draft-ietf-mmusic-sdpng-01.txt   draft-ietf-mmusic-sdpng-02.txt 
Network Working Group Kutscher Network Working Group Kutscher
Internet-Draft Ott Internet-Draft Ott
Expires: January 18, 2002 Bormann Expires: February 22, 2002 Bormann
TZI, Universitaet Bremen TZI, Universitaet Bremen
July 20, 2001 August 24, 2001
Session Description and Capability Negotiation Session Description and Capability Negotiation
draft-ietf-mmusic-sdpng-01.txt draft-ietf-mmusic-sdpng-02.txt
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved. Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract Abstract
This document defines a language for describing multimedia sessions This document defines a language for describing multimedia sessions
with respect to configuration parameters and capabilities of end with respect to configuration parameters and capabilities of end
systems. systems.
This document is a product of the Multiparty Multimedia Session This document is a product of the Multiparty Multimedia Session
Control (MMUSIC) working group of the Internet Engineering Task Control (MMUSIC) working group of the Internet Engineering Task
Force. Comments are solicited and should be addressed to the working Force. Comments are solicited and should be addressed to the working
group's mailing list at confctrl@isi.edu and/or the authors. group's mailing list at confctrl@isi.edu and/or the authors.
Document Revision Document Revision
$Revision: 2.7 $
$Revision: 2.0 $
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology and System Model . . . . . . . . . . . . . . . 6 2. Terminology and System Model . . . . . . . . . . . . . . . 6
3. SDPng . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3. SDPng . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1 Conceptual Outline . . . . . . . . . . . . . . . . . . . . 9 3.1 Conceptual Outline . . . . . . . . . . . . . . . . . . . . 9
3.1.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . 9 3.1.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . 9
3.1.2 Components & Configurations . . . . . . . . . . . . . . . 11 3.1.2 Components & Configurations . . . . . . . . . . . . . . . 11
3.1.3 Constraints . . . . . . . . . . . . . . . . . . . . . . . 13 3.1.3 Constraints . . . . . . . . . . . . . . . . . . . . . . . 13
3.1.4 Session Attributes . . . . . . . . . . . . . . . . . . . . 14 3.1.4 Session Attributes . . . . . . . . . . . . . . . . . . . . 14
3.1.4.1 Owner . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.1.4.1 Owner . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.1.4.2 Session Identification . . . . . . . . . . . . . . . . . . 15 3.1.4.2 Session Identification . . . . . . . . . . . . . . . . . . 15
3.1.4.3 Time Specification (SDP 't=', 'r=', and 'z=' lines) . . . 16 3.1.4.3 Time Specification (SDP 't=', 'r=', and 'z=' lines) . . . 16
3.1.4.4 Component Semantic Specification . . . . . . . . . . . . . 17 3.1.4.4 Component Semantic Specification . . . . . . . . . . . . . 17
3.2 Syntax Definition Mechanisms . . . . . . . . . . . . . . . 18 3.2 Syntax Definition Mechanisms . . . . . . . . . . . . . . . 18
3.3 External Definition Packages . . . . . . . . . . . . . . . 20 3.3 External Definition Packages . . . . . . . . . . . . . . . 21
3.3.1 Profile Definitions . . . . . . . . . . . . . . . . . . . 20 3.3.1 Profile Definitions . . . . . . . . . . . . . . . . . . . 21
3.3.2 Library Definitions . . . . . . . . . . . . . . . . . . . 21 3.3.2 Library Definitions . . . . . . . . . . . . . . . . . . . 21
3.4 Mappings . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.4 Mappings . . . . . . . . . . . . . . . . . . . . . . . . . 23
4. Formal Specification . . . . . . . . . . . . . . . . . . . 24 4. Formal Specification . . . . . . . . . . . . . . . . . . . 24
4.1 XML Schema as a Definition Mechanism . . . . . . . . . . . 24
4.2 SDPng Schema . . . . . . . . . . . . . . . . . . . . . . . 25
4.3 Profiles . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.4 SDPng Documents . . . . . . . . . . . . . . . . . . . . . 26
4.5 Libraries . . . . . . . . . . . . . . . . . . . . . . . . 27
4.6 Details on the use of specific XML Mechanisms . . . . . . 28
4.6.1 Default Namespace . . . . . . . . . . . . . . . . . . . . 28
4.6.2 Qualified Locals . . . . . . . . . . . . . . . . . . . . . 29
4.6.3 Fixed Namespace Prefixes . . . . . . . . . . . . . . . . . 29
4.7 SDPng Schema Definitions . . . . . . . . . . . . . . . . . 29
4.7.1 SDPng Base Definition . . . . . . . . . . . . . . . . . . 30
4.7.2 Audio Codec Profile . . . . . . . . . . . . . . . . . . . 36
4.7.3 RTP profile . . . . . . . . . . . . . . . . . . . . . . . 37
4.8 Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 39
5. Use of SDPng in conjunction with other IETF Signaling 5. Use of SDPng in conjunction with other IETF Signaling
Protocols . . . . . . . . . . . . . . . . . . . . . . . . 25 Protocols . . . . . . . . . . . . . . . . . . . . . . . . 41
5.1 The Session Announcement Protocol (SAP) . . . . . . . . . 25 5.1 The Session Announcement Protocol (SAP) . . . . . . . . . 41
5.2 Session Initiation Protocol (SIP) . . . . . . . . . . . . 26 5.2 Session Initiation Protocol (SIP) . . . . . . . . . . . . 42
5.3 Real-Time Streaming Protocol (RTSP) . . . . . . . . . . . 26 5.3 Real-Time Streaming Protocol (RTSP) . . . . . . . . . . . 42
5.4 Media Gateway Control Protocol (MEGACOP) . . . . . . . . . 27 5.4 Media Gateway Control Protocol (MEGACOP) . . . . . . . . . 43
6. Open Issues . . . . . . . . . . . . . . . . . . . . . . . 28 6. Open Issues . . . . . . . . . . . . . . . . . . . . . . . 44
References . . . . . . . . . . . . . . . . . . . . . . . . 29 References . . . . . . . . . . . . . . . . . . . . . . . . 45
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 30 Authors' Addresses . . . . . . . . . . . . . . . . . . . . 46
A. Base SDPng Specifications for Audio Codec Descriptions . . 31 A. Base SDPng Specifications for Audio Codec Descriptions . . 47
A.1 DVI4 . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 A.1 DVI4 . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
A.2 G.722 . . . . . . . . . . . . . . . . . . . . . . . . . . 32 A.2 G.722 . . . . . . . . . . . . . . . . . . . . . . . . . . 48
A.3 G.726 . . . . . . . . . . . . . . . . . . . . . . . . . . 32 A.3 G.726 . . . . . . . . . . . . . . . . . . . . . . . . . . 48
A.4 G.728 . . . . . . . . . . . . . . . . . . . . . . . . . . 32 A.4 G.728 . . . . . . . . . . . . . . . . . . . . . . . . . . 48
A.5 G.729 . . . . . . . . . . . . . . . . . . . . . . . . . . 32 A.5 G.729 . . . . . . . . . . . . . . . . . . . . . . . . . . 48
A.6 G.729 Annex D and E . . . . . . . . . . . . . . . . . . . 33 A.6 G.729 Annex D and E . . . . . . . . . . . . . . . . . . . 49
A.7 GSM . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 A.7 GSM . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
A.7.1 GSM Full Rate . . . . . . . . . . . . . . . . . . . . . . 33 A.7.1 GSM Full Rate . . . . . . . . . . . . . . . . . . . . . . 49
A.7.2 GSM Half Rate . . . . . . . . . . . . . . . . . . . . . . 33 A.7.2 GSM Half Rate . . . . . . . . . . . . . . . . . . . . . . 49
A.7.3 GSM Enhanced Full Rate . . . . . . . . . . . . . . . . . . 33 A.7.3 GSM Enhanced Full Rate . . . . . . . . . . . . . . . . . . 49
A.8 L8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 A.8 L8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
A.9 L16 . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 A.9 L16 . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
A.10 LPC . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 A.10 LPC . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
A.11 MPA . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 A.11 MPA . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
A.12 PCMA and PCMU . . . . . . . . . . . . . . . . . . . . . . 34 A.12 PCMA and PCMU . . . . . . . . . . . . . . . . . . . . . . 50
A.13 QCELP . . . . . . . . . . . . . . . . . . . . . . . . . . 34 A.13 QCELP . . . . . . . . . . . . . . . . . . . . . . . . . . 50
A.14 VDVI . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 A.14 VDVI . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Full Copyright Statement . . . . . . . . . . . . . . . . . 35 B. Change History . . . . . . . . . . . . . . . . . . . . . . 51
Full Copyright Statement . . . . . . . . . . . . . . . . . 52
1. Introduction 1. Introduction
Multiparty multimedia conferencing is one of the applications that Multiparty multimedia conferencing is one of the applications that
require dynamic interchange of end system capabilities and the require dynamic interchange of end system capabilities and the
negotiation of a parameter set that is appropriate for all sending negotiation of a parameter set that is appropriate for all sending
and receiving end systems in a conference. For some applications, and receiving end systems in a conference. For some applications,
e.g. for loosely coupled conferences or for broadcast scenarios, it e.g. for loosely coupled conferences or for broadcast scenarios, it
may be sufficient to simply have session parameters be fixed by the may be sufficient to simply have session parameters be fixed by the
initiator of a conference. In such a scenario no negotiation is initiator of a conference. In such a scenario no negotiation is
required because only those participants with media tools that required because only those participants with media tools that
support the predefined settings can join a media session and/or a support the predefined settings can join a media session and/or a
conference. conference.
This approach is applicable for conferences that are announced some This approach is applicable for conferences that are announced some
time ahead of the actual start date of the conference. Potential time ahead of the actual start date of the conference. Potential
participants can check the availability of media tools in advance participants can check the availability of media tools in advance and
and tools like session directories can configure media tools on tools like session directories can configure media tools on startup.
startup. This procedure however fails to work for conferences This procedure however fails to work for conferences initiated
initiated spontaneously like Internet phone calls or ad-hoc spontaneously like Internet phone calls or ad-hoc multiparty
multiparty conferences. Fixed settings for parameters like media conferences. Fixed settings for parameters like media types, their
types, their encoding etc. can easily inhibit the initiation of encoding etc. can easily inhibit the initiation of conferences, for
conferences, for example in situations where a caller insists on a example in situations where a caller insists on a fixed audio
fixed audio encoding that is not available at the callee's end encoding that is not available at the callee's end system.
system.
To allow for spontaneous conferences, the process of defining a To allow for spontaneous conferences, the process of defining a
conference's parameter set must therefore be performed either at conference's parameter set must therefore be performed either at
conference start (for closed conferences) or maybe (potentially) conference start (for closed conferences) or maybe (potentially) even
even repeatedly every time a new participant joins an active repeatedly every time a new participant joins an active conference.
conference. The latter approach may not be appropriate for every The latter approach may not be appropriate for every type of
type of conference without applying certain policies: For conference without applying certain policies: For conferences with
conferences with TV-broadcast or lecture characteristics (one main TV-broadcast or lecture characteristics (one main active source) it
active source) it is usually not desired to re-negotiate parameters is usually not desired to re-negotiate parameters every time a new
every time a new participant with an exotic configuration joins participant with an exotic configuration joins because it may
because it may inconvenience existing participants or even exclude inconvenience existing participants or even exclude the main source
the main source from media sessions. But conferences with equal from media sessions. But conferences with equal "rights" for
"rights" for participants that are open for new participants on the participants that are open for new participants on the other hand
other hand would need a different model of dynamic capability would need a different model of dynamic capability negotiation, for
negotiation, for example a telephone call that is extended to a example a telephone call that is extended to a 3-parties conference
3-parties conference at some time during the session. at some time during the session.
SDP [2] allows to specify multimedia sessions (i.e. conferences, SDP [2] allows to specify multimedia sessions (i.e. conferences,
"session" as used here is not to be confused with "RTP session"!) "session" as used here is not to be confused with "RTP session"!) by
by providing general information about the session as a whole and providing general information about the session as a whole and
specifications for all the media streams (RTP sessions and others) specifications for all the media streams (RTP sessions and others) to
to be used to exchange information within the multimedia session. be used to exchange information within the multimedia session.
Currently, media descriptions in SDP are used for two purposes: Currently, media descriptions in SDP are used for two purposes:
o to describe session parameters for announcements and invitations o to describe session parameters for announcements and invitations
(the original purpose of SDP) and (the original purpose of SDP) and
o to describe the capabilities of a system and possibly provide a o to describe the capabilities of a system and possibly provide a
choice between a number of alternatives (which SDP was not choice between a number of alternatives (which SDP was not
designed for). designed for).
