draft-ietf-avt-profile-new-11.txt   draft-ietf-avt-profile-new-12.txt 
Internet Engineering Task Force AVT WG Internet Engineering Task Force AVT WG
Internet Draft Schulzrinne/Casner Internet Draft Schulzrinne/Casner
draft-ietf-avt-profile-new-11.txt Columbia U./Packet Design draft-ietf-avt-profile-new-12.txt Columbia U./Packet Design
July 20, 2001 November 20, 2001
Expires: January 2002 Expires: May 2002
RTP Profile for Audio and Video Conferences with Minimal Control RTP Profile for Audio and Video Conferences with Minimal Control
STATUS OF THIS MEMO STATUS OF THIS MEMO
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt http://www.ietf.org/ietf/1id-abstracts.txt
To view the list Internet-Draft Shadow Directories, see To view the list Internet-Draft Shadow Directories, see
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
Abstract Abstract
This memorandum is a revision of RFC 1890 in preparation for This memorandum is a revision of RFC 1890 in preparation for
advancement from Proposed Standard to Draft Standard status. Readers advancement from Proposed Standard to Draft Standard status.
are encouraged to use the PostScript form of this draft to see where
changes from RFC 1890 are marked by change bars.
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.
This document also describes how audio and video data may be carried This document also describes how audio and video data may be carried
within RTP. It defines a set of standard encodings and their names within RTP. It defines a set of standard encodings and their names
when used within RTP. The descriptions provide pointers to reference when used within RTP. The descriptions provide pointers to reference
implementations and the detailed standards. This document is meant as implementations and the detailed standards. This document is meant as
an aid for implementors of audio, video and other real-time an aid for implementors of audio, video and other real-time
multimedia applications. multimedia applications.
Resolution of Open Issues Contents
[Note to the RFC Editor: This section is to be deleted when this 1 Introduction ........................................ 3
draft is published as an RFC but is shown here for reference during 1.1 Terminology ......................................... 3
the Last Call. The first paragraph of the Abstract is also to be 2 RTP and RTCP Packet Forms and Protocol Behavior ..... 4
deleted. All RFC XXXX should be filled in with the number of the RTP 3 IANA Considerations ................................. 6
3.1 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 .......... 10
4.5 Audio Encodings ..................................... 11
4.5.1 DVI4 ................................................ 12
4.5.2 G722 ................................................ 13
4.5.3 G723 ................................................ 13
4.5.4 G726-40, G726-32, G726-24, and G726-16 .............. 17
4.5.5 G728 ................................................ 18
4.5.6 G729 ................................................ 19
4.5.7 G729D and G729E ..................................... 21
4.5.8 GSM ................................................. 24
4.5.8.1 General Packaging Issues ............................ 24
4.5.8.2 GSM variable names and numbers ...................... 25
4.5.9 GSM-EFR ............................................. 25
4.5.10 L8 .................................................. 25
4.5.11 L16 ................................................. 25
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 ................................................. 28
4.5.17 VDVI ................................................ 29
5 Video ............................................... 29
5.1 CelB ................................................ 30
5.2 JPEG ................................................ 30
5.3 H261 ................................................ 30
5.4 H263 ................................................ 30
5.5 H263-1998 ........................................... 31
5.6 MPV ................................................. 31
5.7 MP2T ................................................ 31
5.8 nv .................................................. 31
6 Payload Type Definitions ............................ 31
7 RTP over TCP and Similar Byte Stream Protocols ...... 32
8 Port Assignment ..................................... 32
9 Changes from RFC 1890 ............................... 34
10 Security Considerations ............................. 37
11 Full Copyright Statement ............................ 37
12 Acknowledgments ..................................... 38
13 Addresses of Authors ................................ 38
1 Introduction
[Note to the RFC Editor: This paragraph and the first paragraph of
the Abstract are to be deleted when this 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 specification RFC submitted for Draft Standard status, and all RFC
YYYY should be filled in with the number of the draft specifying MIME YYYY should be filled in with the number of the draft specifying MIME
registration of RTP payload types as it is submitted for Proposed registration of RTP payload types as it is submitted for Proposed
Standard status. These latter references are intended to be non- Standard status. These latter references are intended to be non-
normative.] normative as this Profile may be used independently of the MIME
registrations.]
