G.729.1 RTP Payload Format Update: Discontinuous Transmission (DTX) Support
RFC 5459
Document | Type |
RFC - Proposed Standard
(January 2009; No errata)
Updates RFC 4749
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Author | Aurelien Sollaud | ||
Last updated | 2015-10-14 | ||
Replaces | draft-sollaud-avt-rfc4749-dtx-update | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 5459 (Proposed Standard) | |
Action Holders |
(None)
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||
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Cullen Jennings | ||
Send notices to | (None) |
Network Working Group A. Sollaud Request for Comments: 5459 France Telecom Updates: 4749 January 2009 Category: Standards Track G.729.1 RTP Payload Format Update: Discontinuous Transmission (DTX) Support 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) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document updates the Real-time Transport Protocol (RTP) payload format to be used for the International Telecommunication Union (ITU-T) Recommendation G.729.1 audio codec. It adds Discontinuous Transmission (DTX) support to the RFC 4749 specification, in a backward-compatible way. An updated media type registration is included for this payload format. Sollaud Standards Track [Page 1] RFC 5459 G.729.1 DTX Support in RTP January 2009 Table of Contents 1. Introduction ....................................................2 2. Background ......................................................2 3. RTP Header Usage ................................................3 4. Payload Format ..................................................3 5. Payload Format Parameters .......................................4 5.1. Media Type Registration Update .............................4 5.2. Mapping to SDP Parameters ..................................5 5.2.1. DTX Offer-Answer Model Considerations ...............5 5.2.2. DTX Declarative SDP Considerations ..................6 6. Congestion Control ..............................................6 7. Security Considerations .........................................6 8. IANA Considerations .............................................6 9. References ......................................................6 9.1. Normative References .......................................6 9.2. Informative References .....................................7 1. Introduction The International Telecommunication Union (ITU-T) Recommendation G.729.1 [ITU-G.729.1] is a scalable and wideband extension of the Recommendation G.729 [ITU-G.729] audio codec. [RFC4749] specifies the payload format for packetization of G.729.1-encoded audio signals into the Real-time Transport Protocol (RTP) [RFC3550]. Annex C of G.729.1 [ITU-G.729.1-C] adds Discontinuous Transmission (DTX) support to G.729.1. This document updates the RTP payload format to allow usage of this Annex. Only changes or additions to [RFC4749] will be described in the following sections. 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 [RFC2119]. 2. Background G.729.1 supports Discontinuous Transmission (DTX), a.k.a. "silence suppression". It means that the coder includes a Voice Activity Detection (VAD) algorithm to determine if an audio frame contains silence or actual audio. During silence periods, the coder may significantly decrease the transmitted bit rate by sending a small frame called a Silence Insertion Descriptor (SID) and then stop transmission. The receiver's decoder will generate comfort noise (CNG) according to the parameters contained in the SID. This DTX/CNG scheme is specified in [ITU-G.729.1-C]. Sollaud Standards Track [Page 2] RFC 5459 G.729.1 DTX Support in RTP January 2009 The G.729.1 SID has an embedded structure. The core SID is the same as the legacy G.729 SID [ITU-G.729-B]. The first enhancement layer adds some parameters for narrowband comfort noise, while a second enhancement layer adds wideband information. The G.729.1 SID can be 2, 3, or 6 octets long. 3. RTP Header Usage The fields of the RTP header must be used as described in [RFC4749], except for the Marker (M) bit. If DTX is used, the first packet of a talkspurt -- that is, the first packet after a silence period during which packets have not beenShow full document text