRC0 .........................16
      12.3. Registration of Media Type SMV ...........................17
      12.4. Registration of Media Type SMV0 ..........................18
   13. Mapping to SDP Parameters .................................... 19
   14. Security Considerations ...................................... 20
   15. Adding Support of Other Frame-Based Vocoders ................. 20
   16. Acknowledgements ............................................. 21
   17. References ................................................... 21
      17.1 Normative ................................................ 21
      17.2 Informative .............................................. 22
   18. Author's Address ............................................. 22
   19. Full Copyright Statement ..................................... 23

1. Introduction

   This document describes how speech compressed with EVRC [1] or SMV
   [2] may be formatted for use as an RTP payload type.  The format is
   also extensible to other codecs that generate a similar set of frame
   types.  Two methods are provided to packetize the codec data frames
   into RTP packets: an interleaved/bundled format and a zero-header
   format.  The sender may choose the best format for each application
   scenario, based on network conditions, bandwidth availability, delay
   requirements, and packet-loss tolerance.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this

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