Readers are directed to Appendix 9, Changes from RFC 1890, for a
listing of the changes that have been made in this draft. The
changes from RFC 1890 are marked with change bars in the PostScript
form of this draft.
The changes in this revision of the draft from the previous one are:
o Added back G723, GSM-EFR, H263 (1996), MP2T payload formats
since reports of interoperable implementations of these were
received.
o Added references to optional parameters in the payload format
MIME registrations [6] for G723, G729, L16, MPA and MPV.
o Clarified that the marker bit for audio is set only when
packets are intentionally not sent during silence.
o Removed a reference in the Security Considerations section to
the previously removed mapping of a user pass-phrase into an
encryption key.
This version of the draft is intended to be complete for Last Call.
The following open issues from previous drafts have been addressed:
o The procedure for registering RTP encoding names as MIME
subtypes was moved to a separate RFC-to-be that may also serve
to specify how (some of) the encodings here may be used with
mail and other not-RTP transports. That procedure is not
required to implement this profile, but may be used in those
contexts where it is needed.
o This profile follows the suggestion in the RTP spec that RTCP
bandwidth may be specified separately from the session
bandwidth and separately for active senders and passive
receivers.
o No specific action is taken in this document to address
generic payload formats; it is assumed that if any generic
payload formats are developed, they can be specified in
separate RFCs and that the session parameters they require for
operation can be specified in the MIME registration of those
formats.
o The specification of the CN (comfort noise) payload format has
been removed to a separate draft so that it may be enhanced as
a result of additional work in ITU-T. That draft is intended
for publication at Proposed Standard status. Static payload
type 13 is marked reserved here for the use of that payload
format (since CN has already been implemented from earlier
drafts of this profile). Static payload type 19 is also
reserved because some revisions of the draft assigned that
number to CN to avoid an historic use of 13.
o The requirement for congestion control in RTP is addressed in
the RTP spec with an explanation that the behavior is context
specific and should be defined in RTP profiles. Text has been
added to this profile in Section 2 to describe the
requirements only in general terms because specific algorithms
have not been devised yet for multicast congestion control.
1 Introduction
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 XXXX) [2]. 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 expected parameters or membership control is provided. The profile is expected
to be useful in sessions where no negotiation or membership control to be useful in sessions where no negotiation or membership control
are used (e.g., using the static payload types and the membership are used (e.g., using the static payload types and the membership
indications provided by RTCP), but this profile may also be useful in indications provided by RTCP), but this profile may also be useful in
conjunction with a higher-level control protocol. 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 Section 3. directories may use the name for this profile specified in Section 3.
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. audio and video. These payload format descriptions are included here
only as a matter of convenience since they are too small to warrant
separate documents. Use of these payload formats is NOT REQUIRED 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.
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 [1] 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 draft defines the term media type as dividing encodings of audio
and video content into three classes: audio, video and audio/video and video content into three classes: audio, video and audio/video
(interleaved). (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 RFC The section "RTP Profiles and Payload Format Specification" of RFC
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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 this profile MAY specify a separate parameter for the under this profile MAY specify a separate parameter for the
RTCP traffic bandwidth rather than using the default RTCP traffic bandwidth rather than using the default
fraction of the session bandwidth. The RTCP traffic fraction of the session bandwidth. The RTCP traffic
bandwidth MAY be divided into two separate session bandwidth MAY be divided into two separate session
parameters for those participants which are active data parameters for those participants which are 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 recommendation in the RTP specification [2] that 1/4 of the
RTCP bandwidth be dedicated to data senders, the RTCP bandwidth be dedicated to data senders, the
RECOMMENDED default values for these two parameters would RECOMMENDED default values for these two parameters would
be 1.25% and 3.75%, respectively. For a particular session, be 1.25% and 3.75%, respectively. For a particular session,
the RTCP bandwidth for non-data-senders MAY be set to zero the RTCP bandwidth for non-data-senders MAY be set to zero
when operating on unidirectional links or for sessions that when operating on unidirectional links or for sessions that
don't require feedback on the quality of reception. The don't require feedback on the quality of reception. The
RTCP bandwidth for data senders SHOULD be kept non-zero so RTCP bandwidth for data senders SHOULD be kept non-zero so
that sender reports can still be sent for inter-media that sender reports can still be sent for inter-media
synchronization and to identify the source by CNAME. The synchronization and to identify the source by CNAME. The
means by which the one or two session parameters for RTCP means by which the one or two session parameters for RTCP
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NAME is sent in RTCP packets 1, 4, 7, 10, 13, 16, 19, NAME is sent in RTCP packets 1, 4, 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 (RFC 1633) [3] or Differentiated Services (RFC Services (RFC 1633) [4] or Differentiated Services (RFC
2475) [4], or they may be used with best effort service. 2475) [5], or they may be used with best effort service.
