draft-ietf-mmusic-sdp-media-capabilities-14.txt   draft-ietf-mmusic-sdp-media-capabilities-15.txt 
MMUSIC R. Gilman MMUSIC R. Gilman
Internet-Draft Independent Internet-Draft Independent
Intended status: Standards Track R. Even Updates: 5939 (if approved) R. Even
Expires: January 10, 2013 Gesher Erove Ltd Intended status: Standards Track Gesher Erove Ltd
F. Andreasen Expires: April 4, 2013 F. Andreasen
Cisco Systems Cisco Systems
July 9, 2012 October 1, 2012
SDP Media Capabilities Negotiation Session Description Protocol (SDP) Media Capabilities Negotiation
draft-ietf-mmusic-sdp-media-capabilities-14 draft-ietf-mmusic-sdp-media-capabilities-15
Abstract Abstract
Session Description Protocol (SDP) capability negotiation provides a Session Description Protocol (SDP) capability negotiation provides a
general framework for indicating and negotiating capabilities in SDP. general framework for indicating and negotiating capabilities in SDP.
The base framework defines only capabilities for negotiating The base framework defines only capabilities for negotiating
transport protocols and attributes. In this document, we extend the transport protocols and attributes. In this document, we extend the
framework by defining media capabilities that can be used to framework by defining media capabilities that can be used to
negotiate media types and their associated parameters. negotiate media types and their associated parameters.
This document updates the IANA Considerations of RFC 5939.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 10, 2013. This Internet-Draft will expire on April 4, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 3, line 34 skipping to change at page 3, line 34
3.4.2. Generating the Answer . . . . . . . . . . . . . . . . 39 3.4.2. Generating the Answer . . . . . . . . . . . . . . . . 39
3.4.3. Offerer Processing of the Answer . . . . . . . . . . . 43 3.4.3. Offerer Processing of the Answer . . . . . . . . . . . 43
3.4.4. Modifying the Session . . . . . . . . . . . . . . . . 43 3.4.4. Modifying the Session . . . . . . . . . . . . . . . . 43
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.1. Alternative Codecs . . . . . . . . . . . . . . . . . . . . 45 4.1. Alternative Codecs . . . . . . . . . . . . . . . . . . . . 45
4.2. Alternative Combinations of Codecs (Session 4.2. Alternative Combinations of Codecs (Session
Configurations) . . . . . . . . . . . . . . . . . . . . . 48 Configurations) . . . . . . . . . . . . . . . . . . . . . 48
4.3. Latent Media Streams . . . . . . . . . . . . . . . . . . . 48 4.3. Latent Media Streams . . . . . . . . . . . . . . . . . . . 48
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 51 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 51
5.1. New SDP Attributes . . . . . . . . . . . . . . . . . . . . 51 5.1. New SDP Attributes . . . . . . . . . . . . . . . . . . . . 51
5.2. New SDP Option Tag . . . . . . . . . . . . . . . . . . . . 52 5.2. New SDP Capability Negotiation Option Tag . . . . . . . . 52
5.3. New SDP Capability Negotiation Parameters . . . . . . . . 52 5.3. SDP Capability Negotiation Configuration Parameters
6. Security Considerations . . . . . . . . . . . . . . . . . . . 53 Registry . . . . . . . . . . . . . . . . . . . . . . . . . 52
7. Changes from previous versions . . . . . . . . . . . . . . . . 54 5.4. SDP Capability Negotiation Configuration Parameter
7.1. Changes from version 13 . . . . . . . . . . . . . . . . . 54 Registrations . . . . . . . . . . . . . . . . . . . . . . 53
7.2. Changes from version 12 . . . . . . . . . . . . . . . . . 54 6. Security Considerations . . . . . . . . . . . . . . . . . . . 55
7.3. Changes from version 11 . . . . . . . . . . . . . . . . . 54 7. Changes from previous versions . . . . . . . . . . . . . . . . 56
7.4. Changes from version 10 . . . . . . . . . . . . . . . . . 54 7.1. Changes from version 14 . . . . . . . . . . . . . . . . . 56
7.5. Changes from version 09 . . . . . . . . . . . . . . . . . 55 7.2. Changes from version 13 . . . . . . . . . . . . . . . . . 56
7.6. Changes from version 08 . . . . . . . . . . . . . . . . . 55 7.3. Changes from version 12 . . . . . . . . . . . . . . . . . 56
7.7. Changes from version 04 . . . . . . . . . . . . . . . . . 55 7.4. Changes from version 11 . . . . . . . . . . . . . . . . . 56
7.8. Changes from version 03 . . . . . . . . . . . . . . . . . 56 7.5. Changes from version 10 . . . . . . . . . . . . . . . . . 56
7.9. Changes from version 02 . . . . . . . . . . . . . . . . . 56 7.6. Changes from version 09 . . . . . . . . . . . . . . . . . 57
7.10. Changes from version 01 . . . . . . . . . . . . . . . . . 57 7.7. Changes from version 08 . . . . . . . . . . . . . . . . . 57
7.11. Changes from version 00 . . . . . . . . . . . . . . . . . 57 7.8. Changes from version 04 . . . . . . . . . . . . . . . . . 57
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 58 7.9. Changes from version 03 . . . . . . . . . . . . . . . . . 58
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 59 7.10. Changes from version 02 . . . . . . . . . . . . . . . . . 58
9.1. Normative References . . . . . . . . . . . . . . . . . . . 59 7.11. Changes from version 01 . . . . . . . . . . . . . . . . . 59
9.2. Informative References . . . . . . . . . . . . . . . . . . 59 7.12. Changes from version 00 . . . . . . . . . . . . . . . . . 59
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 60 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 60
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 61
9.1. Normative References . . . . . . . . . . . . . . . . . . . 61
9.2. Informative References . . . . . . . . . . . . . . . . . . 61
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 63
1. Introduction 1. Introduction
Session Description Protocol (SDP) capability negotiation [RFC5939] Session Description Protocol (SDP) capability negotiation [RFC5939]
provides a general framework for indicating and negotiating provides a general framework for indicating and negotiating
capabilities in SDP[RFC4566]. The base framework defines only capabilities in SDP[RFC4566]. The base framework defines only
capabilities for negotiating transport protocols and attributes. capabilities for negotiating transport protocols and attributes.
The [RFC5939] document lists some of the issues with the current SDP The [RFC5939] document lists some of the issues with the current SDP
capability negotiation process. An additional real life case is to capability negotiation process. An additional real life case is to
skipping to change at page 6, line 5 skipping to change at page 5, line 33
configurations as combinations of media stream configurations. The configurations as combinations of media stream configurations. The
definitions of new attributes for media capability negotiation are definitions of new attributes for media capability negotiation are
chosen to make the translation from these attributes to chosen to make the translation from these attributes to
"conventional" SDP [RFC4566] media attributes as straightforward as "conventional" SDP [RFC4566] media attributes as straightforward as
possible in order to simplify implementation. This goal is intended possible in order to simplify implementation. This goal is intended
to reduce processing in two ways: each proposed configuration in an to reduce processing in two ways: each proposed configuration in an
offer may be easily translated into a conventional SDP media stream offer may be easily translated into a conventional SDP media stream
record for processing by the receiver; and the construction of an record for processing by the receiver; and the construction of an
answer based on a selected proposed configuration is straightforward. answer based on a selected proposed configuration is straightforward.
This document updates [RFC5939] by updating the IANA Considerations.
All other extensions defined in this document are considered
extensions above and beyond [RFC5939].
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [RFC2119] and document are to be interpreted as described in RFC2119 [RFC2119] and
indicate requirement levels for compliant RTP implementations. indicate requirement levels for compliant RTP implementations.
"Actual Configuration": An actual configuration specifies which "Actual Configuration": An actual configuration specifies which
combinations of SDP session parameters and media stream components combinations of SDP session parameters and media stream components
can be used in the current offer/answer exchange and with what can be used in the current offer/answer exchange and with what
skipping to change at page 6, line 35 skipping to change at page 6, line 35
or any other capability negotiation document. In an offer SDP, the or any other capability negotiation document. In an offer SDP, the
base configuration corresponds to the actual configuration as defined base configuration corresponds to the actual configuration as defined
in [RFC5939]. in [RFC5939].
"Conventional Attribute": Any SDP attribute other than those defined "Conventional Attribute": Any SDP attribute other than those defined
by the series of capability negotiation specifications. by the series of capability negotiation specifications.
"Conventional SDP": An SDP record devoid of capability negotiation "Conventional SDP": An SDP record devoid of capability negotiation
attributes. attributes.
"Media Capability": A media format, typically a media subtype such as "Media Format Capability": A media format, typically a media subtype
PCMU, H263-1998, or T38. The media capability may also include media such as PCMU, H263-1998, or T38, expressed in the form of a
format parameters and associated attributes. capability.
"Media Format Parameter Capability": A media format parameter
("a=fmtp" in conventional SDP) expressed in the form of a capability.
The media format parameter capability is associated with a media
format capability.
"Media Capability": The combined set of capabilities associated with
expressing a media format and its relevant parameters (e.g. media
format parameters and media specific parameters).
"Potential Configuration": A potential configuration indicates which "Potential Configuration": A potential configuration indicates which
combinations of capabilities can be used for the session and its combinations of capabilities can be used for the session and its
associated media stream components. Potential configurations are not associated media stream components. Potential configurations are not
ready for use, however they are offered for potential use in the ready for use, however they are offered for potential use in the
current offer/answer exchange. They provide an alternative that may current offer/answer exchange. They provide an alternative that may
be used instead of the actual configuration, subject to negotiation be used instead of the actual configuration, subject to negotiation
in the current offer/answer exchange. See [RFC5939] for further in the current offer/answer exchange. See [RFC5939] for further
details. details.
skipping to change at page 10, line 5 skipping to change at page 10, line 5
The solution consists of new capability attributes corresponding to The solution consists of new capability attributes corresponding to
conventional SDP line types, new parameters for the pcfg, acfg, and conventional SDP line types, new parameters for the pcfg, acfg, and
the new lcfg attributes extending the base attributes from [RFC5939], the new lcfg attributes extending the base attributes from [RFC5939],
and a use of the pcfg attribute to return capability information in and a use of the pcfg attribute to return capability information in
the SDP answer. the SDP answer.
