draft-ietf-avt-profile-new-13.txt   rfc3551.txt 
Internet Engineering Task Force AVT WG Network Working Group H. Schulzrinne
Internet Draft Schulzrinne/Casner Request for Comments: 3551 Columbia University
draft-ietf-avt-profile-new-13.txt Columbia U./Packet Design Obsoletes: 1890 S. Casner
March 2, 2003 Category: Standards Track Packet Design
Expires: September 2003 July 2003
RTP Profile for Audio and Video Conferences with Minimal Control
STATUS OF THIS MEMO
This document is an Internet-Draft and is subject to all provisions RTP Profile for Audio and Video Conferences
of Section 10 of RFC 2026. with Minimal Control
Internet-Drafts are working documents of the Internet Engineering Status of this Memo
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months This document specifies an Internet standards track protocol for the
and may be updated, replaced, or obsoleted by other documents at any Internet community, and requests discussion and suggestions for
time. It is inappropriate to use Internet-Drafts as reference improvements. Please refer to the current edition of the "Internet
material or to cite them other than as "work in progress". Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
The list of current Internet-Drafts can be accessed at Copyright Notice
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The list of Internet-Draft Shadow Directories can be accessed at Copyright (C) The Internet Society (2003). All Rights Reserved.
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Abstract Abstract
This document describes a profile called "RTP/AVP" for the use of the This document describes a profile called "RTP/AVP" for the use of the
real-time transport protocol (RTP), version 2, and the associated real-time transport protocol (RTP), version 2, and the associated
control protocol, RTCP, within audio and video multiparticipant control protocol, RTCP, within audio and video multiparticipant
conferences with minimal control. It provides interpretations of conferences with minimal control. It provides interpretations of
generic fields within the RTP specification suitable for audio and generic fields within the RTP specification suitable for audio and
video conferences. In particular, this document defines a set of video conferences. In particular, this document defines a set of
default mappings from payload type numbers to encodings. default mappings from payload type numbers to encodings.
skipping to change at page 2, line 12 skipping to change at page 2, line 5
implementations and the detailed standards. This document is meant implementations and the detailed standards. This document is meant
as an aid for implementors of audio, video and other real-time as an aid for implementors of audio, video and other real-time
multimedia applications. multimedia applications.
This memorandum obsoletes RFC 1890. It is mostly backwards- This memorandum obsoletes RFC 1890. It is mostly backwards-
compatible except for functions removed because two interoperable compatible except for functions removed because two interoperable
implementations were not found. The additions to RFC 1890 codify implementations were not found. The additions to RFC 1890 codify
existing practice in the use of payload formats under this profile existing practice in the use of payload formats under this profile
and include new payload formats defined since RFC 1890 was published. and include new payload formats defined since RFC 1890 was published.
Contents Table of Contents
1 Introduction ........................................ 3
1.1 Terminology ......................................... 4
2 RTP and RTCP Packet Forms and Protocol Behavior ..... 4
3 Registering Additional Encodings .................... 6
4 Audio ............................................... 8
4.1 Encoding-Independent Rules .......................... 8
4.2 Operating Recommendations ........................... 10
4.3 Guidelines for Sample-Based Audio Encodings ......... 10
4.4 Guidelines for Frame-Based Audio Encodings .......... 11
4.5 Audio Encodings ..................................... 12
4.5.1 DVI4 ................................................ 13
4.5.2 G722 ................................................ 14
4.5.3 G723 ................................................ 14
4.5.4 G726-40, G726-32, G726-24, and G726-16 .............. 18
4.5.5 G728 ................................................ 19
4.5.6 G729 ................................................ 20
4.5.7 G729D and G729E ..................................... 22
4.5.8 GSM ................................................. 25
4.5.9 GSM-EFR ............................................. 26
4.5.10 L8 .................................................. 26
4.5.11 L16 ................................................. 26
4.5.12 LPC ................................................. 28
4.5.13 MPA ................................................. 29
4.5.14 PCMA and PCMU ....................................... 29
4.5.15 QCELP ............................................... 29
4.5.16 RED ................................................. 30
4.5.17 VDVI ................................................ 30
5 Video ............................................... 30
5.1 CelB ................................................ 31
5.2 JPEG ................................................ 31
5.3 H261 ................................................ 31
5.4 H263 ................................................ 31
5.5 H263-1998 ........................................... 32
5.6 MPV ................................................. 32
5.7 MP2T ................................................ 32
5.8 nv .................................................. 32
6 Payload Type Definitions ............................ 33
7 RTP over TCP and Similar Byte Stream Protocols ...... 33
8 Port Assignment ..................................... 35
A Changes from RFC 1890 ............................... 36
B Security Considerations ............................. 38
C IANA Considerations ................................. 39
D References .......................................... 39
E Current Locations of Related Resources .............. 41
F Acknowledgments ..................................... 43
G Addresses of Authors ................................ 43
H Intellectual Property Rights Statement .............. 43
I Full Copyright Statement ............................ 44
1 Introduction 1. Introduction ................................................. 3
1.1 Terminology ............................................. 3
2. RTP and RTCP Packet Forms and Protocol Behavior .............. 4
3. Registering Additional Encodings ............................. 6
4. Audio ........................................................ 8
4.1 Encoding-Independent Rules .............................. 8
4.2 Operating Recommendations ............................... 9
4.3 Guidelines for Sample-Based Audio Encodings ............. 10
4.4 Guidelines for Frame-Based Audio Encodings .............. 11
4.5 Audio Encodings ......................................... 12
4.5.1 DVI4 ............................................ 13
4.5.2 G722 ............................................ 14
4.5.3 G723 ............................................ 14
4.5.4 G726-40, G726-32, G726-24, and G726-16 .......... 18
4.5.5 G728 ............................................ 19
4.5.6 G729 ............................................ 20
4.5.7 G729D and G729E ................................. 22
4.5.8 GSM ............................................. 24
4.5.9 GSM-EFR ......................................... 27
4.5.10 L8 .............................................. 27
4.5.11 L16 ............................................. 27
4.5.12 LPC ............................................. 27
4.5.13 MPA ............................................. 28
4.5.14 PCMA and PCMU ................................... 28
4.5.15 QCELP ........................................... 28
4.5.16 RED ............................................. 29
4.5.17 VDVI ............................................ 29
5. Video ........................................................ 30
5.1 CelB .................................................... 30
5.2 JPEG .................................................... 30
5.3 H261 .................................................... 30
5.4 H263 .................................................... 31
5.5 H263-1998 ............................................... 31
5.6 MPV ..................................................... 31
5.7 MP2T .................................................... 31
5.8 nv ...................................................... 32
6. Payload Type Definitions ..................................... 32
7. RTP over TCP and Similar Byte Stream Protocols ............... 34
8. Port Assignment .............................................. 34
9. Changes from RFC 1890 ........................................ 35
10. Security Considerations ...................................... 38
11. IANA Considerations .......................................... 39
12. References ................................................... 39
12.1 Normative References .................................... 39
12.2 Informative References .................................. 39
13. Current Locations of Related Resources ....................... 41
14. Acknowledgments .............................................. 42
15. Intellectual Property Rights Statement ....................... 43
16. Authors' Addresses ........................................... 43
17. Full Copyright Statement ..................................... 44
[Note to the RFC Editor: This paragraph is to be deleted when this 1. Introduction
draft is published as an RFC. All RFC XXXX should be filled in with
the number of the RTP specification RFC submitted for Draft Standard
status, and all RFC YYYY should be filled in with the number of the
draft specifying MIME registration of RTP payload types as it is
submitted for Proposed Standard status. These latter references are
intended to be non-normative as this Profile may be used
independently of the MIME registrations.]
This profile defines aspects of RTP left unspecified in the RTP This profile defines aspects of RTP left unspecified in the RTP
Version 2 protocol definition (RFC XXXX) [1]. This profile is Version 2 protocol definition (RFC 3550) [1]. This profile is
intended for the use within audio and video conferences with minimal intended for the use within audio and video conferences with minimal
session control. In particular, no support for the negotiation of session control. In particular, no support for the negotiation of
parameters or membership control is provided. The profile is parameters or membership control is provided. The profile is
expected to be useful in sessions where no negotiation or membership expected to be useful in sessions where no negotiation or membership
control are used (e.g., using the static payload types and the control are used (e.g., using the static payload types and the
membership indications provided by RTCP), but this profile may also membership indications provided by RTCP), but this profile may also
be useful in conjunction with a higher-level control protocol. be useful in conjunction with a higher-level control protocol.
Use of this profile may be implicit in the use of the appropriate Use of this profile may be implicit in the use of the appropriate
applications; there may be no explicit indication by port number, applications; there may be no explicit indication by port number,
protocol identifier or the like. Applications such as session protocol identifier or the like. Applications such as session
directories may use the name for this profile specified in directories may use the name for this profile specified in Section
Appendix C. 11.
Other profiles may make different choices for the items specified Other profiles may make different choices for the items specified
here. here.
This document also defines a set of encodings and payload formats for This document also defines a set of encodings and payload formats for
audio and video. These payload format descriptions are included here audio and video. These payload format descriptions are included here
only as a matter of convenience since they are too small to warrant only as a matter of convenience since they are too small to warrant
separate documents. Use of these payload formats is NOT REQUIRED to separate documents. Use of these payload formats is NOT REQUIRED to
use this profile. Only the binding of some of the payload formats to use this profile. Only the binding of some of the payload formats to
static payload type numbers in Tables 4 and 5 is normative. static payload type numbers in Tables 4 and 5 is normative.
1.1 Terminology 1.1 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [2] and document are to be interpreted as described in RFC 2119 [2] and
indicate requirement levels for implementations compliant with this indicate requirement levels for implementations compliant with this
RTP profile. RTP profile.
This draft defines the term media type as dividing encodings of audio This document defines the term media type as dividing encodings of
and video content into three classes: audio, video and audio/video audio and video content into three classes: audio, video and
(interleaved). audio/video (interleaved).
2 RTP and RTCP Packet Forms and Protocol Behavior 2. RTP and RTCP Packet Forms and Protocol Behavior
The section "RTP Profiles and Payload Format Specification" of The section "RTP Profiles and Payload Format Specifications" of RFC
RFC XXXX enumerates a number of items that can be specified or 3550 enumerates a number of items that can be specified or modified
modified in a profile. This section addresses these items. in a profile. This section addresses these items. Generally, this
Generally, this profile follows the default and/or recommended profile follows the default and/or recommended aspects of the RTP
aspects of the RTP specification. specification.
RTP data header: The standard format of the fixed RTP data RTP data header: The standard format of the fixed RTP data
header is used (one marker bit). header is used (one marker bit).
Payload types: Static payload types are defined in Section 6. Payload types: Static payload types are defined in Section 6.
RTP data header additions: No additional fixed fields are RTP data header additions: No additional fixed fields are
appended to the RTP data header. appended to the RTP data header.
RTP data header extensions: No RTP header extensions are RTP data header extensions: No RTP header extensions are
defined, but applications operating under this profile MAY defined, but applications operating under this profile MAY use
use such extensions. Thus, applications SHOULD NOT assume such extensions. Thus, applications SHOULD NOT assume that the
that the RTP header X bit is always zero and SHOULD be RTP header X bit is always zero and SHOULD be prepared to ignore
prepared to ignore the header extension. If a header the header extension. If a header extension is defined in the
extension is defined in the future, that definition MUST future, that definition MUST specify the contents of the first 16
specify the contents of the first 16 bits in such a way bits in such a way that multiple different extensions can be
that multiple different extensions can be identified. identified.
RTCP packet types: No additional RTCP packet types are defined RTCP packet types: No additional RTCP packet types are defined
by this profile specification. by this profile specification.
RTCP report interval: The suggested constants are to be used for RTCP report interval: The suggested constants are to be used for
the RTCP report interval calculation. Sessions operating the RTCP report interval calculation. Sessions operating under
under this profile MAY specify a separate parameter for the this profile MAY specify a separate parameter for the RTCP traffic
RTCP traffic bandwidth rather than using the default bandwidth rather than using the default fraction of the session
fraction of the session bandwidth. The RTCP traffic bandwidth. The RTCP traffic bandwidth MAY be divided into two
bandwidth MAY be divided into two separate session separate session parameters for those participants which are
parameters for those participants which are active data active data senders and those which are not. Following the
senders and those which are not. Following the recommendation in the RTP specification [1] that 1/4 of the RTCP
recommendation in the RTP specification [1] that 1/4 of the bandwidth be dedicated to data senders, the RECOMMENDED default
RTCP bandwidth be dedicated to data senders, the values for these two parameters would be 1.25% and 3.75%,
RECOMMENDED default values for these two parameters would respectively. For a particular session, the RTCP bandwidth for
be 1.25% and 3.75%, respectively. For a particular non-data-senders MAY be set to zero when operating on
session, the RTCP bandwidth for non-data-senders MAY be set unidirectional links or for sessions that don't require feedback
to zero when operating on unidirectional links or for on the quality of reception. The RTCP bandwidth for data senders
sessions that don't require feedback on the quality of SHOULD be kept non-zero so that sender reports can still be sent
reception. The RTCP bandwidth for data senders SHOULD be for inter-media synchronization and to identify the source by
kept non-zero so that sender reports can still be sent for CNAME. The means by which the one or two session parameters for
inter-media synchronization and to identify the source by RTCP bandwidth are specified is beyond the scope of this memo.
CNAME. The means by which the one or two session
parameters for RTCP bandwidth are specified is beyond the
scope of this memo.
SR/RR extension: No extension section is defined for the RTCP SR SR/RR extension: No extension section is defined for the RTCP SR
or RR packet. or RR packet.
SDES use: Applications MAY use any of the SDES items described SDES use: Applications MAY use any of the SDES items described
in the RTP specification. While CNAME information MUST be in the RTP specification. While CNAME information MUST be sent
sent every reporting interval, other items SHOULD only be every reporting interval, other items SHOULD only be sent every
sent every third reporting interval, with NAME sent seven third reporting interval, with NAME sent seven out of eight times
out of eight times within that slot and the remaining SDES within that slot and the remaining SDES items cyclically taking up
items cyclically taking up the eighth slot, as defined in the eighth slot, as defined in Section 6.2.2 of the RTP
Section 6.2.2 of the RTP specification. In other words, specification. In other words, NAME is sent in RTCP packets 1, 4,
NAME is sent in RTCP packets 1, 4, 7, 10, 13, 16, 19, 7, 10, 13, 16, 19, while, say, EMAIL is used in RTCP packet 22.
while, say, EMAIL is used in RTCP packet 22.
Security: The RTP default security services are also the default Security: The RTP default security services are also the default
under this profile. under this profile.
String-to-key mapping: No mapping is specified by this profile. String-to-key mapping: No mapping is specified by this profile.
Congestion: RTP and this profile may be used in the context of Congestion: RTP and this profile may be used in the context of
enhanced network service, for example, through Integrated enhanced network service, for example, through Integrated Services
Services (RFC 1633) [4] or Differentiated Services (RFC 1633) [4] or Differentiated Services (RFC 2475) [5], or they
(RFC 2475) [5], or they may be used with best effort may be used with best effort service.
service.
If enhanced service is being used, RTP receivers SHOULD If enhanced service is being used, RTP receivers SHOULD monitor
monitor packet loss to ensure that the service that was packet loss to ensure that the service that was requested is
requested is actually being delivered. If it is not, then actually being delivered. If it is not, then they SHOULD assume
they SHOULD assume that they are receiving best-effort that they are receiving best-effort service and behave
service and behave accordingly. accordingly.
If best-effort service is being used, RTP receivers SHOULD If best-effort service is being used, RTP receivers SHOULD monitor
monitor packet loss to ensure that the packet loss rate is packet loss to ensure that the packet loss rate is within
within acceptable parameters. Packet loss is considered acceptable parameters. Packet loss is considered acceptable if a
acceptable if a TCP flow across the same network path and TCP flow across the same network path and experiencing the same
experiencing the same network conditions would achieve an network conditions would achieve an average throughput, measured
average throughput, measured on a reasonable timescale, on a reasonable timescale, that is not less than the RTP flow is
that is not less than the RTP flow is achieving. This achieving. This condition can be satisfied by implementing
condition can be satisfied by implementing congestion congestion control mechanisms to adapt the transmission rate (or
control mechanisms to adapt the transmission rate (or the the number of layers subscribed for a layered multicast session),
number of layers subscribed for a layered multicast or by arranging for a receiver to leave the session if the loss
session), or by arranging for a receiver to leave the rate is unacceptably high.
session if the loss rate is unacceptably high.
The comparison to TCP cannot be specified exactly, but is The comparison to TCP cannot be specified exactly, but is intended
intended as an "order-of-magnitude" comparison in timescale as an "order-of-magnitude" comparison in timescale and throughput.
and throughput. The timescale on which TCP throughput is The timescale on which TCP throughput is measured is the round-
measured is the round-trip time of the connection. In trip time of the connection. In essence, this requirement states
essence, this requirement states that it is not acceptable that it is not acceptable to deploy an application (using RTP or
to deploy an application (using RTP or any other transport any other transport protocol) on the best-effort Internet which
protocol) on the best-effort Internet which consumes consumes bandwidth arbitrarily and does not compete fairly with
bandwidth arbitrarily and does not compete fairly with TCP TCP within an order of magnitude.
within an order of magnitude.
Underlying protocol: The profile specifies the use of RTP over Underlying protocol: The profile specifies the use of RTP over
unicast and multicast UDP as well as TCP. (This does not unicast and multicast UDP as well as TCP. (This does not preclude
preclude the use of these definitions when RTP is carried the use of these definitions when RTP is carried by other lower-
by other lower-layer protocols.) layer protocols.)
Transport mapping: The standard mapping of RTP and RTCP to Transport mapping: The standard mapping of RTP and RTCP to
transport-level addresses is used. transport-level addresses is used.
Encapsulation: This profile leaves to applications the Encapsulation: This profile leaves to applications the
specification of RTP encapsulation in protocols other than specification of RTP encapsulation in protocols other than UDP.
UDP.