If enhanced service is being used, RTP receivers SHOULD If enhanced service is being used, RTP receivers SHOULD
monitor packet loss to ensure that the service that was monitor packet loss to ensure that the service that was
requested is actually being delivered. If it is not, then requested is actually being delivered. If it is not, then
they SHOULD assume that they are receiving best-effort they SHOULD assume that they are receiving best-effort
service and behave accordingly. service and behave accordingly.
If best-effort service is being used, RTP receivers SHOULD If best-effort service is being used, RTP receivers SHOULD
monitor packet loss to ensure that the packet loss rate is monitor packet loss to ensure that the packet loss rate is
within acceptable parameters. Packet loss is considered within acceptable parameters. Packet loss is considered
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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 IANA Considerations 3 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 [5], 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".
3.1 Registering Additional Encodings 3.1 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 [5], 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 [6] form of a MIME content-type. To facilitate this, RFC YYYY [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 [7]. 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 is encodings are kept unique. RFC YYYY specifies the information that is
required for the registration of RTP encodings. required for the registration of RTP encodings.
In addition to assigning names to encodings, this profile also also In addition to assigning names to encodings, this profile also
assigns static RTP payload type numbers to some of them. However, the assigns static RTP payload type numbers to some of them. However, the
payload type number space is relatively small and cannot accommodate payload type number space is relatively small and cannot accommodate
assignments for all existing and future encodings. During the early assignments for all existing and future encodings. During the early
stages of RTP development, it was necessary to use statically stages of RTP development, it was necessary to use statically
assigned payload types because no other mechanism had been specified assigned payload types because no other mechanism had been specified
to bind encodings to payload types. It was anticipated that non-RTP to bind encodings to payload types. It was anticipated that non-RTP
means beyond the scope of this memo (such as directory services or means beyond the scope of this memo (such as directory services or
invitation protocols) would be specified to establish a dynamic invitation protocols) would be specified to establish a dynamic
mapping between a payload type and an encoding. Now, mechanisms for mapping between a payload type and an encoding. Now, mechanisms for
defining dynamic payload type bindings have been specified in the defining dynamic payload type bindings have been specified in the
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noise packets during silence, the first packet of a talkspurt, that noise packets during silence, the first packet of a talkspurt, that
is, the first packet after a silence period during which packets have is, the first packet after a silence period during which packets have
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 bits in all the marker bit in the RTP data header to one. The marker bits 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 equals the independent of the number of channels and the encoding; it usually
number of sampling periods per second. For N-channel encodings, each equals the number of sampling periods per second. For N-channel
sampling period (say, 1/8000 of a second) generates N samples. (This encodings, each sampling period (say, 1/8000 of a second) generates N
terminology is standard, but somewhat confusing, as the total number samples. (This terminology is standard, but somewhat confusing, as
of samples generated per second is then the sampling rate times the the total number of samples generated per second is then the sampling
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 [8], 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
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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
The characteristics of the audio encodings described in this document
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
sampling rate, some sample-based algorithms (indicated by an entry of
"var." in the sampling rate column of Table 1) may be used with
different sampling rates, resulting in different coded bit rates.
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
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
sampling rate for audio.
4.5.1 DVI4
DVI4 is specified, with pseudo-code, in [9] as the IMA ADPCM wave
type.