Several new attributes are defined in a manner that can be related to Several new attributes are defined in a manner that can be related to
the capabilities specified in a media line, and its corresponding the capabilities specified in a media line, and its corresponding
rtpmap and fmtp attributes. rtpmap and fmtp attributes.
o A new media attribute ("a=rmcap") defines RTP-based media o A new attribute ("a=rmcap") defines RTP-based media format
capabilities in the form of a media subtype (e.g. "PCMU"), and capabilities in the form of a media subtype (e.g. "PCMU"), and
its encoding parameters (e.g. "/8000/2"). Each resulting media its encoding parameters (e.g. "/8000/2"). Each resulting media
format type/subtype capability has an associated handle called a format type/subtype capability has an associated handle called a
media capability number. The encoding parameters are as specified media capability number. The encoding parameters are as specified
for the rtpmap attribute defined in [RFC4566], without the payload for the rtpmap attribute defined in [RFC4566], without the payload
type number part. type number part.
o A new media attribute ("a=omcap") defines other (non RTP-based) o A new attribute ("a=omcap") defines other (non RTP-based) media
media capabilities in the form of a media subtype only (e.g. format capabilities in the form of a media subtype only (e.g.
"T38"). Each resulting media format type/subtype capability has "T38"). Each resulting media format type/subtype capability has
an associated handle called a media capability number. an associated handle called a media capability number.
o A new attribute ("a=mfcap") specifies media format parameters o A new attribute ("a=mfcap") specifies media format parameters
associated with one or more media capabilities. The mfcap associated with one or more media format capabilities. The mfcap
attribute is used primarily to associate the formatting attribute is used primarily to associate the media format
capabilities normally carried in the fmtp attribute. Note that parameters normally carried in the fmtp attribute. Note that
media format parameters can be used with RTP and non-RTP based media format parameters can be used with RTP and non-RTP based
media formats. media formats.
o A new attribute ("a=mscap") that specifies media parameters o A new attribute ("a=mscap") that specifies media parameters
associated with one or more media capabilities. The mscap associated with one or more media format capabilities. The mscap
attribute is used to associate capabilities with attributes other attribute is used to associate capabilities with attributes other
than fmtp or rtpmap, for example, the rtcp-fb attribute defined in than fmtp or rtpmap, for example, the rtcp-fb attribute defined in
[RFC4585]. [RFC4585].
o A new attribute ("a=lcfg") specifies latent media stream o A new attribute ("a=lcfg") specifies latent media stream
configurations when no corresponding media line ("m=") is offered. configurations when no corresponding media line ("m=") is offered.
An example is the offer of latent configurations for video even An example is the offer of latent configurations for video even
though no video is currently offered. If the peer indicates though no video is currently offered. If the peer indicates
support for one or more offered latent configurations, the support for one or more offered latent configurations, the
corresponding media stream(s) may be added via a new offer/answer corresponding media stream(s) may be added via a new offer/answer
skipping to change at page 11, line 13 skipping to change at page 11, line 13
of media capabilities (including their associated parameters) and of media capabilities (including their associated parameters) and
combinations thereof for the configuration. For example, the combinations thereof for the configuration. For example, the
"a=pcfg:" line might specify PCMU and telephone events [RFC4733] "a=pcfg:" line might specify PCMU and telephone events [RFC4733]
or G.729B and telephone events as acceptable configurations. The or G.729B and telephone events as acceptable configurations. The
"a=acfg:" line in the answer would specify the configuration "a=acfg:" line in the answer would specify the configuration
chosen. chosen.
o A new parameter type ("pt=") is added to the potential o A new parameter type ("pt=") is added to the potential
configuration, actual configuration, and latent configuration configuration, actual configuration, and latent configuration
attributes. This parameter associates RTP payload type numbers attributes. This parameter associates RTP payload type numbers
with the referenced RTP-based media capabilities, and is with the referenced RTP-based media format capabilities, and is
appropriate only when the transport protocol uses RTP. appropriate only when the transport protocol uses RTP.
o A new parameter type ("mt=") is used to specify the media type for o A new parameter type ("mt=") is used to specify the media type for
latent configurations. latent configurations.
Special processing rules are defined for capability attribute Special processing rules are defined for capability attribute
arguments in order to reduce the need to replicate essentially- arguments in order to reduce the need to replicate essentially-
identical attribute lines for the base configuration and potential identical attribute lines for the base configuration and potential
configurations. configurations.
skipping to change at page 11, line 38 skipping to change at page 11, line 38
o Replacement rules are defined for the conventional SDP equivalents o Replacement rules are defined for the conventional SDP equivalents
of the mfcap and mscap capability attributes. This reduces the of the mfcap and mscap capability attributes. This reduces the
necessity to use the deletion qualifier in the a=pcfg parameter in necessity to use the deletion qualifier in the a=pcfg parameter in
order to ignore rtpmap, fmtp, and certain other attributes in the order to ignore rtpmap, fmtp, and certain other attributes in the
base configuration. base configuration.
o An argument concatenation rule is defined for mfcap attributes o An argument concatenation rule is defined for mfcap attributes
which refer to the same media capability number. This makes it which refer to the same media capability number. This makes it
convenient to combine format options concisely by associating convenient to combine format options concisely by associating
multiple mfcap lines with multiple media capabilities. multiple mfcap lines with multiple media format capabilities.
This document extends the base protocol extensions to the offer/ This document extends the base protocol extensions to the offer/
answer model that allow for capabilities and potential configurations answer model that allow for capabilities and potential configurations
to be included in an offer. Media capabilities constitute to be included in an offer. Media capabilities constitute
capabilities that can be used in potential and latent configurations. capabilities that can be used in potential and latent configurations.
Whereas potential configurations constitute alternative offers that Whereas potential configurations constitute alternative offers that
may be accepted by the answerer instead of the actual may be accepted by the answerer instead of the actual
configuration(s) included in the "m=" line(s) and associated configuration(s) included in the "m=" line(s) and associated
parameters, latent configurations merely inform the other side of parameters, latent configurations merely inform the other side of
possible configurations supported by the entity. Those latent possible configurations supported by the entity. Those latent
skipping to change at page 13, line 43 skipping to change at page 13, line 43
The "a=acap:1" line specified in the base protocol provides the The "a=acap:1" line specified in the base protocol provides the
"crypto" attribute which provides the keying material for SRTP using "crypto" attribute which provides the keying material for SRTP using
SDP security descriptions. SDP security descriptions.
The "a=pcfg:" attributes provide the potential configurations The "a=pcfg:" attributes provide the potential configurations
included in the offer by reference to the media capabilities, included in the offer by reference to the media capabilities,
transport capabilities, attribute capabilities and specified payload transport capabilities, attribute capabilities and specified payload
type number mappings. Three explicit alternatives are provided; the type number mappings. Three explicit alternatives are provided; the
lowest-numbered one is the preferred one. The "a=pcfg:1 ..." line lowest-numbered one is the preferred one. The "a=pcfg:1 ..." line
specifies media capabilities 4 and 5, i.e., G.729B and DTMF, or media specifies media capabilities 4 and 5, i.e., G.729B and DTMF (incl.
capability 1 and 5, i.e., G.729 and DTMF. Furthermore, it specifies their associated media format parameters), or media capability 1 and
transport protocol capability 1 (i.e. the RTP/SAVP profile - secure 5, i.e., G.729 and DTMF (incl. their associated media format
RTP), and the attribute capability 1, i.e. the crypto attribute parameters). Furthermore, it specifies transport protocol capability
provided. Lastly, it specifies a payload type number mapping for 1 (i.e. the RTP/SAVP profile - secure RTP), and the attribute
(RTP-based) media capabilities 1, 4, and 5, thereby permitting the capability 1, i.e. the crypto attribute provided. Lastly, it
offerer to distinguish between encrypted media and unencrypted media specifies a payload type number mapping for (RTP-based) media
received prior to receipt of the answer. capabilities 1, 4, and 5, thereby permitting the offerer to
distinguish between encrypted media and unencrypted media received
prior to receipt of the answer.
Use of unique payload type numbers in alternative configurations is Use of unique payload type numbers in alternative configurations is
not required; codecs such as AMR-WB [RFC4867] have the potential for not required; codecs such as AMR-WB [RFC4867] have the potential for
so many combinations of options that it may be impractical to define so many combinations of options that it may be impractical to define
unique payload type numbers for all supported combinations. If unique payload type numbers for all supported combinations. If
unique payload type numbers cannot be specified, then the offerer unique payload type numbers cannot be specified, then the offerer
will be obliged to wait for the SDP answer before rendering received will be obliged to wait for the SDP answer before rendering received
media. For SRTP using SDES inline keying [RFC4568], the offerer will media. For SRTP using SDES inline keying [RFC4568], the offerer will
still need to receive the answer before being able to decrypt the still need to receive the answer before being able to decrypt the
stream. stream.
skipping to change at page 15, line 25 skipping to change at page 15, line 27
negotiation. The approach taken is to keep things similar to the negotiation. The approach taken is to keep things similar to the
existing media capabilities defined by the existing media existing media capabilities defined by the existing media
descriptions ("m=" lines) and the associated "rtpmap" and "fmtp" descriptions ("m=" lines) and the associated "rtpmap" and "fmtp"
attributes. We use media subtypes and "media capability numbers" to attributes. We use media subtypes and "media capability numbers" to
link the relevant media capability parameters. This permits the link the relevant media capability parameters. This permits the
capabilities to be defined at the session level and be used for capabilities to be defined at the session level and be used for
multiple streams, if desired. For RTP-based media formats, payload multiple streams, if desired. For RTP-based media formats, payload
types are then specified at the media level (see Section 3.3.4.2). types are then specified at the media level (see Section 3.3.4.2).