3 Registering Additional Encodings 3. Registering Additional Encodings
This profile lists a set of encodings, each of which is comprised of This profile lists a set of encodings, each of which is comprised of
a particular media data compression or representation plus a payload a particular media data compression or representation plus a payload
format for encapsulation within RTP. Some of those payload formats format for encapsulation within RTP. Some of those payload formats
are specified here, while others are specified in separate RFCs. It are specified here, while others are specified in separate RFCs. It
is expected that additional encodings beyond the set listed here will is expected that additional encodings beyond the set listed here will
be created in the future and specified in additional payload format be created in the future and specified in additional payload format
RFCs. RFCs.
This profile also assigns to each encoding a short name which MAY be This profile also assigns to each encoding a short name which MAY be
used by higher-level control protocols, such as the Session used by higher-level control protocols, such as the Session
Description Protocol (SDP), RFC 2327 [6], to identify encodings Description Protocol (SDP), RFC 2327 [6], to identify encodings
selected for a particular RTP session. selected for a particular RTP session.
In some contexts it may be useful to refer to these encodings in the In some contexts it may be useful to refer to these encodings in the
form of a MIME content-type. To facilitate this, RFC YYYY [7] form of a MIME content-type. To facilitate this, RFC 3555 [7]
provides registrations for all of the encodings names listed here as provides registrations for all of the encodings names listed here as
MIME subtype names under the "audio" and "video" MIME types through MIME subtype names under the "audio" and "video" MIME types through
the MIME registration procedure as specified in RFC 2048 [8]. the MIME registration procedure as specified in RFC 2048 [8].
Any additional encodings specified for use under this profile (or Any additional encodings specified for use under this profile (or
others) may also be assigned names registered as MIME subtypes with others) may also be assigned names registered as MIME subtypes with
the Internet Assigned Numbers Authority (IANA). This registry the Internet Assigned Numbers Authority (IANA). This registry
provides a means to insure that the names assigned to the additional provides a means to insure that the names assigned to the additional
encodings are kept unique. RFC YYYY specifies the information that encodings are kept unique. RFC 3555 specifies the information that
is required for the registration of RTP encodings. is required for the registration of RTP encodings.
In addition to assigning names to encodings, this profile also In addition to assigning names to encodings, this profile also
assigns static RTP payload type numbers to some of them. However, assigns static RTP payload type numbers to some of them. However,
the payload type number space is relatively small and cannot the payload type number space is relatively small and cannot
accommodate assignments for all existing and future encodings. accommodate assignments for all existing and future encodings.
During the early stages of RTP development, it was necessary to use During the early stages of RTP development, it was necessary to use
statically assigned payload types because no other mechanism had been statically assigned payload types because no other mechanism had been
specified to bind encodings to payload types. It was anticipated specified to bind encodings to payload types. It was anticipated
that non-RTP means beyond the scope of this memo (such as directory that non-RTP means beyond the scope of this memo (such as directory
services or invitation protocols) would be specified to establish a services or invitation protocols) would be specified to establish a
dynamic mapping between a payload type and an encoding. Now, dynamic mapping between a payload type and an encoding. Now,
mechanisms for defining dynamic payload type bindings have been mechanisms for defining dynamic payload type bindings have been
specified in the Session Description Protocol (SDP) and in other specified in the Session Description Protocol (SDP) and in other
protocols such as ITU-T recommendation H.323/H.245. These mechanisms protocols such as ITU-T Recommendation H.323/H.245. These mechanisms
associate the registered name of the encoding/payload format, along associate the registered name of the encoding/payload format, along
with any additional required parameters such as the RTP timestamp with any additional required parameters, such as the RTP timestamp
clock rate and number of channels, to a payload type number. This clock rate and number of channels, with a payload type number. This
association is effective only for the duration of the RTP session in association is effective only for the duration of the RTP session in
which the dynamic payload type binding is made. This association which the dynamic payload type binding is made. This association
applies only to the RTP session for which it is made, thus the applies only to the RTP session for which it is made, thus the
numbers can be re-used for different encodings in different sessions numbers can be re-used for different encodings in different sessions
so the number space limitation is avoided. so the number space limitation is avoided.
This profile reserves payload type numbers in the range 96-127 This profile reserves payload type numbers in the range 96-127
exclusively for dynamic assignment. Applications SHOULD first use exclusively for dynamic assignment. Applications SHOULD first use
values in this range for dynamic payload types. Those applications values in this range for dynamic payload types. Those applications
which need to define more than 32 dynamic payload types MAY bind which need to define more than 32 dynamic payload types MAY bind
skipping to change at page 8, line 17 skipping to change at page 7, line 43
payload types. payload types.
This specification establishes the policy that no additional static This specification establishes the policy that no additional static
payload types will be assigned beyond the ones defined in this payload types will be assigned beyond the ones defined in this
document. Establishing this policy avoids the problem of trying to document. Establishing this policy avoids the problem of trying to
create a set of criteria for accepting static assignments and create a set of criteria for accepting static assignments and
encourages the implementation and deployment of the dynamic payload encourages the implementation and deployment of the dynamic payload
type mechanisms. type mechanisms.
The final set of static payload type assignments is provided in The final set of static payload type assignments is provided in
Tables 4 and 5. In particular, IANA should note that types 1 and 2 Tables 4 and 5.
have been marked reserved and the set of "dyn" payload types included
has been updated. These changes are explained in Section 6 and
Appendix A.
4 Audio 4. Audio
4.1 Encoding-Independent Rules 4.1 Encoding-Independent Rules
Since the ability to suppress silence is one of the primary Since the ability to suppress silence is one of the primary
motivations for using packets to transmit voice, the RTP header motivations for using packets to transmit voice, the RTP header
carries both a sequence number and a timestamp to allow a receiver to carries both a sequence number and a timestamp to allow a receiver to
distinguish between lost packets and periods of time when no data was distinguish between lost packets and periods of time when no data was
transmitted. Discontiguous transmission (silence suppression) MAY be transmitted. Discontiguous transmission (silence suppression) MAY be
used with any audio payload format. Receivers MUST assume that used with any audio payload format. Receivers MUST assume that
senders may suppress silence unless this is restricted by signaling senders may suppress silence unless this is restricted by signaling
specified elsewhere. (Even if the transmitter does not suppress specified elsewhere. (Even if the transmitter does not suppress
silence, the receiver should be prepared to handle periods when no silence, the receiver should be prepared to handle periods when no
skipping to change at page 9, line 12 skipping to change at page 8, line 43
not been transmitted contiguously, SHOULD be distinguished by setting not been transmitted contiguously, SHOULD be distinguished by setting
the marker bit in the RTP data header to one. The marker bit in all the marker bit in the RTP data header to one. The marker bit in all
other packets is zero. The beginning of a talkspurt MAY be used to other packets is zero. The beginning of a talkspurt MAY be used to
adjust the playout delay to reflect changing network delays. adjust the playout delay to reflect changing network delays.
Applications without silence suppression MUST set the marker bit to Applications without silence suppression MUST set the marker bit to
zero. zero.
The RTP clock rate used for generating the RTP timestamp is The RTP clock rate used for generating the RTP timestamp is
independent of the number of channels and the encoding; it usually independent of the number of channels and the encoding; it usually
equals the number of sampling periods per second. For N-channel equals the number of sampling periods per second. For N-channel
encodings, each sampling period (say, 1/8000 of a second) generates N encodings, each sampling period (say, 1/8,000 of a second) generates
samples. (This terminology is standard, but somewhat confusing, as N samples. (This terminology is standard, but somewhat confusing, as
the total number of samples generated per second is then the sampling the total number of samples generated per second is then the sampling
rate times the channel count.) rate times the channel count.)
If multiple audio channels are used, channels are numbered left-to- If multiple audio channels are used, channels are numbered left-to-
right, starting at one. In RTP audio packets, information from right, starting at one. In RTP audio packets, information from
lower-numbered channels precedes that from higher-numbered channels. lower-numbered channels precedes that from higher-numbered channels.
For more than two channels, the convention followed by the AIFF-C For more than two channels, the convention followed by the AIFF-C
audio interchange format SHOULD be followed [3], using the following audio interchange format SHOULD be followed [3], using the following
notation, unless some other convention is specified for a particular notation, unless some other convention is specified for a particular
encoding or payload format: encoding or payload format:
l left l left
r right r right
c center c center
S surround S surround
F front F front
R rear R rear
channels description channel channels description channel
1 2 3 4 5 6 1 2 3 4 5 6
_________________________________________________ _________________________________________________
2 stereo l r 2 stereo l r
3 l r c 3 l r c
4 l c r S 4 l c r S
5 Fl Fr Fc Sl Sr 5 Fl Fr Fc Sl Sr
6 l lc c r rc S 6 l lc c r rc S
Note: RFC 1890 defined two conventions for the ordering of Note: RFC 1890 defined two conventions for the ordering of four
four audio channels. Since the ordering is indicated audio channels. Since the ordering is indicated implicitly by
implicitly by the number of channels, this was ambiguous. the number of channels, this was ambiguous. In this revision,
In this revision, the order described as "quadrophonic" has the order described as "quadrophonic" has been eliminated to
been eliminated to remove the ambiguity. This choice was remove the ambiguity. This choice was based on the observation
based on the observation that quadrophonic consumer audio that quadrophonic consumer audio format did not become popular
format did not become popular whereas surround-sound whereas surround-sound subsequently has.
subsequently has.
Samples for all channels belonging to a single sampling instant MUST Samples for all channels belonging to a single sampling instant MUST
be within the same packet. The interleaving of samples from be within the same packet. The interleaving of samples from
different channels depends on the encoding. General guidelines are different channels depends on the encoding. General guidelines are
given in Section 4.3 and 4.4. given in Section 4.3 and 4.4.
The sampling frequency SHOULD be drawn from the set: 8000, 11025, The sampling frequency SHOULD be drawn from the set: 8,000, 11,025,
16000, 22050, 24000, 32000, 44100 and 48000 Hz. (Older Apple 16,000, 22,050, 24,000, 32,000, 44,100 and 48,000 Hz. (Older Apple
Macintosh computers had a native sample rate of 22254.54 Hz, which Macintosh computers had a native sample rate of 22,254.54 Hz, which
can be converted to 22050 with acceptable quality by dropping 4 can be converted to 22,050 with acceptable quality by dropping 4
samples in a 20 ms frame.) However, most audio encodings are defined samples in a 20 ms frame.) However, most audio encodings are defined
for a more restricted set of sampling frequencies. Receivers SHOULD for a more restricted set of sampling frequencies. Receivers SHOULD
be prepared to accept multi-channel audio, but MAY choose to only be prepared to accept multi-channel audio, but MAY choose to only
play a single channel. play a single channel.
4.2 Operating Recommendations 4.2 Operating Recommendations
The following recommendations are default operating parameters. The following recommendations are default operating parameters.
Applications SHOULD be prepared to handle other values. The ranges Applications SHOULD be prepared to handle other values. The ranges
given are meant to give guidance to application writers, allowing a given are meant to give guidance to application writers, allowing a
set of applications conforming to these guidelines to interoperate set of applications conforming to these guidelines to interoperate
without additional negotiation. These guidelines are not intended to without additional negotiation. These guidelines are not intended to
restrict operating parameters for applications that can negotiate a restrict operating parameters for applications that can negotiate a
set of interoperable parameters, e.g., through a conference control set of interoperable parameters, e.g., through a conference control
protocol. protocol.
skipping to change at page 10, line 44 skipping to change at page 10, line 23
interval determines the minimum end-to-end delay; longer packets interval determines the minimum end-to-end delay; longer packets
introduce less header overhead but higher delay and make packet loss introduce less header overhead but higher delay and make packet loss
more noticeable. For non-interactive applications such as lectures more noticeable. For non-interactive applications such as lectures
or for links with severe bandwidth constraints, a higher or for links with severe bandwidth constraints, a higher
packetization delay MAY be used. A receiver SHOULD accept packets packetization delay MAY be used. A receiver SHOULD accept packets
representing between 0 and 200 ms of audio data. (For framed audio representing between 0 and 200 ms of audio data. (For framed audio
encodings, a receiver SHOULD accept packets with a number of frames encodings, a receiver SHOULD accept packets with a number of frames
equal to 200 ms divided by the frame duration, rounded up.) This equal to 200 ms divided by the frame duration, rounded up.) This
restriction allows reasonable buffer sizing for the receiver. restriction allows reasonable buffer sizing for the receiver.
4.3 Guidelines for Sample-Based Audio Encodings 4.3 Guidelines for Sample-Based Audio Encodings
In sample-based encodings, each audio sample is represented by a In sample-based encodings, each audio sample is represented by a
fixed number of bits. Within the compressed audio data, codes for fixed number of bits. Within the compressed audio data, codes for
individual samples may span octet boundaries. An RTP audio packet individual samples may span octet boundaries. An RTP audio packet
may contain any number of audio samples, subject to the constraint may contain any number of audio samples, subject to the constraint
that the number of bits per sample times the number of samples per that the number of bits per sample times the number of samples per
packet yields an integral octet count. Fractional encodings produce packet yields an integral octet count. Fractional encodings produce
less than one octet per sample. less than one octet per sample.
The duration of an audio packet is determined by the number of The duration of an audio packet is determined by the number of
samples in the packet. samples in the packet.
For sample-based encodings producing one or more octets per sample, For sample-based encodings producing one or more octets per sample,
samples from different channels sampled at the same sampling instant samples from different channels sampled at the same sampling instant
SHOULD be packed in consecutive octets. For example, for a two- SHOULD be packed in consecutive octets. For example, for a two-
channel encoding, the octet sequence is (left channel, first sample), channel encoding, the octet sequence is (left channel, first sample),
(right channel, first sample), (left channel, second sample), (right (right channel, first sample), (left channel, second sample), (right
skipping to change at page 11, line 25 skipping to change at page 11, line 5
SHOULD be transmitted in network byte order (i.e., most significant SHOULD be transmitted in network byte order (i.e., most significant
octet first). octet first).
The packing of sample-based encodings producing less than one octet The packing of sample-based encodings producing less than one octet
per sample is encoding-specific. per sample is encoding-specific.
The RTP timestamp reflects the instant at which the first sample in The RTP timestamp reflects the instant at which the first sample in
the packet was sampled, that is, the oldest information in the the packet was sampled, that is, the oldest information in the
packet. packet.
4.4 Guidelines for Frame-Based Audio Encodings 4.4 Guidelines for Frame-Based Audio Encodings
Frame-based encodings encode a fixed-length block of audio into Frame-based encodings encode a fixed-length block of audio into
another block of compressed data, typically also of fixed length. another block of compressed data, typically also of fixed length.
For frame-based encodings, the sender MAY choose to combine several For frame-based encodings, the sender MAY choose to combine several
such frames into a single RTP packet. The receiver can tell the such frames into a single RTP packet. The receiver can tell the
number of frames contained in an RTP packet, if all the frames have number of frames contained in an RTP packet, if all the frames have
the same length, by dividing the RTP payload length by the audio the same length, by dividing the RTP payload length by the audio
frame size which is defined as part of the encoding. This does not frame size which is defined as part of the encoding. This does not
work when carrying frames of different sizes unless the frame sizes work when carrying frames of different sizes unless the frame sizes
are relatively prime. If not, the frames MUST indicate their size. are relatively prime. If not, the frames MUST indicate their size.
skipping to change at page 12, line 9 skipping to change at page 12, line 7
RTP packets SHALL contain a whole number of frames, with frames RTP packets SHALL contain a whole number of frames, with frames
inserted according to age within a packet, so that the oldest frame inserted according to age within a packet, so that the oldest frame
(to be played first) occurs immediately after the RTP packet header. (to be played first) occurs immediately after the RTP packet header.
The RTP timestamp reflects the instant at which the first sample in The RTP timestamp reflects the instant at which the first sample in
the first frame was sampled, that is, the oldest information in the the first frame was sampled, that is, the oldest information in the
packet. packet.
4.5 Audio Encodings 4.5 Audio Encodings
name of sampling default name of sampling default
encoding sample/frame bits/sample rate ms/frame ms/packet encoding sample/frame bits/sample rate ms/frame ms/packet
__________________________________________________________________ __________________________________________________________________
DVI4 sample 4 var. 20 DVI4 sample 4 var. 20
G722 sample 8 16,000 20 G722 sample 8 16,000 20
G723 frame N/A 8,000 30 30 G723 frame N/A 8,000 30 30
G726-40 sample 5 8,000 20 G726-40 sample 5 8,000 20
G726-32 sample 4 8,000 20 G726-32 sample 4 8,000 20
G726-24 sample 3 8,000 20 G726-24 sample 3 8,000 20
G726-16 sample 2 8,000 20 G726-16 sample 2 8,000 20
G728 frame N/A 8,000 2.5 20 G728 frame N/A 8,000 2.5 20
G729 frame N/A 8,000 10 20 G729 frame N/A 8,000 10 20
G729D frame N/A 8,000 10 20 G729D frame N/A 8,000 10 20
G729E frame N/A 8,000 10 20 G729E frame N/A 8,000 10 20
GSM frame N/A 8,000 20 20 GSM frame N/A 8,000 20 20
GSM-EFR frame N/A 8,000 20 20 GSM-EFR frame N/A 8,000 20 20
L8 sample 8 var. 20 L8 sample 8 var. 20
L16 sample 16 var. 20 L16 sample 16 var. 20
LPC frame N/A 8,000 20 20 LPC frame N/A 8,000 20 20
MPA frame N/A var. var. MPA frame N/A var. var.
PCMA sample 8 var. 20 PCMA sample 8 var. 20
PCMU sample 8 var. 20 PCMU sample 8 var. 20
QCELP frame N/A 8,000 20 20 QCELP frame N/A 8,000 20 20
VDVI sample var. var. 20 VDVI sample var. var. 20
Table 1: Properties of Audio Encodings (N/A: not applicable; var.: Table 1: Properties of Audio Encodings (N/A: not applicable; var.:
variable) variable)
The characteristics of the audio encodings described in this document The characteristics of the audio encodings described in this document
are shown in Table 1; they are listed in order of their payload type are shown in Table 1; they are listed in order of their payload type
in Table 4. While most audio codecs are only specified for a fixed in Table 4. While most audio codecs are only specified for a fixed
sampling rate, some sample-based algorithms (indicated by an entry of sampling rate, some sample-based algorithms (indicated by an entry of
"var." in the sampling rate column of Table 1) may be used with "var." in the sampling rate column of Table 1) may be used with
different sampling rates, resulting in different coded bit rates. different sampling rates, resulting in different coded bit rates.