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we provide a formal definition of the SDPng session description we provide a formal definition of the SDPng session description
language. Finally, we overview aspects of using SDPng with various language. Finally, we overview aspects of using SDPng with various
IETF signaling protocols in section 5. In Appendix A, we introduce IETF signaling protocols in section 5. In Appendix A, we introduce
basic audio codec and payload type definitions. basic audio codec and payload type definitions.
2. Terminology and System Model 2. Terminology and System Model
Any (computer) system has, at a time, a number of rather fixed Any (computer) system has, at a time, a number of rather fixed
hardware as well as software resources. These resources ultimately hardware as well as software resources. These resources ultimately
define the limitations on what can be captured, displayed, rendered, define the limitations on what can be captured, displayed, rendered,
replayed, etc. with this particular device. We term features enabled replayed, etc. with this particular device. We term features
and restricted by these resources "system capabilities". enabled and restricted by these resources "system capabilities".
Example: System capabilities may include: a limitation of the Example: System capabilities may include: a limitation of the
screen resolution for true color by the graphics board; available screen resolution for true color by the graphics board; available
audio hardware or software may offer only certain media encodings audio hardware or software may offer only certain media encodings
(e.g. G.711 and G.723.1 but not GSM); and CPU processing power (e.g. G.711 and G.723.1 but not GSM); and CPU processing power
and quality of implementation may constrain the possible video and quality of implementation may constrain the possible video
encoding algorithms. encoding algorithms.
In multiparty multimedia conferences, participants employ different In multiparty multimedia conferences, participants employ different
"components" in conducting the conference. "components" in conducting the conference.
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transparencies of a presentation visible to the audience on the transparencies of a presentation visible to the audience on the
Mbone. This can be achieved either by a video camera capturing Mbone. This can be achieved either by a video camera capturing
the image and transmitting a video stream via some video tool or the image and transmitting a video stream via some video tool or
by loading a copy of the slides into a distributed electronic by loading a copy of the slides into a distributed electronic
whiteboard. For each of these cases, additional parameters may whiteboard. For each of these cases, additional parameters may
exist, variations of which lead to additional configurations (see exist, variations of which lead to additional configurations (see
below). below).
Two configurations are considered different regardless of whether Two configurations are considered different regardless of whether
they employ entirely different mechanisms and protocols (as in the they employ entirely different mechanisms and protocols (as in the
previous example) or they choose the same and differ only in a previous example) or they choose the same and differ only in a single
single parameter. parameter.
Example: In case of video transmission, a JPEG-based still image Example: In case of video transmission, a JPEG-based still image
protocol may be used, H.261 encoded CIF images could be sent as protocol may be used, H.261 encoded CIF images could be sent as
could H.261 encoded QCIF images. All three cases constitute could H.261 encoded QCIF images. All three cases constitute
different configurations. Of course there are many more detailed different configurations. Of course there are many more detailed
protocol parameters. protocol parameters.
Each component's configurations are limited by the participating Each component's configurations are limited by the participating
system's capabilities. In addition, the intended use of a component system's capabilities. In addition, the intended use of a component
may constrain the possible configurations further to a subset may constrain the possible configurations further to a subset
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the component responsible for audio may decide not to use the the component responsible for audio may decide not to use the
available G.723.1 audio codec to avoid the additional latency but available G.723.1 audio codec to avoid the additional latency but
only use G.711. This would be reflected in this component only only use G.711. This would be reflected in this component only
showing configurations based upon G.711. Still, multiple showing configurations based upon G.711. Still, multiple
configurations are possible, e.g. depending on the use of A-law configurations are possible, e.g. depending on the use of A-law
or u-Law, packetization and redundancy parameters, etc. or u-Law, packetization and redundancy parameters, etc.
In this system model, we distinguish two types of configurations: In this system model, we distinguish two types of configurations:
o potential configurations o potential configurations
(a set of any number of configurations per component) indicating (a set of any number of configurations per component) indicating a
a system's functional capabilities as constrained by the intended system's functional capabilities as constrained by the intended
use of the various components; use of the various components;
o actual configurations o actual configurations
(exactly one per instance of a component) reflecting the mode of (exactly one per instance of a component) reflecting the mode of
operation of this component's particular instantiation. operation of this component's particular instantiation.
Example: The potential configuration of the aforementioned video Example: The potential configuration of the aforementioned video
component may indicate support for JPEG, H.261/CIF, and component may indicate support for JPEG, H.261/CIF, and
H.261/QCIF. A particular instantiation for a video conference may H.261/QCIF. A particular instantiation for a video conference may
use the actual configuration of H.261/CIF for exchanging video use the actual configuration of H.261/CIF for exchanging video
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was originally developed, the negotiation procedure is non-existent. was originally developed, the negotiation procedure is non-existent.
Instead, the announcement contains the media stream description sent Instead, the announcement contains the media stream description sent
out (i.e. the actual configurations) which implicitly describe what out (i.e. the actual configurations) which implicitly describe what
a receiver must understand to participate. a receiver must understand to participate.
In point-to-point scenarios, the negotiation procedure is typically In point-to-point scenarios, the negotiation procedure is typically
carried out implicitly: each party informs the other about what it carried out implicitly: each party informs the other about what it
can receive and the respective sender chooses from this set a can receive and the respective sender chooses from this set a
configuration that it can transmit. configuration that it can transmit.
Capability negotiation must not only work for 2-party conferences Capability negotiation must not only work for 2-party conferences but
but is also required for multi-party conferences. Especially for the is also required for multi-party conferences. Especially for the
latter case it is required that the process of determining the latter case it is required that the process of determining the subset
subset of allowable potential configurations is deterministic to of allowable potential configurations is deterministic to reduce the
reduce the number of required round trips before a session can be number of required round trips before a session can be established.
established.
The requirements for the SDPng specification, subdivided into The requirements for the SDPng specification, subdivided into general
general requirements and requirements for session descriptions, requirements and requirements for session descriptions, potential and
potential and actual configurations as well as negotiation rules, actual configurations as well as negotiation rules, are captured in a
are captured in a companion document [1]. companion document [1].
3. SDPng 3. SDPng
This section introduces the underlying concepts of the Session This section introduces the underlying concepts of the Session
Description Protocol - next generation (SDPng) that is to meet most Description Protocol - next generation (SDPng) that is to meet most
of the above requirements. The focus of this section is on the of the above requirements. The focus of this section is on the
concepts of such a capability description and negotiation language concepts of such a capability description and negotiation language
with a stepwise introduction of the various syntactical elements; a with a stepwise introduction of the various syntactical elements; a
full formal specification is provided in section 4. full formal specification is provided in section 4.
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Constraints; see Section 3.1.3. Constraints; see Section 3.1.3.
Session attributes; see Section 3.1.4. Session attributes; see Section 3.1.4.
3.1.1 Definitions 3.1.1 Definitions
The definition section specifies a number of basic abstractions that The definition section specifies a number of basic abstractions that
are later referenced to avoid repetitions in more complex are later referenced to avoid repetitions in more complex
specifications and allow for a concise representation. Definition specifications and allow for a concise representation. Definition
elements are labelled with an identifier by which they may be elements are labelled with an identifier by which they may be
referenced. They may be elementary or compound (i.e. combinations of referenced. They may be elementary or compound (i.e. combinations
elementary entities). Examples of definitions of that sections of elementary entities). Examples of definitions of that sections
include (but are not limited to) codec definitions, redundancy include (but are not limited to) codec definitions, redundancy
schemes, transport mechanisms and payload formats. schemes, transport mechanisms and payload formats.
Elementary definition elements do not reference other elements. Each Elementary definition elements do not reference other elements. Each
elementary entity only consists of one of more attributes and their elementary entity only consists of one of more attributes and their
values. Default values specified in the definition section may be values. Default values specified in the definition section may be
overridden in descriptions for potential (and later actual) overridden in descriptions for potential (and later actual)
configurations. A mechanisms for overriding definitions is specified configurations. A mechanisms for overriding definitions is specified
below. below.
For the moment, elementary elements are defined for media types For the moment, elementary elements are defined for media types (i.e.
(i.e. codecs) and for media transports. For each transport and for
each codec to be used, the respective attributes need to be defined.
This definition may either be provided within the "Definitions" codecs) and for media transports. For each transport and for each
section itself or in an external document (similar to the codec to be used, the respective attributes need to be defined. This
audio-video profile or an IANA registry that define payload types definition may either be provided within the "Definitions" section
and media stream identifiers. itself or in an external document (similar to the audio-video profile
or an IANA registry that define payload types and media stream
identifiers.
It is not required to define all codec, transport mechanisms in a It is not required to define all codec, transport mechanisms in a
definitions sections and reference them in the definition of definitions sections and reference them in the definition of
potential and actual configurations. Instead, a syntactic mechanism potential and actual configurations. Instead, a syntactic mechanism
is defined that allows to specify some definitions directly in a is defined that allows to specify some definitions directly in a
configurations section. configurations section.
Examples for elementary definitions: Examples for elementary definitions:
<audio-codec name="audio-basic" encoding="PCMU" <audio:codec name="audio-basic" encoding="PCMU"
sampling="8000 channels="1"/> sampling="8000 channels="1"/>
<audio-codec name="audio-L16-mono" encoding="L16" <audio:codec name="audio-L16-mono" encoding="L16"
sampling="44100 channels="1"/> sampling="44100 channels="1"/>
The element type "audio-codec" is used in these examples to define The element type "audio:codec" is used in these examples to define
audio codec configurations. The configuration parameters are given audio codec configurations. The configuration parameters are given
as attribute values. as attribute values.
Definitions may have default values specified along with them for Definitions may have default values specified along with them for
each attribute (as well as for their contents). Some of these each attribute (as well as for their contents). Some of these
default values may be overridden so that a codec definition can default values may be overridden so that a codec definition can
easily be re-used in a different context (e.g. by specifying a easily be re-used in a different context (e.g. by specifying a
different sampling rate) without the need for a large number of base different sampling rate) without the need for a large number of base
specifications. In the following example the definition of specifications. In the following example the definition of audio-
audio-L16-mono is re-used for the defintion of the corresponding L16-mono is re-used for the defintion of the corresponding stereo
stereo codec. Appendix A provides a complete set of corresponding codec. Appendix A provides a complete set of corresponding
audio-codec definitions of the codec used in RFC 1890 [4]. audio:codec definitions of the codec used in RFC 1890 [4].
<audio-codec name="audio-L16-stereo" ref="audio-L16-mono" <audio:codec name="audio-L16-stereo" ref="audio-L16-mono"
channels="2"/> channels="2"/>
The example shows how exisiting defintions can be referenced in new The example shows how exisiting defintions can be referenced in new
definitiones. This approach allows to have simple as well as more definitiones. This approach allows to have simple as well as more
complex definitions which are commonly used be available in an complex definitions which are commonly used be available in an
extensible set of reference documents. Section 3.3 specifies the extensible set of reference documents. Section 3.3 specifies the
mechanisms for external references. mechanisms for external references.
Besides definitions of audio codecs there will be other definitions Besides definitions of audio codecs there will be other definitions
like RTP payload format and specific transport mechanisms that are like RTP payload format and specific transport mechanisms that are
suitable to be defined in a defintion section for later referencing. suitable to be defined in a defintion section for later referencing.
The following example shows how RTP payload types are defined using
a pre-defined codec.
<rtp-pt name="rtp-avp-0" pt="0" format="audio-basic"/> The following example shows how RTP payload types are defined using a
<rtp-pt name="rtp-avp-11" pt="11" format="audio-L16-mono"/> pre-defined codec.
<rtp:pt name="rtp-avp-0" pt="0" format="audio-basic"/>
<rtp:pt name="rtp-avp-11" pt="11" format="audio-L16-mono"/>
In this example, the payload type "rtp-avp-11" is defined with In this example, the payload type "rtp-avp-11" is defined with
payload type number 11, referencing the codec "audio-L16-mono". payload type number 11, referencing the codec "audio-L16-mono".
Instead of referencing an existing definition it is also possible to Instead of referencing an existing definition it is also possible to
define the format "inline": define the format "inline":
<rtp-pt name="rtp-avp-10" pt="10"> <rtp:pt name="rtp-avp-10" pt="10">
<audio-codec encoding="L16" sampling="44100 channels="2"/> <audio:codec encoding="L16" sampling="44100 channels="2"/>
</rtp-pt> </rtp:pt>
Note: For negotiation between endpoints, it may be helpful to define Note: For negotiation between endpoints, it may be helpful to define
two modes of operation: explicit and implicit. Implicit two modes of operation: explicit and implicit. Implicit
specifications may refer to externally defined entities to minimize specifications may refer to externally defined entities to minimize
traffic volume, explicit specifications would list all external traffic volume, explicit specifications would list all external
definitions used in a description in the "Definitions" section. definitions used in a description in the "Definitions" section.
