RFC-7655RTPPayloadFormatforG.711.0(G.711)资源-CSDN文库

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Internet Engineering Task Force (IETF) M. Ramalho, Ed.

Request for Comments: 7655 P. Jones

Category: Standards Track Cisco Systems

ISSN: 2070-1721 N. Harada

NTT

M. Perumal

Ericsson

L. Miao

Huawei Technologies

November 2015

RTP Payload Format for G.711.0

Abstract

This document specifies the Real-time Transport Protocol (RTP)

payload format for ITU-T Recommendation G.711.0. ITU-T Rec. G.711.0

defines a lossless and stateless compression for G.711 packet

payloads typically used in IP networks. This document also defines a

storage mode format for G.711.0 and a media type registration for the

G.711.0 RTP payload format.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force

(IETF). It represents the consensus of the IETF community. It has

received public review and has been approved for publication by the

Internet Engineering Steering Group (IESG). Further information on

Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata,

and how to provide feedback on it may be obtained at

http://www.rfc-editor.org/info/rfc7655.

Ramalho, et al. Standards Track [Page 1]

RFC 7655 G.711.0 Payload Format November 2015

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4

2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4

3. G.711.0 Codec Background . . . . . . . . . . . . . . . . . . 4

3.1. General Information and Use of the ITU-T G.711.0 Codec . 4

3.2. Key Properties of G.711.0 Design . . . . . . . . . . . . 6

3.3. G.711 Input Frames to G.711.0 Output Frames . . . . . . . 8

3.3.1. Multiple G.711.0 Output Frames per RTP Payload

Considerations . . . . . . . . . . . . . . . . . . . 9

4. RTP Header and Payload . . . . . . . . . . . . . . . . . . . 10

4.1. G.711.0 RTP Header . . . . . . . . . . . . . . . . . . . 10

4.2. G.711.0 RTP Payload . . . . . . . . . . . . . . . . . . . 12

4.2.1. Single G.711.0 Frame per RTP Payload Example . . . . 12

4.2.2. G.711.0 RTP Payload Definition . . . . . . . . . . . 13

4.2.2.1. G.711.0 RTP Payload Encoding Process . . . . . . 14

4.2.3. G.711.0 RTP Payload Decoding Process . . . . . . . . 15

4.2.4. G.711.0 RTP Payload for Multiple Channels . . . . . . 17

5. Payload Format Parameters . . . . . . . . . . . . . . . . . . 19

5.1. Media Type Registration . . . . . . . . . . . . . . . . . 20

5.2. Mapping to SDP Parameters . . . . . . . . . . . . . . . . 22

5.3. Offer/Answer Considerations . . . . . . . . . . . . . . . 22

5.4. SDP Examples . . . . . . . . . . . . . . . . . . . . . . 23

5.4.1. SDP Example 1 . . . . . . . . . . . . . . . . . . . . 23

5.4.2. SDP Example 2 . . . . . . . . . . . . . . . . . . . . 23

6. G.711.0 Storage Mode Conventions and Definition . . . . . . . 24

6.1. G.711.0 PLC Frame . . . . . . . . . . . . . . . . . . . . 24

6.2. G.711.0 Erasure Frame . . . . . . . . . . . . . . . . . . 25

6.3. G.711.0 Storage Mode Definition . . . . . . . . . . . . . 26

7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27

8. Security Considerations . . . . . . . . . . . . . . . . . . . 27

9. Congestion Control . . . . . . . . . . . . . . . . . . . . . 28

10. References . . . . . . . . . . . . . . . . . . . . . . . . . 29

10.1. Normative References . . . . . . . . . . . . . . . . . . 29

10.2. Informative References . . . . . . . . . . . . . . . . . 30

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 31

Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 31

Ramalho, et al. Standards Track [Page 3]

RFC 7655 G.711.0 Payload Format November 2015

1. Introduction

The International Telecommunication Union (ITU-T) Recommendation

G.711.0 [G.711.0] specifies a stateless and lossless compression for

G.711 packet payloads typically used in Voice over IP (VoIP)

networks. This document specifies the Real-time Transport Protocol

(RTP) RFC 3550 [RFC3550] payload format and storage modes for this

compression.