A media capability merely indicates possible support for the media A media capability merely indicates possible support for the media
type and media format(s) in question. In order to actually use a type and media format(s) and parameters in question. In order to
media capability in an offer/answer exchange, it MUST be referenced actually use a media capability in an offer/answer exchange, it MUST
in a potential configuration. be referenced in a potential configuration.
Media capabilities can be provided at the session-level and/or the Media capabilities, i.e. the attributes associated with expressing
media-level. Media capabilities provided at the session level may be media capability formats, parameters, etc., can be provided at the
referenced in any pcfg or lcfg attribute at the media level session-level and/or the media-level. Media capabilities provided at
(consistent with the media type), whereas media capabilities provided the session level may be referenced in any pcfg or lcfg attribute at
at the media level may be referenced only by the pcfg or lcfg the media level (consistent with the media type), whereas media
attribute within that media stream only. In either case, the scope capabilities provided at the media level may be referenced only by
of the <med-cap-num> is the entire session description. This enables the pcfg or lcfg attribute within that media stream. In either case,
each media capability to be uniquely referenced across the entire the scope of the <med-cap-num> is the entire session description.
session description (e.g. in a potential configuration). This enables each media capability to be uniquely referenced across
the entire session description (e.g. in a potential configuration).
3.3.1. The Media Format Capability Attributes 3.3.1. The Media Format Capability Attributes
Media subtypes can be expressed as media format capabilities by use Media subtypes can be expressed as media format capabilities by use
of the "a=rmcap" and "a=omcap" attributes. The "a=rmcap" attribute of the "a=rmcap" and "a=omcap" attributes. The "a=rmcap" attribute
MUST be used for RTP-based media whereas the "a=omcap" attribute MUST MUST be used for RTP-based media whereas the "a=omcap" attribute MUST
be used for non-RTP-based (other) media formats. The two attributes be used for non-RTP-based (other) media formats. The two attributes
are defined as follows: are defined as follows:
a=rmcap:<media-cap-num-list> <encoding-name>/<clock-rate> a=rmcap:<media-cap-num-list> <encoding-name>/<clock-rate>
skipping to change at page 16, line 14 skipping to change at page 16, line 20
where <media-cap-num-list> is a (list of) media capability number(s) where <media-cap-num-list> is a (list of) media capability number(s)
used to number a media format capability, the <encoding name> or used to number a media format capability, the <encoding name> or
<format name> is the media subtype, e.g., H263-1998, PCMU, or T38, <format name> is the media subtype, e.g., H263-1998, PCMU, or T38,
<clock rate> is the encoding rate, and <encoding parms> are the media <clock rate> is the encoding rate, and <encoding parms> are the media
encoding parameters for the media subtype. All media format encoding parameters for the media subtype. All media format
capabilities in the list are assigned to the same media type/subtype. capabilities in the list are assigned to the same media type/subtype.
Each occurrence of the rmcap and omcap attribute MUST use unique Each occurrence of the rmcap and omcap attribute MUST use unique
values in their <media-cap-num-list>; the media capability numbers values in their <media-cap-num-list>; the media capability numbers
are shared between the two attributes and the numbers MUST be unique are shared between the two attributes and the numbers MUST be unique
across the entire SDP session. In short, the rmcap and omcap across the entire SDP session. In short, the rmcap and omcap
attributes define media capabilities and associate them with a media attributes define media format capabilities and associate them with a
capability number in the same manner as the rtpmap attribute defines media capability number in the same manner as the rtpmap attribute
them and associates them with a payload type number. Additionally, defines them and associates them with a payload type number.
the attributes allow multiple capability numbers to be defined for Additionally, the attributes allow multiple capability numbers to be
the media format in question. This permits the media format to be defined for the media format in question. This permits the media
associated with different media parameters in different format to be associated with different media parameters in different
configurations. configurations.
In ABNF, we have: In ABNF [RFC5234], we have:
media-capability-line = rtp-mcap / non-rtp-mcap media-capability-line = rtp-mcap / non-rtp-mcap
rtp-mcap = "a=rmcap:" media-cap-num-list rtp-mcap = "a=rmcap:" media-cap-num-list
1*WSP encoding-name "/" clock-rate 1*WSP encoding-name "/" clock-rate
["/" encoding-parms] ["/" encoding-parms]
non-rtp-mcap = "a=omcap:" media-cap-num-list 1*WSP format-name non-rtp-mcap = "a=omcap:" media-cap-num-list 1*WSP format-name
media-cap-num-list = media-cap-num-element media-cap-num-list = media-cap-num-element
*["," media-cap-num-element] *("," media-cap-num-element)
media-cap-num-element = media-cap-num media-cap-num-element = media-cap-num
/ media-cap-num-range / media-cap-num-range
media-cap-num-range = media-cap-num "-" media-cap-num media-cap-num-range = media-cap-num "-" media-cap-num
media-cap-num = 1*10(DIGIT) media-cap-num = 1*10(DIGIT)
encoding-name = token ; defined in RFC4566 encoding-name = token ;defined in RFC4566
clock-rate = 1*10(DIGIT) clock-rate = 1*10(DIGIT)
encoding-parms = token encoding-parms = token
format-name = token ;defined in RFC4566 format-name = token ;defined in RFC4566
The encoding-name, clock-rate and encoding-params are as defined to The encoding-name, clock-rate and encoding-params are as defined to
appear in an rtpmap attribute for each media type/subtype. Thus, it appear in an rtpmap attribute for each media type/subtype. Thus, it
is easy to convert an rmcap attribute line into one or more rtpmap is easy to convert an rmcap attribute line into one or more rtpmap
attribute lines, once a payload type number is assigned to a media- attribute lines, once a payload type number is assigned to a media-
cap-num (see Section 3.3.5). cap-num (see Section 3.3.5).
skipping to change at page 17, line 44 skipping to change at page 17, line 50
m=audio 54320 RTP/AVP 0 m=audio 54320 RTP/AVP 0
a=pcfg:1 m=1|2, pt=1:99,2:98 a=pcfg:1 m=1|2, pt=1:99,2:98
m=video 66544 RTP/AVP 100 m=video 66544 RTP/AVP 100
a=rtpmap:100 H264/90000 a=rtpmap:100 H264/90000
a=pcfg:10 m=3 pt=3:101 a=pcfg:10 m=3 pt=3:101
a=tcap:1 TCP a=tcap:1 TCP
a=pcfg:11 m=4 t=1 a=pcfg:11 m=4 t=1
3.3.2. The Media Format Parameter Capability Attribute 3.3.2. The Media Format Parameter Capability Attribute
This attribute is used to associate media format specific format This attribute is used to associate media format specific parameters
parameters with one or more media capabilities. The form of the with one or more media format capabilities. The form of the
attribute is: attribute is:
a=mfcap:<media-caps> <list of parameters> a=mfcap:<media-caps> <list of parameters>
where <media-caps> permits the list of parameters to be associated where <media-caps> permits the list of parameters to be associated
with one or more media capabilities and the format parameters are with one or more media format capabilities and the format parameters
specific to the type of media format. The mfcap lines map to a are specific to the type of media format. The mfcap lines map to a
single traditional SDP fmtp attribute line (one for each entry in single traditional SDP fmtp attribute line (one for each entry in
<media-caps>) of the form <media-caps>) of the form
a=fmtp:<fmt> <list of parameters> a=fmtp:<fmt> <list of parameters>
where <fmt> is the media format description defined in RFC 4566 where <fmt> is the media format parameter defined in RFC 4566
[RFC4566], as appropriate for the particular media stream. The mfcap [RFC4566], as appropriate for the particular media stream. The mfcap
attribute MUST be used to encode attributes for media capabilities, attribute MUST be used to encode attributes for media capabilities,
which would conventionally appear in an fmtp attribute. The existing which would conventionally appear in an fmtp attribute. The existing
acap attribute MUST NOT be used to encode fmtp attributes. acap attribute MUST NOT be used to encode fmtp attributes.
The mfcap attribute adheres to [RFC4566] attribute production rules The mfcap attribute adheres to [RFC4566] attribute production rules
with with
media-format-capability = "a=mfcap:" media-cap-num-list 1*WSP media-format-parameter-capability =
fmt-specific-param-list "a=mfcap:" media-cap-num-list 1*WSP fmt-specific-param-list
fmt-specific-param-list = text ; defined in RFC4566 fmt-specific-param-list = text ; defined in RFC4566
Note that media format parameters can be used with RTP-based and non- Note that media format parameters can be used with RTP-based and non-
RTP based media formats. RTP based media formats.
3.3.2.1. Media Format Parameter Concatenation Rule 3.3.2.1. Media Format Parameter Concatenation Rule
The appearance of media subtypes with a large number of formatting The appearance of media subtypes with a large number of formatting
options (e.g., AMR-WB [RFC4867]) coupled with the restriction that options (e.g., AMR-WB [RFC4867]) coupled with the restriction that
only a single fmtp attribute can appear per media format, suggests only a single fmtp attribute can appear per media format, suggests
skipping to change at page 19, line 29 skipping to change at page 19, line 33
session or media level. The unique media-cap-num is used to session or media level. The unique media-cap-num is used to
associate the parameters with a media capability. associate the parameters with a media capability.