When used with a sampling rate other than that for which a static When used with a sampling rate other than that for which a static
payload type is defined, non-RTP means beyond the scope of this memo payload type is defined, non-RTP means beyond the scope of this memo
MUST be used to define a dynamic payload type and MUST indicate the MUST be used to define a dynamic payload type and MUST indicate the
selected RTP timestamp clock rate, which is usually the same as the selected RTP timestamp clock rate, which is usually the same as the
sampling rate for audio. sampling rate for audio.
4.5.1 DVI4 4.5.1 DVI4
DVI4 is specified, with pseudo-code, in [10] as the IMA ADPCM wave DVI4 uses an adaptive delta pulse code modulation (ADPCM) encoding
type. scheme that was specified by the Interactive Multimedia Association
(IMA) as the "IMA ADPCM wave type". However, the encoding defined
However, the encoding defined here as DVI4 differs in three respects here as DVI4 differs in three respects from the IMA specification:
from this recommendation:
o The RTP DVI4 header contains the predicted value rather than o The RTP DVI4 header contains the predicted value rather than the
the first sample value contained the IMA ADPCM block header. first sample value contained the IMA ADPCM block header.
o IMA ADPCM blocks contain an odd number of samples, since the o IMA ADPCM blocks contain an odd number of samples, since the first
first sample of a block is contained just in the header sample of a block is contained just in the header (uncompressed),
(uncompressed), followed by an even number of compressed followed by an even number of compressed samples. DVI4 has an
samples. DVI4 has an even number of compressed samples only, even number of compressed samples only, using the `predict' word
using the `predict' word from the header to decode the first from the header to decode the first sample.
sample.
o For DVI4, the 4-bit samples are packed with the first sample o For DVI4, the 4-bit samples are packed with the first sample in
in the four most significant bits and the second sample in the the four most significant bits and the second sample in the four
four least significant bits. In the IMA ADPCM codec, the least significant bits. In the IMA ADPCM codec, the samples are
samples are packed in the opposite order. packed in the opposite order.
Each packet contains a single DVI block. This profile only defines Each packet contains a single DVI block. This profile only defines
the 4-bit-per-sample version, while IMA also specifies a 3-bit-per- the 4-bit-per-sample version, while IMA also specified a 3-bit-per-
sample encoding. sample encoding.
The "header" word for each channel has the following structure: The "header" word for each channel has the following structure:
int16 predict; /* predicted value of first sample int16 predict; /* predicted value of first sample
from the previous block (L16 format) */ from the previous block (L16 format) */
u_int8 index; /* current index into stepsize table */ u_int8 index; /* current index into stepsize table */
u_int8 reserved; /* set to zero by sender, ignored by receiver */ u_int8 reserved; /* set to zero by sender, ignored by receiver */
Each octet following the header contains two 4-bit samples, thus the Each octet following the header contains two 4-bit samples, thus the
number of samples per packet MUST be even because there is no means number of samples per packet MUST be even because there is no means
to indicate a partially filled last octet. to indicate a partially filled last octet.
Packing of samples for multiple channels is for further study. Packing of samples for multiple channels is for further study.
The document IMA Recommended Practices for Enhancing Digital Audio The IMA ADPCM algorithm was described in the document IMA Recommended
Compatibility in Multimedia Systems (version 3.0) contains the Practices for Enhancing Digital Audio Compatibility in Multimedia
algorithm description. It is available from Systems (version 3.0). However, the Interactive Multimedia
Association ceased operations in 1997. Resources for an archived
Interactive Multimedia Association copy of that document and a software implementation of the RTP DVI4
48 Maryland Avenue, Suite 202 encoding are listed in Section 13.
Annapolis, MD 21401-8011
USA
phone: +1 410 626-1380
4.5.2 G722 4.5.2 G722
G722 is specified in ITU-T Recommendation G.722, "7 kHz audio-coding G722 is specified in ITU-T Recommendation G.722, "7 kHz audio-coding
within 64 kbit/s". The G.722 encoder produces a stream of octets, within 64 kbit/s". The G.722 encoder produces a stream of octets,
each of which SHALL be octet-aligned in an RTP packet. The first bit each of which SHALL be octet-aligned in an RTP packet. The first bit
transmitted in the G.722 octet, which is the most significant bit of transmitted in the G.722 octet, which is the most significant bit of
the higher sub-band sample, SHALL correspond to the most significant the higher sub-band sample, SHALL correspond to the most significant
bit of the octet in the RTP packet. bit of the octet in the RTP packet.
Even though the actual sampling rate for G.722 audio is 16000 Hz, the Even though the actual sampling rate for G.722 audio is 16,000 Hz,
RTP clock rate for the G722 payload format is 8000 Hz because that the RTP clock rate for the G722 payload format is 8,000 Hz because
value was erroneously assigned in RFC 1890 and must remain unchanged that value was erroneously assigned in RFC 1890 and must remain
for backward compatibility. The octet rate or sample-pair rate is unchanged for backward compatibility. The octet rate or sample-pair
8000 Hz. rate is 8,000 Hz.
4.5.3 G723 4.5.3 G723
G723 is specified in ITU Recommendation G.723.1, "Dual-rate speech G723 is specified in ITU Recommendation G.723.1, "Dual-rate speech
coder for multimedia communications transmitting at 5.3 and 6.3 coder for multimedia communications transmitting at 5.3 and 6.3
kbit/s". The G.723.1 5.3/6.3 kbit/s codec was defined by the ITU-T kbit/s". The G.723.1 5.3/6.3 kbit/s codec was defined by the ITU-T
as a mandatory codec for ITU-T H.324 GSTN videophone terminal as a mandatory codec for ITU-T H.324 GSTN videophone terminal
applications. The algorithm has a floating point specification in applications. The algorithm has a floating point specification in
Annex B to G.723.1, a silence compression algorithm in Annex A to Annex B to G.723.1, a silence compression algorithm in Annex A to
G.723.1 and an encoded signal bit-error sensitivity specification in G.723.1 and a scalable channel coding scheme for wireless
G.723.1 Annex C. applications in G.723.1 Annex C.
This Recommendation specifies a coded representation that can be used This Recommendation specifies a coded representation that can be used
for compressing the speech signal component of multi-media services for compressing the speech signal component of multi-media services
at a very low bit rate. Audio is encoded in 30 ms frames, with an at a very low bit rate. Audio is encoded in 30 ms frames, with an
additional delay of 7.5 ms due to look-ahead. A G.723.1 frame can be additional delay of 7.5 ms due to look-ahead. A G.723.1 frame can be
one of three sizes: 24 octets (6.3 kb/s frame), 20 octets (5.3 kb/s one of three sizes: 24 octets (6.3 kb/s frame), 20 octets (5.3 kb/s
frame), or 4 octets. These 4-octet frames are called SID frames frame), or 4 octets. These 4-octet frames are called SID frames
(Silence Insertion Descriptor) and are used to specify comfort noise (Silence Insertion Descriptor) and are used to specify comfort noise
parameters. There is no restriction on how 4, 20, and 24 octet parameters. There is no restriction on how 4, 20, and 24 octet
frames are intermixed. The least significant two bits of the first frames are intermixed. The least significant two bits of the first
octet in the frame determine the frame size and codec type: octet in the frame determine the frame size and codec type:
bits content octets/frame bits content octets/frame
00 high-rate speech (6.3 kb/s) 24 00 high-rate speech (6.3 kb/s) 24
01 low-rate speech (5.3 kb/s) 20 01 low-rate speech (5.3 kb/s) 20
10 SID frame 4 10 SID frame 4
11 reserved 11 reserved
It is possible to switch between the two rates at any 30 ms frame It is possible to switch between the two rates at any 30 ms frame
boundary. Both (5.3 kb/s and 6.3 kb/s) rates are a mandatory part of boundary. Both (5.3 kb/s and 6.3 kb/s) rates are a mandatory part of
the encoder and decoder. Receivers MUST accept both data rates and the encoder and decoder. Receivers MUST accept both data rates and
MUST accept SID frames unless restriction of these capabilities has MUST accept SID frames unless restriction of these capabilities has
been signaled. The MIME registration for G723 in RFC YYYY [7] been signaled. The MIME registration for G723 in RFC 3555 [7]
specifies parameters that MAY be used with MIME or SDP to restrict to specifies parameters that MAY be used with MIME or SDP to restrict to
a single data rate or to restrict the use of SID frames. This coder a single data rate or to restrict the use of SID frames. This coder
was optimized to represent speech with near-toll quality at the above was optimized to represent speech with near-toll quality at the above
rates using a limited amount of complexity. rates using a limited amount of complexity.
The packing of the encoded bit stream into octets and the The packing of the encoded bit stream into octets and the
transmission order of the octets is specified in Rec. G.723.1 and is transmission order of the octets is specified in Rec. G.723.1 and is
the same as that produced by the G.723 C code reference the same as that produced by the G.723 C code reference
implementation. For the 6.3 kb/s data rate, this packing is implementation. For the 6.3 kb/s data rate, this packing is
illustrated as follows, where the header (HDR) bits are always "0 0" illustrated as follows, where the header (HDR) bits are always "0 0"
as shown in Fig. 1 to indicate operation at 6.3 kb/s, and the Z bit as shown in Fig. 1 to indicate operation at 6.3 kb/s, and the Z bit
is always set to zero. The diagrams show the bit packing in "network is always set to zero. The diagrams show the bit packing in "network
byte order," also known as big-endian order. The bits of each 32-bit byte order", also known as big-endian order. The bits of each 32-bit
word are numbered 0 to 31, with the most significant bit on the left word are numbered 0 to 31, with the most significant bit on the left
and numbered 0. The octets (bytes) of each word are transmitted most and numbered 0. The octets (bytes) of each word are transmitted most
significant octet first. The bits of each data field are numbered in significant octet first. The bits of each data field are numbered in
the order of the bit stream representation of the encoding (least the order of the bit stream representation of the encoding (least
significant bit first). The vertical bars indicate the boundaries significant bit first). The vertical bars indicate the boundaries
between field fragments. between field fragments.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LPC |HDR| LPC | LPC | ACL0 |LPC| | LPC |HDR| LPC | LPC | ACL0 |LPC|
| | | | | | | | | | | | | |
|0 0 0 0 0 0|0 0|1 1 1 1 0 0 0 0|2 2 1 1 1 1 1 1|0 0 0 0 0 0|2 2| |0 0 0 0 0 0|0 0|1 1 1 1 0 0 0 0|2 2 1 1 1 1 1 1|0 0 0 0 0 0|2 2|
|5 4 3 2 1 0| |3 2 1 0 9 8 7 6|1 0 9 8 7 6 5 4|5 4 3 2 1 0|3 2| |5 4 3 2 1 0| |3 2 1 0 9 8 7 6|1 0 9 8 7 6 5 4|5 4 3 2 1 0|3 2|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACL2 |ACL|A| GAIN0 |ACL|ACL| GAIN0 | GAIN1 | | ACL2 |ACL|A| GAIN0 |ACL|ACL| GAIN0 | GAIN1 |
| | 1 |C| | 3 | 2 | | | | | 1 |C| | 3 | 2 | | |
|0 0 0 0 0|0 0|0|0 0 0 0|0 0|0 0|1 1 0 0 0 0 0 0|0 0 0 0 0 0 0 0| |0 0 0 0 0|0 0|0|0 0 0 0|0 0|0 0|1 1 0 0 0 0 0 0|0 0 0 0 0 0 0 0|
|4 3 2 1 0|1 0|6|3 2 1 0|1 0|6 5|1 0 9 8 7 6 5 4|7 6 5 4 3 2 1 0| |4 3 2 1 0|1 0|6|3 2 1 0|1 0|6 5|1 0 9 8 7 6 5 4|7 6 5 4 3 2 1 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GAIN2 | GAIN1 | GAIN2 | GAIN3 | GRID | GAIN3 | | GAIN2 | GAIN1 | GAIN2 | GAIN3 | GRID | GAIN3 |
| | | | | | | | | | | | | |
|0 0 0 0|1 1 0 0|1 1 0 0 0 0 0 0|0 0 0 0 0 0 0 0|0 0 0 0|1 1 0 0| |0 0 0 0|1 1 0 0|1 1 0 0 0 0 0 0|0 0 0 0 0 0 0 0|0 0 0 0|1 1 0 0|
|3 2 1 0|1 0 9 8|1 0 9 8 7 6 5 4|7 6 5 4 3 2 1 0|3 2 1 0|1 0 9 8| |3 2 1 0|1 0 9 8|1 0 9 8 7 6 5 4|7 6 5 4 3 2 1 0|3 2 1 0|1 0 9 8|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSBPOS |Z|POS| MSBPOS | POS0 |POS| POS0 | | MSBPOS |Z|POS| MSBPOS | POS0 |POS| POS0 |
| | | 0 | | | 1 | | | | | 0 | | | 1 | |
|0 0 0 0 0 0 0|0|0 0|1 1 1 0 0 0|0 0 0 0 0 0 0 0|0 0|1 1 1 1 1 1| |0 0 0 0 0 0 0|0|0 0|1 1 1 0 0 0|0 0 0 0 0 0 0 0|0 0|1 1 1 1 1 1|
|6 5 4 3 2 1 0| |1 0|2 1 0 9 8 7|9 8 7 6 5 4 3 2|1 0|5 4 3 2 1 0| |6 5 4 3 2 1 0| |1 0|2 1 0 9 8 7|9 8 7 6 5 4 3 2|1 0|5 4 3 2 1 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| POS1 | POS2 | POS1 | POS2 | POS3 | POS2 | | POS1 | POS2 | POS1 | POS2 | POS3 | POS2 |
| | | | | | | | | | | | | |
|0 0 0 0 0 0 0 0|0 0 0 0|1 1 1 1|1 1 0 0 0 0 0 0|0 0 0 0|1 1 1 1| |0 0 0 0 0 0 0 0|0 0 0 0|1 1 1 1|1 1 0 0 0 0 0 0|0 0 0 0|1 1 1 1|
|9 8 7 6 5 4 3 2|3 2 1 0|3 2 1 0|1 0 9 8 7 6 5 4|3 2 1 0|5 4 3 2| |9 8 7 6 5 4 3 2|3 2 1 0|3 2 1 0|1 0 9 8 7 6 5 4|3 2 1 0|5 4 3 2|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| POS3 | PSIG0 |POS|PSIG2| PSIG1 | PSIG3 |PSIG2| | POS3 | PSIG0 |POS|PSIG2| PSIG1 | PSIG3 |PSIG2|
| | | 3 | | | | | | | | 3 | | | | |
|1 1 0 0 0 0 0 0|0 0 0 0 0 0|1 1|0 0 0|0 0 0 0 0|0 0 0 0 0|0 0 0| |1 1 0 0 0 0 0 0|0 0 0 0 0 0|1 1|0 0 0|0 0 0 0 0|0 0 0 0 0|0 0 0|
|1 0 9 8 7 6 5 4|5 4 3 2 1 0|3 2|2 1 0|4 3 2 1 0|4 3 2 1 0|5 4 3| |1 0 9 8 7 6 5 4|5 4 3 2 1 0|3 2|2 1 0|4 3 2 1 0|4 3 2 1 0|5 4 3|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: G.723 (6.3 kb/s) bit packing Figure 1: G.723 (6.3 kb/s) bit packing
For the 5.3 kb/s data rate, the header (HDR) bits are always "0 1", For the 5.3 kb/s data rate, the header (HDR) bits are always "0 1",
as shown in Fig. 2, to indicate operation at 5.3 kb/s. as shown in Fig. 2, to indicate operation at 5.3 kb/s.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LPC |HDR| LPC | LPC | ACL0 |LPC| | LPC |HDR| LPC | LPC | ACL0 |LPC|
| | | | | | | | | | | | | |
|0 0 0 0 0 0|0 1|1 1 1 1 0 0 0 0|2 2 1 1 1 1 1 1|0 0 0 0 0 0|2 2| |0 0 0 0 0 0|0 1|1 1 1 1 0 0 0 0|2 2 1 1 1 1 1 1|0 0 0 0 0 0|2 2|
|5 4 3 2 1 0| |3 2 1 0 9 8 7 6|1 0 9 8 7 6 5 4|5 4 3 2 1 0|3 2| |5 4 3 2 1 0| |3 2 1 0 9 8 7 6|1 0 9 8 7 6 5 4|5 4 3 2 1 0|3 2|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACL2 |ACL|A| GAIN0 |ACL|ACL| GAIN0 | GAIN1 | | ACL2 |ACL|A| GAIN0 |ACL|ACL| GAIN0 | GAIN1 |
| | 1 |C| | 3 | 2 | | | | | 1 |C| | 3 | 2 | | |
|0 0 0 0 0|0 0|0|0 0 0 0|0 0|0 0|1 1 0 0 0 0 0 0|0 0 0 0 0 0 0 0| |0 0 0 0 0|0 0|0|0 0 0 0|0 0|0 0|1 1 0 0 0 0 0 0|0 0 0 0 0 0 0 0|
|4 3 2 1 0|1 0|6|3 2 1 0|1 0|6 5|1 0 9 8 7 6 5 4|7 6 5 4 3 2 1 0| |4 3 2 1 0|1 0|6|3 2 1 0|1 0|6 5|1 0 9 8 7 6 5 4|7 6 5 4 3 2 1 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GAIN2 | GAIN1 | GAIN2 | GAIN3 | GRID | GAIN3 | | GAIN2 | GAIN1 | GAIN2 | GAIN3 | GRID | GAIN3 |
| | | | | | | | | | | | | |
|0 0 0 0|1 1 0 0|1 1 0 0 0 0 0 0|0 0 0 0 0 0 0 0|0 0 0 0|1 1 0 0| |0 0 0 0|1 1 0 0|1 1 0 0 0 0 0 0|0 0 0 0 0 0 0 0|0 0 0 0|1 1 0 0|
|3 2 1 0|1 0 9 8|1 0 9 8 7 6 5 4|7 6 5 4 3 2 1 0|4 3 2 1|1 0 9 8| |3 2 1 0|1 0 9 8|1 0 9 8 7 6 5 4|7 6 5 4 3 2 1 0|4 3 2 1|1 0 9 8|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| POS0 | POS1 | POS0 | POS1 | POS2 | | POS0 | POS1 | POS0 | POS1 | POS2 |
| | | | | | | | | | | |
|0 0 0 0 0 0 0 0|0 0 0 0|1 1 0 0|1 1 0 0 0 0 0 0|0 0 0 0 0 0 0 0| |0 0 0 0 0 0 0 0|0 0 0 0|1 1 0 0|1 1 0 0 0 0 0 0|0 0 0 0 0 0 0 0|
|7 6 5 4 3 2 1 0|3 2 1 0|1 0 9 8|1 0 9 8 7 6 5 4|7 6 5 4 3 2 1 0| |7 6 5 4 3 2 1 0|3 2 1 0|1 0 9 8|1 0 9 8 7 6 5 4|7 6 5 4 3 2 1 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| POS3 | POS2 | POS3 | PSIG1 | PSIG0 | PSIG3 | PSIG2 | | POS3 | POS2 | POS3 | PSIG1 | PSIG0 | PSIG3 | PSIG2 |
| | | | | | | | | | | | | | | |
|0 0 0 0|1 1 0 0|1 1 0 0 0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0| |0 0 0 0|1 1 0 0|1 1 0 0 0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0|
|3 2 1 0|1 0 9 8|1 0 9 8 7 6 5 4|3 2 1 0|3 2 1 0|3 2 1 0|3 2 1 0| |3 2 1 0|1 0 9 8|1 0 9 8 7 6 5 4|3 2 1 0|3 2 1 0|3 2 1 0|3 2 1 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: G.723 (5.3 kb/s) bit packing Figure 2: G.723 (5.3 kb/s) bit packing
The packing of G.723.1 SID (silence) frames, which are indicated by The packing of G.723.1 SID (silence) frames, which are indicated by
the header (HDR) bits having the pattern "1 0", is depicted in the header (HDR) bits having the pattern "1 0", is depicted in Fig.