Again, see Section 3.3 for complete discussion of external Again, see Section 3.3 for complete discussion of external
definitions. definitions.
The "Definitions" section may be empty if all transport, codecs, and The "Definitions" section may be empty if all transport, codecs, and
other pieces needed to the specify Potential and Actual other pieces needed to the specify Potential and Actual
Configurations (as detailed below) are either included by Configurations (as detailed below) are either included by referencing
referencing external definitions or are explicitly described within external definitions or are explicitly described within the
the Configurations themselves. Configurations themselves.
3.1.2 Components & Configurations 3.1.2 Components & Configurations
The "Configurations" section contains all the components that The "Configurations" section contains all the components that
constitute the multimedia conference (IP telephone call, multiplayer constitute the multimedia conference (IP telephone call, multiplayer
gaming session etc.). For each of these components, the potential gaming session etc.). For each of these components, the potential
and, later, the actual configurations are given. Potential and, later, the actual configurations are given. Potential
configurations are used during capability exchange and/or configurations are used during capability exchange and/or
negotiation, actual configurations to configure media streams after negotiation, actual configurations to configure media streams after
negotiation (e.g. with RTSP) or in session announcements (e.g. via negotiation (e.g. with RTSP) or in session announcements (e.g. via
skipping to change at page 10, line 53 skipping to change at page 12, line 7
Each component is labelled with an identifier so that it can be Each component is labelled with an identifier so that it can be
referenced, e.g. to associate semantics with a particular media referenced, e.g. to associate semantics with a particular media
stream. For such a component, any number of configurations may be stream. For such a component, any number of configurations may be
given with each configuration describing an alternate way to realize given with each configuration describing an alternate way to realize
the functionality of the respective component. the functionality of the respective component.
Each configuration (potential as well as actual) is labelled with an Each configuration (potential as well as actual) is labelled with an
identifier. A configuration combines one or more (elementary and/or identifier. A configuration combines one or more (elementary and/or
compound) entities from the "Definitions" section to describe a compound) entities from the "Definitions" section to describe a
potential or an actual configuration. Within the specification of potential or an actual configuration. Within the specification of
the configuration, default values from the referenced entities may the configuration, default values from the referenced entities may be
be overwritten. overwritten.
Note: Not all protocol environments and their respective operation Note: Not all protocol environments and their respective operation
allow to explicitly distinguish between Potential and Actual allow to explicitly distinguish between Potential and Actual
Configurations. Therefore, SDPng so far does not provide for Configurations. Therefore, SDPng so far does not provide for
syntactical identification of a Configurations as being a Potential syntactical identification of a Configurations as being a Potential
or an Actual one. or an Actual one.
The following example shows how RTP sessions can be described by The following example shows how RTP sessions can be described by
referencing payload definitions. referencing payload definitions.
<cfg> <cfg>
<component name="interactive-audio" media="audio"> <component name="interactive-audio" media="audio">
<alt name="AVP-audio-0"> <alt name="AVP-audio-0">
<rtp format="rtp-avp-0"> <rtp:session format="rtp-avp-0">
<udp addr="224.2.0.53" rtp-port="7800" rtcp-port="7801"/> <rtp:udp addr="224.2.0.53" rtp-port="7800" rtcp-port="7801"/>
</rtp> </rtp:session>
</alt> </alt>
<alt name= AVP-audio-11"> <alt name= AVP-audio-11">
<rtp format="rtp-avp-11"> <rtp:session format="rtp-avp-11">
<udp addr="224.2.0.53" rtp-port="7800" rtcp-port="7801"/> <rtp:udp addr="224.2.0.53" rtp-port="7800" rtcp-port="7801"/>
</rtp> </rtp:session>
</alt> </alt>
</component> </component>
</cfg> </cfg>
For example, an IP telephone call may require just a single For example, an IP telephone call may require just a single component
component "name=interactive-audio" with two possible ways of "name=interactive-audio" with two possible ways of implementing it.
implementing it. The two corresponding configurations are The two corresponding configurations are "AVP-audio-0" without
"AVP-audio-0" without modification, the other ("AVP-audio-11") uses modification, the other ("AVP-audio-11") uses linear 16-bit encoding.
linear 16-bit encoding. Typically, transport address parameters such Typically, transport address parameters such as the port number would
as the port number would also be provided. In this example, this also be provided. In this example, this information is given by the
information is given by the "udp" element. Of course, it must be "udp" element. Of course, it must be possible to specify other
possible to specify other transport mechanisms as well. See Section transport mechanisms as well. See Section 3.2 for a discussion of
3.2 for a discussion of extension mechanisms that allow applications extension mechanisms that allow applications to use non-standard
to use non-standard transport (or other) specifications. transport (or other) specifications.
During/after the negotiation phase, an actual configuration is During/after the negotiation phase, an actual configuration is chosen
chosen out of a number of alternative potential configurations, the out of a number of alternative potential configurations, the actual
actual configuration may refer to the potential configuration just configuration may refer to the potential configuration just by its
by its "id", possibly allowing for some parameter modifications. "id", possibly allowing for some parameter modifications.
Alternatively, the full actual configuration may be given. Alternatively, the full actual configuration may be given.
Instead of referencing existing payload type definitions it is also Instead of referencing existing payload type definitions it is also
possible to provide the required information "inline". The following possible to provide the required information "inline". The following
example illustrates this: example illustrates this:
<cfg> <cfg>
<component name="audio1" media="audio"> <component name="audio1" media="audio">
<alt name= AVP-audio-0"> <alt name= AVP-audio-0">
<rtp> <rtp:session>
<rtp-pt pt="0"> <rtp:pt pt="0">
<audio-codec name="audio-basic" encoding="PCMU" <audio:codec name="audio-basic" encoding="PCMU"
sampling="8000 channels="1"/> sampling="8000 channels="1"/>
</rtp-pt> </rtp:pt>
<udp addr="224.2.0.53" rtp-port="7800" rtcp-port="7801"/> <rtp:udp addr="224.2.0.53" rtp-port="7800" rtcp-port="7801"/>
</rtp> </rtp:session>
</alt> </alt>
</component> </component>
</cfg> </cfg>
The UDP/IPv4 multicast transport that is used in the examples is a The UDP/IPv4 multicast transport that is used in the examples is a
simple variant of a transport specification. More complex ones are simple variant of a transport specification. More complex ones are
conceivable. For example, it must also be possible to specify the conceivable. For example, it must also be possible to specify the
usage of source filters (inclusion and exclusion), Source Specific usage of source filters (inclusion and exclusion), Source Specific
Multicast, the usage of multi-unicast, or other parameters. Multicast, the usage of multi-unicast, or other parameters.
Therefore it is possible to extend the definition of transport Therefore it is possible to extend the definition of transport
mechanisms by providing the required information in the element mechanisms by providing the required information in the element
content. An example: content. An example:
<cfg> <cfg>
<component name="audio1" media="audio"> <component name="audio1" media="audio">
<alt name= AVP-audio-0"> <alt name= AVP-audio-0">
<rtp format="rtp-avp-0"> <rtp:session format="rtp-avp-0">
<udp addr="224.2.0.53" rtp-port="7800" rtcp-port="7801"> <rtp:udp addr="224.2.0.53" rtp-port="7800" rtcp-port="7801">
<option name="ssm" sender="sender.example.com"/> <option name="ssm" sender="sender.example.com"/>
</udp> </rtp:udp>
</rtp> </rtp:session>
</alt> </alt>
</component> </component>
</cfg> </cfg>
More transport mechanisms and options will be defined in future More transport mechanisms and options will be defined in future
versions of this document. versions of this document.
3.1.3 Constraints 3.1.3 Constraints
Definitions specify media, transport, and other capabilities, Definitions specify media, transport, and other capabilities, whereas
whereas configurations indicate which combinations of these could be configurations indicate which combinations of these could be used to
used to provide the desired functionality in a certain setting. provide the desired functionality in a certain setting.
There may, however, be further constraints within a system (such as There may, however, be further constraints within a system (such as
CPU cycles, DSP available, dedicated hardware, etc.) that limit CPU cycles, DSP available, dedicated hardware, etc.) that limit which
which of these configurations can be instantiated in parallel (and of these configurations can be instantiated in parallel (and how many
how many instances of these may exist). We deliberately do not instances of these may exist). We deliberately do not couple this
couple this aspect of system resource limitations to the various aspect of system resource limitations to the various application
application semantics as the constraints exist across application semantics as the constraints exist across application boundaries.
boundaries. Also, in many cases, expressing such constraints is Also, in many cases, expressing such constraints is simply not
simply not necessary (as many uses of the current SDP show), so necessary (as many uses of the current SDP show), so additional
additional overhead can be avoided where this is not needed. overhead can be avoided where this is not needed.
Therefore, we introduce a "Constraints" section to contain these Therefore, we introduce a "Constraints" section to contain these
additional limitations. Constraints refer to potential additional limitations. Constraints refer to potential
configurations and to entity definitions and express and use simple configurations and to entity definitions and express and use simple
logic to express mutual exclusion, limit the number of logic to express mutual exclusion, limit the number of
instantiations, and allow only certain combinations. The following instantiations, and allow only certain combinations. The following
example shows the definition of a constraints that restricts the example shows the definition of a constraints that restricts the
maximum number of instantiation of two alternatives (that would have maximum number of instantiation of two alternatives (that would have
to be defined in the configuration section before) when they are to be defined in the configuration section before) when they are used
used in parallel: in parallel:
<constraints> <constraints>
<par> <par>
<use-alt ref="AVP-audio-11" max="5"> <use-alt ref="AVP-audio-11" max="5">
<use-alt ref="AVP-video-32" max="1"> <use-alt ref="AVP-video-32" max="1">
</par> </par>
</constraints> </constraints>
As the example shows, contraints are defined by defining limits on As the example shows, contraints are defined by defining limits on
simultaneous instantiations of alternatives. They are not defined by simultaneous instantiations of alternatives. They are not defined by
skipping to change at page 14, line 20 skipping to change at page 15, line 27
<owner user="username" id="session-id" version="version" nettype="IN" <owner user="username" id="session-id" version="version" nettype="IN"
addrtype="IP4" addr="130.149.25.97"/> addrtype="IP4" addr="130.149.25.97"/>
The owner field MUST be present if SDPng is used with SAP. For all The owner field MUST be present if SDPng is used with SAP. For all
other protocols, the owner field MAY be specified. The attributes other protocols, the owner field MAY be specified. The attributes
listed above match those from the SDP specification; all attributes listed above match those from the SDP specification; all attributes
MUST be present and they MUST be created following the rules of MUST be present and they MUST be created following the rules of
RFC2327. RFC2327.
Note: There are several possible ways ahead on this part: "owner" Note: There are several possible ways ahead on this part: "owner"
could stand as it is right now, but the various values of the could stand as it is right now, but the various values of the various
various attributes could be concatenated (separated by blanks) the attributes could be concatenated (separated by blanks) the result
result being identical to the contents of the SDP "o=" line -- which being identical to the contents of the SDP "o=" line -- which then
then could be represented as either a single attribute or as could be represented as either a single attribute or as contents of
contents of the "owner" element. Alternatively, the owner element the "owner" element. Alternatively, the owner element could become
could become part of the "session" element described below. Or the part of the "session" element described below. Or the contents of
contents of the owner element could become an attribute of the the owner element could become an attribute of the "session" element
"session" element below. below.
3.1.4.2 Session Identification 3.1.4.2 Session Identification
The "session" element is used to identify the session and to provide The "session" element is used to identify the session and to provide
a description and possible further references. The following a description and possible further references. The following
attributes are defined: attributes are defined:
name: The session name as it is to appear e.g. in a session name: The session name as it is to appear e.g. in a session
directory. This is equivalent to the SDP "s=" line. This directory. This is equivalent to the SDP "s=" line. This
attribute MUST be present. attribute MUST be present.
info: A pointer to further information about the session; this info: A pointer to further information about the session; this
attribute MUST contain a URI. The attribute itself is OPTIONAL. attribute MUST contain a URI. The attribute itself is OPTIONAL.
The session element MAY contain arbitrary text of any length (but The session element MAY contain arbitrary text of any length (but
authors are encouraged to keep the inline description brief and authors are encouraged to keep the inline description brief and
provide additional information via URLs. This text is used to provide additional information via URLs. This text is used to
provide a description of the session; it is the equivalent of the provide a description of the session; it is the equivalent of the SDP
SDP "i=" lines. "i=" lines.