As a simple example, a G.729 capability is, by default, considered to As a simple example, a G.729 capability is, by default, considered to
support comfort noise as defined by Annex B. Capabilities for G.729 support comfort noise as defined by Annex B. Capabilities for G.729
with and without comfort noise support may thus be defined by: with and without comfort noise support may thus be defined by:
a=rmcap:1,2 G729/8000 a=rmcap:1,2 G729/8000
a=mfcap:2 annexb:no a=mfcap:2 annexb:no
Media format capability 1 supports G.729 with Annex B, whereas media Media capability 1 supports G.729 with Annex B, whereas media
format capability 2 supports G.729 without Annex B. capability 2 supports G.729 without Annex B.
Example for H.263 video: Example for H.263 video:
a=rmcap:1 H263-1998/90000 a=rmcap:1 H263-1998/90000
a=rmcap:2 H263-2000/90000 a=rmcap:2 H263-2000/90000
a=mfcap:1 CIF=4;QCIF=2;F=1;K=1 a=mfcap:1 CIF=4;QCIF=2;F=1;K=1
a=mfcap:2 profile=2;level=2.2 a=mfcap:2 profile=2;level=2.2
Finally, for six format combinations of the Adaptive MultiRate codec: Finally, for six format combinations of the Adaptive MultiRate codec:
skipping to change at page 20, line 49 skipping to change at page 21, line 5
attribute defined in [RFC4585]. Such media-specific attributes, attribute defined in [RFC4585]. Such media-specific attributes,
beyond the rtpmap and fmtp attributes, may be associated with media beyond the rtpmap and fmtp attributes, may be associated with media
capability numbers via a new media-specific attribute, mscap, of the capability numbers via a new media-specific attribute, mscap, of the
following form: following form:
a=mscap:<media caps star> <att field> <att value> a=mscap:<media caps star> <att field> <att value>
where <media caps star> is a (list of) media capability number(s), where <media caps star> is a (list of) media capability number(s),
<att field> is the attribute name, and <att value> is the value field <att field> is the attribute name, and <att value> is the value field
for the named attribute. Note that the media capability numbers for the named attribute. Note that the media capability numbers
refer to media capabilities specified elsewhere in the SDP ("rmcap" refer to media format capabilities specified elsewhere in the SDP
and/or "omcap"). The media capability numbers may include a wildcard ("rmcap" and/or "omcap"). The media capability numbers may include a
("*"), which will be used instead of any payload type mappings in the wildcard ("*"), which will be used instead of any payload type
resulting SDP (see, e.g. [RFC4585] and the example below). In ABNF, mappings in the resulting SDP (see, e.g. [RFC4585] and the example
we have: below). In ABNF, we have:
media-specific-capability = "a=mscap:" media-specific-capability = "a=mscap:"
media-caps-star media-caps-star
1*WSP att-field ; from RFC4566 1*WSP att-field ; from RFC4566
1*WSP att-value ; from RFC4566 1*WSP att-value ; from RFC4566
media-caps-star = media-cap-star-element media-caps-star = media-cap-star-element
*["," media-cap-star-element] *("," media-cap-star-element)
media-cap-star-element = media-cap-num [wildcard] media-cap-star-element = (media-cap-num [wildcard])
/ media-cap-num-range [wildcard] / (media-cap-num-range [wildcard])
wildcard = "*" wildcard = "*"
Given an association between a media capability and a payload type Given an association between a media capability and a payload type
number as specified by the pt= parameters in a pcfg attribute line, a number as specified by the pt= parameters in a pcfg attribute line, a
mscap line may be translated easily into a conventional SDP attribute mscap line may be translated easily into a conventional SDP attribute
line of the form line of the form
a=<att field>":"<fmt> <att value> ; <fmt> defined in [RFC4566] a=<att field>":"<fmt> <att value> ; <fmt> defined in [RFC4566]
A resulting attribute that is not a legal SDP attribute as specified A resulting attribute that is not a legal SDP attribute as specified
skipping to change at page 22, line 32 skipping to change at page 22, line 35
3.3.4. New Configuration Parameters 3.3.4. New Configuration Parameters
Along with the new attributes for media capabilities, new extension Along with the new attributes for media capabilities, new extension
parameters are defined for use in the potential configuration, the parameters are defined for use in the potential configuration, the
actual configuration, and/or the new latent configuration defined in actual configuration, and/or the new latent configuration defined in
Section 3.3.5. Section 3.3.5.
3.3.4.1. The Media Configuration Parameter (m=) 3.3.4.1. The Media Configuration Parameter (m=)
The media configuration parameter is used to specify the media The media configuration parameter is used to specify the media
encoding(s) and related parameters for a potential, actual, or latent format(s) and related parameters for a potential, actual, or latent
configuration. Adhering to the ABNF for extension-config-list in configuration. Adhering to the ABNF for extension-config-list in
[RFC5939] with [RFC5939] with
ext-cap-name = "m" ext-cap-name = "m"
ext-cap-list = media-cap-num-list ext-cap-list = media-cap-num-list
[*(BAR media-cap-num-list)] [*(BAR media-cap-num-list)]
we have we have
media-config-list = ["+"]"m=" media-cap-num-list media-config-list = ["+"] "m=" media-cap-num-list
[*(BAR media-cap-num-list)] *(BAR media-cap-num-list)
; BAR is defined in RFC5939 ;BAR is defined in RFC5939
; media-cap-num-list is defined above ;media-cap-num-list is defined above
Alternative media configurations are separated by a vertical bar Alternative media configurations are separated by a vertical bar
("|"). The alternatives are ordered by preference, most-preferred ("|"). The alternatives are ordered by preference, most-preferred
first. When media capabilities are not included in a potential first. When media capabilities are not included in a potential
configuration at the media level, the media type and media format configuration at the media level, the media type and media format
from the associated "m=" line will be used. The use of the plus sign from the associated "m=" line will be used. The use of the plus sign
("+") is described in RFC5939. ("+") is described in RFC5939.
3.3.4.2. The Payload Type Number Mapping Parameter (pt=) 3.3.4.2. The Payload Type Number Mapping Parameter (pt=)
The payload type number mapping parameter is used to specify the The payload type number mapping parameter is used to specify the
payload type number to be associated with each media type in a payload type number to be associated with each RTP-based media format
potential, actual, or latent configuration. We define the payload in a potential, actual, or latent configuration. We define the
type number mapping parameter, payload-number-config-list, in payload type number mapping parameter, payload-number-config-list, in
accordance with the extension-config-list format defined in accordance with the extension-config-list format defined in
[RFC5939]. In ABNF: [RFC5939]. In ABNF:
payload-number-config-list = ["+"]"pt=" media-map-list payload-number-config-list = ["+"] "pt=" media-map-list
media-map-list = media-map *["," media-map] media-map-list = media-map *("," media-map)
media-map = media-cap-num ":" payload-type-number media-map = media-cap-num ":" payload-type-number
; media-cap-num is defined in 3.3.1 ; media-cap-num is defined in 3.3.1
payload-type-number = 1*3(DIGIT) ; RTP payload type number payload-type-number = 1*3(DIGIT) ; RTP payload type number
The example in Section 3.3.7 shows how the parameters from the rmcap The example in Section 3.3.7 shows how the parameters from the rmcap
line are mapped to payload type numbers from the pcfg "pt" parameter. line are mapped to payload type numbers from the pcfg "pt" parameter.
The use of the plus sign ("+") is described in [RFC5939]. The use of the plus sign ("+") is described in [RFC5939].
A latent configuration represents a future capability, hence the pt= A latent configuration represents a future capability, hence the pt=
parameter is not directly meaningful in the lcfg attribute because no parameter is not directly meaningful in the lcfg attribute because no
actual media session is being offered or accepted; it is permitted in actual media session is being offered or accepted; it is permitted in
order to tie any payload type number parameters within attributes to order to tie any payload type number parameters within attributes to
skipping to change at page 25, line 18 skipping to change at page 25, line 20
The latent configuration attribute is of the form: The latent configuration attribute is of the form:
a=lcfg:<config-number> <latent-cfg-list> a=lcfg:<config-number> <latent-cfg-list>
which adheres to the [RFC4566] "attribute" production with att-field which adheres to the [RFC4566] "attribute" production with att-field
and att-value defined as: and att-value defined as:
att-field = "lcfg" att-field = "lcfg"
att-value = config-number 1*WSP lcfg-cfg-list att-value = config-number 1*WSP lcfg-cfg-list
config-number = 1*10(DIGIT) ; defined in RFC5234 config-number = 1*10(DIGIT) ; defined in RFC5234
lcfg-cfg-list = media-type 1*WSP pot-cfg-list lcfg-cfg-list = media-type 1*WSP pot-cfg-list
; as defined in RFC5939 ; as defined in RFC5939
; and extended herein ; and extended herein
The media-type (mt=) parameter identifies the media type (audio, The media-type (mt=) parameter identifies the media type (audio,
video, etc.) to be associated with the latent media stream, and MUST video, etc.) to be associated with the latent media stream, and MUST
be present. The pot-cfg-list MUST contain a transport-protocol- be present. The pot-cfg-list MUST contain a transport-protocol-
config-list (t=) parameter and a media-config-list (m=) parameter. config-list (t=) parameter and a media-config-list (m=) parameter.
