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.
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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
datatracker.ietf.org