Furthermore, the session element MAY contain other elements of the Furthermore, the session element MAY contain other elements of the
following types to provide further information about the session and following types to provide further information about the session and
its creator: its creator:
info: The info element is intended to provide a pointer to further info: The info element is intended to provide a pointer to further
information on the session itself. Its contents MUST be exactly information on the session itself. Its contents MUST be exactly
one URI. If both the info attribute and one or more info elements one URI. If both the info attribute and one or more info elements
are present, the union of the respective values is used. Info are present, the union of the respective values is used. Info
elements are OPTIONAL, they MAY be repeated any number of times. elements are OPTIONAL, they MAY be repeated any number of times.
skipping to change at page 15, line 39 skipping to change at page 16, line 47
SDP. Time specifications are usually only meaningful when used in SDP. Time specifications are usually only meaningful when used in
conjunction with SAP and hence are OPTIONAL. SDPng uses the conjunction with SAP and hence are OPTIONAL. SDPng uses the
following elements and attributes to specify timing: following elements and attributes to specify timing:
The element "time" is used to indicate a schedule for the session; The element "time" is used to indicate a schedule for the session;
time has two optional attributes: time has two optional attributes:
start: The starting time of the first occurrence of the session as start: The starting time of the first occurrence of the session as
defined in RFC2327. defined in RFC2327.
end: The ending time of the last occurrence of the session as end: The ending time of the last occurrence of the session as defined
defined in RFC2327. in RFC2327.
The time element MAY contain the following elements but otherwise The time element MAY contain the following elements but otherwise
MUST be empty: MUST be empty:
repeat: This element specifies the repetition pattern for the repeat: This element specifies the repetition pattern for the
schedule. There MAY be zero or more occurrences of this element schedule. There MAY be zero or more occurrences of this element
within the time element. "repeat" has two MANDATORY and one within the time element. "repeat" has two MANDATORY and one
OPTIONAL attribute and no further contents; the attributes are as OPTIONAL attribute and no further contents; the attributes are as
defined in SDP: defined in SDP:
skipping to change at page 16, line 18 skipping to change at page 17, line 28
starting at each repetition interval. This attribute MUST be starting at each repetition interval. This attribute MUST be
present. present.
offset: The offset relative to "start" attribute at which this offset: The offset relative to "start" attribute at which this
repetition of the session is start. This attribute is repetition of the session is start. This attribute is
OPTIONAL; if it is absent, a default value of "0" is assumed. OPTIONAL; if it is absent, a default value of "0" is assumed.
Formatting of the attribute values MUST follow the rules defined Formatting of the attribute values MUST follow the rules defined
in RFC2327. in RFC2327.
zone: The zone element specifies one or more time zone adjustments zone: The zone element specifies one or more time zone adjustments as
as defined in RFC2327. This element MAY have zero or more defined in RFC2327. This element MAY have zero or more
occurrences in the time element. It has two attributes as defined occurrences in the time element. It has two attributes as defined
in SDP: in SDP:
adjtime: The time at which the next adjustment will take place. adjtime: The time at which the next adjustment will take place.
delta: The adjustment offset (typically +/- 1 hours). delta: The adjustment offset (typically +/- 1 hours).
The example from RFC2327, page 16, expressed in SDPng: The example from RFC2327, page 16, expressed in SDPng:
<time start="3034423619" stop="3042462419"> <time start="3034423619" stop="3042462419">
skipping to change at page 17, line 8 skipping to change at page 18, line 19
</info> </info>
The above example shows a simple definition of the semantics for a The above example shows a simple definition of the semantics for a
the component "interactive-audio". Further options may be added to the component "interactive-audio". Further options may be added to
provide additional information, e.g. language, and other functions provide additional information, e.g. language, and other functions
may be specified (e.g. "panel", "audience", "chair", etc.). may be specified (e.g. "panel", "audience", "chair", etc.).
3.2 Syntax Definition Mechanisms 3.2 Syntax Definition Mechanisms
In order to allow for the possibility to validate session In order to allow for the possibility to validate session
descriptions and in order to allow for structured extensibility it descriptions and in order to allow for structured extensibility it is
is proposed to rely on a syntax framework that provides concepts as proposed to rely on a syntax framework that provides concepts as well
well as concrete procedures for document validation and extending as concrete procedures for document validation and extending the set
the set of allowed syntax elements. of allowed syntax elements.
SGML/XML technologies allow for the preparation of Document Type SGML/XML technologies allow for the preparation of Document Type
Definitions (DTDs) that can define the allowed content models for Definitions (DTDs) that can define the allowed content models for the
the elements of conforming documents. Documents can be formally elements of conforming documents. Documents can be formally
validated against a given DTD to check their conformance and validated against a given DTD to check their conformance and
correctness. XML DTDs however, cannot easily be extended. It is not correctness. XML DTDs however, cannot easily be extended. It is not
possible to alter to content models of element types or to add new possible to alter to content models of element types or to add new
element types after the DTD has been specified. element types after the DTD has been specified.
For SDPng a mechanism is needed that allows the specification of a For SDPng, a mechanism is needed that allows the specification of a
base syntax -- for example basic elements for the high level base syntax -- for example basic elements for the high level
structure of description documents -- while allowing extensions, for structure of description documents -- while allowing extensions, for
example elements and attributes for new transport mechanisms, new example elements and attributes for new transport mechanisms, new
media types etc. to added on demand. Still, it has to be ensured media types etc. to be added on demand. Still, it has to be ensured
that extensions do not result in name collisions. Furthermore, it that extensions do not result in name collisions. Furthermore, it
must be possible for applications that process descriptios documents must be possible for applications that process descriptios documents
to disinguish extensions from base definitions. to disinguish extensions from base definitions.
For XML, mechanisms have been defined that allow for structured For XML, mechanisms have been defined that allow for structured
extensibility of a model of allowed syntax: XML Namespace and XML extensibility of a model of allowed syntax: XML Namespace and XML
Schema. Schema.
XML Schema mechanisms allows to constrain the allowed document XML Schema mechanisms allows to constrain the allowed document
content, e.g. for documents that contain structured data and also content, e.g. for documents that contain structured data and also
provide the possibility that document instances can conform to provide the possibility that document instances can conform to
several XML Schema definitions at the same time, while allowing several XML Schema definitions at the same time, while allowing
Schema validators to check the conformance of these documents. Schema validators to check the conformance of these documents.
Extensions of the session description language, say for allowing to Extensions of the session description language, say for allowing to
express the parameters of a new media type, would require the express the parameters of a new media type, would require the
creation of a corresponding XML schema definition that contains the creation of a corresponding XML schema definition that contains the
specification of element types that can be used to describe specification of element types that can be used to describe
configurations of components for the new media type. Session configurations of components for the new media type. Session
description documents have to reference the non-standard Schema description documents have to reference the non-standard Schema
module, thus enabling parsers and validators to identify the module, thus enabling parsers and validators to identify the elements
elements of the new extension module and to either ignore them (if of the new extension module and to either ignore them (if they are
they are not supported) or to consider them for processing the not supported) or to consider them for processing the
session/capability description. session/capability description.
It is important to note that the functionality of validating It is important to note that the functionality of validating
capability and session description documents is not necessarily capability and session description documents is not necessarily
required to generate or process them. For example, endpoints would required to generate or process them. For example, endpoints would
be configured to understand only those parts of description be configured to understand only those parts of description documents
documents that are conforming to the baseline specification and that are conforming to the baseline specification and simply ignore
simply ignore extensions they cannot support. The usage of XML and extensions they cannot support. The usage of XML and XML Schema is
XML Schema is thus rather motivated by the need to allow for thus rather motivated by the need to allow for extensions being
extensions being defined and added to the language in a structured defined and added to the language in a structured way that does not
way that does not preclude the possibility to have applications to preclude the possibility to have applications to identify and process
identify and process the extensions elements they might support. The the extensions elements they might support. The baseline
baseline specification of XML Schema definitions and profiles must specification of XML Schema definitions and profiles must be well-
be well-defined and targeted to the set of parameters that are defined and targeted to the set of parameters that are relevant for
relevant for the protocols and algorithms of the Internet Multimedia the protocols and algorithms of the Internet Multimedia Conferencing
Conferencing Architecture, i.e. transport over RTP/UDP/IP, the audio Architecture, i.e. transport over RTP/UDP/IP, the audio video
video profile of RFC1890 etc. profile of RFC1890 etc.
Section 3.3 describes profile definitions and library definition. A Section 3.3 describes profile definitions and library definition. A
detailed definition of how the formal SDPng syntax and the detailed definition of how the formal SDPng syntax and the
corresponding extension mechanisms is to be provided in future corresponding extension mechanisms is provided in Section 4.
versions of this document.
The example below shows how the definition of codecs, The example below shows how the definition of codecs, transport-
transport-variants and configuration of components could be variants and configuration of components could be realized. Please
realized. Please note that this is not a complete example and that note that this is not a complete example and that identifiers have
identifiers have been chosen arbitrarily. been chosen arbitrarily.
<def> <def>
<audio-codec name="audio-basic" encoding="PCMU" <audio:codec name="audio-basic" encoding="PCMU"
sampling="8000 channels="1"/> sampling="8000 channels="1"/>
<audio-codec name="audio-L16-mono" encoding="L16" <audio:codec name="audio-L16-mono" encoding="L16"
sampling="44100 channels="1"/> sampling="44100 channels="1"/>
<rtp-pt name="rtp-avp-0" pt="0" format="audio-basic"/> <rtp:pt name="rtp-avp-0" pt="0" format="audio-basic"/>
<rtp-pt name="rtp-avp-11" pt="11" format="audio-L16-mono"/> <rtp:pt name="rtp-avp-11" pt="11" format="audio-L16-mono"/>
</def> </def>
<cfg> <cfg>
<component name="interactive-audio" media="audio"> <component name="interactive-audio" media="audio">
<alt name= AVP-audio-0"> <alt name= AVP-audio-0">
<rtp format="rtp-avp-0"> <rtp:session format="rtp-avp-0">
<udp addr="224.2.0.53" rtp-port="7800" rtcp-port="7801"/> <rtp:udp addr="224.2.0.53" rtp-port="7800" rtcp-port="7801"/>
</rtp> </rtp:session>
</alt> </alt>
<alt name= AVP-audio-11"> <alt name= AVP-audio-11">
<rtp format="rtp-avp-11"> <rtp:session format="rtp-avp-11">
<udp addr="224.2.0.53" rtp-port="7800" rtcp-port="7801"/> <rtp:udp addr="224.2.0.53" rtp-port="7800" rtcp-port="7801"/>
</rtp> </rtp:session>
</alt> </alt>
</component> </component>
</cfg> </cfg>
<constraints> <constraints>
<par> <par>
<use-alt ref="AVP-audio-11" max="1"> <use-alt ref="AVP-audio-11" max="1">
</par> </par>
</constraints> </constraints>
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factored-out to profile definition documents that would only be factored-out to profile definition documents that would only be
referenced in capability description documents. referenced in capability description documents.
3.3 External Definition Packages 3.3 External Definition Packages
3.3.1 Profile Definitions 3.3.1 Profile Definitions
In order to allow for extensibility it must be possible to define In order to allow for extensibility it must be possible to define
extensions to the basic SDPng configuration options. extensions to the basic SDPng configuration options.
For example if some application requires the use of a new esoteric For example, if some application requires the use of a new esoteric
transport protocol endpoints must be able describe their transport protocol, endpoints must be able describe their
configuration with respect to the parameters of that transport configuration with respect to the parameters of that transport
protocol. The mandatory and optional parameters that can be protocol. The mandatory and optional parameters that can be
configured and negotiated when using the transport protocol will be configured and negotiated when using the transport protocol will be
specified in a definition document. Such a definition document is specified in a definition document. Such a definition document is
called a "profile". called a "profile".
A profile contains rules that specify how SDPng is used to describe A profile contains rules that specify how SDPng is used to describe
conferences or endsystem capabilities with respect to the parameters conferences or endsystem capabilities with respect to the parameters
of the profile. The concrete properties of the profile definitions of the profile. The concrete properties of the profile definitions
mechanism are still to be defined. mechanism are still to be defined.
skipping to change at page 20, line 33 skipping to change at page 21, line 47
profile definition. profile definition.
3.3.2 Library Definitions 3.3.2 Library Definitions
While profile definitions specify the allowed parameters for a given While profile definitions specify the allowed parameters for a given
profile SDPng definition sections refer to profile definitions and profile SDPng definition sections refer to profile definitions and
define concrete configurations based on a specific profile. define concrete configurations based on a specific profile.
In order for such definitions to be imported into SDPng documents, In order for such definitions to be imported into SDPng documents,
there will be the notion of "SDPng libraries". A library is a set of there will be the notion of "SDPng libraries". A library is a set of
definitions that is conforming to a certain profile definition (or definitions that is conforming to a certain profile definition (or to
to more than one profile definition -- this needs to be defined). more than one profile definition -- this needs to be defined).