The pot-cfg-list MUST NOT contain more than one instance of each type The pot-cfg-list MUST NOT contain more than one instance of each type
of parameter list. As specified in [RFC5939], the use of the "+" of parameter list. As specified in [RFC5939], the use of the "+"
skipping to change at page 27, line 51 skipping to change at page 28, line 7
included by the offerer, these capabilities MUST NOT be used to form included by the offerer, these capabilities MUST NOT be used to form
any base level media description in the answer. For this reason, it any base level media description in the answer. For this reason, it
is advisable for the offerer to include most, if not all, potential is advisable for the offerer to include most, if not all, potential
and latent configurations it can support in the initial offer, unless and latent configurations it can support in the initial offer, unless
the size of the resulting SDP is a concern. Either party MAY later the size of the resulting SDP is a concern. Either party MAY later
announce additional capabilities by renegotiating the session in a announce additional capabilities by renegotiating the session in a
second offer/answer exchange. second offer/answer exchange.
3.3.6.2. Payload Type Number Mapping 3.3.6.2. Payload Type Number Mapping
When media capabilities defined in rmcap attributes are used in When media format capabilities defined in rmcap attributes are used
potential configuration lines, the transport protocol uses RTP and it in potential configuration lines, the transport protocol uses RTP and
is necessary to assign payload type numbers. In some cases, it is it is necessary to assign payload type numbers. In some cases, it is
desirable to assign different payload type numbers to the same media desirable to assign different payload type numbers to the same media
capability when used in different potential configurations. One format capability when used in different potential configurations.
example is when configurations for AVP and SAVP are offered: the One example is when configurations for AVP and SAVP are offered: the
offerer would like the answerer to use different payload type numbers offerer would like the answerer to use different payload type numbers
for encrypted and unencrypted media so that it (the offerer) can for encrypted and unencrypted media, so the offerer can decide
decide whether or not to render early media which arrives before the whether or not to render early media which arrives before the answer
answer is received. is received.
For example, if use of AVP was selected by the answerer, then For example, if use of AVP was selected by the answerer, then
media received by the offerer is not encrypted and hence can be media received by the offerer is not encrypted and hence can be
played out prior to receiving the answer. Conversely, if SAVP was played out prior to receiving the answer. Conversely, if SAVP was
selected, cryptographic parameters and keying material present in selected, cryptographic parameters and keying material present in
the answer may be needed to decrypt received media. If the offer the answer may be needed to decrypt received media. If the offer
configuration indicated that AVP media uses one set of payload configuration indicated that AVP media uses one set of payload
types and SAVP a different set, then the offerer will know whether types and SAVP a different set, then the offerer will know whether
media received prior to the answer is encrypted or not by simply media received prior to the answer is encrypted or not by simply
looking at the RTP payload type number in the received packet. looking at the RTP payload type number in the received packet.
This association of distinct payload type number(s) with different This association of distinct payload type number(s) with different
transport protocols requires a separate pcfg line for each protocol. transport protocols requires a separate pcfg line for each protocol.
Clearly, this technique cannot be used if the number of potential Clearly, this technique cannot be used if the number of potential
configurations exceeds the number of possible payload type numbers. configurations exceeds the number of possible payload type numbers.
3.3.6.3. Processing of Media-Format-Related Conventional Attributes for 3.3.6.3. Processing of Media-Format-Related Conventional Attributes for
Potential Configurations Potential Configurations
In cases in which media capabilities negotiation is employed, SDP When media capabilities negotiation is employed, SDP records are
records are likely to contain conventional attributes such as rtpmap, likely to contain conventional attributes such as rtpmap, fmtp, and
fmtp, and other media-format-related lines, as well as capability other media-format-related lines, as well as capability attributes
attributes such as rmcap, omcap, mfcap, and mscap which map into such as rmcap, omcap, mfcap, and mscap which map into those
those conventional attributes when invoked by a potential conventional attributes when invoked by a potential configuration.
configuration. In such cases, it MAY be appropriate to employ the In such cases, it MAY be appropriate to employ the delete-attributes
delete-attributes option [RFC5939] in the attribute configuration option [RFC5939] in the attribute configuration list parameter in
list parameter in order to avoid the generation of conflicting fmtp order to avoid the generation of conflicting fmtp attributes for a
attributes for a particular configuration. Any media-specific particular configuration. Any media-specific attributes in the media
attributes in the media block which refer to media formats not used block which refer to media formats not used by the potential
by the potential configuration MUST be ignored. configuration MUST be ignored.
For example: For example:
v=0 v=0
o=- 25678 753849 IN IP4 192.0.2.1 o=- 25678 753849 IN IP4 192.0.2.1
s= s=
c=IN IP4 192.0.2.1 c=IN IP4 192.0.2.1
t=0 0 t=0 0
a=creq:med-v0 a=creq:med-v0
m=audio 3456 RTP/AVP 0 18 100 m=audio 3456 RTP/AVP 0 18 100
skipping to change at page 31, line 29 skipping to change at page 31, line 32
described by: described by:
"a=sescap:" <session num> <list of configs> "a=sescap:" <session num> <list of configs>
which corresponds to the standard value attribute definition with which corresponds to the standard value attribute definition with
att-field = "sescap" att-field = "sescap"
att-value = session-num 1*WSP list-of-configs att-value = session-num 1*WSP list-of-configs
[1*WSP optional-configs] [1*WSP optional-configs]
session-num = 1*10(DIGIT) ; defined in RFC5234 session-num = 1*10(DIGIT) ; defined in RFC5234
list-of-configs = alt-config *["," alt-config] list-of-configs = alt-config *("," alt-config)
optional-configs = "[" list-of-configs "]" optional-configs = "[" list-of-configs "]"
alt-config = config-number *["|" config-number] alt-config = config-number *("|" config-number)
; config-number defined in RFC5939 ; config-number defined in RFC5939
The session-num identifies the session; a lower-number session is The session-num identifies the session; a lower-number session is
preferred over a higher-numbered session. Each alt-config list preferred over a higher-numbered session. Each alt-config list
specifies alternative media configurations within the session; specifies alternative media configurations within the session;
preference is based on config-num as specified in [RFC5939]. Note preference is based on config-num as specified in [RFC5939]. Note
that the session preference order, when present, takes precedence that the session preference order, when present, takes precedence
over the individual media stream configuration preference order. over the individual media stream configuration preference order.
Use of session capability attributes requires that configuration Use of session capability attributes requires that configuration
skipping to change at page 35, line 22 skipping to change at page 35, line 22
This exchange supports immediate establishment of an audio stream for This exchange supports immediate establishment of an audio stream for
preliminary conversation. This exchange would presumably be followed preliminary conversation. This exchange would presumably be followed
at the appropriate time with a "reconfiguration" offer/answer at the appropriate time with a "reconfiguration" offer/answer
exchange to add the video and chair control streams. exchange to add the video and chair control streams.
3.4. Offer/Answer Model Extensions 3.4. Offer/Answer Model Extensions
In this section, we define extensions to the offer/answer model In this section, we define extensions to the offer/answer model
defined in RFC 3264 [RFC3264] and RFC 5939 [RFC5939] to allow for defined in RFC 3264 [RFC3264] and RFC 5939 [RFC5939] to allow for
media capabilities and parameters, latent configurations and media format and associated parameter capabilities, latent
acceptable combinations of media stream configurations to be used configurations and acceptable combinations of media stream
with the SDP Capability Negotiation framework. Note that the configurations to be used with the SDP Capability Negotiation
procedures defined in this section extend the offer/answer procedures framework. Note that the procedures defined in this section extend
defined in [RFC5939] Section 6; those procedures form a baseline set the offer/answer procedures defined in [RFC5939] Section 6; those
of capability negotiation offer/answer procedures that MUST be procedures form a baseline set of capability negotiation offer/answer
followed, subject to the extensions defined here. procedures that MUST be followed, subject to the extensions defined
here.
The [RFC5939] provides a relatively compact means to offer the The [RFC5939] provides a relatively compact means to offer the
equivalent of an ordered list of alternative configurations for equivalent of an ordered list of alternative configurations for
offered media streams (as would be described by separate m= lines and offered media streams (as would be described by separate m= lines and
associated attributes). The attributes acap, mscap, mfcap and rmcap associated attributes). The attributes acap, mscap, mfcap, omcap and
are designed to map somewhat straightforwardly into equivalent m= rmcap are designed to map somewhat straightforwardly into equivalent
lines and conventional attributes when invoked by a pcfg, lcfg, or m= lines and conventional attributes when invoked by a pcfg, lcfg, or
acfg attribute with appropriate parameters. The a=pcfg: lines, along acfg attribute with appropriate parameters. The a=pcfg: lines, along
with the m= line itself, represent offered media configurations. The with the m= line itself, represent offered media configurations. The
a=lcfg: lines represent alternative capabilities for future use. a=lcfg: lines represent alternative capabilities for future use.
3.4.1. Generating the Initial Offer 3.4.1. Generating the Initial Offer
The Media Capabilities negotiation extensions defined in this The Media Capabilities negotiation extensions defined in this
document cover the following categories of features: document cover the following categories of features:
o Media Capabilities and associated parameters (rmcap, omcap, mfcap, o Media Format Capabilities and associated parameters (rmcap, omcap,
and mscap attributes) mfcap, and mscap attributes)
o Potential configurations using those media capabilities and o Potential configurations using those media format capabilities and
associated parameters associated parameters
o Latent media streams (lcfg attribute) o Latent media streams (lcfg attribute)
o Acceptable combinations of media stream configurations (sescap o Acceptable combinations of media stream configurations (sescap
attribute). attribute).
The high-level description of the operation is as follows: The high-level description of the operation is as follows:
When an endpoint generates an initial offer and wants to use the When an endpoint generates an initial offer and wants to use the
skipping to change at page 36, line 47 skipping to change at page 36, line 47
required only for specific media descriptions, the "med-v0" value required only for specific media descriptions, the "med-v0" value
MUST be provided only in creq attributes within those media MUST be provided only in creq attributes within those media
descriptions, as described in [RFC5939]. descriptions, as described in [RFC5939].