Fig. 3. 3.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LPC |HDR| LPC | LPC | GAIN |LPC| | LPC |HDR| LPC | LPC | GAIN |LPC|
| | | | | | | | | | | | | |
|0 0 0 0 0 0|1 0|1 1 1 1 0 0 0 0|2 2 1 1 1 1 1 1|0 0 0 0 0 0|2 2| |0 0 0 0 0 0|1 0|1 1 1 1 0 0 0 0|2 2 1 1 1 1 1 1|0 0 0 0 0 0|2 2|
|5 4 3 2 1 0| |3 2 1 0 9 8 7 6|1 0 9 8 7 6 5 4|5 4 3 2 1 0|3 2| |5 4 3 2 1 0| |3 2 1 0 9 8 7 6|1 0 9 8 7 6 5 4|5 4 3 2 1 0|3 2|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: G.723 SID mode bit packing Figure 3: G.723 SID mode bit packing
4.5.4 G726-40, G726-32, G726-24, and G726-16 4.5.4 G726-40, G726-32, G726-24, and G726-16
ITU-T Recommendation G.726 describes, among others, the algorithm ITU-T Recommendation G.726 describes, among others, the algorithm
recommended for conversion of a single 64 kbit/s A-law or mu-law PCM recommended for conversion of a single 64 kbit/s A-law or mu-law PCM
channel encoded at 8000 samples/sec to and from a 40, 32, 24, or 16 channel encoded at 8,000 samples/sec to and from a 40, 32, 24, or 16
kbit/s channel. The conversion is applied to the PCM stream using an kbit/s channel. The conversion is applied to the PCM stream using an
Adaptive Differential Pulse Code Modulation (ADPCM) transcoding Adaptive Differential Pulse Code Modulation (ADPCM) transcoding
technique. The ADPCM representation consists of a series of technique. The ADPCM representation consists of a series of
codewords with a one-to-one correspondence to the samples in the PCM codewords with a one-to-one correspondence to the samples in the PCM
stream. The G726 data rates of 40, 32, 24, and 16 kbit/s have stream. The G726 data rates of 40, 32, 24, and 16 kbit/s have
codewords of 5, 4, 3, and 2 bits respectively. codewords of 5, 4, 3, and 2 bits, respectively.
The 16 and 24 kbit/s encodings do not provide toll quality speech. The 16 and 24 kbit/s encodings do not provide toll quality speech.
They are designed for used in overloaded Digital Circuit They are designed for used in overloaded Digital Circuit
Multiplication Equipment (DCME). ITU-T G.726 recommends that the 16 Multiplication Equipment (DCME). ITU-T G.726 recommends that the 16
and 24 kbit/s encodings should be alternated with higher data rate and 24 kbit/s encodings should be alternated with higher data rate
encodings to provide an average sample size of between 3.5 and 3.7 encodings to provide an average sample size of between 3.5 and 3.7
bits per sample. bits per sample.
The encodings of G.726 are here denoted as G726-40, G726-32, G726-24, The encodings of G.726 are here denoted as G726-40, G726-32, G726-24,
and G726-16. Prior to 1990, G721 described the 32 kbit/s ADPCM and G726-16. Prior to 1990, G721 described the 32 kbit/s ADPCM
encoding, and G723 described the 40, 32, and 16 kbit/s encodings. encoding, and G723 described the 40, 32, and 16 kbit/s encodings.
Thus, G726-32 designates the same algorithm as G721 in RFC 1890. Thus, G726-32 designates the same algorithm as G721 in RFC 1890.
A stream of G726 codewords contains no information on the encoding A stream of G726 codewords contains no information on the encoding
being used, therefore transitions between G726 encoding types is not being used, therefore transitions between G726 encoding types are not
permitted within a sequence of packed codewords. Applications MUST permitted within a sequence of packed codewords. Applications MUST
determine the encoding type of packed codewords from the RTP payload determine the encoding type of packed codewords from the RTP payload
identifier. identifier.
No payload-specific header information SHALL be included as part of No payload-specific header information SHALL be included as part of
the audio data. A stream of G726 codewords MUST be packed into the audio data. A stream of G726 codewords MUST be packed into
octets as follows: the first codeword is placed into the first octet octets as follows: the first codeword is placed into the first octet
such that the least significant bit of the codeword aligns with the such that the least significant bit of the codeword aligns with the
least significant bit in the octet, the second codeword is then least significant bit in the octet, the second codeword is then
packed so that its least significant bit coincides with the least packed so that its least significant bit coincides with the least
significant unoccupied bit in the octet. When a complete codeword significant unoccupied bit in the octet. When a complete codeword
cannot be placed into an octet, the bits overlapping the octet cannot be placed into an octet, the bits overlapping the octet
boundary are placed into the least significant bits of the next boundary are placed into the least significant bits of the next
octet. Packing MUST end with a completely packed final octet. The octet. Packing MUST end with a completely packed final octet. The
number of codewords packed will therefore be a multiple of 8, 2, 8, number of codewords packed will therefore be a multiple of 8, 2, 8,
and 4 for G726-40, G726-32, G726-24, and G726-16 respectively. An and 4 for G726-40, G726-32, G726-24, and G726-16, respectively. An
example of the packing scheme for G726-32 codewords is as shown, example of the packing scheme for G726-32 codewords is as shown,
where bit 7 is the least significant bit of the first octet, and bit where bit 7 is the least significant bit of the first octet, and bit
A3 is the least significant bit of the first codeword: A3 is the least significant bit of the first codeword:
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
|B B B B|A A A A|D D D D|C C C C| ... |B B B B|A A A A|D D D D|C C C C| ...
|0 1 2 3|0 1 2 3|0 1 2 3|0 1 2 3| |0 1 2 3|0 1 2 3|0 1 2 3|0 1 2 3|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
An example of the packing scheme for G726-24 codewords follows, where An example of the packing scheme for G726-24 codewords follows, where
again bit 7 is the least significant bit of the first octet, and bit again bit 7 is the least significant bit of the first octet, and bit
A2 is the least significant bit of the first codeword: A2 is the least significant bit of the first codeword:
0 1 2 0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
|C C|B B B|A A A|F|E E E|D D D|C|H H H|G G G|F F| ... |C C|B B B|A A A|F|E E E|D D D|C|H H H|G G G|F F| ...
|1 2|0 1 2|0 1 2|2|0 1 2|0 1 2|0|0 1 2|0 1 2|0 1| |1 2|0 1 2|0 1 2|2|0 1 2|0 1 2|0|0 1 2|0 1 2|0 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Note that the "little-endian" direction in which samples are packed Note that the "little-endian" direction in which samples are packed
into octets in the G726-16, -24, -32 and -48 payload formats into octets in the G726-16, -24, -32 and -40 payload formats
specified here is consistent with ITU-T Recommendation X.420, but is specified here is consistent with ITU-T Recommendation X.420, but is
the opposite of what is specified in ITU-T Recommendation I.366.2 the opposite of what is specified in ITU-T Recommendation I.366.2
Annex E for ATM AAL2 transport. A second set of RTP payload formats Annex E for ATM AAL2 transport. A second set of RTP payload formats
matching the packetization of I.366.2 Annex E and identified by MIME matching the packetization of I.366.2 Annex E and identified by MIME
subtypes AAL2-G726-16, -24, -32 and -48 will be specified in a subtypes AAL2-G726-16, -24, -32 and -40 will be specified in a
separate document. separate document.
4.5.5 G728 4.5.5 G728
G728 is specified in ITU-T Recommendation G.728, "Coding of speech at G728 is specified in ITU-T Recommendation G.728, "Coding of speech at
16 kbit/s using low-delay code excited linear prediction". 16 kbit/s using low-delay code excited linear prediction".
A G.278 encoder translates 5 consecutive audio samples into a 10-bit A G.278 encoder translates 5 consecutive audio samples into a 10-bit
codebook index, resulting in a bit rate of 16 kb/s for audio sampled codebook index, resulting in a bit rate of 16 kb/s for audio sampled
at 8,000 samples per second. The group of five consecutive samples at 8,000 samples per second. The group of five consecutive samples
is called a vector. Four consecutive vectors, labeled V1 to V4 is called a vector. Four consecutive vectors, labeled V1 to V4
(where V1 is to be played first by the receiver), build one G.728 (where V1 is to be played first by the receiver), build one G.728
frame. The four vectors of 40 bits are packed into 5 octets, labeled frame. The four vectors of 40 bits are packed into 5 octets, labeled
B1 through B5. B1 SHALL be placed first in the RTP packet. B1 through B5. B1 SHALL be placed first in the RTP packet.
Referring to the figure below, the principle for bit order is Referring to the figure below, the principle for bit order is
"maintenance of bit significance". Bits from an older vector are "maintenance of bit significance". Bits from an older vector are
more significant than bits from newer vectors. The MSB of the frame more significant than bits from newer vectors. The MSB of the frame
goes to the MSB of B1 and the LSB of the frame goes to LSB of B5. goes to the MSB of B1 and the LSB of the frame goes to LSB of B5.
1 2 3 3 1 2 3 3
0 0 0 0 9 0 0 0 0 9
++++++++++++++++++++++++++++++++++++++++ ++++++++++++++++++++++++++++++++++++++++
<---V1---><---V2---><---V3---><---V4---> vectors <---V1---><---V2---><---V3---><---V4---> vectors
<--B1--><--B2--><--B3--><--B4--><--B5--> octets <--B1--><--B2--><--B3--><--B4--><--B5--> octets
<------------- frame 1 ----------------> <------------- frame 1 ---------------->
In particular, B1 contains the eight most significant bits of V1, In particular, B1 contains the eight most significant bits of V1,
with the MSB of V1 being the MSB of B1. B2 contains the two least with the MSB of V1 being the MSB of B1. B2 contains the two least
significant bits of V1, the more significant of the two in its MSB, significant bits of V1, the more significant of the two in its MSB,
and the six most significant bits of V2. B1 SHALL be placed first in and the six most significant bits of V2. B1 SHALL be placed first in
the RTP packet and B5 last. the RTP packet and B5 last.
4.5.6 G729 4.5.6 G729
G729 is specified in ITU-T Recommendation G.729, "Coding of speech at G729 is specified in ITU-T Recommendation G.729, "Coding of speech at
skipping to change at page 20, line 40 skipping to change at page 20, line 32
prediction (CS-ACELP)". A reduced-complexity version of the G.729 prediction (CS-ACELP)". A reduced-complexity version of the G.729
algorithm is specified in Annex A to Rec. G.729. The speech coding algorithm is specified in Annex A to Rec. G.729. The speech coding
algorithms in the main body of G.729 and in G.729 Annex A are fully algorithms in the main body of G.729 and in G.729 Annex A are fully
interoperable with each other, so there is no need to further interoperable with each other, so there is no need to further
distinguish between them. An implementation that signals or accepts distinguish between them. An implementation that signals or accepts
use of G729 payload format may implement either G.729 or G.729A use of G729 payload format may implement either G.729 or G.729A
unless restricted by additional signaling specified elsewhere related unless restricted by additional signaling specified elsewhere related
specifically to the encoding rather than the payload format. The specifically to the encoding rather than the payload format. The
G.729 and G.729 Annex A codecs were optimized to represent speech G.729 and G.729 Annex A codecs were optimized to represent speech
with high quality, where G.729 Annex A trades some speech quality for with high quality, where G.729 Annex A trades some speech quality for
an approximate 50% complexity reduction [11]. See the next Section an approximate 50% complexity reduction [10]. See the next Section
(4.5.7) for other data rates added in later G.729 Annexes. For all (4.5.7) for other data rates added in later G.729 Annexes. For all
data rates, the sampling frequency (and RTP timestamp clock rate) is data rates, the sampling frequency (and RTP timestamp clock rate) is
8000 Hz. 8,000 Hz.
A voice activity detector (VAD) and comfort noise generator (CNG) A voice activity detector (VAD) and comfort noise generator (CNG)
algorithm in Annex B of G.729 is RECOMMENDED for digital simultaneous algorithm in Annex B of G.729 is RECOMMENDED for digital simultaneous
voice and data applications and can be used in conjunction with G.729 voice and data applications and can be used in conjunction with G.729
or G.729 Annex A. A G.729 or G.729 Annex A frame contains 10 octets, or G.729 Annex A. A G.729 or G.729 Annex A frame contains 10 octets,
while the G.729 Annex B comfort noise frame occupies 2 octets. while the G.729 Annex B comfort noise frame occupies 2 octets.
Receivers MUST accept comfort noise frames if restriction of their Receivers MUST accept comfort noise frames if restriction of their
use has not been signaled. The MIME registration for G729 in use has not been signaled. The MIME registration for G729 in RFC
RFC YYYY [7] specifies a parameter that MAY be used with MIME or SDP 3555 [7] specifies a parameter that MAY be used with MIME or SDP to
to restrict the use of comfort noise frames. restrict the use of comfort noise frames.
A G729 RTP packet may consist of zero or more G.729 or G.729 Annex A A G729 RTP packet may consist of zero or more G.729 or G.729 Annex A
frames, followed by zero or one G.729 Annex B frames. The presence frames, followed by zero or one G.729 Annex B frames. The presence
of a comfort noise frame can be deduced from the length of the RTP of a comfort noise frame can be deduced from the length of the RTP
payload. The default packetization interval is 20 ms (two frames), payload. The default packetization interval is 20 ms (two frames),
but in some situations it may be desirable to send 10 ms packets. An but in some situations it may be desirable to send 10 ms packets. An
example would be a transition from speech to comfort noise in the example would be a transition from speech to comfort noise in the
first 10 ms of the packet. For some applications, a longer first 10 ms of the packet. For some applications, a longer
packetization interval may be required to reduce the packet rate. packetization interval may be required to reduce the packet rate.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| L1 | L2 | L3 | P1 |P| C1 |
|0| | | | |0| |
| |0 1 2 3 4 5 6|0 1 2 3 4|0 1 2 3 4|0 1 2 3 4 5 6 7| |0 1 2 3 4|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C1 | S1 | GA1 | GB1 | P2 | C2 |
| 1 1 1| | | | | |
|5 6 7 8 9 0 1 2|0 1 2 3|0 1 2|0 1 2 3|0 1 2 3 4|0 1 2 3 4 5 6 7|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C2 | S2 | GA2 | GB2 |
| 1 1 1| | | |
|8 9 0 1 2|0 1 2 3|0 1 2|0 1 2 3|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: G.729 and G.729A bit packing
The transmitted parameters of a G.729/G.729A 10-ms frame, consisting The transmitted parameters of a G.729/G.729A 10-ms frame, consisting
of 80 bits, are defined in Recommendation G.729, Table 8/G.729. The of 80 bits, are defined in Recommendation G.729, Table 8/G.729. The
mapping of the these parameters is given below in Fig. 4. The mapping of the these parameters is given below in Fig. 4. The
diagrams show the bit packing in "network byte order," also known as diagrams show the bit packing in "network byte order", also known as
big-endian order. The bits of each 32-bit word are numbered 0 to 31, big-endian order. The bits of each 32-bit word are numbered 0 to 31,
with the most significant bit on the left and numbered 0. The octets with the most significant bit on the left and numbered 0. The octets
(bytes) of each word are transmitted most significant octet first. (bytes) of each word are transmitted most significant octet first.
The bits of each data field are numbered in the order as produced by The bits of each data field are numbered in the order as produced by
the G.729 C code reference implementation. the G.729 C code reference implementation.
0 1 2 3 The packing of the G.729 Annex B comfort noise frame is shown in Fig.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 5.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| L1 | L2 | L3 | P1 |P| C1 |
|0| | | | |0| |
| |0 1 2 3 4 5 6|0 1 2 3 4|0 1 2 3 4|0 1 2 3 4 5 6 7| |0 1 2 3 4|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C1 | S1 | GA1 | GB1 | P2 | C2 |
| 1 1 1| | | | | |
|5 6 7 8 9 0 1 2|0 1 2 3|0 1 2|0 1 2 3|0 1 2 3 4|0 1 2 3 4 5 6 7|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C2 | S2 | GA2 | GB2 |
| 1 1 1| | | |
|8 9 0 1 2|0 1 2 3|0 1 2|0 1 2 3|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: G.729 and G.729A bit packing
The packing of the G.729 Annex B comfort noise frame is shown in
Fig. 5.
