RTP Payload Format for ITU-T Recommendation G.722.1
RFC 5577

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Network Working Group                                           P. Luthi
Request for Comments: 5577                                      Tandberg
Obsoletes: 3047                                                  R. Even
Category: Standards Track                               Gesher Erove Ltd
                                                               July 2009

          RTP Payload Format for ITU-T Recommendation G.722.1

Abstract

   International Telecommunication Union (ITU-T) Recommendation G.722.1
   is a wide-band audio codec.  This document describes the payload
   format for including G.722.1-generated bit streams within an RTP
   packet.  The document also describes the syntax and semantics of the
   Session Description Protocol (SDP) parameters needed to support
   G.722.1 audio codec.

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

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   document authors.  All rights reserved.

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   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Luthi & Even                Standards Track                     [Page 1]
RFC 5577                         G7221                         July 2009

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................3
   3. RTP Usage for G.722.1 ...........................................3
      3.1. RTP G.722.1 Header Fields ..................................3
      3.2. RTP Payload Format for G.722.1 .............................3
      3.3. Multiple G.722.1 Frames in an RTP Packet ...................5
      3.4. Computing the Number of G.722.1 Frames .....................6
   4. IANA Considerations .............................................6
      4.1. Media Type Registration ....................................6
           4.1.1. Registration of Media Type audio/G7221 ..............6
   5. SDP Parameters ..................................................8
      5.1. Usage with the SDP Offer/Answer Model ......................8
   6. Security Considerations .........................................8
   7. Changes from RFC 3047 ...........................................9
   8. Acknowledgments .................................................9
   9. References ......................................................9
      9.1. Normative References .......................................9
      9.2. Informative References ....................................10

1.  Introduction

   ITU-T G.722.1 [ITU.G7221] is a low-complexity coder; it compresses 50
   Hz - 14 kHz audio signals into one of the following bit rates: 24
   kbit/s, 32 kbit/s, or 48 kbit/s.

   The coder may be used for speech, music, and other types of audio.

   Some of the applications for which this coder is suitable are:

   o  Real-time communications such as videoconferencing and telephony

   o  Streaming audio

   o  Archival and messaging

   ITU-T G.722.1 [ITU.G7221] uses 20-ms frames and a sampling rate clock
   of 16 kHz or 32kHz.  The encoding and decoding algorithm can change
   the bit rate at any 20-ms frame boundary, but no bit rate change
   notification is provided in-band with the bit stream.

   For any given bit rate, the number of bits in a frame is a constant.
   Within this fixed frame, G.722.1 uses variable-length coding (e.g.,
   Huffman coding) to represent most of the encoded parameters.  All
   variable-length codes are transmitted in order from the leftmost bit
   (most significant bit -- MSB) to the rightmost bit (least significant
   bit -- LSB), see [ITU.G7221] for more details.

Luthi & Even                Standards Track                     [Page 2]