Below, we provide a more detailed description of how to construct the Below, we provide a more detailed description of how to construct the
offer SDP. offer SDP.
3.4.1.1. Offer with Media Capabilities 3.4.1.1. Offer with Media Capabilities
For each RTP-based media format the offerer wants to include as a For each RTP-based media format the offerer wants to include as a
media capability, the offer MUST include an "rmcap" attribute for the media format capability, the offer MUST include an "rmcap" attribute
media format as defined in Section 3.3.1. for the media format as defined in Section 3.3.1.
For each non RTP-based media format the offer wants to include as a For each non RTP-based media format the offer wants to include as a
media capability, the offer MUST include an "omcap" attribute for the media format capability, the offer MUST include an "omcap" attribute
media format as defined in Section 3.3.1. for the media format as defined in Section 3.3.1.
Since the media format capability number space is shared between the Since the media capability number space is shared between the rmcap
rmcap and omcap attributes, each media capability number provided and omcap attributes, each media capability number provided
(including ranges) MUST be unique in the entire SDP. (including ranges) MUST be unique in the entire SDP.
If an "fmtp" parameter value is needed for a media format (whether If an "fmtp" parameter value is needed for a media format (whether
RTP-based or not) in a media capability, then the offer MUST include RTP-based or not) in a media capability, then the offer MUST include
one or more "mfcap" parameters with the relevant fmtp parameter one or more "mfcap" parameters with the relevant fmtp parameter
values for that media format as defined in Section 3.3.2. When values for that media format as defined in Section 3.3.2. When
multiple "mfcap" parameters are provided for a given media multiple "mfcap" parameters are provided for a given media
capability, they MUST be provided in accordance with the capability, they MUST be provided in accordance with the
concatenation rules in Section 3.3.2.1. concatenation rules in Section 3.3.2.1.
For each of the media capabilities above, the offer MAY include one For each of the media format capabilities above, the offer MAY
or more "mscap" parameters with attributes needed for those specific include one or more "mscap" parameters with attributes needed for
media formats as defined in Section 3.3.3. Such attributes will be those specific media formats as defined in Section 3.3.3. Such
instantiated at the media-level, and hence session-level only attributes will be instantiated at the media-level, and hence
attributes MUST NOT be used in the "mscap" parameter. The "mscap" session-level only attributes MUST NOT be used in the "mscap"
parameter MUST NOT include an "rtpmap" or "fmtp" attribute (rmcap and parameter. The "mscap" parameter MUST NOT include an "rtpmap" or
mfcap are used instead). "fmtp" attribute (rmcap and mfcap are used instead).
If the offerer wants to limit the relevance (and use of) a media If the offerer wants to limit the relevance (and use) of a media
capability or parameter to a particular media stream, the media format capability or parameter to a particular media stream, the
capability or parameter MUST be provided within the corresponding media format capability or parameter MUST be provided within the
media description. Otherwise, the media capabilities and parameters corresponding media description. Otherwise, the media format
MUST be provided at the session level. Note however, that the capabilities and parameters MUST be provided at the session level.
attribute or parameter embedded in these will always be instantiated Note however, that the attribute or parameter embedded in these will
at the media-level. always be instantiated at the media-level.
This is due to those parameters being effectively media-level This is due to those parameters being effectively media-level
parameters. If session-level attributes are needed, the "acap" parameters. If session-level attributes are needed, the "acap"
attribute defined in [RFC5939] can be used, however it does not attribute defined in [RFC5939] can be used, however it does not
provide for media format-specific instantiation. provide for media format-specific instantiation.
Inclusion of the above does not constitute an offer to use the Inclusion of the above does not constitute an offer to use the
capabilities; a potential configuration is needed for that. If the capabilities; a potential configuration is needed for that. If the
offerer wants to offer one or more of the media capabilities above, offerer wants to offer one or more of the media capabilities above,
they MUST be included as part of a potential configuration (pcfg) they MUST be included as part of a potential configuration (pcfg)
skipping to change at page 39, line 32 skipping to change at page 39, line 32
3.4.2. Generating the Answer 3.4.2. Generating the Answer
When receiving an offer, the answerer MUST check the offer for creq When receiving an offer, the answerer MUST check the offer for creq
attributes containing the value "med-v0"; answerers compliant with attributes containing the value "med-v0"; answerers compliant with
this specification will support this value in accordance with the this specification will support this value in accordance with the
procedures specified in [RFC5939]. procedures specified in [RFC5939].
The SDP MAY contain The SDP MAY contain
o Media capabilities and associated parameters (rmcap, omcap, mfcap, o Media format capabilities and associated parameters (rmcap, omcap,
and mscap attributes) mfcap, and mscap attributes)
o Potential configurations using those media capabilities and o Potential configurations using those media format capabilities and
associated parameters associated parameters
o Latent media streams (lcfg attribute) o Latent media streams (lcfg attribute)
o Acceptable combinations of media stream configurations (sescap o Acceptable combinations of media stream configurations (sescap
attribute) attribute)
The high-level informative description of the operation is as The high-level informative description of the operation is as
follows: follows:
skipping to change at page 40, line 21 skipping to change at page 40, line 21
of those configurations it might wish to offer in the future. of those configurations it might wish to offer in the future.
Below we provide a more detailed normative description of how the Below we provide a more detailed normative description of how the
answerer processes the offer SDP and generates an answer SDP. answerer processes the offer SDP and generates an answer SDP.
3.4.2.1. Processing Media Capabilities and Potential Configurations 3.4.2.1. Processing Media Capabilities and Potential Configurations
The answerer MUST first determine if it needs to perform media The answerer MUST first determine if it needs to perform media
capability negotiation by examining the SDP for valid and preferred capability negotiation by examining the SDP for valid and preferred
potential configuration attributes that include media configuration potential configuration attributes that include media configuration
parameters (i.e. an "m" parameter in the pcfg attribute). parameters (i.e., an "m" parameter in the pcfg attribute).
Such a potential configuration is valid if: Such a potential configuration is valid if:
1. It is valid according to the rules defined in [RFC5939] 1. It is valid according to the rules defined in [RFC5939]
2. It contains a config-number that is unique in the entire SDP and 2. It contains a config-number that is unique in the entire SDP and
does not overlap with any latent configuration config-numbers does not overlap with any latent configuration config-numbers
3. All media format capabilities (rmcap or omcap), media format 3. All media format capabilities (rmcap or omcap), media format
parameter capabilities (mfcap), and media-specific capabilities parameter capabilities (mfcap), and media-specific capabilities
(mscap) referenced by the potential configuration ("m" parameter) (mscap) referenced by the potential configuration ("m" parameter)
are valid themselves (as defined in Section 3.3.1, 3.3.2, and are valid themselves (as defined in Section 3.3.1, 3.3.2, and
3.3.3) and each of them is provided either at the session level 3.3.3) and each of them is provided either at the session level
or within this particular media description. or within this particular media description.
4. All RTP-based media capabilities (rmcap) have a corresponding 4. All RTP-based media format capabilities (rmcap) have a
payload type ("pt") parameter in the potential configuration that corresponding payload type ("pt") parameter in the potential
results in mapping to a valid payload type that is unique within configuration that result in mapping to a valid payload type that
the resulting SDP. is unique within the resulting SDP.
5. Any concatenation (see Section 3.3.2.1) and substitution (see 5. Any concatenation (see Section 3.3.2.1) and substitution (see
Section 3.3.7) applied to any capability (mfcap, mscap, or acap) Section 3.3.7) applied to any capability (mfcap, mscap, or acap)
referenced by this potential configuration results in a valid referenced by this potential configuration results in a valid
SDP. SDP.
Note that, since SDP does not interpret the value of fmtp parameters, Note that, since SDP does not interpret the value of fmtp parameters,
any resulting fmtp parameter value will be considered valid. any resulting fmtp parameter value will be considered valid.
Secondly, the answerer MUST determine the order in which potential Secondly, the answerer MUST determine the order in which potential
skipping to change at page 49, line 32 skipping to change at page 49, line 32
a=lcfg:3 mt=message t=2 m=20 a=lcfg:3 mt=message t=2 m=20
a=tcap:2 TCP/MSRP a=tcap:2 TCP/MSRP
a=omcap:20 * a=omcap:20 *
The first lcfg attribute line ("lcfg:2") announces support for H.263 The first lcfg attribute line ("lcfg:2") announces support for H.263
and H.264 video (H.263 preferred) for future negotiation. The second and H.264 video (H.263 preferred) for future negotiation. The second
lcfg attribute line ("lcfg:3") announces support for MSRP for future lcfg attribute line ("lcfg:3") announces support for MSRP for future
negotiation. The m-line and the rtpmap attribute offer an audio negotiation. The m-line and the rtpmap attribute offer an audio
stream and provide the lowest precedence configuration (PCMU without stream and provide the lowest precedence configuration (PCMU without
any DTMF encoding). The rmcap lines define the RTP-based media any DTMF encoding). The rmcap lines define the RTP-based media
capabilities (PCMU, G729, telephone-event, H263-1998 and H264) and format capabilities (PCMU, G729, telephone-event, H263-1998 and H264)
the omcap line defines the non-RTP based media capability (wildcard). and the omcap line defines the non-RTP based media format capability
The mfcap attribute provides the format parameters for telephone- (wildcard). The mfcap attribute provides the format parameters for
events, specifying the 12 commercial DTMF 'digits'. The pcfg telephone-events, specifying the 12 commercial DTMF 'digits'. The
attribute line defines the most-preferred media configuration as PCMU pcfg attribute line defines the most-preferred media configuration as
plus DTMF events and the next-most-preferred configuration as G.729B PCMU plus DTMF events and the next-most-preferred configuration as
plus DTMF events. G.729B plus DTMF events.