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| LSF1 | LSF2 | GAIN |R| |L| LSF1 | LSF2 | GAIN |R|
|S| | | |E| |S| | | |E|
|F| | | |S| |F| | | |S|
|0|0 1 2 3 4|0 1 2 3|0 1 2 3 4|V| RESV = Reserved (zero) |0|0 1 2 3 4|0 1 2 3|0 1 2 3 4|V| RESV = Reserved (zero)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: G.729 Annex B bit packing Figure 5: G.729 Annex B bit packing
4.5.7 G729D and G729E 4.5.7 G729D and G729E
Annexes D and E to ITU-T Recommendation G.729 provide additional data Annexes D and E to ITU-T Recommendation G.729 provide additional data
rates. Because the data rate is not signaled in the bitstream, the rates. Because the data rate is not signaled in the bitstream, the
different data rates are given distinct RTP encoding names which are different data rates are given distinct RTP encoding names which are
mapped to distinct payload type numbers. G729D indicates a 6.4 mapped to distinct payload type numbers. G729D indicates a 6.4
kbit/s coding mode (G.729 Annex D, for momentary reduction in channel kbit/s coding mode (G.729 Annex D, for momentary reduction in channel
capacity), while G729E indicates an 11.8 kbit/s mode (G.729 Annex E, capacity), while G729E indicates an 11.8 kbit/s mode (G.729 Annex E,
for improved performance with a wide range of narrow-band input for improved performance with a wide range of narrow-band input
signals, e.g. music and background noise). Annex E has two operating signals, e.g., music and background noise). Annex E has two
modes, backward adaptive and forward adaptive, which are signaled by operating modes, backward adaptive and forward adaptive, which are
the first two bits in each frame (the most significant two bits of signaled by the first two bits in each frame (the most significant
the first octet). two bits of the first octet).
The voice activity detector (VAD) and comfort noise generator (CNG) The voice activity detector (VAD) and comfort noise generator (CNG)
algorithm specified in Annex B of G.729 may be used with Annex D and algorithm specified in Annex B of G.729 may be used with Annex D and
Annex E frames in addition to G.729 and G.729 Annex A frames. The Annex E frames in addition to G.729 and G.729 Annex A frames. The
algorithm details for the operation of Annexes D and E with the Annex algorithm details for the operation of Annexes D and E with the Annex
B CNG are specified in G.729 Annexes F and G. Note that Annexes F B CNG are specified in G.729 Annexes F and G. Note that Annexes F
and G do not introduce any new encodings. Receivers MUST accept and G do not introduce any new encodings. Receivers MUST accept
comfort noise frames if restriction of their use has not been comfort noise frames if restriction of their use has not been
signaled. The MIME registrations for G729D and G729E in RFC YYYY [7] signaled. The MIME registrations for G729D and G729E in RFC 3555 [7]
specify a parameter that MAY be used with MIME or SDP to restrict the specify a parameter that MAY be used with MIME or SDP to restrict the
use of comfort noise frames. use of comfort noise frames.
For G729D, an RTP packet may consist of zero or more G.729 Annex D For G729D, an RTP packet may consist of zero or more G.729 Annex D
frames, followed by zero or one G.729 Annex B frame. Similarly, for frames, followed by zero or one G.729 Annex B frame. Similarly, for
G729E, an RTP packet may consist of zero or more G.729 Annex E G729E, an RTP packet may consist of zero or more G.729 Annex E
frames, followed by zero or one G.729 Annex B frame. The presence of frames, followed by zero or one G.729 Annex B frame. The presence of
a comfort noise frame can be deduced from the length of the RTP a comfort noise frame can be deduced from the length of the RTP
payload. payload.
A single RTP packet must contain frames of only one data rate, A single RTP packet must contain frames of only one data rate,
optionally followed by one comfort noise frame. The data rate may be optionally followed by one comfort noise frame. The data rate may be
changed from packet to packet by changing the payload type number. changed from packet to packet by changing the payload type number.
G.729 Annexes D, E and H describe what the encoding and decoding G.729 Annexes D, E and H describe what the encoding and decoding
algorithms must do to accommodate a change in data rate. algorithms must do to accommodate a change in data rate.
For G729D, the bits of a G.729 Annex D frame are formatted as shown For G729D, the bits of a G.729 Annex D frame are formatted as shown
below in Fig. 6 (cf. Table D.1/G.729). The frame length is 64 bits. below in Fig. 6 (cf. Table D.1/G.729). The frame length is 64 bits.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| L1 | L2 | L3 | P1 | C1 | |L| L1 | L2 | L3 | P1 | C1 |
|0| | | | | | |0| | | | | |
| |0 1 2 3 4 5 6|0 1 2 3 4|0 1 2 3 4|0 1 2 3 4 5 6 7|0 1 2 3 4 5| | |0 1 2 3 4 5 6|0 1 2 3 4|0 1 2 3 4|0 1 2 3 4 5 6 7|0 1 2 3 4 5|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C1 |S1 | GA1 | GB1 | P2 | C2 |S2 | GA2 | GB2 | | C1 |S1 | GA1 | GB1 | P2 | C2 |S2 | GA2 | GB2 |
| | | | | | | | | | | | | | | | | | | |
|6 7 8|0 1|0 1 2|0 1 2|0 1 2 3|0 1 2 3 4 5 6 7 8|0 1|0 1 2|0 1 2| |6 7 8|0 1|0 1 2|0 1 2|0 1 2 3|0 1 2 3 4 5 6 7 8|0 1|0 1 2|0 1 2|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: G.729 Annex D bit packing Figure 6: G.729 Annex D bit packing
The net bit rate for the G.729 Annex E algorithm is 11.8 kbit/s and a The net bit rate for the G.729 Annex E algorithm is 11.8 kbit/s and a
total of 118 bits are used. Two bits are appended as "don't care" total of 118 bits are used. Two bits are appended as "don't care"
bits to complete an integer number of octets for the frame. For bits to complete an integer number of octets for the frame. For
G729E, the bits of a data frame are formatted as shown in the next G729E, the bits of a data frame are formatted as shown in the next
two diagrams (cf. Table E.1/G.729). The fields for the G729E forward two diagrams (cf. Table E.1/G.729). The fields for the G729E forward
adaptive mode are packed as shown in Fig. 7. adaptive mode are packed as shown in Fig. 7.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0|L| L1 | L2 | L3 | P1 |P| C0_1| |0 0|L| L1 | L2 | L3 | P1 |P| C0_1|
| |0| | | | |0| | | |0| | | | |0| |
| | |0 1 2 3 4 5 6|0 1 2 3 4|0 1 2 3 4|0 1 2 3 4 5 6 7| |0 1 2| | | |0 1 2 3 4 5 6|0 1 2 3 4|0 1 2 3 4|0 1 2 3 4 5 6 7| |0 1 2|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | C1_1 | C2_1 | C3_1 | C4_1 | | | C1_1 | C2_1 | C3_1 | C4_1 |
| | | | | | | | | | | |
|3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5 6| |3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GA1 | GB1 | P2 | C0_2 | C1_2 | C2_2 | | GA1 | GB1 | P2 | C0_2 | C1_2 | C2_2 |
| | | | | | | | | | | | | |
|0 1 2|0 1 2 3|0 1 2 3 4|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5| |0 1 2|0 1 2 3|0 1 2 3 4|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | C3_2 | C4_2 | GA2 | GB2 |DC | | | C3_2 | C4_2 | GA2 | GB2 |DC |
| | | | | | | | | | | | | |
|6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2|0 1 2 3|0 1| |6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2|0 1 2 3|0 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: G.729 Annex E (forward adaptive mode) bit packing Figure 7: G.729 Annex E (forward adaptive mode) bit packing
The fields for the G729E backward adaptive mode are packed as shown The fields for the G729E backward adaptive mode are packed as shown
in Fig. 8. in Fig. 8.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1| P1 |P| C0_1 | C1_1 | |1 1| P1 |P| C0_1 | C1_1 |
| | |0| 1 1 1| | | | |0| 1 1 1| |
| |0 1 2 3 4 5 6 7|0|0 1 2 3 4 5 6 7 8 9 0 1 2|0 1 2 3 4 5 6 7| | |0 1 2 3 4 5 6 7|0|0 1 2 3 4 5 6 7 8 9 0 1 2|0 1 2 3 4 5 6 7|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | C2_1 | C3_1 | C4_1 |GA1 | GB1 |P2 | | | C2_1 | C3_1 | C4_1 |GA1 | GB1 |P2 |
| | | | | | | | | | | | | | | |
|8 9|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2|0 1 2 3|0 1| |8 9|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2|0 1 2 3|0 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | C0_2 | C1_2 | C2_2 | | | C0_2 | C1_2 | C2_2 |
| | 1 1 1| | | | | 1 1 1| | |
|2 3 4|0 1 2 3 4 5 6 7 8 9 0 1 2|0 1 2 3 4 5 6 7 8 9|0 1 2 3 4 5| |2 3 4|0 1 2 3 4 5 6 7 8 9 0 1 2|0 1 2 3 4 5 6 7 8 9|0 1 2 3 4 5|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | C3_2 | C4_2 | GA2 | GB2 |DC | | | C3_2 | C4_2 | GA2 | GB2 |DC |
| | | | | | | | | | | | | |
|6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2|0 1 2 3|0 1| |6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2|0 1 2 3|0 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: G.729 Annex E (backward adaptive mode) bit packing Figure 8: G.729 Annex E (backward adaptive mode) bit packing
4.5.8 GSM 4.5.8 GSM
GSM (group speciale mobile) denotes the European GSM 06.10 standard GSM (Group Speciale Mobile) denotes the European GSM 06.10 standard
for full-rate speech transcoding, ETS 300 961, which is based on for full-rate speech transcoding, ETS 300 961, which is based on
RPE/LTP (residual pulse excitation/long term prediction) coding at a RPE/LTP (residual pulse excitation/long term prediction) coding at a
rate of 13 kb/s [12,13,14]. The text of the standard can be obtained rate of 13 kb/s [11,12,13]. The text of the standard can be obtained
from from:
ETSI (European Telecommunications Standards Institute) ETSI (European Telecommunications Standards Institute)
ETSI Secretariat: B.P.152 ETSI Secretariat: B.P.152
F-06561 Valbonne Cedex F-06561 Valbonne Cedex
France France
Phone: +33 92 94 42 00 Phone: +33 92 94 42 00
Fax: +33 93 65 47 16 Fax: +33 93 65 47 16
Blocks of 160 audio samples are compressed into 33 octets, for an Blocks of 160 audio samples are compressed into 33 octets, for an
effective data rate of 13,200 b/s. effective data rate of 13,200 b/s.
General Packaging Issues 4.5.8.1 General Packaging Issues
The GSM standard (ETS 300 961) specifies the bit stream produced by The GSM standard (ETS 300 961) specifies the bit stream produced by
the codec, but does not specify how these bits should be packed for the codec, but does not specify how these bits should be packed for
transmission. The packetization specified here has subsequently been transmission. The packetization specified here has subsequently been
adopted in ETSI Technical Specification TS 101 318. Some software adopted in ETSI Technical Specification TS 101 318. Some software
implementations of the GSM codec use a different packing than that implementations of the GSM codec use a different packing than that
specified here. specified here.
In the GSM packing used by RTP, the bits SHALL be packed beginning field field name bits field field name bits
from the most significant bit. Every 160 sample GSM frame is coded ________________________________________________
into one 33 octet (264 bit) buffer. Every such buffer begins with a 1 LARc[0] 6 39 xmc[22] 3
4 bit signature (0xD), followed by the MSB encoding of the fields of 2 LARc[1] 6 40 xmc[23] 3
the frame. The first octet thus contains 1101 in the 4 most 3 LARc[2] 5 41 xmc[24] 3
significant bits (0-3) and the 4 most significant bits of F1 (0-3) in 4 LARc[3] 5 42 xmc[25] 3
the 4 least significant bits (4-7). The second octet contains the 2 5 LARc[4] 4 43 Nc[2] 7
least significant bits of F1 in bits 0-1, and F2 in bits 2-7, and so 6 LARc[5] 4 44 bc[2] 2
on. The order of the fields in the frame is described in Table 2. 7 LARc[6] 3 45 Mc[2] 2
8 LARc[7] 3 46 xmaxc[2] 6
GSM variable names and numbers 9 Nc[0] 7 47 xmc[26] 3
10 bc[0] 2 48 xmc[27] 3
In the RTP encoding we have the bit pattern described in Table 3, 11 Mc[0] 2 49 xmc[28] 3
where F.i signifies the ith bit of the field F, bit 0 is the most 12 xmaxc[0] 6 50 xmc[29] 3
significant bit, and the bits of every octet are numbered from 0 to 7 13 xmc[0] 3 51 xmc[30] 3
from most to least significant. 14 xmc[1] 3 52 xmc[31] 3
15 xmc[2] 3 53 xmc[32] 3
4.5.9 GSM-EFR 16 xmc[3] 3 54 xmc[33] 3
17 xmc[4] 3 55 xmc[34] 3
GSM-EFR denotes GSM 06.60 enhanced full rate speech transcoding, 18 xmc[5] 3 56 xmc[35] 3
specified in ETS 300 969 which is available from ETSI at the address 19 xmc[6] 3 57 xmc[36] 3
given in Section 4.5.8. This codec has a frame length of 244 bits. 20 xmc[7] 3 58 xmc[37] 3
For transmission in RTP, each codec frame is packed into a 31 octet 21 xmc[8] 3 59 xmc[38] 3
(248 bit) buffer beginning with a 4-bit signature 0xC in a manner 22 xmc[9] 3 60 Nc[3] 7
similar to that specified here for the original GSM 06.10 codec. The 23 xmc[10] 3 61 bc[3] 2
packing is specified in ETSI Technical Specification TS 101 318. 24 xmc[11] 3 62 Mc[3] 2
25 xmc[12] 3 63 xmaxc[3] 6
4.5.10 L8 26 Nc[1] 7 64 xmc[39] 3
27 bc[1] 2 65 xmc[40] 3
L8 denotes linear audio data samples, using 8-bits of precision with 28 Mc[1] 2 66 xmc[41] 3
an offset of 128, that is, the most negative signal is encoded as 29 xmaxc[1] 6 67 xmc[42] 3
zero. 30 xmc[13] 3 68 xmc[43] 3
31 xmc[14] 3 69 xmc[44] 3
4.5.11 L16 32 xmc[15] 3 70 xmc[45] 3
33 xmc[16] 3 71 xmc[46] 3
L16 denotes uncompressed audio data samples, using 16-bit signed 34 xmc[17] 3 72 xmc[47] 3
representation with 65535 equally divided steps between minimum and 35 xmc[18] 3 73 xmc[48] 3
maximum signal level, ranging from -32768 to 32767. The value is 36 xmc[19] 3 74 xmc[49] 3
represented in two's complement notation and transmitted in network 37 xmc[20] 3 75 xmc[50] 3
byte order (most significant byte first). 38 xmc[21] 3 76 xmc[51] 3
field field name bits field field name bits
________________________________________________
1 LARc[0] 6 39 xmc[22] 3
2 LARc[1] 6 40 xmc[23] 3
3 LARc[2] 5 41 xmc[24] 3
4 LARc[3] 5 42 xmc[25] 3
5 LARc[4] 4 43 Nc[2] 7
6 LARc[5] 4 44 bc[2] 2
7 LARc[6] 3 45 Mc[2] 2
8 LARc[7] 3 46 xmaxc[2] 6
9 Nc[0] 7 47 xmc[26] 3
10 bc[0] 2 48 xmc[27] 3
11 Mc[0] 2 49 xmc[28] 3
12 xmaxc[0] 6 50 xmc[29] 3
13 xmc[0] 3 51 xmc[30] 3
14 xmc[1] 3 52 xmc[31] 3
15 xmc[2] 3 53 xmc[32] 3
16 xmc[3] 3 54 xmc[33] 3
17 xmc[4] 3 55 xmc[34] 3
18 xmc[5] 3 56 xmc[35] 3
19 xmc[6] 3 57 xmc[36] 3
20 xmc[7] 3 58 xmc[37] 3
21 xmc[8] 3 59 xmc[38] 3
22 xmc[9] 3 60 Nc[3] 7
23 xmc[10] 3 61 bc[3] 2
24 xmc[11] 3 62 Mc[3] 2
25 xmc[12] 3 63 xmaxc[3] 6
26 Nc[1] 7 64 xmc[39] 3
27 bc[1] 2 65 xmc[40] 3
28 Mc[1] 2 66 xmc[41] 3
29 xmaxc[1] 6 67 xmc[42] 3
30 xmc[13] 3 68 xmc[43] 3
31 xmc[14] 3 69 xmc[44] 3
32 xmc[15] 3 70 xmc[45] 3
33 xmc[16] 3 71 xmc[46] 3
34 xmc[17] 3 72 xmc[47] 3
35 xmc[18] 3 73 xmc[48] 3
36 xmc[19] 3 74 xmc[49] 3
37 xmc[20] 3 75 xmc[50] 3
38 xmc[21] 3 76 xmc[51] 3
Table 2: Ordering of GSM variables Table 2: Ordering of GSM variables
The MIME registration for L16 in RFC YYYY [7] specifies parameters
that MAY be used with MIME or SDP to indicate that analog preemphasis
was applied to the signal before quantization or to indicate that a
multiple-channel audio stream follows a different channel ordering
Octet Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7 Octet Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7
_____________________________________________________________________ _____________________________________________________________________
0 1 1 0 1 LARc0.0 LARc0.1 LARc0.2 LARc0.3 0 1 1 0 1 LARc0.0 LARc0.1 LARc0.2 LARc0.3
1 LARc0.4 LARc0.5 LARc1.0 LARc1.1 LARc1.2 LARc1.3 LARc1.4 LARc1.5 1 LARc0.4 LARc0.5 LARc1.0 LARc1.1 LARc1.2 LARc1.3 LARc1.4 LARc1.5
2 LARc2.0 LARc2.1 LARc2.2 LARc2.3 LARc2.4 LARc3.0 LARc3.1 LARc3.2 2 LARc2.0 LARc2.1 LARc2.2 LARc2.3 LARc2.4 LARc3.0 LARc3.1 LARc3.2
3 LARc3.3 LARc3.4 LARc4.0 LARc4.1 LARc4.2 LARc4.3 LARc5.0 LARc5.1 3 LARc3.3 LARc3.4 LARc4.0 LARc4.1 LARc4.2 LARc4.3 LARc5.0 LARc5.1
4 LARc5.2 LARc5.3 LARc6.0 LARc6.1 LARc6.2 LARc7.0 LARc7.1 LARc7.2 4 LARc5.2 LARc5.3 LARc6.0 LARc6.1 LARc6.2 LARc7.0 LARc7.1 LARc7.2
5 Nc0.0 Nc0.1 Nc0.2 Nc0.3 Nc0.4 Nc0.5 Nc0.6 bc0.0 5 Nc0.0 Nc0.1 Nc0.2 Nc0.3 Nc0.4 Nc0.5 Nc0.6 bc0.0
6 bc0.1 Mc0.0 Mc0.1 xmaxc00 xmaxc01 xmaxc02 xmaxc03 xmaxc04 6 bc0.1 Mc0.0 Mc0.1 xmaxc00 xmaxc01 xmaxc02 xmaxc03 xmaxc04
7 xmaxc05 xmc0.0 xmc0.1 xmc0.2 xmc1.0 xmc1.1 xmc1.2 xmc2.0 7 xmaxc05 xmc0.0 xmc0.1 xmc0.2 xmc1.0 xmc1.1 xmc1.2 xmc2.0
skipping to change at page 28, line 40 skipping to change at page 26, line 41
24 xmc33.2 xmc34.0 xmc34.1 xmc34.2 xmc35.0 xmc35.1 xmc35.2 xmc36.0 24 xmc33.2 xmc34.0 xmc34.1 xmc34.2 xmc35.0 xmc35.1 xmc35.2 xmc36.0
25 Xmc36.1 xmc36.2 xmc37.0 xmc37.1 xmc37.2 xmc38.0 xmc38.1 xmc38.2 25 Xmc36.1 xmc36.2 xmc37.0 xmc37.1 xmc37.2 xmc38.0 xmc38.1 xmc38.2
26 Nc3.0 Nc3.1 Nc3.2 Nc3.3 Nc3.4 Nc3.5 Nc3.6 bc3.0 26 Nc3.0 Nc3.1 Nc3.2 Nc3.3 Nc3.4 Nc3.5 Nc3.6 bc3.0
27 bc3.1 Mc3.0 Mc3.1 xmaxc30 xmaxc31 xmaxc32 xmaxc33 xmaxc34 27 bc3.1 Mc3.0 Mc3.1 xmaxc30 xmaxc31 xmaxc32 xmaxc33 xmaxc34
28 xmaxc35 xmc39.0 xmc39.1 xmc39.2 xmc40.0 xmc40.1 xmc40.2 xmc41.0 28 xmaxc35 xmc39.0 xmc39.1 xmc39.2 xmc40.0 xmc40.1 xmc40.2 xmc41.0
29 xmc41.1 xmc41.2 xmc42.0 xmc42.1 xmc42.2 xmc43.0 xmc43.1 xmc43.2 29 xmc41.1 xmc41.2 xmc42.0 xmc42.1 xmc42.2 xmc43.0 xmc43.1 xmc43.2
30 xmc44.0 xmc44.1 xmc44.2 xmc45.0 xmc45.1 xmc45.2 xmc46.0 xmc46.1 30 xmc44.0 xmc44.1 xmc44.2 xmc45.0 xmc45.1 xmc45.2 xmc46.0 xmc46.1
31 xmc46.2 xmc47.0 xmc47.1 xmc47.2 xmc48.0 xmc48.1 xmc48.2 xmc49.0 31 xmc46.2 xmc47.0 xmc47.1 xmc47.2 xmc48.0 xmc48.1 xmc48.2 xmc49.0
32 xmc49.1 xmc49.2 xmc50.0 xmc50.1 xmc50.2 xmc51.0 xmc51.1 xmc51.2 32 xmc49.1 xmc49.2 xmc50.0 xmc50.1 xmc50.2 xmc51.0 xmc51.1 xmc51.2
Table 3: GSM payload format Table 3: GSM payload format
convention than is specified in Section 4.1. In the GSM packing used by RTP, the bits SHALL be packed beginning
from the most significant bit. Every 160 sample GSM frame is coded
into one 33 octet (264 bit) buffer. Every such buffer begins with a
4 bit signature (0xD), followed by the MSB encoding of the fields of
the frame. The first octet thus contains 1101 in the 4 most
significant bits (0-3) and the 4 most significant bits of F1 (0-3) in
the 4 least significant bits (4-7). The second octet contains the 2
least significant bits of F1 in bits 0-1, and F2 in bits 2-7, and so
on. The order of the fields in the frame is described in Table 2.