The purpose of the library concept is to allow certain common The purpose of the library concept is to allow certain common
definitions to be factored-out so that not every SDPng document has definitions to be factored-out so that not every SDPng document has
to include the basic definitions, for example the PCMU codec to include the basic definitions, for example the PCMU codec
definition. SDP [2] uses a similar concept by relying on the well definition. SDP [2] uses a similar concept by relying on the well
known static payload types (defined in RFC1890 [4]) that are also known static payload types (defined in RFC1890 [4]) that are also
just referenced but never defined in SDP documents. just referenced but never defined in SDP documents.
An SPDng document that references definitions from an external An SPDng document that references definitions from an external
library has to declare the use of the external library. The external library has to declare the use of the external library. The external
library, being a set of configuration definitions for a given library, being a set of configuration definitions for a given
profile, again needs to declare the use of the profile that it is profile, again needs to declare the use of the profile that it is
conformant to. conforming to.
There are different possibilities of how profiles definitions and There are different possibilities of how profiles definitions and
libraries can be used in SDPng documents: libraries can be used in SDPng documents:
o In an SPDng document a profile definition can be referenced and o In an SPDng document, a profile definition can be referenced and
all the configuration definitions are provided within the all the configuration definitions are provided within the document
document itself. The SDPng document is self-contained with itself. The SDPng document is self-contained with respect to the
respect to the definitions it uses. definitions it uses.
o In an SPDng document the use of an external library can be o In an SPDng document, the use of an external library can be
declared. The library references a profile definition and the declared. The library references a profile definition and the
SDPng document references the library. There are two alternatives SDPng document references the library. There are two alternatives
how external libraries can be referenced: how external libraries can be referenced:
by name: Referencing libraries by names implies the use of a by name: Referencing libraries by names implies the use of a
registration authority where definitions and reference names registration authority where definitions and reference names
can be registered with. It is conceivable that the most common can be registered with. It is conceivable that the most common
SDPng definitions be registered that way and that there will SDPng definitions be registered that way and that there will be
be a baseline set of definitions that minimal implementations a baseline set of definitions that minimal implementations must
must understand. Secondly, a registration procedure will be understand. Secondly, a registration procedure will be
defined, that allows vendors to register frequently used defined, that allows vendors to register frequently used
definitions with a registration authority (e.g., IANA) and to definitions with a registration authority (e.g., IANA) and to
declare the use of registered definition packages in declare the use of registered definition packages in conforming
conforming SDPng documents. Of course, care should be taken SDPng documents. Of course, care should be taken not to make
not to make the external references too complex and thus the external references too complex and thus require too much a
require too much a priori knowledge in a protocol engine priori knowledge in a protocol engine implementing SDPng.
implementing SDPng. Relying on this mechanism in general is Relying on this mechanism in general is also problematic
also problematic because it impedes the extensiblity, because because it impedes the extensiblity, because it requires
it requires implementors to provide support for new extensions implementors to provide support for new extensions in their
in their products before they can interoperate. Registration products before they can interoperate. Registration is not
is not useful for spontaneous or experimental extensions that useful for spontaneous or experimental extensions that are
are defined in an SDPng library. defined in an SDPng library.
by address: An alternative to referencing libraries by name is to by address: An alternative to referencing libraries by name is to
declare the use of an external library by providing an declare the use of an external library by providing an address,
address, i.e., an URL, that specifies where the library can be i.e., an URL, that specifies where the library can be obtained.
obtained. While is allows the use of arbitrary third-party While is allows the use of arbitrary third-party libraries that
libraries that can extend the basic SDPng set of configuration can extend the basic SDPng set of configuration options in many
options in many ways there are problems if the referenced ways there are problems if the referenced libraries cannot be
libraries cannot be accessed by all communication partners. accessed by all communication partners.
o Because of these problematic properties of external libraries, o Because of these problematic properties of external libraries, the
the final SDPng specification will have to provide a set of final SDPng specification will have to provide a set of
recommendations under which circumstances the different recommendations under which circumstances the different mechanisms
mechanisms of externalizing definitions should be used. of externalizing definitions should be used.
3.4 Mappings 3.4 Mappings
A mapping needs to be defined in particular to SDP that allows to A mapping needs to be defined in particular to SDP that allows to
translate final session descriptions (i.e. the result of capability translate final session descriptions (i.e. the result of capability
negotiation processes) to SDP documents. In principle, this can be negotiation processes) to SDP documents. In principle, this can be
done in a rather schematic fashion. done in a rather schematic fashion for the basic definitions.
Furthermore, to accommodate SIP-H.323 gateways, a mapping from SDPng Furthermore, to accommodate SIP-H.323 gateways, a mapping from SDPng
to H.245 needs to be specified at some point. to H.245 needs to be specified at some point.
4. Formal Specification 4. Formal Specification
To be provided. 4.1 XML Schema as a Definition Mechanism
SDPng document reference profile schema definitions and libraries.
Profile schema definitions contain schema definitions of SDPng
document elements. For example, the general structure is specified
by a schema definition and extensions to SDPng for specific
applications are specified as schema definitions as well.
The baseline SDPng specification consists of a profile (a schema
definition) and a library of commonly used definitions.
SDPng uses XML-Schema [15][16] for defining the possible logical
structures of SDPng documents for the following reasons:
Extensibility: XML-Schema provides mechanisms that allow to extend
exisiting definitions allowing to uniquely identify element types
(by relying on XML namespaces [13]).
Modularity: XML-Schema provide mechanisms that allow to organize
schema definitions in multiple components.
Expressiveness: XML-Schema provides many data types, that can be
refined by user-supplied definitions.
SDPng documents are schema instances of the SDPng schema. The
following example shows, how a Schema definition can be referenced in
a document instance.
Beginning of an SDPng-document:
<?xml version="1.0" ?>
<sdpng:desc xmlns:sdpng="http://www.iana.org/sdpng"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-Instance"
xsi:schemaLocation="http://www.iana.org/sdpng sdpng.xsd"
>
XML-Schema specifies, that documents can assign a namespace when
referencing a schema definition. A SDPng namespace will be defined
for this purpose (it has to be decided later which namespace name to
use -- this can be a URI, as in the example, or a URN). It is
proposed that a commonly used namespace prefix is used (e.g. fixed
to "sdpng") for the SDPng schema definition.
It will be worked-out, how much of this initial declaration can be
added implicitely by applications, so that declarations like the one
above do not have to be included in every description document.
4.2 SDPng Schema
The basic SDPng schema definitions specifies the general document
structures, e.g., "definitions" sections followed by "configurations"
sections, followed by "constraints" sections followed by a "conf"
section (for meta-information).
It also specifies "abstract" base data types (by means of XML-Schema
type definitions) for elements that should be used by documents in
the corresponding sections. The base data types can provide common
required attributes, e.g. a "name" attribute for naming definition
elements.
The following example shows the definition of the base type for
definition elements:
<xsd:complexType name="Definition" abstract="true" mixed="false">
<xsd:attribute name="name" type="xsd:string"> </xsd:attribute>
</xsd:complexType>
Profiles can then define concrete types that augment the base type
definitions. Common attributes or content models, that have been
defined by this base definition, do not have to be provided by those
concrete type definitions. The type definitions can be identified as
allowed element types for the content models that are specified in
the base SDPng schema definition. This allows for automatic
validation of profile definitions and faciliates the extension of
SDPng.
4.3 Profiles
The baseline SDPng specification consists of a profile (a schema
definition) and a library of commonly used definitions.
The library of commonly used definitions provides data types for IP
(or other) addresses etc. Details have to be provided at a later
time.
A profile definition imports (using the XML-Schema import mechanism)
the base SDPng schema definition and provided extension definition,
e.g., specializations of base element types. They also provide a
target namespace name for the definitions of the corresponding
profile. For well-known (registered) profiles the namespace name
will be registered by IANA. Proprietary profiles will use other
namespace names, for example, based on domain names, that are
registered by vendors providing a profile.
The following example shows such a declaration at the beginning of a
profile definition:
<xsd:schema targetNamespace="http://www.iana.org/sdpng/audio"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:sdpng="http://www.iana.org/sdpng"
xmlns:audio="http://www.iana.org/sdpng/audio"
>
<xsd:import namespace="http://www.iana.org/sdpng" schemaLocation="sdpng.xsd">
</xsd:import>
In this example the namespace prefix "audio" is defined and later
used in schema definitions. (The example profile provides definition
mechanisms for audio codecs.)
The following example shows, how a derived type for "definition"
elements can be specified with XML-Schema mechanisms. In this case
the abstract type "Definition" (fully qualified as
"sdpng:Definition") is augemented by three attributes that are useful
for defining audio codecs.
<xsd:complexType name="AudioCodec" mixed="false">
<xsd:complexContent>
<xsd:extension base="sdpng:Definition">
<xsd:attribute name="encoding" type="xsd:string">
</xsd:attribute>
<xsd:attribute name="sampling" type="xsd::positiveInteger">
</xsd:attribute>
<xsd:attribute name="channels" type="xsd:positiveInteger">
</xsd:attribute>
</xsd:extension>
</xsd:complexContent>
</xsd:complexType>
This type definition is then used to define an XML element type
called "codec".
<xsd:element name="codec" type="AudioCodec"> </xsd:element>
When used by SDPng documents, the general identifier is qualified
with a namespace prefix, for example like in: "audio:codec".
4.4 SDPng Documents
SDPng documents have to reference the employed profiles and provide
namespace prefixes for the namespace names of the profiles. For
example:
<sdpng:desc xmlns:sdpng="http://www.iana.org/sdpng"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-Instance"
xsi:schemaLocation="http://www.iana.org/sdpng sdpng.xsd"
xmlns:audio="http://www.iana.org/sdpng/audio"
xmlns:rtp="http://www.iana.org/sdpng/rtp"
>
It is proposed that for well-known registered profiles, the namespace
name AND the used namespace prefix is registered to allow for simple
basic implementations that can match identifiers by using fixed fully
qualified names without having to interpret namespace declarations.
There is one issue with declaring used XML-Schema definitions in
documents (see section "Issues" below).
The general structure of an SDPng would conform to the basic SDPng
schema definition and provide a "def" element for definitions, a
"cfg" element for the configuration section etc.
The following example shows a sample definition section where the
element "codec" of the "audio codec profile" is used (plus the
element type "pt" of an "RTP profile"):
<def>
<audio:codec name="dvi4" encoding="DVI4" channels="1"
sampling="8000"/>
<audio:codec name="g722" encoding="G722" channels="1"
sampling="16000"/>
<audio:codec name="g729" encoding="G729" channels="1"
sampling="8000"/>
<rtp:pt name="rtp-avp-18" pt="18" format="g729"/>
</def>
It can be seen how the attribute name (provided by the base type for
definition elements) and the profile specific attributes "encoding",
"channels" and "sampling" are used together.
The element "rtp:pt" is used to defined a payload type. "rtp:pt"
would have been defined in another profile, again using a type
derived from the base definition type. "rtp:pt" provides attribute
for referencing other definitions, e.g., the definition of audio-
codes as seen before.
4.5 Libraries
SDPng libraries are collections of definitions that are referenced by
documents. Libraries are thus independent, valid SDPng documents.
For example, the definition of the different audio codecs as shown in
the previous example could be provided by a library that can be
referenced by documents without having to define such common codecs
in every document.
The XML mechanism XIncludes [14] will be used for referencing
libraries in SDPng documents. XInlcude work at the "infoset" level,
i.e. the mechanisms allows to have an integrating document reference
fragment document, while these fragment are well-formed (and, if
applicable valid) document themselves. By resolving XInclude
directives in integrating documents the documents' infosets are
"merged" together, enabling applications to operate on the resulting
infosets as if it had been generated by parsing a single, monolithic
document.
Inclusion at the XML infoset level has the advantage that documents
are standalone -- they can be validated independently. Another
advantage is that is relatively easy to generate a "merged" infoset
for applications that are not able to resolve references to libraries
themselves.
An alternative for XInclude would be to use references that are
resolved by applications. For XML, this would probably mean to use
an XLink-based approach. This solution would require the definition
of an SDPng link element type and require applications to support
XLink (or at least the SDPng-relevant subset thereof). The inclusion
at the application level is however problematic, because it does not
result in a common integrated XML document infoset but would require
applications to handle multiple infosets, i.e. multiple documents.
More details on library inclusion plus an example have to be provided
at a later time.
4.6 Details on the use of specific XML Mechanisms
This section specifies the use of specific XML mechanisms for SDPng.
In order to allow for efficient parsing and processing, not all
features of XML Schema are allowed. Some variable information is set
to fixed values to allow the development of simplistic servers.