If the answerer is able to support all the potential configurations, If the answerer is able to support all the potential configurations,
and also support H.263 video (but not H.264), it would reply with an and also support H.263 video (but not H.264), it would reply with an
answer like: answer like:
v=0 v=0
o=- 24351 621814 IN IP4 192.0.2.2 o=- 24351 621814 IN IP4 192.0.2.2
s= s=
c=IN IP4 192.0.2.2 c=IN IP4 192.0.2.2
t=0 0 t=0 0
skipping to change at page 51, line 12 skipping to change at page 51, line 12
reconfiguration of the media stream to use G.729 in order to reduce reconfiguration of the media stream to use G.729 in order to reduce
packet sizes. packet sizes.
5. IANA Considerations 5. IANA Considerations
5.1. New SDP Attributes 5.1. New SDP Attributes
The IANA is hereby requested to register the following new SDP The IANA is hereby requested to register the following new SDP
attributes: attributes:
Attribute name: rmcap Attribute name: rmcap
Long form name: RTP-based media capability Long form name: RTP-based media format capability
Type of attribute: session-level and media-level Type of attribute: session-level and media-level
Subject to charset: no Subject to charset: no
Purpose: associate RTP-based media capability number(s) Purpose: associate RTP-based media capability number(s) with
with media subtype and encoding parameters
media subtype and encoding parameters Appropriate Values: see Section 3.3.1
Appropriate Values: see Section 3.3.1 Contact name: Flemming Andreasen, fandres@cisco.com
Attribute name: omcap Attribute name: omcap
Long form name: Non RTP-based media capability Long form name: Non RTP-based media format capability
Type of attribute: session-level and media-level Type of attribute: session-level and media-level
Subject to charset: no Subject to charset: no
Purpose: associate non RTP-based media capability number(s) Purpose: associate non RTP-based media capability number(s) with
with media subtype and encoding parameters
media subtype and encoding parameters Appropriate Values: see Section 3.3.1
Appropriate Values: see Section 3.3.1 Contact name: Flemming Andreasen, fandreas@cisco.com
Attribute name: mfcap Attribute name: mfcap
Long form name: media format capability Long form name: media format parameter capability
Type of attribute: session-level and media-level Type of attribute: session-level and media-level
Subject to charset: no Subject to charset: no
Purpose: associate media format attributes and Purpose: associate media format attributes and
parameters with media format capabilities parameters with media format capabilities
Appropriate Values: see Section 3.3.2 Appropriate Values: see Section 3.3.2
Contact name: Flemming Andreasen, fandreas@cisco.com
Attribute name: mscap Attribute name: mscap
Long form name: media-specific capability Long form name: media-specific capability
Type of attribute: session-level and media-level Type of attribute: session-level and media-level
Subject to charset: no Subject to charset: no
Purpose: associate media-specific attributes and Purpose: associate media-specific attributes and
parameters with media capabilities parameters with media capabilities
Appropriate Values: see Section 3.3.3 Appropriate Values: see Section 3.3.3
Contact name: Flemming Andreasen, fandreas@cisco.com
Attribute name: lcfg Attribute name: lcfg
Long form name: latent configuration Long form name: latent configuration
Type of attribute: media-level Type of attribute: media-level
Subject to charset: no Subject to charset: no
Purpose: to announce supportable media streams Purpose: to announce supportable media streams
without offering them for immediate use. without offering them for immediate use.
Appropriate Values: see Section 3.3.5 Appropriate Values: see Section 3.3.5
Attribute name: sescap Contact name: Flemming Andreasen, fandreas@cisco.com
Long form name: session capability
Type of attribute: session-level
Subject to charset: no
Purpose: to specify and prioritize acceptable
combinations of media stream configurations.
Appropriate Values: see Section 3.3.8
5.2. New SDP Option Tag Attribute name: sescap
Long form name: session capability
Type of attribute: session-level
Subject to charset: no
Purpose: to specify and prioritize acceptable
combinations of media stream configurations.
Appropriate Values: see Section 3.3.8
Contact name: Flemming Andreasen, fandreas@cisco.com
5.2. New SDP Capability Negotiation Option Tag
The IANA is hereby requested to add the new option tag "med-v0", The IANA is hereby requested to add the new option tag "med-v0",
defined in this document, to the SDP Capability Option Negotiation defined in this document, to the SDP Capability Negotiation Option
Capability registry created for [RFC5939]. Capability registry created for [RFC5939].
5.3. New SDP Capability Negotiation Parameters 5.3. SDP Capability Negotiation Configuration Parameters Registry
The IANA is hereby requested to expand the SDP Capability Negotiation The IANA is hereby requested to change the "SDP Capability
Potential Configuration Parameter Registry established by [RFC5939] Negotiation Potential Configuration Parameters" registry currently
to become the SDP Capability Negotiation Configuration Parameter registered and defined by [RFC5939] as follows:
Registry and to include parameters for the potential, actual and
latent configuration attributes. The new parameters to be registered The name of the registry should be "SDP Capability Negotiation
are the "m" for "media", "pt" for "payload type number", and "mt" for Configuration Parameters Registry" and it should contain a table with
"media type" parameters. Note that the "mt" parameter is defined for the following column headings:
use only in the latent configuration attribute.
o Encoding Name: The syntactical value used for the capability
negotiation configuration parameter, as defined in [RFC5939],
Section 3.5.
o Descriptive Name: The name commonly used to refer to the
capability negotiation configuration parameter.
o Potential Configuration Definition: A reference to the RFC that
defines the configuration parameter in the context of a potential
configuration attribute. If the configuration parameter is not
defined for potential configurations, the string "N/A" (Not
Applicable) MUST be present instead.
o Actual Configuration Definition: A reference to the RFC that
defines the configuration parameter in the context of an actual
configuration attribute. If the configuration parameter is not
defined for actual configurations, the string "N/A" (Not
Applicable) MUST be present instead.
o Latent Configuration Definition: A reference to the RFC that
defines the configuration parameter in the context of a latent
configuration attribute. If the configuration parameter is not
defined for latent configurations, the string "N/A" (Not
Applicable) MUST be present instead.
An IANA SDP Capability Negotiation Configuration registration MUST be
documented in an RFC in accordance with the [RFC5226] IETF Review
policy. Furthermore:
o The RFC MUST define the syntax and semantics of each new potential
configuration parameter.
o The syntax MUST adhere to the syntax provided for extension
configuration lists in [RFC5939] Section 3.5.1 and the semantics
MUST adhere to the semantics provided for extension configuration
lists in [RFC5939] Section 3.5.1 and 3.5.2.
o Configuration parameters that apply to latent configurations MUST
furthermore adhere to the syntax provided in Section 3.3.5 and the
semantics defined overall in this document.
o Associated with each registration MUST be the encoding name for
the parameter as well as a short descriptive name for it.
o Each registration MUST specify if it applies to
* Potential configurations
* Actual configurations
* Latent configurations
5.4. SDP Capability Negotiation Configuration Parameter Registrations
The IANA is hereby requested to register the following capability
negotiation configuration parameters:
Encoding Name: a
Descriptive Name: Attribute Configuration
Potential Configuration Definition: [RFC5939]
Actual Configuration Definition: [RFC5939]
Latent Configuration Definition: [Note to RFC Editor: This RFC]
Encoding Name: t
Descriptive Name: Transport Protocol Configuration
Potential Configuration Definition: [RFC5939]
Actual Configuration Definition: [RFC5939]
Latent Configuration Definition: [Note to RFC Editor: This RFC]
Encoding Name: m
Descriptive Name: Media Configuration
Potential Configuration Definition: [Note to RFC Editor: This
RFC]
Actual Configuration Definition: [Note to RFC Editor: This RFC]
Latent Configuration Definition: [Note to RFC Editor: This RFC]
Encoding Name: pt
Descriptive Name: Payload Type Number Mapping
Potential Configuration Definition: [Note to RFC Editor: This
RFC]
Actual Configuration Definition: [Note to RFC Editor: This RFC]
Latent Configuration Definition: [Note to RFC Editor: This RFC]
Encoding Name: mt
Descriptive Name: Media Type
Potential Configuration Definition: N/A
Actual Configuration Definition: N/A
Latent Configuration Definition: [Note to RFC Editor: This RFC]
6. Security Considerations 6. Security Considerations
The security considerations of [RFC5939] apply for this document. The security considerations of [RFC5939] apply for this document.
In [RFC5939], it was noted that negotiation of transport protocols In [RFC5939], it was noted that negotiation of transport protocols
(e.g. secure and non-secure) and negotiation of keying methods and (e.g. secure and non-secure) and negotiation of keying methods and
material are potential security issues that warrant integrity material are potential security issues that warrant integrity
protection to remedy. Latent configuration support provides hints to protection to remedy. Latent configuration support provides hints to
the other side about capabilities supported for further offer/answer the other side about capabilities supported for further offer/answer
skipping to change at page 54, line 7 skipping to change at page 56, line 7
feature. As for the initial CapNeg work [RFC5939], the SDP answer is feature. As for the initial CapNeg work [RFC5939], the SDP answer is
formulated in such a way that it always carries the selected media formulated in such a way that it always carries the selected media
encoding for every media stream selected. Pending an understanding encoding for every media stream selected. Pending an understanding
of capabilities negotiation, the middlebox should examine the answer of capabilities negotiation, the middlebox should examine the answer
SDP to obtain the best picture of the media streams being SDP to obtain the best picture of the media streams being
established. As always, middleboxes can best do their job if they established. As always, middleboxes can best do their job if they
fully understand media capabilities negotiation. fully understand media capabilities negotiation.
