draft-ietf-mmusic-sdp-capability-negotiation-07.txt   draft-ietf-mmusic-sdp-capability-negotiation-08.txt 
MMUSIC Working Group F. Andreasen MMUSIC Working Group F. Andreasen
Internet-Draft Cisco Systems Internet-Draft Cisco Systems
Intended Status: Proposed Standard October 28, 2007 Intended Status: Proposed Standard December 11, 2007
SDP Capability Negotiation SDP Capability Negotiation
draft-ietf-mmusic-sdp-capability-negotiation-07.txt draft-ietf-mmusic-sdp-capability-negotiation-08.txt
Status of this Memo Status of this Memo
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aware have been or will be disclosed, and any of which he or she aware have been or will be disclosed, and any of which he or she
becomes aware will be disclosed, in accordance with Section 6 of becomes aware will be disclosed, in accordance with Section 6 of
BCP 79. BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
skipping to change at page 1, line 33 skipping to change at page 1, line 33
months and may be updated, replaced, or obsoleted by other documents months and may be updated, replaced, or obsoleted by other documents
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This Internet-Draft will expire on April 28, 2008. This Internet-Draft will expire on June 11, 2008.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
Abstract Abstract
The Session Description Protocol (SDP) was intended for describing The Session Description Protocol (SDP) was intended for describing
multimedia sessions for the purposes of session announcement, multimedia sessions for the purposes of session announcement,
session invitation, and other forms of multimedia session session invitation, and other forms of multimedia session
skipping to change at page 2, line 30 skipping to change at page 2, line 30
for other types of capabilities (e.g. media types and media formats) for other types of capabilities (e.g. media types and media formats)
may be provided in other documents. may be provided in other documents.
Table of Contents Table of Contents
1. Introduction...................................................3 1. Introduction...................................................3
2. Conventions used in this document..............................7 2. Conventions used in this document..............................7
3. SDP Capability Negotiation Solution............................7 3. SDP Capability Negotiation Solution............................7
3.1. SDP Capability Negotiation Model..........................7 3.1. SDP Capability Negotiation Model..........................7
3.2. Solution Overview........................................10 3.2. Solution Overview........................................10
3.3. Version and Extension Indication Attributes..............13 3.3. Version and Extension Indication Attributes..............14
3.3.1. Supported Capability Negotiation Extensions Attribute13 3.3.1. Supported Capability Negotiation Extensions Attribute14
3.3.2. Required Capability Negotiation Extensions Attribute14 3.3.2. Required Capability Negotiation Extensions Attribute15
3.4. Capability Attributes....................................16 3.4. Capability Attributes....................................17
3.4.1. Attribute Capability Attribute......................16 3.4.1. Attribute Capability Attribute......................17
3.4.2. Transport Protocol Capability Attribute.............18 3.4.2. Transport Protocol Capability Attribute.............19
3.4.3. Extension Capability Attributes.....................19 3.4.3. Extension Capability Attributes.....................20
3.5. Configuration Attributes.................................19 3.5. Configuration Attributes.................................21
3.5.1. Potential Configuration Attribute...................19 3.5.1. Potential Configuration Attribute...................21
3.5.2. Actual Configuration Attribute......................27 3.5.2. Actual Configuration Attribute......................28
3.6. Offer/Answer Model Extensions............................29 3.6. Offer/Answer Model Extensions............................30
3.6.1. Generating the Initial Offer........................29 3.6.1. Generating the Initial Offer........................31
3.6.2. Generating the Answer...............................32 3.6.2. Generating the Answer...............................34
3.6.2.1. Example Views of Potential Configurations......38 3.6.2.1. Example Views of Potential Configurations......40
3.6.3. Offerer Processing of the Answer....................40 3.6.3. Offerer Processing of the Answer....................42
3.6.4. Modifying the Session...............................41 3.6.4. Modifying the Session...............................43