However, the encoding defined here as DVI4 differs in three respects
from this recommendation:
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
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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
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
sampling rate, some sample-based algorithms (indicated by an entry of
"var." in the sampling rate column of Table 1) may be used with
different sampling rates, resulting in different coded bit rates.
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
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
sampling rate for audio.
4.5.1 DVI4
DVI4 is specified, with pseudo-code, in [9] as the IMA ADPCM wave
type.
However, the encoding defined here as DVI4 differs in three respects
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 first sample value contained the IMA ADPCM block header. the 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 sample of a block is contained just in the header first sample of a block is contained just in the header
(uncompressed), followed by an even number of compressed (uncompressed), followed by an even number of compressed
samples. DVI4 has an even number of compressed samples only, samples. DVI4 has an even number of compressed samples only,
using the `predict' word from the header to decode the first using the `predict' word from the header to decode the first
sample. sample.
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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. The MIME registration for G723 in RFC YYYY the encoder and decoder. The MIME registration for G723 in RFC YYYY
[6] specifies parameters that MAY be used with MIME or SDP to [7] 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. restrict to a single data rate or to restrict the use of SID frames.
This coder was optimized to represent speech with near-toll quality This coder was optimized to represent speech with near-toll quality
at the above rates using a limited amount of complexity. at the above 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
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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 8000 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 codewords technique. The ADPCM representation consists of a series of codewords
with a one-to-one correspondance to the samples in the PCM stream. 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 codewords of 5, The G726 data rates of 40, 32, 24, and 16 kbit/s have codewords of 5,
4, 3, and 2 bits respectively. 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.
skipping to change at page 20, line 6 skipping to change at page 20, line 6
trades some speech quality for an approximate 50% complexity trades some speech quality for an approximate 50% complexity
reduction [10]. See the next Section (4.5.7) for other data rates reduction [10]. See the next Section (4.5.7) for other data rates
added in later G.729 Annexes. For all data rates, the sampling added in later G.729 Annexes. For all data rates, the sampling
frequency (and RTP timestamp clock rate) is 8000 Hz. frequency (and RTP timestamp clock rate) is 8000 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. The while the G.729 Annex B comfort noise frame occupies 2 octets. The
MIME registration for G729 in RFC YYYY [6] specifies a parameter that MIME registration for G729 in RFC YYYY [7] specifies a parameter that
MAY be used with MIME or SDP to restrict the use of comfort noise MAY be used with MIME or SDP to restrict the use of comfort noise
frames. 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 of 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 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 desireable 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.
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
skipping to change at page 21, line 36 skipping to change at page 21, line 36
modes, backward adaptive and forward adaptive, which are signaled by modes, backward adaptive and forward adaptive, which are signaled by
the first two bits in each frame (the most significant two bits of the first two bits in each frame (the most significant two bits of
the first octet). 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 and B CNG are specified in G.729 Annexes F and G. Note that Annexes F and
G do not introduce any new encodings. The MIME registrations for G do not introduce any new encodings. The MIME registrations for
G729D and G729E in RFC YYYY [6] specify a parameter that MAY be used G729D and G729E in RFC YYYY [7] specify a parameter that MAY be used
with MIME or SDP to restrict the use of comfort noise frames. with MIME or SDP to restrict the 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,
skipping to change at page 25, line 49 skipping to change at page 25, line 49
zero. zero.
4.5.11 L16 4.5.11 L16
L16 denotes uncompressed audio data samples, using 16-bit signed L16 denotes uncompressed audio data samples, using 16-bit signed
representation with 65535 equally divided steps between minimum and representation with 65535 equally divided steps between minimum and
maximum signal level, ranging from -32768 to 32767. The value is maximum signal level, ranging from -32768 to 32767. The value is
represented in two's complement notation and transmitted in network represented in two's complement notation and transmitted in network
byte order (most significant byte first). byte order (most significant byte first).