2. Requirements Language

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 [RFC2119].

3. G.711.0 Codec Background

ITU-T Recommendation G.711.0 [G.711.0] is a lossless and stateless

compression mechanism for ITU-T Recommendation G.711 [G.711] and thus

is not a "codec" in the sense of "lossy" codecs typically carried by

RTP. When negotiated end-to-end, ITU-T Rec. G.711.0 is negotiated as

if it were a codec, with the understanding that ITU-T Rec. G.711.0

losslessly encoded the underlying (lossy) G.711 Pulse Code Modulation

(PCM) sample representation of an audio signal. For this reason,

ITU-T Rec. G.711.0 will be interchangeably referred to in this

document as a "lossless data compression algorithm" or a "codec",

depending on context. Within this document, individual G.711 PCM

samples will be referred to as "G.711 symbols" or just "symbols" for

brevity.

This section describes the ITU-T Recommendation G.711 [G.711] codec,

its properties, typical uses cases, and its key design properties.

3.1. General Information and Use of the ITU-T G.711.0 Codec

ITU-T Recommendation G.711 is the benchmark standard for narrowband

telephony. It has been successful for many decades because of its

proven voice quality, ubiquity, and utility. A new ITU-T

recommendation, G.711.0, has been established for defining a

stateless and lossless compression for G.711 packet payloads

typically used in VoIP networks. ITU-T Rec. G.711.0 is also known as

ITU-T Rec. G.711 Annex A [G.711-A1], as ITU-T Rec. G.711 Annex A is

effectively a pointer ITU-T Rec. G.711.0. Henceforth in this

document, ITU-T Rec. G.711.0 will simply be referred to as "G.711.0"

and ITU-T Rec. G.711 simply as "G.711".

Ramalho, et al. Standards Track [Page 4]

RFC 7655 G.711.0 Payload Format November 2015

G.711.0 may be employed end-to-end, in which case the RTP payload

format specification and use is nearly identical to the G.711 RTP

specification found in RFC 3551 [RFC3551]. The only significant

difference for G.711.0 is the required use of a dynamic payload type

(the static PT of 0 or 8 is presently almost always used with G.711

even though dynamic assignment of other payload types is allowed) and

the recommendation not to use Voice Activity Detection (see

Section 4.1).

G.711.0, being both lossless and stateless, may also be employed as a

lossless compression mechanism for G.711 payloads anywhere between

end systems that have negotiated use of G.711. Because the only

significant difference between the G.711 RTP payload format header

and the G.711.0 payload format header defined in this document is the

payload type, a G.711 RTP packet can be losslessly converted to a

G.711.0 RTP packet simply by compressing the G.711 payload (thus

creating a G.711.0 payload), changing the payload type to the dynamic

value desired and copying all the remaining G.711 RTP header fields

into the corresponding G.711.0 RTP header. In a similar manner, the

corresponding decompression of the G.711.0 RTP packet thus created

back to the original source G.711 RTP packet can be accomplished by

losslessly decompressing the G.711.0 payload back to the original

source G.711 payload, changing the payload type back to the payload

type of the original G.711 RTP packet and copying all the remaining

G.711.0 RTP header fields into the corresponding G.711 RTP header.

As a packet produced by the compression and decompression as

described above is indistinguishable in every detail to the source

G.711 packet, such compression can be made invisible to the end

systems. Specification of how systems on the path between the end

systems discover each other and negotiate the use of G.711.0

compression as described in this paragraph is outside the scope of

this document.

It is informative to note that G.711.0, being both lossless and

stateless, can be employed multiple times (e.g., on multiple,

individual hops or series of hops) of a given flow with no

degradation of quality relative to end-to-end G.711. Stated another

way, multiple "lossless transcodes" from/to G.711.0/G.711 do not

affect voice quality as typically occurs with lossy transcodes to/

from dissimilar codecs.

Lastly, it is expected that G.711.0 will be used as an archival

format for recorded G.711 streams. Therefore, a G.711.0 Storage Mode

Format is also included in this document.

Ramalho, et al. Standards Track [Page 5]

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