4.6.1 Default Namespace
SDPng document instances MUST use the SDPng namespace
"http://www.iana.org/sdpng" (tentative). That means, the general
SDPng identifiers can be used without namespace prefix.
4.6.2 Qualified Locals
XML Schema allows to specify qualification of elements and
attributes. It is possible to use non-qualified element and
attribute names in Schema definitions and document instances (this is
the default setting). In order to simplify parsing and processing of
SDPng document instances, all element MUST be fully qualified.
Attribute names MUST NOT be fully qualified.
This means, the SDPng Schema definition contains the following
attributes for the "schema" element, that MUST also be used by SDPng
profiles:
o elementFormDefault="qualified"
This means that "local" elements that used within the scope of
fully-qualified elements MUST be fully qualified.
o attributeFormDefault="unqualified"
This means, that attribute names do not have to be fully
qualified. Implementations MUST infer the namespace for
attributes from the namespace of the element that the attribute is
used in. Note that the specification of XML Namespaces [13]
defines that default namespaces do not apply to attributes.
These rules make SDPng document instances processable by non-Schema-
aware XML parsers by requiring all element names to be fully
qualified (no "local elements").
4.6.3 Fixed Namespace Prefixes
In order to facilitate the development of basic implementations, a
few commonly namespaces names may be associated with fixed prefixes,
i.e. document instances and libraries MUST always use these
prefixes. Theses prefixes MUST NOT be used for other namespaces
names than the ones that are assigned to them. A possible solution
could be to provide the possibility to register namespace prefixes as
well as namespace names.
The tentative prefix for the SDPng namespace is "sdpng".
4.7 SDPng Schema Definitions
This section provides an initial set of SDPng XML Schema definitions.
1. Section 4.7.1 contains the base definition that provide the
general element types for SDPng.
2. Section 4.7.2 contains a profile for audio codecs.
3. Section 4.7.3 contains a profile for RTP payload type
definitions.
4.7.1 SDPng Base Definition
This schema definition defines the general structure of SDPng
document instances. It defines the top-level element type "desc"
that can have a sequence of "def", "cfg", "contraints" and "conf"
elements as element content.
In addition, "extensions hooks" are provided that can be used by
extension profiles providing definitions for specific applications.
In general, these extension are implemented by deriving profile
definitions from SDPng base definitions. The deployed XML Schema
mechanisms are "deriving by extension" and "substitution groups".
The SDPng base definition provides different base types (as
complexType definitions) for elements that are to be used in "def",
"cfg" and "conf" sections. In addition, it also defines specific
element types as "head elements" with assigned types that are used
for defining the content model of, e.g., the "def" element type.
Profiles that provide new element types for specific applications
will define types that are derived from the base types and provide
the additional attributes and element content definitions that are
required for the application. The XML element types that are defined
in a profile are declared as valid subsitutes for the base elements
("head elements") by setting the "substitutionGroup" attribute to the
name of the "head element" type.
For an extension-profile definition, that defines new definition
element types, e.g. for codec definitions, a new complexType would
be defined that extends sdpng:Definition (see below). An element
type definition that assigns that new type must then be declared to
be in the substitutionGroup "sdpng:d".
This mechanism allows common attribute and content model rules to be
defined in base element definition and re-used by extension profiles
and it also allows validating parsers to identify the correct type of
elements that have been defined by profile definitions.
<xsd:schema targetNamespace="http://www.iana.org/sdpng"
xmlns:sdpng="http://www.iana.org/sdpng"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<xsd:annotation>
<xsd:documentation>
This schema definition defines the general structure of SDPng
document instances. It provides base type and base element
definition for elements to occur in the different sections (def,
cfg, constraints, conf) to be derived from in extension-profile
definitions.
For an extension-profile definition, that defines new definition
element types, e.g. for codec definitions, a new complexType would
be defined that extends sdpng:Definition (see below). An element
type definition that assigns that new type must then be declared
to be in the substitutionGroup "sdpng:d".
</xsd:documentation>
</xsd:annotation>
<xsd:element name="desc">
<xsd:annotation>
<xsd:documentation>
The top-level element of an SDPng document. It defines the
overall structure of an SPDng document.
</xsd:documentation>
</xsd:annotation>
<xsd:complexType mixed="false">
<xsd:sequence>
<xsd:element ref="sdpng:def" minOccurs="0"/>
<xsd:element ref="sdpng:cfg"/>
<xsd:element ref="sdpng:constraints" minOccurs="0"/>
<xsd:element ref="sdpng:conf" minOccurs="0"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<xsd:element name="def">
<xsd:annotation>
<xsd:documentation>The definitions section</xsd:documentation>
</xsd:annotation>
<xsd:complexType mixed="false">
<xsd:sequence>
<xsd:element ref="sdpng:d" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<xsd:element name="cfg">
<xsd:annotation>
<xsd:documentation>The configurations section</xsd:documentation>
</xsd:annotation>
<xsd:complexType mixed="false">
<xsd:sequence>
<xsd:element ref="sdpng:c" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<xsd:element name="constraints">
<xsd:annotation>
<xsd:documentation>The constraints section</xsd:documentation>
</xsd:annotation>
<xsd:complexType mixed="false">
<xsd:sequence>
<xsd:element ref="sdpng:cn" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<xsd:element name="conf" type="sdpng:Conference">
<xsd:annotation>
<xsd:documentation>The conference section</xsd:documentation>
</xsd:annotation>
</xsd:element>
<!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<xsd:element name="d" type="sdpng:Definition">
<xsd:annotation>
<xsd:documentation>
Placeholder base element for a definition element in the
definitions section. To be derived from by specific definition
element type definitions.
</xsd:documentation>
</xsd:annotation>
</xsd:element>
<!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<xsd:element name="c" type="sdpng:Component">
<xsd:annotation>
<xsd:documentation>
Placeholder base element for a configuration element in the
configurations section. To be derived from by specific
configuration element type definitions.
</xsd:documentation>
</xsd:annotation>
</xsd:element>
<!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<xsd:element name="cn" type="sdpng:Constraint">
<xsd:annotation>
<xsd:documentation>
Placeholder base element for a contraint element in the
contraints section. To be derived from by specific constraint
element type definitions.
</xsd:documentation>
</xsd:annotation>
</xsd:element>
<!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<xsd:complexType name="Definition" abstract="true" mixed="false">
<xsd:annotation>
<xsd:documentation>
The base type for definition. Defines a attribute "name" for
naming definitions.
</xsd:documentation>
</xsd:annotation>
<xsd:attribute name="name" type="xsd:string"/>
</xsd:complexType>
<!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<xsd:complexType name="Component" mixed="false">
<xsd:annotation>
<xsd:documentation>
The specification of a component consists of a sequence of
alternatives.
</xsd:documentation>
</xsd:annotation>
<xsd:sequence>
<xsd:element ref="sdpng:alt" minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
<xsd:attribute name="name" type="xsd:string"/>
<xsd:attribute name="media" type="xsd:string"/>
</xsd:complexType>
<xsd:element name="alt">
<xsd:annotation>
<xsd:documentation>
Each alternative consists of a "sc" (session configuration)
element. The "sc" element is a base element of base type
"sdpng:Session" that is used to derive specific session types
in extension profiles.
</xsd:documentation>
</xsd:annotation>
<xsd:complexType mixed="false">
<xsd:sequence>
<xsd:element ref="sdpng:sc" minOccurs="1" maxOccurs="1"/>
</xsd:sequence>
<xsd:attribute name="name" type="xsd:string"/>
</xsd:complexType>
</xsd:element>
<xsd:element name="sc" type="sdpng:SessionConfig"/>
<xsd:complexType name="SessionConfig" abstract="true" mixed="false">
<xsd:annotation>
<xsd:documentation>
The (abstract) base type for session elements. To be derived
from in extension profiles.
</xsd:documentation>
</xsd:annotation>
</xsd:complexType>
<!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<xsd:complexType name="Constraint" mixed="false">
<xsd:annotation>
<xsd:documentation>
The current content model for constraints is a sequence of
"sdpng:par" elements. In each "par" element a sequence of
"use-alt" elements may be used to specific the definitions
that may used in parallel. Each "use-alt" element can define
the number of minimum and maximum instantiations.
</xsd:documentation>
</xsd:annotation>
<xsd:sequence>
<xsd:element ref="sdpng:par"/>
</xsd:sequence>
</xsd:complexType>
<xsd:element name="par">
<xsd:complexType mixed="false">
<xsd:sequence>
<xsd:element ref="sdpng:use-alt">
</xsd:element>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="use-alt">
<xsd:complexType mixed="false">
<xsd:attribute name="ref" type="xsd:string"/>
<xsd:attribute name="min" type="xsd:positiveInteger"
use="optional"/>
<xsd:attribute name="max" type="xsd:positiveInteger"
use="optional"/>
</xsd:complexType>
</xsd:element>
<!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<xsd:complexType name="Conference" mixed="false">
<xsd:sequence>
<xsd:element name="meta" type="sdpng:ConfItem"/>
</xsd:sequence>
<!-- TBD -->
</xsd:complexType>
<xsd:complexType name="ConfItem" abstract="true" mixed="false">
<xsd:annotation>
<xsd:documentation>
The base type for conference meta inforformation
element. Currently, there is no common content model defined.
</xsd:documentation>
</xsd:annotation>
</xsd:complexType>
<!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<xsd:element name="owner">
<xsd:complexType mixed="false">
<xsd:complexContent mixed="false">
<xsd:extension base="sdpng:ConfItem">
<xsd:attribute name="user" type="xsd:string"/>
<xsd:attribute name="id" type="xsd:string"/>
<xsd:attribute name="version" type="xsd:string"/>
<xsd:attribute name="nettype" type="xsd:string"/>
<xsd:attribute name="addrtype" type="xsd:string"/>
<xsd:attribute name="addr" type="xsd:string">
<!-- FIXME: re-use common address type! -->
</xsd:attribute>
</xsd:extension>
</xsd:complexContent>
</xsd:complexType>
</xsd:element>
<!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<xsd:element name="session">
<xsd:complexType mixed="false">
<xsd:complexContent mixed="false">
<xsd:extension base="sdpng:ConfItem">
<xsd:sequence>
<xsd:element name="description" type="xsd:string"/>
<xsd:element name="info">
<xsd:complexType mixed="false">
<xsd:attribute name="href" type="xsd:string"/>
</xsd:complexType>
</xsd:element>
<xsd:sequence minOccurs="0">
<xsd:element name="contact" type="xsd:string"/>
</xsd:sequence>
</xsd:sequence>
</xsd:extension>
</xsd:complexContent>
</xsd:complexType>
</xsd:element>
</xsd:schema>
4.7.2 Audio Codec Profile
The following profile defines an element type that can be used for
specifying audio codec characteristics. The element "audio:codec" is
of type "audio:AudioCodec" which is derived from the SDPng base type
"sdpng:Definition". The element "audio:codec" is declared to have
the subsitution group "sdpng:d" (the "head element" of the SDPng base
definition).
This means, "audio:codec" element can be used as child elements in
"sdpng:def" elements. In addition to the attributes specified here
"audio:codec" elements will also have to provide a "name" attribute
as defined by "sdpng:Definition".
<xsd:schema targetNamespace="http://www.iana.org/sdpng/audio"
xmlns:audio="http://www.iana.org/sdpng/audio"
xmlns:sdpng="http://www.iana.org/sdpng"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<xsd:import namespace="http://www.iana.org/sdpng" schemaLocation="sdpng.xsd"/>
<!-- AudioCodecs extends the abstract type "Definition" -->
<!-- The data types for the attributes could be more restrictive... -->
<xsd:complexType name="AudioCodec" mixed="false">
<xsd:complexContent mixed="false">
<xsd:extension base="sdpng:Definition">
<xsd:attribute name="encoding" type="xsd:string"/>
<xsd:attribute name="sampling" type="xsd:positiveInteger"/>
<xsd:attribute name="channels" type="xsd:positiveInteger"/>
</xsd:extension>
</xsd:complexContent>
</xsd:complexType>
<xsd:element name="codec" substitutionGroup="sdpng:d">
<xsd:complexType>
<xsd:complexContent>
<xsd:extension base="audio:AudioCodec"/>
</xsd:complexContent>
</xsd:complexType>
</xsd:element>
</xsd:schema>
4.7.3 RTP profile
The following profile defines element types that can be used for
specifying RTP payload types and RTP session configurations. The
element "rtp:pt" is of type "rtp:PayloadType" which is derived from
the SDPng base type "sdpng:Definition". The element "rtp:pt" is
declared to have the subsitution group "sdpng:d" (the "head element"
of the SDPng base definition).