4.5.8.2 GSM Variable Names and Numbers
In the RTP encoding we have the bit pattern described in Table 3,
where F.i signifies the ith bit of the field F, bit 0 is the most
significant bit, and the bits of every octet are numbered from 0 to 7
from most to least significant.
4.5.9 GSM-EFR
GSM-EFR denotes GSM 06.60 enhanced full rate speech transcoding,
specified in ETS 300 726 which is available from ETSI at the address
given in Section 4.5.8. This codec has a frame length of 244 bits.
For transmission in RTP, each codec frame is packed into a 31 octet
(248 bit) buffer beginning with a 4-bit signature 0xC in a manner
similar to that specified here for the original GSM 06.10 codec. The
packing is specified in ETSI Technical Specification TS 101 318.
4.5.10 L8
L8 denotes linear audio data samples, using 8-bits of precision with
an offset of 128, that is, the most negative signal is encoded as
zero.
4.5.11 L16
L16 denotes uncompressed audio data samples, using 16-bit signed
representation with 65,535 equally divided steps between minimum and
maximum signal level, ranging from -32,768 to 32,767. The value is
represented in two's complement notation and transmitted in network
byte order (most significant byte first).
The MIME registration for L16 in RFC 3555 [7] specifies parameters
that MAY be used with MIME or SDP to indicate that analog pre-
emphasis was applied to the signal before quantization or to indicate
that a multiple-channel audio stream follows a different channel
ordering convention than is specified in Section 4.1.
4.5.12 LPC 4.5.12 LPC
LPC designates an experimental linear predictive encoding contributed LPC designates an experimental linear predictive encoding contributed
by Ron Frederick, which is based on an implementation written by Ron by Ron Frederick, which is based on an implementation written by Ron
Zuckerman posted to the Usenet group comp.dsp on June 26, 1992. The Zuckerman posted to the Usenet group comp.dsp on June 26, 1992. The
codec generates 14 octets for every frame. The framesize is set to codec generates 14 octets for every frame. The framesize is set to
20 ms, resulting in a bit rate of 5,600 b/s. 20 ms, resulting in a bit rate of 5,600 b/s.
4.5.13 MPA 4.5.13 MPA
MPA denotes MPEG-1 or MPEG-2 audio encapsulated as elementary MPA denotes MPEG-1 or MPEG-2 audio encapsulated as elementary
streams. The encoding is defined in ISO standards ISO/IEC 11172-3 streams. The encoding is defined in ISO standards ISO/IEC 11172-3
and 13818-3. The encapsulation is specified in RFC 2250 [15]. and 13818-3. The encapsulation is specified in RFC 2250 [14].
The encoding may be at any of three levels of complexity, called The encoding may be at any of three levels of complexity, called
Layer I, II and III. The selected layer as well as the sampling rate Layer I, II and III. The selected layer as well as the sampling rate
and channel count are indicated in the payload. The RTP timestamp and channel count are indicated in the payload. The RTP timestamp
clock rate is always 90000, independent of the sampling rate. MPEG-1 clock rate is always 90,000, independent of the sampling rate.
audio supports sampling rates of 32, 44.1, and 48 kHz (ISO/IEC MPEG-1 audio supports sampling rates of 32, 44.1, and 48 kHz (ISO/IEC
11172-3, section 1.1; "Scope"). MPEG-2 supports sampling rates of 11172-3, section 1.1; "Scope"). MPEG-2 supports sampling rates of
16, 22.05 and 24 kHz. The number of samples per frame is fixed, but 16, 22.05 and 24 kHz. The number of samples per frame is fixed, but
the frame size will vary with the sampling rate and bit rate. the frame size will vary with the sampling rate and bit rate.
The MIME registration for MPA in RFC YYYY [7] specifies parameters The MIME registration for MPA in RFC 3555 [7] specifies parameters
that MAY be used with MIME or SDP to restrict the selection of layer, that MAY be used with MIME or SDP to restrict the selection of layer,
channel count, sampling rate, and bit rate. channel count, sampling rate, and bit rate.
4.5.14 PCMA and PCMU 4.5.14 PCMA and PCMU
PCMA and PCMU are specified in ITU-T Recommendation G.711. Audio PCMA and PCMU are specified in ITU-T Recommendation G.711. Audio
data is encoded as eight bits per sample, after logarithmic scaling. data is encoded as eight bits per sample, after logarithmic scaling.
PCMU denotes mu-law scaling, PCMA A-law scaling. A detailed PCMU denotes mu-law scaling, PCMA A-law scaling. A detailed
description is given by Jayant and Noll [16]. Each G.711 octet SHALL description is given by Jayant and Noll [15]. Each G.711 octet SHALL
be octet-aligned in an RTP packet. The sign bit of each G.711 octet be octet-aligned in an RTP packet. The sign bit of each G.711 octet
SHALL correspond to the most significant bit of the octet in the RTP SHALL correspond to the most significant bit of the octet in the RTP
packet (i.e., assuming the G.711 samples are handled as octets on the packet (i.e., assuming the G.711 samples are handled as octets on the
host machine, the sign bit SHALL be the most significant bit of the host machine, the sign bit SHALL be the most significant bit of the
octet as defined by the host machine format). The 56 kb/s and 48 octet as defined by the host machine format). The 56 kb/s and 48
kb/s modes of G.711 are not applicable to RTP, since PCMA and PCMU kb/s modes of G.711 are not applicable to RTP, since PCMA and PCMU
MUST always be transmitted as 8-bit samples. MUST always be transmitted as 8-bit samples.
See Section 4.1 regarding silence suppression. See Section 4.1 regarding silence suppression.
4.5.15 QCELP 4.5.15 QCELP
The Electronic Industries Association (EIA) & Telecommunications The Electronic Industries Association (EIA) & Telecommunications
Industry Association (TIA) standard IS-733, "TR45: High Rate Speech Industry Association (TIA) standard IS-733, "TR45: High Rate Speech
Service Option for Wideband Spread Spectrum Communications Systems," Service Option for Wideband Spread Spectrum Communications Systems",
defines the QCELP audio compression algorithm for use in wireless defines the QCELP audio compression algorithm for use in wireless
CDMA applications. The QCELP CODEC compresses each 20 milliseconds CDMA applications. The QCELP CODEC compresses each 20 milliseconds
of 8000 Hz, 16- bit sampled input speech into one of four different of 8,000 Hz, 16-bit sampled input speech into one of four different
size output frames: Rate 1 (266 bits), Rate 1/2 (124 bits), Rate 1/4 size output frames: Rate 1 (266 bits), Rate 1/2 (124 bits), Rate 1/4
(54 bits) or Rate 1/8 (20 bits). For typical speech patterns, this (54 bits) or Rate 1/8 (20 bits). For typical speech patterns, this
results in an average output of 6.8 k bits/sec for normal mode and results in an average output of 6.8 kb/s for normal mode and 4.7 kb/s
4.7 k bits/sec for reduced rate mode. The packetization of the QCELP for reduced rate mode. The packetization of the QCELP audio codec is
audio codec is described in [17]. described in [16].
4.5.16 RED 4.5.16 RED
The redundant audio payload format "RED" is specified by The redundant audio payload format "RED" is specified by RFC 2198
RFC 2198 [18]. It defines a means by which multiple redundant copies [17]. It defines a means by which multiple redundant copies of an
of an audio packet may be transmitted in a single RTP stream. Each audio packet may be transmitted in a single RTP stream. Each packet
packet in such a stream contains, in addition to the audio data for in such a stream contains, in addition to the audio data for that
that packetization interval, a (more heavily compressed) copy of the packetization interval, a (more heavily compressed) copy of the data
data from a previous packetization interval. This allows an from a previous packetization interval. This allows an approximation
approximation of the data from lost packets to be recovered upon of the data from lost packets to be recovered upon decoding of a
decoding of a subsequent packet, giving much improved sound quality subsequent packet, giving much improved sound quality when compared
when compared with silence substitution for lost packets. with silence substitution for lost packets.
4.5.17 VDVI 4.5.17 VDVI
VDVI is a variable-rate version of DVI4, yielding speech bit rates of VDVI is a variable-rate version of DVI4, yielding speech bit rates of
between 10 and 25 kb/s. It is specified for single-channel operation between 10 and 25 kb/s. It is specified for single-channel operation
only. Samples are packed into octets starting at the most- only. Samples are packed into octets starting at the most-
significant bit. The last octet is padded with 1 bits if the last significant bit. The last octet is padded with 1 bits if the last
sample does not fill the last octet. This padding is distinct from sample does not fill the last octet. This padding is distinct from
the valid codewords. The receiver needs to detect the padding the valid codewords. The receiver needs to detect the padding
because there is no explicit count of samples in the packet. because there is no explicit count of samples in the packet.
It uses the following encoding: It uses the following encoding:
DVI4 codeword VDVI bit pattern DVI4 codeword VDVI bit pattern
_______________________________ _______________________________
0 00 0 00
1 010 1 010
2 1100 2 1100
3 11100 3 11100
4 111100 4 111100
5 1111100 5 1111100
6 11111100 6 11111100
7 11111110 7 11111110
8 10 8 10
9 011 9 011
10 1101 10 1101
11 11101 11 11101
12 111101 12 111101
13 1111101 13 1111101
14 11111101 14 11111101
15 11111111 15 11111111
5 Video 5. Video
The following sections describe the video encodings that are defined The following sections describe the video encodings that are defined
in this memo and give their abbreviated names used for in this memo and give their abbreviated names used for
identification. These video encodings and their payload types are identification. These video encodings and their payload types are
listed in Table 5. listed in Table 5.
All of these video encodings use an RTP timestamp frequency of 90,000 All of these video encodings use an RTP timestamp frequency of 90,000
Hz, the same as the MPEG presentation time stamp frequency. This Hz, the same as the MPEG presentation time stamp frequency. This
frequency yields exact integer timestamp increments for the typical frequency yields exact integer timestamp increments for the typical
24 (HDTV), 25 (PAL), and 29.97 (NTSC) and 30 Hz (HDTV) frame rates 24 (HDTV), 25 (PAL), and 29.97 (NTSC) and 30 Hz (HDTV) frame rates
skipping to change at page 31, line 32 skipping to change at page 30, line 37
If a video image occupies more than one packet, the timestamp is the If a video image occupies more than one packet, the timestamp is the
same on all of those packets. Packets from different video images same on all of those packets. Packets from different video images
are distinguished by their different timestamps. are distinguished by their different timestamps.
Most of these video encodings also specify that the marker bit of the Most of these video encodings also specify that the marker bit of the
RTP header SHOULD be set to one in the last packet of a video frame RTP header SHOULD be set to one in the last packet of a video frame
and otherwise set to zero. Thus, it is not necessary to wait for a and otherwise set to zero. Thus, it is not necessary to wait for a
following packet with a different timestamp to detect that a new following packet with a different timestamp to detect that a new
frame should be displayed. frame should be displayed.
5.1 CelB 5.1 CelB
The CELL-B encoding is a proprietary encoding proposed by Sun The CELL-B encoding is a proprietary encoding proposed by Sun
Microsystems. The byte stream format is described in RFC 2029 [19]. Microsystems. The byte stream format is described in RFC 2029 [18].
5.2 JPEG 5.2 JPEG
The encoding is specified in ISO Standards 10918-1 and 10918-2. The The encoding is specified in ISO Standards 10918-1 and 10918-2. The
RTP payload format is as specified in RFC 2435 [20]. RTP payload format is as specified in RFC 2435 [19].
5.3 H261 5.3 H261
The encoding is specified in ITU-T Recommendation H.261, "Video codec The encoding is specified in ITU-T Recommendation H.261, "Video codec
for audiovisual services at p x 64 kbit/s". The packetization and for audiovisual services at p x 64 kbit/s". The packetization and
RTP-specific properties are described in RFC 2032 [21]. RTP-specific properties are described in RFC 2032 [20].
5.4 H263 5.4 H263
The encoding is specified in the 1996 version of ITU-T Recommendation The encoding is specified in the 1996 version of ITU-T Recommendation
H.263, "Video coding for low bit rate communication". The H.263, "Video coding for low bit rate communication". The
packetization and RTP-specific properties are described in packetization and RTP-specific properties are described in RFC 2190
RFC 2190 [22]. The H263-1998 payload format is RECOMMENDED over this [21]. The H263-1998 payload format is RECOMMENDED over this one for
one for use by new implementations. use by new implementations.
5.5 H263-1998 5.5 H263-1998
The encoding is specified in the 1998 version of ITU-T Recommendation The encoding is specified in the 1998 version of ITU-T Recommendation
H.263, "Video coding for low bit rate communication". The H.263, "Video coding for low bit rate communication". The
packetization and RTP-specific properties are described in packetization and RTP-specific properties are described in RFC 2429
RFC 2429 [23]. Because the 1998 version of H.263 is a superset of [22]. Because the 1998 version of H.263 is a superset of the 1996
the 1996 syntax, this payload format can also be used with the 1996 syntax, this payload format can also be used with the 1996 version of
version of H.263, and is RECOMMENDED for this use by new H.263, and is RECOMMENDED for this use by new implementations. This
implementations. This payload format does not replace RFC 2190, payload format does not replace RFC 2190, which continues to be used
which continues to be used by existing implementations, and may be by existing implementations, and may be required for backward
required for backward compatibility in new implementations. compatibility in new implementations. Implementations using the new
Implementations using the new features of the 1998 version of H.263 features of the 1998 version of H.263 MUST use the payload format
MUST use the payload format described in RFC 2429. described in RFC 2429.