The MIME registration for L16 in RFC YYYY [6] specifies parameters The MIME registration for L16 in RFC YYYY [7] specifies parameters
field field name bits field field name bits field field name bits field field name bits
________________________________________________ ________________________________________________
1 LARc[0] 6 39 xmc[22] 3 1 LARc[0] 6 39 xmc[22] 3
2 LARc[1] 6 40 xmc[23] 3 2 LARc[1] 6 40 xmc[23] 3
3 LARc[2] 5 41 xmc[24] 3 3 LARc[2] 5 41 xmc[24] 3
4 LARc[3] 5 42 xmc[25] 3 4 LARc[3] 5 42 xmc[25] 3
5 LARc[4] 4 43 Nc[2] 7 5 LARc[4] 4 43 Nc[2] 7
6 LARc[5] 4 44 bc[2] 2 6 LARc[5] 4 44 bc[2] 2
7 LARc[6] 3 45 Mc[2] 2 7 LARc[6] 3 45 Mc[2] 2
8 LARc[7] 3 46 xmaxc[2] 6 8 LARc[7] 3 46 xmaxc[2] 6
skipping to change at page 27, line 6 skipping to change at page 27, line 6
38 xmc[21] 3 76 xmc[51] 3 38 xmc[21] 3 76 xmc[51] 3
Table 2: Ordering of GSM variables Table 2: Ordering of GSM variables
that MAY be used with MIME or SDP to indicate that analog preemphasis 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 was applied to the signal before quantization or to indicate that a
multiple-channel audio stream follows a different channel ordering multiple-channel audio stream follows a different channel ordering
convention than is specified in Section 4.1. convention than is specified in Section 4.1.
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
8 xmc2.1 xmc2.2 xmc3.0 xmc3.1 xmc3.2 xmc4.0 xmc4.1 xmc4.2 8 xmc2.1 xmc2.2 xmc3.0 xmc3.1 xmc3.2 xmc4.0 xmc4.1 xmc4.2
9 xmc5.0 xmc5.1 xmc5.2 xmc6.0 xmc6.1 xmc6.2 xmc7.0 xmc7.1 9 xmc5.0 xmc5.1 xmc5.2 xmc6.0 xmc6.1 xmc6.2 xmc7.0 xmc7.1
skipping to change at page 28, line 20 skipping to change at page 28, line 20
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 90000, independent of the sampling rate. MPEG-1
audio supports sampling rates of 32, 44.1, and 48 kHz (ISO/IEC 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 16, 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 the 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. frame size will vary with the sampling rate and bit rate.
The MIME registration for MPA in RFC YYYY [6] specifies parameters The MIME registration for MPA in RFC YYYY [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 data PCMA and PCMU are specified in ITU-T Recommendation G.711. Audio data
is encoded as eight bits per sample, after logarithmic scaling. PCMU is encoded as eight bits per sample, after logarithmic scaling. PCMU
denotes mu-law scaling, PCMA A-law scaling. A detailed description is denotes mu-law scaling, PCMA A-law scaling. A detailed description is
given by Jayant and Noll [15]. Each G.711 octet SHALL be octet- 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 SHALL 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 packet 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 host (i.e., assuming the G.711 samples are handled as octets on the host
machine, the sign bit SHALL be the most signficant bit of the octet 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 kb/s modes 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 MUST always of G.711 are not applicable to RTP, since PCMA and PCMU MUST always
be transmitted as 8-bit samples. be transmitted as 8-bit samples.
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
skipping to change at page 31, line 26 skipping to change at page 31, line 26
features of the 1998 version of H.263 MUST use the payload format features of the 1998 version of H.263 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 RFC 2250 respectively. The RTP payload format is as specified in RFC 2250
[14], Section 3. [14], Section 3.
The MIME registration for MPV in RFC YYYY [6] specifies a parameter The MIME registration for MPV in RFC YYYY [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 payoad format is described in RFC 2250 [14], 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 from at Xerox PARC by Ron Frederick. Further information is available from
the author: the author:
Ron Frederick Ron Frederick
Cacheflow Inc. Cacheflow Inc.
skipping to change at page 32, line 38 skipping to change at page 32, line 38
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 negotation 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
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 [23] 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.)
