RTP Payload Format for the G.729.1 Audio Codec
RFC 4749

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Network Working Group                                         A. Sollaud
Request for Comments: 4749                                France Telecom
Category: Standards Track                                   October 2006

             RTP Payload Format for the G.729.1 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

   Copyright (C) The Internet Society (2006).

Abstract

   This document specifies a Real-time Transport Protocol (RTP) payload
   format to be used for the International Telecommunication Union
   (ITU-T) G.729.1 audio codec.  A media type registration is included
   for this payload format.

Table of Contents

   1. Introduction ....................................................2
   2. Background ......................................................2
   3. Embedded Bit Rates Considerations ...............................3
   4. RTP Header Usage ................................................3
   5. Payload Format ..................................................4
      5.1. Payload Structure ..........................................4
      5.2. Payload Header: MBS Field ..................................4
      5.3. Payload Header: FT Field ...................................6
      5.4. Audio Data .................................................6
   6. Payload Format Parameters .......................................7
      6.1. Media Type Registration ....................................7
      6.2. Mapping to SDP Parameters ..................................8
           6.2.1. Offer-Answer Model Considerations ...................9
           6.2.2. Declarative SDP Considerations .....................11
   7. Congestion Control .............................................11
   8. Security Considerations ........................................11
   9. IANA Considerations ............................................12
   10. References ....................................................12
      10.1. Normative References .....................................12
      10.2. Informative References ...................................12

Sollaud                     Standards Track                     [Page 1]
RFC 4749             RTP Payload Format for G.729.1         October 2006

1.  Introduction

   The International Telecommunication Union (ITU-T) recommendation
   G.729.1 [1] is a scalable and wideband extension of the
   recommendation G.729 [9] audio codec.  This document specifies the
   payload format for packetization of G.729.1 encoded audio signals
   into the Real-time Transport Protocol (RTP).

   The payload format itself is described in Section 5.  A media type
   registration and the details for the use of G.729.1 with SDP are
   given in Section 6.

   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 [2].

2.  Background

   G.729.1 is an 8-32 kbps scalable wideband (50-7000 Hz) speech and
   audio coding algorithm interoperable with G.729, G.729 Annex A, and
   G.729 Annex B.  It provides a standardized solution for packetized
   voice applications that allows a smooth transition from narrowband to
   wideband telephony.

   The most important services addressed are IP telephony and
   videoconferencing, either for enterprise corporate networks or for
   mass market (like Public Switched Telephone Network (PSTN) emulation
   over DSL or wireless access).  Target devices can be IP phones or
   other VoIP handsets, home gateways, media gateways, IP Private Branch
   Exchange (IPBX), trunking equipment, voice messaging servers, etc.

   For all those applications, the scalability feature allows tuning the
   bit rate versus quality trade-off, possibly in a dynamic way during a
   session, taking into account service requirements and network
   transport constraints.

   The G.729.1 coder produces an embedded bitstream structured in 12
   layers corresponding to 12 available bit rates between 8 and 32 kbps.
   The first layer, at 8 kbps, is called the core layer and is bitstream
   compatible with the ITU-T G.729/G.729A coder.  At 12 kbps, a second
   layer improves the narrowband quality.  Upper layers provide wideband
   audio (50-7000 Hz) between 14 and 32 kbps, with a 2 kbps granularity
   allowing graceful quality improvements.  Only the core layer is
   mandatory to decode understandable speech; upper layers provide
   quality enhancement and wideband enlargement.

Sollaud                     Standards Track                     [Page 2]
RFC 4749             RTP Payload Format for G.729.1         October 2006