5.6 MPV 5.6 MPV
MPV designates the use of MPEG-1 and MPEG-2 video encoding elementary MPV designates the use of MPEG-1 and MPEG-2 video encoding elementary
streams as specified in ISO Standards ISO/IEC 11172 and 13818-2, streams as specified in ISO Standards ISO/IEC 11172 and 13818-2,
respectively. The RTP payload format is as specified in respectively. The RTP payload format is as specified in RFC 2250
RFC 2250 [15], Section 3. [14], Section 3.
The MIME registration for MPV in RFC YYYY [7] specifies a parameter The MIME registration for MPV in RFC 3555 [7] specifies a parameter
that MAY be used with MIME or SDP to restrict the selection of the that MAY be used with MIME or SDP to restrict the selection of the
type of MPEG video. type of MPEG video.
5.7 MP2T 5.7 MP2T
MP2T designates the use of MPEG-2 transport streams, for either audio MP2T designates the use of MPEG-2 transport streams, for either audio
or video. The RTP payload format is described in RFC 2250 [15], or video. The RTP payload format is described in RFC 2250 [14],
Section 2. Section 2.
5.8 nv 5.8 nv
The encoding is implemented in the program `nv', version 4, developed The encoding is implemented in the program `nv', version 4, developed
at Xerox PARC by Ron Frederick. Further information is available at Xerox PARC by Ron Frederick. Further information is available
from the author: from the author:
Ron Frederick Ron Frederick
Blue Coat Systems Inc. Blue Coat Systems Inc.
650 Almanor Avenue 650 Almanor Avenue
Sunnyvale, CA 94085 Sunnyvale, CA 94085
United States United States
electronic mail: ronf@bluecoat.com EMail: ronf@bluecoat.com
6 Payload Type Definitions 6. Payload Type Definitions
Tables 4 and 5 define this profile's static payload type values for Tables 4 and 5 define this profile's static payload type values for
the PT field of the RTP data header. In addition, payload type the PT field of the RTP data header. In addition, payload type
values in the range 96-127 MAY be defined dynamically through a values in the range 96-127 MAY be defined dynamically through a
conference control protocol, which is beyond the scope of this conference control protocol, which is beyond the scope of this
document. For example, a session directory could specify that for a document. For example, a session directory could specify that for a
given session, payload type 96 indicates PCMU encoding, 8,000 Hz given session, payload type 96 indicates PCMU encoding, 8,000 Hz
sampling rate, 2 channels. Entries in Tables 4 and 5 with payload sampling rate, 2 channels. Entries in Tables 4 and 5 with payload
type "dyn" have no static payload type assigned and are only used type "dyn" have no static payload type assigned and are only used
with a dynamic payload type. Payload type 2 was assigned to G721 in with a dynamic payload type. Payload type 2 was assigned to G721 in
skipping to change at page 33, line 29 skipping to change at page 32, line 42
payload formats G726-32 and AAL2-G726-32 (see Section 4.5.4). payload formats G726-32 and AAL2-G726-32 (see Section 4.5.4).
Payload type 13 indicates the Comfort Noise (CN) payload format Payload type 13 indicates the Comfort Noise (CN) payload format
specified in RFC 3389 [9]. Payload type 19 is marked "reserved" specified in RFC 3389 [9]. Payload type 19 is marked "reserved"
because some draft versions of this specification assigned that because some draft versions of this specification assigned that
number to an earlier version of the comfort noise payload format. number to an earlier version of the comfort noise payload format.
The payload type range 72-76 is marked "reserved" so that RTCP and The payload type range 72-76 is marked "reserved" so that RTCP and
RTP packets can be reliably distinguished (see Section "Summary of RTP packets can be reliably distinguished (see Section "Summary of
Protocol Constants" of the RTP protocol specification). Protocol Constants" of the RTP protocol specification).
The payload types currently defined in this profile are assigned to The payload types currently defined in this profile are assigned to
exactly one of three categories or media types : audio only, video exactly one of three categories or media types: audio only, video
only and those combining audio and video. The media types are marked only and those combining audio and video. The media types are marked
in Tables 4 and 5 as "A", "V" and "AV", respectively. Payload types in Tables 4 and 5 as "A", "V" and "AV", respectively. Payload types
of different media types SHALL NOT be interleaved or multiplexed of different media types SHALL NOT be interleaved or multiplexed
within a single RTP session, but multiple RTP sessions MAY be used in within a single RTP session, but multiple RTP sessions MAY be used in
parallel to send multiple media types. An RTP source MAY change parallel to send multiple media types. An RTP source MAY change
payload types within the same media type during a session. See the payload types within the same media type during a session. See the
section "Multiplexing RTP Sessions" of RFC XXXX for additional section "Multiplexing RTP Sessions" of RFC 3550 for additional
explanation. explanation.
PT encoding media type clock rate channels
name (Hz)
___________________________________________________
0 PCMU A 8,000 1
1 reserved A
2 reserved A
3 GSM A 8,000 1
4 G723 A 8,000 1
5 DVI4 A 8,000 1
6 DVI4 A 16,000 1
7 LPC A 8,000 1
8 PCMA A 8,000 1
9 G722 A 8,000 1
10 L16 A 44,100 2
11 L16 A 44,100 1
12 QCELP A 8,000 1
13 CN A 8,000 1
14 MPA A 90,000 (see text)
15 G728 A 8,000 1
16 DVI4 A 11,025 1
17 DVI4 A 22,050 1
18 G729 A 8,000 1
19 reserved A
20 unassigned A
21 unassigned A
22 unassigned A
23 unassigned A
dyn G726-40 A 8,000 1
dyn G726-32 A 8,000 1
dyn G726-24 A 8,000 1
dyn G726-16 A 8,000 1
dyn G729D A 8,000 1
dyn G729E A 8,000 1
dyn GSM-EFR A 8,000 1
dyn L8 A var. var.
dyn RED A (see text)
dyn VDVI A var. 1
Table 4: Payload types (PT) for audio encodings
PT encoding media type clock rate
name (Hz)
_____________________________________________
24 unassigned V
25 CelB V 90,000
26 JPEG V 90,000
27 unassigned V
28 nv V 90,000
29 unassigned V
30 unassigned V
31 H261 V 90,000
32 MPV V 90,000
33 MP2T AV 90,000
34 H263 V 90,000
35-71 unassigned ?
72-76 reserved N/A N/A
77-95 unassigned ?
96-127 dynamic ?
dyn H263-1998 V 90,000
Table 5: Payload types (PT) for video and combined
encodings
Session participants agree through mechanisms beyond the scope of Session participants agree through mechanisms beyond the scope of
this specification on the set of payload types allowed in a given this specification on the set of payload types allowed in a given
session. This set MAY, for example, be defined by the capabilities session. This set MAY, for example, be defined by the capabilities
of the applications used, negotiated by a conference control protocol of the applications used, negotiated by a conference control protocol
or established by agreement between the human participants. or established by agreement between the human participants.
Audio applications operating under this profile SHOULD, at a minimum, Audio applications operating under this profile SHOULD, at a minimum,
be able to send and/or receive payload types 0 (PCMU) and 5 (DVI4). be able to send and/or receive payload types 0 (PCMU) and 5 (DVI4).
This allows interoperability without format negotiation and ensures This allows interoperability without format negotiation and ensures
successful negotiation with a conference control protocol. successful negotiation with a conference control protocol.
7 RTP over TCP and Similar Byte Stream Protocols 7. RTP over TCP and Similar Byte Stream Protocols
PT encoding media type clock rate channels
name (Hz)
___________________________________________________
0 PCMU A 8000 1
1 reserved A
2 reserved A
3 GSM A 8000 1
4 G723 A 8000 1
5 DVI4 A 8000 1
6 DVI4 A 16000 1
7 LPC A 8000 1
8 PCMA A 8000 1
9 G722 A 8000 1
10 L16 A 44100 2
11 L16 A 44100 1
12 QCELP A 8000 1
13 CN A 8000 1
14 MPA A 90000 (see text)
15 G728 A 8000 1
16 DVI4 A 11025 1
17 DVI4 A 22050 1
18 G729 A 8000 1
19 reserved A
20 unassigned A
21 unassigned A
22 unassigned A
23 unassigned A
dyn G726-40 A 8000 1
dyn G726-32 A 8000 1
dyn G726-24 A 8000 1
dyn G726-16 A 8000 1
dyn G729D A 8000 1
dyn G729E A 8000 1
dyn GSM-EFR A 8000 1
dyn L8 A var. var.
dyn RED A (see text)
dyn VDVI A var. 1
Table 4: Payload types (PT) for audio encodings
Under special circumstances, it may be necessary to carry RTP in Under special circumstances, it may be necessary to carry RTP in
protocols offering a byte stream abstraction, such as TCP, possibly protocols offering a byte stream abstraction, such as TCP, possibly
multiplexed with other data. The application MUST define its own multiplexed with other data. The application MUST define its own
method of delineating RTP and RTCP packets (RTSP [24] provides an method of delineating RTP and RTCP packets (RTSP [23] provides an
example of such an encapsulation specification.) example of such an encapsulation specification).
PT encoding media type clock rate
name (Hz)
_____________________________________________
24 unassigned V
25 CelB V 90000
26 JPEG V 90000
27 unassigned V
28 nv V 90000
29 unassigned V
30 unassigned V
31 H261 V 90000
32 MPV V 90000
33 MP2T AV 90000
34 H263 V 90000
35-71 unassigned ?
72-76 reserved N/A N/A
77-95 unassigned ?
96-127 dynamic ?
dyn H263-1998 V 90000
Table 5: Payload types (PT) for video and combined encodings
8 Port Assignment 8. Port Assignment
As specified in the RTP protocol definition, RTP data SHOULD be As specified in the RTP protocol definition, RTP data SHOULD be
carried on an even UDP port number and the corresponding RTCP packets carried on an even UDP port number and the corresponding RTCP packets
SHOULD be carried on the next higher (odd) port number. SHOULD be carried on the next higher (odd) port number.
Applications operating under this profile MAY use any such UDP port Applications operating under this profile MAY use any such UDP port
pair. For example, the port pair MAY be allocated randomly by a pair. For example, the port pair MAY be allocated randomly by a
session management program. A single fixed port number pair cannot session management program. A single fixed port number pair cannot
be required because multiple applications using this profile are be required because multiple applications using this profile are
likely to run on the same host, and there are some operating systems likely to run on the same host, and there are some operating systems
skipping to change at page 36, line 6 skipping to change at page 35, line 26
use this port pair as an indication to select this profile if they use this port pair as an indication to select this profile if they
are not subject to the constraint of the previous paragraph. are not subject to the constraint of the previous paragraph.
Applications need not have a default and MAY require that the port Applications need not have a default and MAY require that the port
pair be explicitly specified. The particular port numbers were pair be explicitly specified. The particular port numbers were
chosen to lie in the range above 5000 to accommodate port number chosen to lie in the range above 5000 to accommodate port number
allocation practice within some versions of the Unix operating allocation practice within some versions of the Unix operating
system, where port numbers below 1024 can only be used by privileged system, where port numbers below 1024 can only be used by privileged
processes and port numbers between 1024 and 5000 are automatically processes and port numbers between 1024 and 5000 are automatically
assigned by the operating system. assigned by the operating system.
A Changes from RFC 1890 9. Changes from RFC 1890
This RFC revises RFC 1890. It is mostly backwards-compatible with This RFC revises RFC 1890. It is mostly backwards-compatible with
RFC 1890 except for functions removed because two interoperable RFC 1890 except for functions removed because two interoperable
implementations were not found. The additions to RFC 1890 codify implementations were not found. The additions to RFC 1890 codify
existing practice in the use of payload formats under this profile. existing practice in the use of payload formats under this profile.
Since this profile may be used without using any of the payload Since this profile may be used without using any of the payload
formats listed here, the addition of new payload formats in this formats listed here, the addition of new payload formats in this
revision does not affect backwards compatibility. The changes are revision does not affect backwards compatibility. The changes are
listed below, categorized into functional and non-functional changes. listed below, categorized into functional and non-functional changes.
Functional changes: Functional changes:
o A new Appendix C "IANA Considerations" was added to specify o Section 11, "IANA Considerations" was added to specify the
the registration of the name for this profile. That appendix registration of the name for this profile. That appendix also
also references a new Section 3 "Registering Additional references a new Section 3 "Registering Additional Encodings"
Encodings" which establishes a policy that no additional which establishes a policy that no additional registration of
registration of static payload types for this profile will be static payload types for this profile will be made beyond those
made beyond those added in this revision and included in added in this revision and included in Tables 4 and 5. Instead,
Tables 4 and 5. Instead, additional encoding names may be additional encoding names may be registered as MIME subtypes for
registered as MIME subtypes for binding to dynamic payload binding to dynamic payload types. Non-normative references were
types. Non-normative references were added to RFC YYYY [7] added to RFC 3555 [7] where MIME subtypes for all the listed
where MIME subtypes for all the listed payload formats are payload formats are registered, some with optional parameters for
registered, some with optional parameters for use of the use of the payload formats.
payload formats.
o Static payload types 4, 16, 17 and 34 were added to
incorporate IANA registrations made since the publication of
RFC 1890, along with the corresponding payload format
descriptions for G723 and H263.
o Following working group discussion, static payload types 12 o Static payload types 4, 16, 17 and 34 were added to incorporate
and 18 were added along with the corresponding payload format IANA registrations made since the publication of RFC 1890, along
descriptions for QCELP and G729. Static payload type 13 was with the corresponding payload format descriptions for G723 and
assigned to the Comfort Noise (CN) payload format defined in H263.
RFC 3389. Payload type 19 was marked reserved because it had
been temporarily allocated to an earlier version of Comfort
Noise present in some draft revisions of this document.
o The payload format for G721 was renamed to G726-32 following o Following working group discussion, static payload types 12 and 18
the ITU-T renumbering, and the payload format description for were added along with the corresponding payload format
G726 was expanded to include the -16, -24 and -40 data rates. descriptions for QCELP and G729. Static payload type 13 was
Because of confusion regarding draft revisions of this assigned to the Comfort Noise (CN) payload format defined in RFC
document, some implementations of these G726 payload formats 3389. Payload type 19 was marked reserved because it had been
packed samples into octets starting with the most significant temporarily allocated to an earlier version of Comfort Noise
bit rather than the least significant bit as specified here. present in some draft revisions of this document.
To partially resolve this incompatibility, new payload formats o The payload format for G721 was renamed to G726-32 following the
named AAL2-G726-16, -24, -32 and -48 will be specified in a ITU-T renumbering, and the payload format description for G726 was
separate document (see note in Section 4.5.4), and use of expanded to include the -16, -24 and -40 data rates. Because of
static payload type 2 is deprecated as explained in Section 6. confusion regarding draft revisions of this document, some
implementations of these G726 payload formats packed samples into
octets starting with the most significant bit rather than the
least significant bit as specified here. To partially resolve
this incompatibility, new payload formats named AAL2-G726-16, -24,
-32 and -40 will be specified in a separate document (see note in
Section 4.5.4), and use of static payload type 2 is deprecated as
explained in Section 6.
o Payload formats G729D and G729E were added following the ITU-T o Payload formats G729D and G729E were added following the ITU-T
addition of Annexes D and E to Recommendation G.729. Listings addition of Annexes D and E to Recommendation G.729. Listings
were added for payload formats GSM-EFR, RED, and H263-1998 were added for payload formats GSM-EFR, RED, and H263-1998
published in other documents subsequent to RFC 1890. These published in other documents subsequent to RFC 1890. These
additional payload formats are referenced only by dynamic additional payload formats are referenced only by dynamic payload
payload type numbers. type numbers.
o The descriptions of the payload formats for G722, G728, GSM, o The descriptions of the payload formats for G722, G728, GSM, VDVI
VDVI were expanded. were expanded.
o The payload format for 1016 audio was removed and its static o The payload format for 1016 audio was removed and its static
payload type assignment 1 was marked "reserved" because two payload type assignment 1 was marked "reserved" because two
interoperable implementations were not found. interoperable implementations were not found.
o Requirements for congestion control were added in Section 2. o Requirements for congestion control were added in Section 2.
o This profile follows the suggestion in the revised RTP spec o This profile follows the suggestion in the revised RTP spec that
that RTCP bandwidth may be specified separately from the RTCP bandwidth may be specified separately from the session
session bandwidth and separately for active senders and bandwidth and separately for active senders and passive receivers.
passive receivers.
o The mapping of a user pass-phrase string into an encryption o The mapping of a user pass-phrase string into an encryption key
key was deleted from Section 2 because two interoperable was deleted from Section 2 because two interoperable
implementations were not found. implementations were not found.
o The "quadrophonic" sample ordering convention for four-channel o The "quadrophonic" sample ordering convention for four-channel
audio was removed to eliminate an ambiguity as noted in audio was removed to eliminate an ambiguity as noted in Section
Section 4.1. 4.1.