8 Port Assignment 8 Port Assignment
skipping to change at page 34, line 46 skipping to change at page 34, line 46
pair be explicitly specified. The particular port numbers were chosen pair be explicitly specified. The particular port numbers were chosen
to lie in the range above 5000 to accommodate port number allocation to lie in the range above 5000 to accommodate port number allocation
practice within some versions of the Unix operating system, where practice within some versions of the Unix operating system, where
port numbers below 1024 can only be used by privileged processes and port numbers below 1024 can only be used by privileged processes and
port numbers between 1024 and 5000 are automatically assigned by the port numbers between 1024 and 5000 are automatically assigned by the
operating system. operating system.
9 Changes from RFC 1890 9 Changes from RFC 1890
This RFC revises RFC 1890. It is mostly backwards-compatible with RFC This RFC revises RFC 1890. It is mostly backwards-compatible with RFC
1890 and codifies existing practice. The changes are listed below. 1890 except for functions removed because two interoperable
implementations were not found. The additions to RFC 1890 codify
existing practice in the use of payload formats under this profile.
Since this profile may be used without using any of the payload
formats listed here, the addition of new payload formats in this
revision does not affect backwards compatibility. The changes are
listed below, categorized into functional and non-functional changes.
o The mapping of a user pass-phrase string into an encryption Functional changes:
key was deleted from Section 2 because two interoperable
implementations were not found. o A new Section "IANA Considerations" was added to specify the
registration of the name for this profile and to establish a
new policy that no additional registration of static payload
types for this profile will be made beyond those added in this
revision and included in Tables 4 and 5. Instead, additional
encoding names may be registered as MIME subtypes for binding
to dynamic payload types. Non-normative references were added
to RFC YYYY [7] where MIME subtypes for all the listed payload
formats are registered, some with optional parameters for use
of the 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
and 18 were added along with the corresponding payload format
descriptions for QCELP and G729. Static payload type 13 was
reserved for a comfort noise payload format to be defined in a
separate RFC. Payload type 19 was marked reserved because it
had been temporarily allocated in some draft revisions of this
document.
o The payload format for G721 was renamed to G726-32 following
the ITU-T renumbering.
o The payload format description for G726 was expanded to
include the -16, -24 and -40 data rates. Payload formats G729D
and G729E were added following the ITU-T addition of Annexes D
and E to Recommendation G.729. Listings were added for payload
formats GSM-EFR, RED, and H263-1998 published in other
documents subsequent to RFC 1890. These additional payload
formats are referenced only by dynamic payload type numbers.
o The descriptions of the payload formats for G722, G728, GSM,
VDVI 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 Additional payload formats and/or expanded descriptions were o Requirements for congestion control were added in Section 2.
included for G722, G723, G726, G728, G729, GSM, GSM-EFR,
QCELP, RED, VDVI, H263 and H263-1998.
o Static payload types 4, 12, 16, 17, 18 and 34 were added, and o This profile follows the suggestion in the revised RTP spec
13 and 19 were reserved. that RTCP bandwidth may be specified separately from the
session bandwidth and separately for active senders and
passive receivers.
o Requirements for congestion control were added in Section 2. o The mapping of a user pass-phrase string into an encryption
key was deleted from Section 2 because two interoperable
implementations were not found.
o A new Section "IANA Considerations" was added to specify the Non-functional changes:
regstration of the name for this profile and to establish a
new policy that no additional registration of static payload
types for this profile will be made beyond those included in
Tables 4 and 5, but that additional encoding names may be
registered as MIME subtypes for binding to dynamic payload
types. Non-normative references were added to RFC YYYY [6]
where MIME subtypes for all the listed payload formats are
registered, some with optional parameters for use of the
payload formats.
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 bit on the first packet after silence for audio was marker bit on the first packet after silence for audio was
changed from "is" to "SHOULD be", and clarified that the changed from "is" to "SHOULD be", and clarified that the
marker bit is set only when packets are intentionally not marker bit is set only 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 set to one on the last packet of a video frame, and SHOULD be set to one on the last packet of a video frame, and
that video frames are distinguished by their timestamps. that video frames are distinguished by their timestamps.
o This profile follows the suggestion in the RTP spec that RTCP
bandwidth may be specified separately from the session
bandwidth and separately for active senders and passive
receivers.
o RFC references are added for payload formats published after o RFC references are added for payload formats published after
RFC 1890. RFC 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 the 22254.54 rate and none the 11127.27 rate, so the used the 22254.54 rate and none the 11127.27 rate, so the
latter was dropped from the discussion of suggested sampling latter was dropped from the discussion of suggested sampling
frequencies. frequencies.
skipping to change at page 36, line 41 skipping to change at page 37, line 24
- The terms MUST, SHOULD, MAY, etc. are used as defined in RFC - The terms MUST, SHOULD, MAY, etc. are used as defined in RFC
2119. 2119.
o A second author for this document was added. o A second author for this document was added.