The element "rtp:session" is of type "rtp:Session" which is derived
from the SDPng base type "sdpng:SessionConfig". The element
"rtp:session" is declared to have the subsitution group "sdpng:sc"
(the "head element" of the SDPng base definition).
The RTP profile in turn defines base types for the specification of
transport parameters that are to be derived from by profiles that
define rules for elements that can be used to specifiy parameters for
specific transport mechanisms.
<xsd:schema targetNamespace="http://www.iana.org/sdpng/rtp"
xmlns:rtp="http://www.iana.org/sdpng/rtp"
xmlns:sdpng="http://www.iana.org/sdpng"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<xsd:import namespace="http://www.iana.org/sdpng" schemaLocation="sdpng.xsd"/>
<xsd:complexType name="PayloadType" mixed="false">
<xsd:annotation>
<xsd:documentation>
PayloadType, the element for payload type definitions is
derived from "sdpng:Definition". Inside an element of this
type, more definitions may be given (derived from
sdpng:Definition themselves). If no definition is given in the
content, a definition may be referenced using the "format
attribute".
</xsd:documentation>
</xsd:annotation>
<xsd:complexContent mixed="false">
<xsd:extension base="sdpng:Definition">
<xsd:sequence>
<xsd:element ref="sdpng:d" minOccurs="0" maxOccurs="unbounded"/>
</xsd:sequence>
<xsd:attribute name="pt" type="xsd:unsignedByte"/>
<xsd:attribute name="format" type="xsd:string">
<!-- IDREF? Issue: unique names for definitions!-->
</xsd:attribute>
</xsd:extension>
</xsd:complexContent>
</xsd:complexType>
<xsd:element name="pt" type="rtp:PayloadType" substitutionGroup="sdpng:d"/>
<!-- ______________________________________________________________________ -->
<xsd:element name="session" type="rtp:Session"
substitutionGroup="sdpng:sc"/>
<xsd:complexType name="Session" mixed="false">
<xsd:complexContent mixed="false">
<xsd:extension base="sdpng:SessionConfig">
<xsd:sequence>
<xsd:element name="transport" type="rtp:Transport"/>
</xsd:sequence>
<xsd:attribute name="format" type="xsd:string"/>
</xsd:extension>
</xsd:complexContent>
</xsd:complexType>
<xsd:complexType name="Transport" abstract="true" mixed="false">
<xsd:attribute name="rtp-port" type="xsd:unsignedShort" use="optional"/>
<xsd:attribute name="rtcp-port" type="xsd:unsignedShort" use="optional"/>
</xsd:complexType>
<xsd:simpleType name="IPAddr">
<xsd:restriction base="xsd:string"/>
</xsd:simpleType>
<xsd:simpleType name="IP4Addr">
<xsd:restriction base="rtp:IPAddr"/>
</xsd:simpleType>
<xsd:simpleType name="IP6Addr">
<xsd:restriction base="rtp:IPAddr"/>
</xsd:simpleType>
<xsd:complexType name="UDP" mixed="false">
<xsd:complexContent mixed="false">
<xsd:extension base="rtp:Transport">
<xsd:choice>
<xsd:element name="option">
<!-- define options -->
</xsd:element>
</xsd:choice>
<xsd:attribute name="addr" type="rtp:IP4Addr"/>
</xsd:extension>
</xsd:complexContent>
</xsd:complexType>
<xsd:element name="udp" type="rtp:UDP"/>
</xsd:schema>
4.8 Issues
o Libraries provide partially specified definitions, i.e. without
transport parameters. How can SDPng documents reference the
definitions and augment them with conrete transport parameters?
o Referencing extension profiles: XML-Schema does not support the
declaration of multiple schemas via the schemaLocation attribute.
Conceivable solution: When extension profiles are used, the SDPng
description is a "multi-part" object, that consists of an
integrating schema definition (that references all necessary
profiles and the base definition) and the actual description
document that is a schema instance of the integrating schema.
o Uniqueness of attribute values: When libraries are used they will
contain definition elements with "name" attributes for later
referencing. How to avoid name clashes for those identifiers?
When an SDPng document uses libraries from different sources they
could be incompatible because of name collisions. Possible
solution: Prefix such IDs with a namespace name (either
explicitely or implicitely by interpreting applications). The
explicit prefixes have the advantage that no special knowledge
would be required to ressolve links at the cost of very long ID
values.
5. Use of SDPng in conjunction with other IETF Signaling Protocols 5. Use of SDPng in conjunction with other IETF Signaling Protocols
SDPng defines the notion of Components to indicate the intended SDPng defines the notion of Components to indicate the intended types
types of collaboration between the users in e.g. a teleconferencing of collaboration between the users in e.g. a teleconferencing
scenario. scenario.
For the means conceivable to realize a particular Component, SDPng For the means conceivable to realize a particular Component, SDPng
conceptually distinguishes three levels of support: conceptually distinguishes three levels of support:
a Capapility refers to the fact that one of the involved parties a Capapility refers to the fact that one of the involved parties
supports one particular way of exchanging media -- defined in supports one particular way of exchanging media -- defined in
terms of transport, codec, and other parameters -- as part of the terms of transport, codec, and other parameters -- as part of the
teleconference. teleconference.
a Potential Configuration denotes a set of matching Capabilities a Potential Configuration denotes a set of matching Capabilities
from all those involved parties required to successfully realize from all those involved parties required to successfully realize
one particular Component. one particular Component.
an Actual Configuration indicates the Potential Configuration an Actual Configuration indicates the Potential Configuration
which was chosen by the involved parties to realize a certain which was chosen by the involved parties to realize a certain
Component at one particular point in time. Component at one particular point in time.
As mentioned before, this abstract notion of the interactions As mentioned before, this abstract notion of the interactions between
between a number of communicating systems needs to be mapped to the a number of communicating systems needs to be mapped to the
application scenarios of SDPng in conjunction with the various IETF application scenarios of SDPng in conjunction with the various IETF
signaling protocols: SAP, SIP, RTSP, and MEGACO. signaling protocols: SAP, SIP, RTSP, and MEGACO.
5.1 The Session Announcement Protocol (SAP) 5.1 The Session Announcement Protocol (SAP)
SAP is used to disseminate a previously created (and typically SAP is used to disseminate a previously created (and typically fixed)
fixed) session description to a potentially large audience. An session description to a potentially large audience. An interested
interested member of the audience will use the SDPng description member of the audience will use the SDPng description contained in
contained in SAP to join the announced media sessions. SAP to join the announced media sessions.
This means that a SAP announcements contains the Actual This means that a SAP announcements contains the Actual
Configurations of all Components that are part of the overall Configurations of all Components that are part of the overall
teleconference or broadcast. teleconference or broadcast.
A SAP announcement may contain multiple Actual Configurations for A SAP announcement may contain multiple Actual Configurations for the
the same Component. In this case, the "same" (i.e. semantically same Component. In this case, the "same" (i.e. semantically
equivalent) media data from one configuration must be available from equivalent) media data from one configuration must be available from
each of the Actual Configurations. In practice, this limits the use each of the Actual Configurations. In practice, this limits the use
of multiple Actual Configurations to single-source multicast or of multiple Actual Configurations to single-source multicast or
broadcast scenarios. broadcast scenarios.
Each receiver of a SAP announcement with SDPng compares its locally Each receiver of a SAP announcement with SDPng compares its locally
stored Capabiities to realize a certain Component against the Actual stored Capabiities to realize a certain Component against the Actual
Configurations contained in the announcement. If the intersection Configurations contained in the announcement. If the intersection
yields one or more Potential Configurations for the receiver, it yields one or more Potential Configurations for the receiver, it
chooses the one it sees fit best. If the intersection is empty, the chooses the one it sees fit best. If the intersection is empty, the
receiver cannot participate in the announced session. receiver cannot participate in the announced session.
SAP may be substituted by HTTP (in the general case, at least), SAP may be substituted by HTTP (in the general case, at least), SMTP,
SMTP, NNTP, or other IETF protocols suitable for conveying a media NNTP, or other IETF protocols suitable for conveying a media
description from one entity to one or more other without the intend description from one entity to one or more other without the intend
for further negotiation of the session parameters. for further negotiation of the session parameters.
Example from the SAP spec. to be provided. Example from the SAP spec. to be provided.
5.2 Session Initiation Protocol (SIP) 5.2 Session Initiation Protocol (SIP)
SIP is used to establish and modify multimedia sessions, and SDPng SIP is used to establish and modify multimedia sessions, and SDPng
may be carried at least in SIP INVITE and ACK messages as well as in may be carried at least in SIP INVITE and ACK messages as well as in
a number of responses. From dealing with legacy SDP (and its a number of responses. From dealing with legacy SDP (and its
skipping to change at page 27, line 7 skipping to change at page 44, line 7
Capabilities. Those will be provided as Potential Configurations, Capabilities. Those will be provided as Potential Configurations,
possibly with extensive Constraints specifications. Whenever a media possibly with extensive Constraints specifications. Whenever a media
path needs to be set up by the MGC between two MGs or an MG needs to path needs to be set up by the MGC between two MGs or an MG needs to
be reconfigured internally, the MGC will use (updated) Actual be reconfigured internally, the MGC will use (updated) Actual
Configurations. Configurations.
Details and examples to be defined. Details and examples to be defined.
6. Open Issues 6. Open Issues
The precise sytnax for referencing profiles and libraries needs The precise sytnax for referencing profiles and libraries needs to
to be worked out. be worked out.
A registry (reuse of SDP mechanisms and names etc.) needs to be A registry (reuse of SDP mechanisms and names etc.) needs to be
set up. set up.
Transport and Payload type specifications need to be defined as Transport and Payload type specifications need to be defined as
additional appendices. additional appendices.
Negotiation mechanisms for multiparty conferencing need to be Negotiation mechanisms for multiparty conferencing need to be
formalized. formalized.
skipping to change at page 28, line 22 skipping to change at page 45, line 22
Protocol", RFC 2327, April 1998. Protocol", RFC 2327, April 1998.
[3] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobsen, [3] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobsen,
"RTP: A Transport Protocol for Real-Time Applications", RFC "RTP: A Transport Protocol for Real-Time Applications", RFC
1889, January 1996. 1889, January 1996.
[4] Schulzrinne, H., "RTP Profile for Audio and Video Conferences [4] Schulzrinne, H., "RTP Profile for Audio and Video Conferences
with Minimal Control", RFC 1890, January 1996. with Minimal Control", RFC 1890, January 1996.
[5] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video [5] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
Conferences with Minimal Control", Internet-Draft Conferences with Minimal Control", draft-ietf-avt-profile-new-
draft-ietf-avt-profile-new-10.txt , March 2001. 10.txt (work in progress), March 2001.
[6] Perkins, C., Kouvelas, I., Hodson, O., Hardman, V., Handley, [6] Perkins, C., Kouvelas, I., Hodson, O., Hardman, V., Handley,
M., Bolot, J., Vega-Garcia, A. and S. Fosse-Parisis, "RTP M., Bolot, J., Vega-Garcia, A. and S. Fosse-Parisis, "RTP
Payload for Redundant Audio Data", RFC 2198, September 1997. Payload for Redundant Audio Data", RFC 2198, September 1997.
[7] Klyne, G., "A Syntax for Describing Media Feature Sets", RFC [7] Klyne, G., "A Syntax for Describing Media Feature Sets", RFC
2533, March 1999. 2533, March 1999.
[8] Klyne, G., "Protocol-independent Content Negotiation [8] Klyne, G., "Protocol-independent Content Negotiation
Framework", RFC 2703, September 1999. Framework", RFC 2703, September 1999.
[9] Rosenberg, J. and H. Schulzrinne, "An RTP Payload Format for [9] Rosenberg, J. and H. Schulzrinne, "An RTP Payload Format for
Generic Forward Error Correction", RFC 2733, December 1999. Generic Forward Error Correction", RFC 2733, December 1999.
[10] Perkins, C. and O. Hodson, "Options for Repair of Streaming [10] Perkins, C. and O. Hodson, "Options for Repair of Streaming
Media", RFC 2354, June 1998. Media", RFC 2354, June 1998.
[11] Handley, M., Perkins, C. and E. Whelan, "Session Announcement [11] Handley, M., Perkins, C. and E. Whelan, "Session Announcement
Protocol", RFC 2974, October 2000. Protocol", RFC 2974, October 2000.
[12] World Wide Web Consortium (W3C), "Extensible Markup Language
(XML) 1.0 (Second Edition)", Status W3C Recommendation, Version
http://www.w3.org/TR/2000/REC-xml-20001006, October 2000.
[13] World Wide Web Consortium (W3C), "Namespaces in XML", Status
W3C Recommendation, Version http://www.w3.org/TR/1999/REC-xml-
names-19990114, January 1999.