Non-functional changes: Non-functional changes:
o In Section 4.1, it is now explicitly stated that silence o In Section 4.1, it is now explicitly stated that silence
suppression is allowed for all audio payload formats. (This suppression is allowed for all audio payload formats. (This has
has always been the case and derives from a fundamental aspect always been the case and derives from a fundamental aspect of
of RTP's design and the motivations for packet audio, but was RTP's design and the motivations for packet audio, but was not
not explicit stated before.) The use of comfort noise is also explicit stated before.) The use of comfort noise is also
explained. explained.
o In Section 4.1, the requirement level for setting of the o In Section 4.1, the requirement level for setting of the marker
marker bit on the first packet after silence for audio was bit on the first packet after silence for audio was changed from
changed from "is" to "SHOULD be", and clarified that the "is" to "SHOULD be", and clarified that the marker bit is set only
marker bit is set only when packets are intentionally not when packets are intentionally not sent.
sent.
o Similarly, text was added to specify that the marker bit o Similarly, text was added to specify that the marker bit SHOULD be
SHOULD be set to one on the last packet of a video frame, and set to one on the last packet of a video frame, and that video
that video frames are distinguished by their timestamps. frames are distinguished by their timestamps.
o RFC references are added for payload formats published after o RFC references are added for payload formats published after RFC
RFC 1890. 1890.
o The security considerations and full copyright sections were o The security considerations and full copyright sections were
added. added.
o According to Peter Hoddie of Apple, only pre-1994 Macintosh o According to Peter Hoddie of Apple, only pre-1994 Macintosh used
used the 22254.54 rate and none the 11127.27 rate, so the the 22254.54 rate and none the 11127.27 rate, so the latter was
latter was dropped from the discussion of suggested sampling dropped from the discussion of suggested sampling frequencies.
frequencies.
o Table 1 was corrected to move some values from the "ms/packet" o Table 1 was corrected to move some values from the "ms/packet"
column to the "default ms/packet" column where they belonged. column to the "default ms/packet" column where they belonged.
o A note has been added for G722 to clarify a discrepancy o Since the Interactive Multimedia Association ceased operations, an
between the actual sampling rate and the RTP timestamp clock alternate resource was provided for a referenced IMA document.
rate.
o Small clarifications of the text have been made in several o A note has been added for G722 to clarify a discrepancy between
places, some in response to questions from readers. In the actual sampling rate and the RTP timestamp clock rate.
particular:
- A definition for "media type" is given in Section 1.1 to o Small clarifications of the text have been made in several places,
allow the explanation of multiplexing RTP sessions in some in response to questions from readers. In particular:
Section 6 to be more clear regarding the multiplexing of
multiple media.
- The explanation of how to determine the number of audio - A definition for "media type" is given in Section 1.1 to allow
frames in a packet from the length was expanded. the explanation of multiplexing RTP sessions in Section 6 to be
more clear regarding the multiplexing of multiple media.
- More description of the allocation of bandwidth to SDES - The explanation of how to determine the number of audio frames
items is given. in a packet from the length was expanded.
- A note was added that the convention for the order of - More description of the allocation of bandwidth to SDES items
channels specified in Section 4.1 may be overridden by a is given.
particular encoding or payload format specification.
- The terms MUST, SHOULD, MAY, etc. are used as defined in - A note was added that the convention for the order of channels
RFC 2119. specified in Section 4.1 may be overridden by a particular
encoding or payload format specification.
o A second author for this document was added. - The terms MUST, SHOULD, MAY, etc. are used as defined in RFC
2119.
o A second author for this document was added.
10. Security Considerations
B Security Considerations
Implementations using the profile defined in this specification are Implementations using the profile defined in this specification are
subject to the security considerations discussed in the RTP subject to the security considerations discussed in the RTP
specification [1]. This profile does not specify any different specification [1]. This profile does not specify any different
security services. The primary function of this profile is to list a security services. The primary function of this profile is to list a
set of data compression encodings for audio and video media. set of data compression encodings for audio and video media.
Confidentiality of the media streams is achieved by encryption. Confidentiality of the media streams is achieved by encryption.
Because the data compression used with the payload formats described Because the data compression used with the payload formats described
in this profile is applied end-to-end, encryption may be performed in this profile is applied end-to-end, encryption may be performed
after compression so there is no conflict between the two operations. after compression so there is no conflict between the two operations.
A potential denial-of-service threat exists for data encodings using A potential denial-of-service threat exists for data encodings using
compression techniques that have non-uniform receiver-end compression techniques that have non-uniform receiver-end
computational load. The attacker can inject pathological datagrams computational load. The attacker can inject pathological datagrams
into the stream which are complex to decode and cause the receiver to into the stream which are complex to decode and cause the receiver to
be overloaded. However, the encodings described in this profile do be overloaded.
not exhibit any significant non-uniformity.
As with any IP-based protocol, in some circumstances a receiver may As with any IP-based protocol, in some circumstances a receiver may
be overloaded simply by the receipt of too many packets, either be overloaded simply by the receipt of too many packets, either
desired or undesired. Network-layer authentication MAY be used to desired or undesired. Network-layer authentication MAY be used to
discard packets from undesired sources, but the processing cost of discard packets from undesired sources, but the processing cost of
the authentication itself may be too high. In a multicast the authentication itself may be too high. In a multicast
environment, pruning of specific sources may be implemented in future environment, source pruning is implemented in IGMPv3 (RFC 3376) [24]
versions of IGMP [25] and in multicast routing protocols to allow a and in multicast routing protocols to allow a receiver to select
receiver to select which sources are allowed to reach it. which sources are allowed to reach it.
C IANA Considerations 11. IANA Considerations
The RTP specification establishes a registry of profile names for use The RTP specification establishes a registry of profile names for use
by higher-level control protocols, such as the Session Description by higher-level control protocols, such as the Session Description
Protocol (SDP), RFC 2327 [6], to refer to transport methods. This Protocol (SDP), RFC 2327 [6], to refer to transport methods. This
profile registers the name "RTP/AVP". profile registers the name "RTP/AVP".
Section 3 establishes the policy that no additional registration of Section 3 establishes the policy that no additional registration of
static RTP payload types for this profile will be made beyond those static RTP payload types for this profile will be made beyond those
added in this document revision and included in Tables 4 and 5. IANA added in this document revision and included in Tables 4 and 5. IANA
may reference that section in declining to accept any additional may reference that section in declining to accept any additional
registration requests. registration requests. In Tables 4 and 5, note that types 1 and 2
have been marked reserved and the set of "dyn" payload types included
has been updated. These changes are explained in Sections 6 and 9.
D References 12. References
Normative References 12.1 Normative References
[1] Schulzrinne, H., S. Casner, R. Frederick, and V. Jacobson, "RTP: [1] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
A Transport Protocol for Real-Time Applications," Work in "RTP: A Transport Protocol for Real-Time Applications", RFC
progress, revision to RFC 1889. 3550, July 2003.
[2] Bradner, S., "Key Words for Use in RFCs to Indicate Requirement [2] Bradner, S., "Key Words for Use in RFCs to Indicate Requirement
Levels," BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[3] Apple Computer, "Audio Interchange File Format AIFF-C," August [3] Apple Computer, "Audio Interchange File Format AIFF-C", August
1991. (also ftp://ftp.sgi.com/sgi/aiff-c.9.26.91.ps.Z). 1991. (also ftp://ftp.sgi.com/sgi/aiff-c.9.26.91.ps.Z).
Informative References 12.2 Informative References
[4] Braden, R., D. Clark, S. Shenker, "Integrated Services in the [4] Braden, R., Clark, D. and S. Shenker, "Integrated Services in
Internet Architecture: an Overview," RFC 1633, June 1994. the Internet Architecture: an Overview", RFC 1633, June 1994.
[5] Blake, S., D. Black, M. Carlson, E. Davies, Z. Wang, W. Weiss, [5] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z. and W.
"An Architecture for Differentiated Service," RFC 2475, December Weiss, "An Architecture for Differentiated Service", RFC 2475,
1998. December 1998.
[6] Handley, M. and V. Jacobson, "SDP: Session Description [6] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol," RFC 2327, April 1998. Protocol", RFC 2327, April 1998.
[7] Casner, S. and P. Hoschka, "MIME Type Registration of RTP [7] Casner, S. and P. Hoschka, "MIME Type Registration of RTP
Payload Types," Internet Draft, Internet Engineering Task Force, Payload Types", RFC 3555, July 2003.
Work in progress.
[8] Freed, N., J. Klensin, and J. Postel, "Multipurpose Internet [8] Freed, N., Klensin, J. and J. Postel, "Multipurpose Internet
Mail Extensions (MIME) Part Four: Registration Procedures," Mail Extensions (MIME) Part Four: Registration Procedures", BCP
BCP 13, RFC 2048, November 1996. 13, RFC 2048, November 1996.
[9] Zopf, R., "Real-time Transport Protocol (RTP) Payload for [9] Zopf, R., "Real-time Transport Protocol (RTP) Payload for
Comfort Noise (CN)," RFC 3389, September 2002. Comfort Noise (CN)", RFC 3389, September 2002.
[10] IMA Digital Audio Focus and Technical Working Groups,
"Recommended practices for enhancing digital audio compatibility
in multimedia systems (version 3.00)," tech. rep., Interactive
Multimedia Association, Annapolis, Maryland, October 1992.
[11] Deleam, D. and J.-P. Petit, "Real-time implementations of the [10] Deleam, D. and J.-P. Petit, "Real-time implementations of the
recent ITU-T low bit rate speech coders on the TI TMS320C54X recent ITU-T low bit rate speech coders on the TI TMS320C54X
DSP: results, methodology, and applications," in Proc. of DSP: results, methodology, and applications", in Proc. of
International Conference on Signal Processing, Technology, and International Conference on Signal Processing, Technology, and
Applications (ICSPAT) , (Boston, Massachusetts), pp. 1656--1660, Applications (ICSPAT) , (Boston, Massachusetts), pp. 1656--1660,
October 1996. October 1996.
[12] Mouly, M. and M.-B. Pautet, The GSM system for mobile [11] Mouly, M. and M.-B. Pautet, The GSM system for mobile
communications Lassay-les-Chateaux, France: Europe Media communications Lassay-les-Chateaux, France: Europe Media
Duplication, 1993. Duplication, 1993.
[13] Degener, J., "Digital Speech Compression," Dr. Dobb's Journal , [12] Degener, J., "Digital Speech Compression", Dr. Dobb's Journal,
December 1994. December 1994.
[14] Redl, S., M. Weber, and M. Oliphant, An Introduction to GSM [13] Redl, S., Weber, M. and M. Oliphant, An Introduction to GSM
Boston: Artech House, 1995. Boston: Artech House, 1995.
[15] Hoffman, D., G. Fernando, V. Goyal, and M. Civanlar, "RTP [14] Hoffman, D., Fernando, G., Goyal, V. and M. Civanlar, "RTP
Payload Format for MPEG1/MPEG2 Video," RFC 2250, January 1998. Payload Format for MPEG1/MPEG2 Video", RFC 2250, January 1998.
[16] Jayant, N. and P. Noll, Digital Coding of Waveforms--Principles [15] Jayant, N. and P. Noll, Digital Coding of Waveforms--Principles
and Applications to Speech and Video Englewood Cliffs, New and Applications to Speech and Video Englewood Cliffs, New
Jersey: Prentice-Hall, 1984. Jersey: Prentice-Hall, 1984.
[17] McKay, K., "RTP Payload Format for PureVoice(tm) Audio", [16] McKay, K., "RTP Payload Format for PureVoice(tm) Audio", RFC
RFC 2658, August 1999. 2658, August 1999.
[18] Perkins, C., I. Kouvelas, O. Hodson, V. Hardman, M. Handley, [17] Perkins, C., Kouvelas, I., Hodson, O., Hardman, V., Handley, M.,
J.-C. Bolot, A. Vega-Garcia, and S. Fosse-Parisis, "RTP Payload Bolot, J.-C., Vega-Garcia, A. and S. Fosse-Parisis, "RTP Payload
for Redundant Audio Data," RFC 2198, September 1997. for Redundant Audio Data", RFC 2198, September 1997.
[19] Speer, M. and D. Hoffman, "RTP Payload Format of Sun's CellB [18] Speer, M. and D. Hoffman, "RTP Payload Format of Sun's CellB
Video Encoding," RFC 2029, October 1996. Video Encoding", RFC 2029, October 1996.
[20] Berc, L., W. Fenner, R. Frederick, and S. McCanne, "RTP Payload [19] Berc, L., Fenner, W., Frederick, R., McCanne, S. and P. Stewart,
Format for JPEG-Compressed Video," RFC 2435, October 1996. "RTP Payload Format for JPEG-Compressed Video", RFC 2435,
October 1998.
[21] Turletti, T. and C. Huitema, "RTP Payload Format for H.261 Video [20] Turletti, T. and C. Huitema, "RTP Payload Format for H.261 Video
Streams," RFC 2032, October 1996. Streams", RFC 2032, October 1996.
[22] Zhu, C., "RTP Payload Format for H.263 Video Streams," RFC 2190, [21] Zhu, C., "RTP Payload Format for H.263 Video Streams", RFC 2190,
September 1997. September 1997.
[23] Bormann, C., L. Cline, G. Deisher, T. Gardos, C. Maciocco, [22] Bormann, C., Cline, L., Deisher, G., Gardos, T., Maciocco, C.,
D. Newell, J. Ott, G. Sullivan, S. Wenger, C. Zhu, "RTP Payload Newell, D., Ott, J., Sullivan, G., Wenger, S. and C. Zhu, "RTP
Format for the 1998 Version of ITU-T Rec. H.263 Video (H.263+)," Payload Format for the 1998 Version of ITU-T Rec. H.263 Video
RFC 2429, October 1998. (H.263+)", RFC 2429, October 1998.
[24] Schulzrinne, H., A. Rao, and R. Lanphier, "Real Time Streaming [23] Schulzrinne, H., Rao, A. and R. Lanphier, "Real Time Streaming
Protocol (RTSP)," RFC 2326, April 1998. Protocol (RTSP)", RFC 2326, April 1998.
[25] Deering, S., "Host Extensions for IP Multicasting," STD 5, [24] Cain, B., Deering, S., Kouvelas, I., Fenner, B. and A.
RFC 1112, August 1989. Thyagarajan, "Internet Group Management Protocol, Version 3",
RFC 3376, October 2002.
E Current Locations of Related Resources 13. Current Locations of Related Resources
Note: Several sections below refer to the ITU-T Software Tool Note: Several sections below refer to the ITU-T Software Tool
Library (STL). It is available from the ITU Sales Service, Place des Library (STL). It is available from the ITU Sales Service, Place des
Nations, CH-1211 Geneve 20, Switzerland (also check Nations, CH-1211 Geneve 20, Switzerland (also check
http://www.itu.int. The ITU-T STL is covered by a license defined in http://www.itu.int). The ITU-T STL is covered by a license defined
ITU-T Recommendation G.191, "Software tools for speech and audio in ITU-T Recommendation G.191, "Software tools for speech and audio
coding standardization". coding standardization".
DVI4 DVI4
An archived copy of the document IMA Recommended Practices for
Enhancing Digital Audio Compatibility in Multimedia Systems (version
3.0), which describes the IMA ADPCM algorithm, is available at:
http://www.cs.columbia.edu/~hgs/audio/dvi/
An implementation is available from Jack Jansen at An implementation is available from Jack Jansen at
ftp://ftp.cwi.nl/local/pub/audio/adpcm.shar ftp://ftp.cwi.nl/local/pub/audio/adpcm.shar
G722 G722
An implementation of the G.722 algorithm is available as part of the An implementation of the G.722 algorithm is available as part of the
ITU-T STL, described above. ITU-T STL, described above.
G723 G723
The reference C code implementation defining the G.723.1 algorithm The reference C code implementation defining the G.723.1 algorithm
and its Annexes A, B, and C are available as an integral part of and its Annexes A, B, and C are available as an integral part of
skipping to change at page 42, line 47 skipping to change at page 42, line 27
I contains the integrated C source code for all G.729 operating I contains the integrated C source code for all G.729 operating
modes. The G.729 algorithm and associated C code are covered by a modes. The G.729 algorithm and associated C code are covered by a
specific license. The contact information for obtaining the license specific license. The contact information for obtaining the license
is available from the ITU-T Secretariat. is available from the ITU-T Secretariat.
GSM GSM
A reference implementation was written by Carsten Bormann and Jutta A reference implementation was written by Carsten Bormann and Jutta
Degener (then at TU Berlin, Germany). It is available at Degener (then at TU Berlin, Germany). It is available at
http://www.dmn.tzi.org/software/gsm/ http://www.dmn.tzi.org/software/gsm/
Although the RPE-LTP algorithm is not an ITU-T standard, there is a C Although the RPE-LTP algorithm is not an ITU-T standard, there is a C
code implementation of the RPE-LTP algorithm available as part of the code implementation of the RPE-LTP algorithm available as part of the
ITU-T STL. The STL implementation is an adaptation of the TU Berlin ITU-T STL. The STL implementation is an adaptation of the TU Berlin
version. version.
LPC LPC
An implementation is available at An implementation is available at
ftp://parcftp.xerox.com/pub/net-research/lpc.tar.Z ftp://parcftp.xerox.com/pub/net-research/lpc.tar.Z
PCMU, PCMA PCMU, PCMA
An implementation of these algorithm is available as part of the An implementation of these algorithms is available as part of the
ITU-T STL, described above. Code to convert between linear and mu- ITU-T STL, described above.
law companded data is also available in [10].
F Acknowledgments 14. Acknowledgments
The comments and careful review of Simao Campos, Richard Cox and AVT The comments and careful review of Simao Campos, Richard Cox and AVT
Working Group participants are gratefully acknowledged. The GSM Working Group participants are gratefully acknowledged. The GSM
description was adopted from the IMTC Voice over IP Forum Service description was adopted from the IMTC Voice over IP Forum Service
Interoperability Implementation Agreement (January 1997). Fred Burg Interoperability Implementation Agreement (January 1997). Fred Burg
and Terry Lyons helped with the G.729 description. and Terry Lyons helped with the G.729 description.
G Addresses of Authors 15. Intellectual Property Rights Statement
Henning Schulzrinne
Department of Computer Science
Columbia University
1214 Amsterdam Avenue
New York, NY 10027
USA
electronic mail: schulzrinne@cs.columbia.edu
Stephen L. Casner
Packet Design
3400 Hillview Avenue, Building 3
Palo Alto, CA 94304
United States
electronic mail: casner@acm.org
H Intellectual Property Rights Statement
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of claims of rights made available for publication and any assurances of
skipping to change at page 44, line 22 skipping to change at page 43, line 27
obtain a general license or permission for the use of such obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat. be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive this standard. Please address the information to the IETF Executive
Director. Director.
I Full Copyright Statement 16. Authors' Addresses
Henning Schulzrinne
Department of Computer Science
Columbia University
1214 Amsterdam Avenue
New York, NY 10027
United States
EMail: schulzrinne@cs.columbia.edu
Stephen L. Casner
Packet Design
3400 Hillview Avenue, Building 3
Palo Alto, CA 94304
United States
EMail: casner@acm.org
17. Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved. Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing document itself may not be modified in any way, such as by removing
skipping to change at line 1979 skipping to change at page 44, line 32
The limited permissions granted above are perpetual and will not be The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns. revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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