10 Security Considerations 10 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 [2]. 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
skipping to change at page 37, line 24 skipping to change at page 38, line 7
environment, pruning of specific sources may be implemented in future environment, pruning of specific sources may be implemented in future
versions of IGMP [24] and in multicast routing protocols to allow a versions of IGMP [24] and in multicast routing protocols to allow a
receiver to select which sources are allowed to reach it. receiver to select which sources are allowed to reach it.
11 Full Copyright Statement 11 Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved. Copyright (C) The Internet Society (2001). 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 implmentation may be prepared, copied, published and or assist in its implementation may be prepared, copied, published
distributed, in whole or in part, without restriction of any kind, and distributed, in whole or in part, without restriction of any
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
the copyright notice or references to the Internet Society or other the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than followed, or as required to translate it into languages other than
English. English.
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.
12 Acknowledgements 12 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.
13 Addresses of Authors 13 Addresses of Authors
Henning Schulzrinne Henning Schulzrinne
skipping to change at page 38, line 22 skipping to change at page 39, line 4
New York, NY 10027 New York, NY 10027
USA USA
electronic mail: schulzrinne@cs.columbia.edu electronic mail: schulzrinne@cs.columbia.edu
Stephen L. Casner Stephen L. Casner
Packet Design Packet Design
2465 Latham Street 2465 Latham Street
Mountain View, CA 94040 Mountain View, CA 94040
United States United States
electronic mail: casner@acm.org electronic mail: casner@acm.org
References
A Bibliography Normative References
[1] H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson, "RTP: A [1] S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels," RFC 2119, Internet Engineering Task Force, Mar. 1997.
[2] H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson, "RTP: A
transport protocol for real-time applications," Internet Draft, transport protocol for real-time applications," Internet Draft,
Internet Engineering Task Force, Feb. 1999 Work in progress, revision Internet Engineering Task Force, Feb. 1999 Work in progress, revision
to RFC 1889. to RFC 1889.
[2] S. Bradner, "Key words for use in RFCs to Indicate Requirement [3] Apple Computer, "Audio interchange file format AIFF-C," Aug.
Levels," RFC 2119, Internet Engineering Task Force, Mar. 1997. 1991. (also ftp://ftp.sgi.com/sgi/aiff-c.9.26.91.ps.Z).
[3] R. Braden, D. Clark, S. Shenker, "Integrated Services in the Non-Normative References
[4] R. Braden, D. Clark, S. Shenker, "Integrated Services in the
Internet Architecture: an Overview," Request for Comments Internet Architecture: an Overview," Request for Comments
(Informational) RFC 1633, Internet Engineering Task Force, June 1994. (Informational) RFC 1633, Internet Engineering Task Force, June 1994.
[4] S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, W. Weiss, "An [5] S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, W. Weiss, "An
Architecture for Differentiated Service," Request for Comments Architecture for Differentiated Service," Request for Comments
(Proposed Standard) RFC 2475, Internet Engineering Task Force, Dec. (Proposed Standard) RFC 2475, Internet Engineering Task Force, Dec.
1998. 1998.
[5] M. Handley and V. Jacobson, "SDP: Session Description Protocol," [6] M. Handley and V. Jacobson, "SDP: Session Description Protocol,"
Request for Comments (Proposed Standard) RFC 2327, Internet Request for Comments (Proposed Standard) RFC 2327, Internet
Engineering Task Force, Apr. 1998. Engineering Task Force, Apr. 1998.