[14] World Wide Web Consortium (W3C), "XML Inclusions (XInclude)
Version 1.0", Status W3C Working Draft, Version
http://www.w3.org/TR/2001/WD-xinclude-20010516, May 2001.
[15] World Wide Web Consortium (W3C), "XML Schema Part 1:
Structures", Version http://www.w3.org/TR/2001/REC-xmlschema-1-
20010502/, Status W3C Recommendation, May 2001.
[16] World Wide Web Consortium (W3C), "XML Schema Part 2:
Datatypes", Version http://www.w3.org/TR/2001/REC-xmlschema-2-
20010502/, Status W3C Recommendation, May 2001.
Authors' Addresses Authors' Addresses
Dirk Kutscher Dirk Kutscher
TZI, Universitaet Bremen TZI, Universitaet Bremen
Bibliothekstr. 1 Bibliothekstr. 1
Bremen 28359 Bremen 28359
Germany Germany
Phone: +49.421.218-7595, sip:dku@tzi.org Phone: +49.421.218-7595, sip:dku@tzi.org
Fax: +49.421.218-7000 Fax: +49.421.218-7000
skipping to change at page 30, line 15 skipping to change at page 47, line 15
Appendix A. Base SDPng Specifications for Audio Codec Descriptions Appendix A. Base SDPng Specifications for Audio Codec Descriptions
[5] specifies a number of audio codecs including short name to be [5] specifies a number of audio codecs including short name to be
used as reference by session description protocols such as SDP and used as reference by session description protocols such as SDP and
SDPng. Those codec names, as listed in the first column of the above SDPng. Those codec names, as listed in the first column of the above
table, are used to identify codecs in SDPng. table, are used to identify codecs in SDPng.
The following sections indicate the default values that are assumed The following sections indicate the default values that are assumed
if nothing else than the codec reference is specified. if nothing else than the codec reference is specified.
The following audio-codec attributes are defined for audio codecs: The following audio:codec attributes are defined for audio codecs:
name: the identifier to be later used for referencing the codec spec name: the identifier to be later used for referencing the codec spec
encoding: the RTP/AVP profile identifier as registered with IANA encoding: the RTP/AVP profile identifier as registered with IANA
mime: the MIME type; may alternatively be specified instead of mime: the MIME type; may alternatively be specified instead of
"encoding" "encoding"
channels: the number of independent media channels channels: the number of independent media channels
pattern: the media channel pattern for mapping channels to payload pattern: the media channel pattern for mapping channels to payload
sampling: the sample rate for the codec (which in most cases equals sampling: the sample rate for the codec (which in most cases equals
the RTP clock) the RTP clock)
Furthermode, options may be defined of the following format: Furthermode, options may be defined of the following format:
<option id="name">value</option> <option id="name">value</option>
if a value is associated with the option (note that arbitrary if a value is associated with the option (note that arbitrary complex
complex values are allowed), or alternatively: values are allowed), or alternatively:
<option id="name"/> <option id="name"/>
if the option is just a boolean indicator. if the option is just a boolean indicator.
Attributes for the "option" tag are the following: Attributes for the "option" tag are the following:
id: the identifier for the option (variable name) id: the identifier for the option (variable name)
collaps: the collapsing rules for this optional element, defined as collaps: the collapsing rules for this optional element, defined as
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Attributes for the "option" tag are the following: Attributes for the "option" tag are the following:
id: the identifier for the option (variable name) id: the identifier for the option (variable name)
collaps: the collapsing rules for this optional element, defined as collaps: the collapsing rules for this optional element, defined as
follows: follows:
min: for numeric values only min: for numeric values only
max: for numeric values only max: for numeric values only
x: intersection of enumerated values, value lists x: intersection of enumerated values, value lists
A.1 DVI4 A.1 DVI4
<audio-codec name="dvi4" encoding="DVI4" channels="1" sampling="8000"> <audio:codec name="dvi4" encoding="DVI4" channels="1" sampling="8000">
<rtp-pt name="rtp-avp-5" pt="5" format="dvi4"/> <rtp:pt name="rtp-avp-5" pt="5" format="dvi4"/>
<rtp-pt name="rtp-avp-6" pt="6"> <rtp:pt name="rtp-avp-6" pt="6">
<audio-codec encoding="DVI4" channels="1" sampling="16000"> <audio:codec encoding="DVI4" channels="1" sampling="16000">
</rtp-pt> </rtp:pt>
Note that there is no default sampling rate specified for DVI4 and Note that there is no default sampling rate specified for DVI4 and
hence a sampling rate MUST be specified. hence a sampling rate MUST be specified.
A.2 G.722 A.2 G.722
<audio-codec name="g722" encoding="G722" channels="1" sampling="16000"/> <audio:codec name="g722" encoding="G722" channels="1" sampling="16000"/>
<rtp-pt name="rtp-avp-9" pt="9" format="g722"/> <rtp:pt name="rtp-avp-9" pt="9" format="g722"/>
Note as per [5] that the RTP clock rate is 8000Hz rather than 16000 Note as per [5] that the RTP clock rate is 8000Hz rather than 16000
Hz. Hz.
A.3 G.726 A.3 G.726
<audio-codec name="g726-40" encoding="G726-40" channels="1" sampling="8000"/> <audio:codec name="g726-40" encoding="G726-40" channels="1" sampling="8000"/>
<audio-codec name="g726-32" encoding="G726-32" channels="1" sampling="8000"/> <audio:codec name="g726-32" encoding="G726-32" channels="1" sampling="8000"/>
<audio-codec name="g726-24" encoding="G726-24" channels="1" sampling="8000"/> <audio:codec name="g726-24" encoding="G726-24" channels="1" sampling="8000"/>
<audio-codec name="g726-16" encoding="G726-16" channels="1" sampling="8000"/> <audio:codec name="g726-16" encoding="G726-16" channels="1" sampling="8000"/>
<rtp-pt name="rtp-avp-5" pt="5" format="g726-32"/> <rtp:pt name="rtp-avp-5" pt="5" format="g726-32"/>
A.4 G.728 A.4 G.728
<audio-codec name="g728" encoding="G728" channels="1" sampling="8000"/> <audio:codec name="g728" encoding="G728" channels="1" sampling="8000"/>
<rtp-pt name="rtp-avp-15" pt="15" format="g728"/> <rtp:pt name="rtp-avp-15" pt="15" format="g728"/>
A.5 G.729 A.5 G.729
G.729 Annex A: reduced complexity of G.729 G.729 Annex A: reduced complexity of G.729
G.729 Annex B: comfort noise G.729 Annex B: comfort noise
<audio-codec name="g729" encoding="G729" channels="1" sampling="8000"/> <audio:codec name="g729" encoding="G729" channels="1" sampling="8000"/>
<rtp-pt name="rtp-avp-18" pt="18" format="g729"/> <rtp:pt name="rtp-avp-18" pt="18" format="g729"/>
For further codec description, the following options (which carry no For further codec description, the following options (which carry no
values associated with them) MAY be included: values associated with them) MAY be included:
<option id="annexA"/> <option id="annexA"/>
<!-- to indicate the use of Annex A reduced complexity --> <!-- to indicate the use of Annex A reduced complexity -->
<option id="annexB"/> <option id="annexB"/>
<!-- to indicate the use of Annex B comfort noise --> <!-- to indicate the use of Annex B comfort noise -->
As stated in [5], the use of these options can be detected within As stated in [5], the use of these options can be detected within the
the media stream. media stream.
A.6 G.729 Annex D and E A.6 G.729 Annex D and E
<audio-codec name="g729d" encoding="G729D" channels="1" sampling="8000"/> <audio:codec name="g729d" encoding="G729D" channels="1" sampling="8000"/>
<audio-codec name="g729e" encoding="G729E" channels="1" sampling="8000"/> <audio:codec name="g729e" encoding="G729E" channels="1" sampling="8000"/>
The following option MAY be used with both Annexes D and E: The following option MAY be used with both Annexes D and E:
<option id="annexB"/> <option id="annexB"/>
<!-- to indicate the use of Annex B comfort noise --> <!-- to indicate the use of Annex B comfort noise -->
A.7 GSM A.7 GSM
A.7.1 GSM Full Rate A.7.1 GSM Full Rate
The GSM Full Rate codec is indicated as follows: The GSM Full Rate codec is indicated as follows:
<audio-codec name="gsm" encoding="GSM" channels="1" sampling="8000"/> <audio:codec name="gsm" encoding="GSM" channels="1" sampling="8000"/>
<rtp-pt name="rtp-avp-3" pt="3" format="gsm"/> <rtp:pt name="rtp-avp-3" pt="3" format="gsm"/>
A.7.2 GSM Half Rate A.7.2 GSM Half Rate
The GSM Half Rate codec is indicated as follows: The GSM Half Rate codec is indicated as follows:
<audio-codec name="gsm-hr" encoding="GSM-HR" channels="1" sampling="8000"/> <audio:codec name="gsm-hr" encoding="GSM-HR" channels="1" sampling="8000"/>
A.7.3 GSM Enhanced Full Rate A.7.3 GSM Enhanced Full Rate
The GSM Enhanced Full Rate codec is indicated as follows: The GSM Enhanced Full Rate codec is indicated as follows:
<audio-codec name="gsm-efr" encoding="GSM-EFR" channels="1" sampling="8000"/> <audio:codec name="gsm-efr" encoding="GSM-EFR" channels="1" sampling="8000"/>
A.8 L8 A.8 L8
<audio-codec name="l8" encoding="L8" channels="1" sampling="8000"/> <audio:codec name="l8" encoding="L8" channels="1" sampling="8000"/>
A.9 L16 A.9 L16
<audio-codec name="l16" encoding="L16" channels="1" sampling="8000"/> <audio:codec name="l16" encoding="L16" channels="1" sampling="8000"/>
<rtp-pt name="rtp-avp-11" pt="11" format="gsm"/> <rtp:pt name="rtp-avp-11" pt="11" format="gsm"/>
<rtp-pt name="rtp-avp-10" pt="11" format="gsm"> <rtp:pt name="rtp-avp-10" pt="11" format="gsm">
<audio-codec encoding="L16" channels="2" sampling="8000"/> <audio:codec encoding="L16" channels="2" sampling="8000"/>
</rtp-pt> </rtp:pt>
A.10 LPC A.10 LPC
<audio-codec name="lpc" encoding="LPC" channels="1" sampling="8000"/> <audio:codec name="lpc" encoding="LPC" channels="1" sampling="8000"/>
A.11 MPA A.11 MPA
<audio-codec name="mpa" encoding="MPA" channels="1" sampling="8000"/> <audio:codec name="mpa" encoding="MPA" channels="1" sampling="8000"/>
<rtp-pt name="rtp-avp-14" pt="14" format="mpa"/> <rtp:pt name="rtp-avp-14" pt="14" format="mpa"/>
A.12 PCMA and PCMU A.12 PCMA and PCMU
<audio-codec name="pcmu" encoding="PCMU" channels="1" sampling="8000"/> <audio:codec name="pcmu" encoding="PCMU" channels="1" sampling="8000"/>
<audio-codec name="pcma" encoding="PCMA" channels="1" sampling="8000"/> <audio:codec name="pcma" encoding="PCMA" channels="1" sampling="8000"/>
<rtp-pt name="rtp-avp-0" pt="0" format="pcmu"/> <rtp:pt name="rtp-avp-0" pt="0" format="pcmu"/>
<rtp-pt name="rtp-avp-8" pt="8" format="pcma"/> <rtp:pt name="rtp-avp-8" pt="8" format="pcma"/>
A.13 QCELP A.13 QCELP
<audio-codec name="qcelp" encoding="QCELP" channels="1" sampling="8000"/> <audio:codec name="qcelp" encoding="QCELP" channels="1" sampling="8000"/>
<rtp-pt name="rtp-avp-12" pt="12" format="qcelp"/> <rtp:pt name="rtp-avp-12" pt="12" format="qcelp"/>
A.14 VDVI A.14 VDVI
<audio-codec name="vdvi" encoding="VDVI" channels="1" sampling="8000"/> <audio:codec name="vdvi" encoding="VDVI" channels="1" sampling="8000"/>
Appendix B. Change History
draft-ietf-mmusic-sdpng-02.txt
* Added a section on formal specification mechanisms (Section 4).
draft-ietf-mmusic-sdpng-01.txt
* renamed section "Syntax Propsal" to "Syntax Definition
Mechanisms". More text on DTD vs. schema. Edited the example
description.
* updated example definitions in section "Definitions" and
"Components & Configurations"
* section "Session Atrributes" replaces section "Session"
* new appendix on audio codec definitions
Full Copyright Statement 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 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 kind, provided that the above copyright notice and this paragraph are
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
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