7. Changes from previous versions 7. Changes from previous versions
7.1. Changes from version 13 7.1. Changes from version 14
o Updated IANA Considerations to fix configuration parameter
registry. Document now updates [RFC5939] (IANA considerations
only)
o Minor ABNF updates to fix errors.
o Editorial nit fixes to address protocol write-up review.
7.2. Changes from version 13
o Various editorial clarifications and updates to address review o Various editorial clarifications and updates to address review
comments. comments.
7.2. Changes from version 12 7.3. Changes from version 12
o Removed "dummy" form in the pcfg payload-type-number, since the o Removed "dummy" form in the pcfg payload-type-number, since the
functionality is redundant with the non-RTP media capability functionality is redundant with the non-RTP media capability
(omcap) and it was inconsistent with other RTP payload type (omcap) and it was inconsistent with other RTP payload type
operation. operation.
o Clarified that latent configuration attribute (lcfg) can only be o Clarified that latent configuration attribute (lcfg) can only be
used at the media level and hence (technically) as part of a media used at the media level and hence (technically) as part of a media
description description
o Rewrote offer/answer sections and expanded significantly on offer/ o Rewrote offer/answer sections and expanded significantly on offer/
answer operation. answer operation.
o Updated security considerations o Updated security considerations
o Various minor editorial clarifications and changes. o Various minor editorial clarifications and changes.
7.3. Changes from version 11 7.4. Changes from version 11
o Corrected several statements implying lcfg was a session-level o Corrected several statements implying lcfg was a session-level
attribute. attribute.
o Added non-RTP based media format capabilities ("a=omcap") and o Added non-RTP based media format capabilities ("a=omcap") and
renamed "mcap" to "rmcap" renamed "mcap" to "rmcap"
7.4. Changes from version 10 7.5. Changes from version 10
o Defined the latent configuration attribute as a media-level o Defined the latent configuration attribute as a media-level
attribute because it specifies a possible future media stream. attribute because it specifies a possible future media stream.
Added text to clarify how to specify alternative configurations of Added text to clarify how to specify alternative configurations of
a single latent stream and/or multiple streams. a single latent stream and/or multiple streams.
o Improved the definition of the session capability attribute to o Improved the definition of the session capability attribute to
permit both required configurations and optional configurations - permit both required configurations and optional configurations -
latent configurations cannot be required because they have not yet latent configurations cannot be required because they have not yet
been offered. been offered.
skipping to change at page 55, line 17 skipping to change at page 57, line 27
o Changed various "must", etc., terms to normative terms ("MUST", o Changed various "must", etc., terms to normative terms ("MUST",
etc.) as appropriate, in Section 3.3.5Section 3.3.6.1 etc.) as appropriate, in Section 3.3.5Section 3.3.6.1
Section 3.3.6.3 and Section 3.3.8 Section 3.3.6.3 and Section 3.3.8
o Attempted to clarify the substitution mechanism in Section 3.3.7 o Attempted to clarify the substitution mechanism in Section 3.3.7
and improve its uniqueness. and improve its uniqueness.
o Made various editorial changes, including changing the title in o Made various editorial changes, including changing the title in
the header, and removing numbering from some SDP examples. the header, and removing numbering from some SDP examples.
7.5. Changes from version 09 7.6. Changes from version 09
o Additional corrections to latent media stream example in o Additional corrections to latent media stream example in
Section 4.3 Section 4.3
o Fixed up attribute formatting examples and corresponding ABNF. o Fixed up attribute formatting examples and corresponding ABNF.
o Removed preference rule for latent configurations. o Removed preference rule for latent configurations.
o Various spelling and other editorial changes were made. o Various spelling and other editorial changes were made.
o updated cross-references. o updated cross-references.
7.6. Changes from version 08 7.7. Changes from version 08
The major change is in Section 4.3, Latent Media Streams, fixing the The major change is in Section 4.3, Latent Media Streams, fixing the
syntax of the answer. All the other changes are editorial. syntax of the answer. All the other changes are editorial.
7.7. Changes from version 04 7.8. Changes from version 04
o The definitions for bcap, ccap, icap, and kcap attributes have o The definitions for bcap, ccap, icap, and kcap attributes have
been removed, and are to be defined in another document. been removed, and are to be defined in another document.
o Corrected formatting of m= and p= configuration parameters to o Corrected formatting of m= and p= configuration parameters to
conform to extension-config-list form defined in [RFC5939] conform to extension-config-list form defined in [RFC5939]
o Reorganized definitions of new parameters to make them easier to o Reorganized definitions of new parameters to make them easier to
find in document. find in document.
o Added ability to renegotiate capabilities when modifying the o Added ability to renegotiate capabilities when modifying the
session (Section 3.4.4). session (Section 3.4.4).
o Made various editorial changes, clarifications, and typo o Made various editorial changes, clarifications, and typo
corrections. corrections.
7.8. Changes from version 03 7.9. Changes from version 03
o A new session capability attribute (sescap) has been added to o A new session capability attribute (sescap) has been added to
permit specification of acceptable media stream combinations. permit specification of acceptable media stream combinations.
o Capability attribute definitions corresponding to the i, c, b, and o Capability attribute definitions corresponding to the i, c, b, and
k SDP line types have been added for completeness. k SDP line types have been added for completeness.
o Use of the pcfg: attribute in SDP answers has been included in o Use of the pcfg: attribute in SDP answers has been included in
order to conveniently return information in the answer about order to conveniently return information in the answer about
acceptable configurations in the media stream offer. acceptable configurations in the media stream offer.
skipping to change at page 56, line 38 skipping to change at page 58, line 47
o The description of the mscap attribute has been modified to make o The description of the mscap attribute has been modified to make
it clear that it should not be used to generate undefined SDP it clear that it should not be used to generate undefined SDP
attributes, or to "extend" existing attributes. attributes, or to "extend" existing attributes.
o <ms-parameters> are made optional in the mscap attribute o <ms-parameters> are made optional in the mscap attribute
definition. definition.
o "AMR" changed to "AMR-WB" in cases in which the sample rate is o "AMR" changed to "AMR-WB" in cases in which the sample rate is
16000. 16000.
7.9. Changes from version 02 7.10. Changes from version 02
This version contains several detail changes intended to simplify This version contains several detail changes intended to simplify
capability processing and mapping into conventional SDP media blocks. capability processing and mapping into conventional SDP media blocks.
o The "mcap" attribute is enhanced to include the role of the "ecap" o The "mcap" attribute is enhanced to include the role of the "ecap"
attribute; the latter is eliminated. attribute; the latter is eliminated.
o The "fcap" attribute has been renamed "mfcap". New replacement o The "fcap" attribute has been renamed "mfcap". New replacement
rules vis-a-vis fmtp attributes in the base media specification rules vis-a-vis fmtp attributes in the base media specification
have been added. have been added.
skipping to change at page 57, line 19 skipping to change at page 59, line 30
attribute. attribute.
o A new parameter, "mt=" is added to the latent configuration o A new parameter, "mt=" is added to the latent configuration
attribute (lcfg) to specify the media stream type (audio, video, attribute (lcfg) to specify the media stream type (audio, video,
etc.) when the lcfg is declared at the session level. etc.) when the lcfg is declared at the session level.
o The examples are expanded. o The examples are expanded.
o Numerous typos and misspellings have been corrected. o Numerous typos and misspellings have been corrected.
7.10. Changes from version 01 7.11. Changes from version 01
The documents adds a new attribute for specifying bandwidth The documents adds a new attribute for specifying bandwidth
capability and a parameter to list in the potential configuration. capability and a parameter to list in the potential configuration.
Other changes are to align the document with the terminology and Other changes are to align the document with the terminology and
attribute names from draft-ietf-mmusic-sdp-capability-negotiation-07. attribute names from draft-ietf-mmusic-sdp-capability-negotiation-07.
The document also clarifies some previous open issues. The document also clarifies some previous open issues.
7.11. Changes from version 00 7.12. Changes from version 00
The major changes include taking out the "mcap" and "cptmap" The major changes include taking out the "mcap" and "cptmap"
parameter. The mapping of payload type is now in the "pt" parameter parameter. The mapping of payload type is now in the "pt" parameter
of "pcfg". Media subtype need to explicitly defined in the "cmed" of "pcfg". Media subtype need to explicitly defined in the "cmed"
attribute if referenced in the "pcfg" attribute if referenced in the "pcfg"
8. Acknowledgements 8. Acknowledgements
This document is heavily influenced by the discussions and work done This document is heavily influenced by the discussions and work done
by the SDP Capability Negotiation Design team. The following people by the SDP Capability Negotiation Design team. The following people
skipping to change at page 59, line 19 skipping to change at page 61, line 19
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, with Session Description Protocol (SDP)", RFC 3264,
June 2002. June 2002.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006. Description Protocol", RFC 4566, July 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008. Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5939] Andreasen, F., "SDP Capability Negotiation", RFC 5939, [RFC5939] Andreasen, F., "Session Description Protocol (SDP)
September 2010. Capability Negotiation", RFC 5939, September 2010.
9.2. Informative References 9.2. Informative References
[RFC2198] "RTP Payload for Redundant Audio Data", September 1997. [RFC2198] Perkins, C., Kouvelas, I., Hodson, O., Hardman, V.,
Handley, M., Bolot, J., Vega-Garcia, A., and S. Fosse-
Parisis, "RTP Payload for Redundant Audio Data", RFC 2198,
September 1997.
[RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session
Description Protocol (SDP) Security Descriptions for Media Description Protocol (SDP) Security Descriptions for Media
Streams", RFC 4568, July 2006. Streams", RFC 4568, July 2006.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control "Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
July 2006. July 2006.
 End of changes. 77 change blocks. 
236 lines changed or deleted 369 lines changed or added

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/