[6] S. Casner and P. Hoschka, "MIME Type Registration of RTP Payload [7] S. Casner and P. Hoschka, "MIME Type Registration of RTP Payload
Types," Internet Draft, Internet Engineering Task Force, July 2001. Types," Internet Draft, Internet Engineering Task Force, July 2001.
Work in progress. Work in progress.
[7] N. Freed, J. Klensin, and J. Postel, "Multipurpose Internet Mail [8] N. Freed, J. Klensin, and J. Postel, "Multipurpose Internet Mail
Extensions (MIME) Part Four: Registration Procedures," RFC 2048, Extensions (MIME) Part Four: Registration Procedures," RFC 2048,
Internet Engineering Task Force, Nov. 1996. Internet Engineering Task Force, Nov. 1996.
[8] Apple Computer, "Audio interchange file format AIFF-C," Aug.
1991. (also ftp://ftp.sgi.com/sgi/aiff-c.9.26.91.ps.Z).
[9] IMA Digital Audio Focus and Technical Working Groups, [9] IMA Digital Audio Focus and Technical Working Groups,
"Recommended practices for enhancing digital audio compatibility in "Recommended practices for enhancing digital audio compatibility in
multimedia systems (version 3.00)," tech. rep., Interactive multimedia systems (version 3.00)," tech. rep., Interactive
Multimedia Association, Annapolis, Maryland, Oct. 1992. Multimedia Association, Annapolis, Maryland, Oct. 1992.
[10] D. Deleam and J.-P. Petit, "Real-time implementations of the [10] D. Deleam and J.-P. Petit, "Real-time implementations of the
recent ITU-T low bit rate speech coders on the TI TMS320C54X DSP: recent ITU-T low bit rate speech coders on the TI TMS320C54X DSP:
results, methodology, and applications," in Proc. of International results, methodology, and applications," in Proc. of International
Conference on Signal Processing, Technology, and Applications Conference on Signal Processing, Technology, and Applications
(ICSPAT) , (Boston, Massachusetts), pp. 1656--1660, Oct. 1996. (ICSPAT) , (Boston, Massachusetts), pp. 1656--1660, Oct. 1996.
skipping to change at page 42, line 16 skipping to change at line 1870
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 algorithm is available as part of the
ITU-T STL, described above. Code to convert between linear and mu-law ITU-T STL, described above. Code to convert between linear and mu-law
companded data is also available in [9]. companded data is also available in [9].
Table of Contents
1 Introduction ........................................ 3
1.1 Terminology ......................................... 4
2 RTP and RTCP Packet Forms and Protocol Behavior ..... 4
3 IANA Considerations ................................. 6
3.1 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 .......... 10
4.5 Audio Encodings ..................................... 11
4.5.1 DVI4 ................................................ 11
4.5.2 G722 ................................................ 13
4.5.3 G723 ................................................ 13
4.5.4 G726-40, G726-32, G726-24, and G726-16 .............. 17
4.5.5 G728 ................................................ 18
4.5.6 G729 ................................................ 19
4.5.7 G729D and G729E ..................................... 21
4.5.8 GSM ................................................. 24
4.5.8.1 General Packaging Issues ............................ 24
4.5.8.2 GSM variable names and numbers ...................... 25
4.5.9 GSM-EFR ............................................. 25
4.5.10 L8 .................................................. 25
4.5.11 L16 ................................................. 25
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 ................................................. 28
4.5.17 VDVI ................................................ 29
5 Video ............................................... 29
5.1 CelB ................................................ 30
5.2 JPEG ................................................ 30
5.3 H261 ................................................ 30
5.4 H263 ................................................ 30
5.5 H263-1998 ........................................... 31
5.6 MPV ................................................. 31
5.7 MP2T ................................................ 31
5.8 nv .................................................. 31
6 Payload Type Definitions ............................ 31
7 RTP over TCP and Similar Byte Stream Protocols ...... 32
8 Port Assignment ..................................... 32
9 Changes from RFC 1890 ............................... 34
10 Security Considerations ............................. 36
11 Full Copyright Statement ............................ 37
12 Acknowledgements .................................... 37
13 Addresses of Authors ................................ 38
A Bibliography ........................................ 38
 End of changes. 

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