3.7. Interactions with ICE....................................42 3.7. Interactions with ICE....................................43
3.8. Interactions with SIP Option Tags........................43 3.8. Interactions with SIP Option Tags........................45
3.9. Processing Media before Answer...........................44 3.9. Processing Media before Answer...........................46
3.10. Indicating Bandwidth Usage..............................45 3.10. Indicating Bandwidth Usage..............................47
3.11. Dealing with Large Number of Potential Configurations...46 3.11. Dealing with Large Number of Potential Configurations...47
3.12. SDP Capability Negotiation and Intermediaries...........47 3.12. SDP Capability Negotiation and Intermediaries...........48
3.13. Considerations for Specific Attribute Capabilities......48 3.13. Considerations for Specific Attribute Capabilities......50
3.13.1. The rtpmap and fmtp Attributes.....................48 3.13.1. The rtpmap and fmtp Attributes.....................50
3.13.2. Direction Attributes...............................49 3.13.2. Direction Attributes...............................51
3.14. Relationship to RFC 3407................................50 3.14. Relationship to RFC 3407................................52
4. Examples......................................................50 4. Examples......................................................52
4.1. Best-Effort Secure RTP...................................50 4.1. Multiple Transport Protocols.............................52
4.2. Multiple Transport Protocols.............................53 4.2. Best-Effort SRTP with Session-Level MIKEY and Media Level
4.3. Best-Effort SRTP with Session-Level MIKEY and Media Level Security Descriptions.........................................56
Security Descriptions.........................................57 4.3. SRTP with Session-Level MIKEY and Media Level Security
4.4. SRTP with Session-Level MIKEY and Media Level Security Descriptions as Alternatives..................................61
Descriptions as Alternatives..................................62 5. Security Considerations.......................................63
5. Security Considerations.......................................64 6. IANA Considerations...........................................66
6. IANA Considerations...........................................67 6.1. New SDP Attributes.......................................66
6.1. New SDP Attributes.......................................67 6.2. New SDP Capability Negotiation Option Tag Registry.......67
6.2. New SDP Capability Negotiation Option Tag Registry.......68
6.3. New SDP Capability Negotiation Potential Configuration 6.3. New SDP Capability Negotiation Potential Configuration
Parameter Registry............................................69 Parameter Registry............................................68
7. Acknowledgments...............................................69 7. Acknowledgments...............................................68
8. Change Log....................................................69 8. Change Log....................................................68
8.1. draft-ietf-mmusic-sdp-capability-negotiation-07..........69 8.1. draft-ietf-mmusic-sdp-capability-negotiation-08..........68
8.2. draft-ietf-mmusic-sdp-capability-negotiation-06..........70 8.2. draft-ietf-mmusic-sdp-capability-negotiation-07..........69
8.3. draft-ietf-mmusic-sdp-capability-negotiation-05..........71 8.3. draft-ietf-mmusic-sdp-capability-negotiation-06..........70
8.4. draft-ietf-mmusic-sdp-capability-negotiation-04..........72 8.4. draft-ietf-mmusic-sdp-capability-negotiation-05..........71
8.5. draft-ietf-mmusic-sdp-capability-negotiation-03..........73 8.5. draft-ietf-mmusic-sdp-capability-negotiation-04..........72
8.6. draft-ietf-mmusic-sdp-capability-negotiation-02..........73 8.6. draft-ietf-mmusic-sdp-capability-negotiation-03..........72
8.7. draft-ietf-mmusic-sdp-capability-negotiation-01..........74 8.7. draft-ietf-mmusic-sdp-capability-negotiation-02..........73
8.8. draft-ietf-mmusic-sdp-capability-negotiation-00..........75 8.8. draft-ietf-mmusic-sdp-capability-negotiation-01..........73
8.9. draft-ietf-mmusic-sdp-capability-negotiation-00..........74
9. References....................................................76 9. References....................................................76
9.1. Normative References.....................................76 9.1. Normative References.....................................76
9.2. Informative References...................................76 9.2. Informative References...................................76
Author's Addresses...............................................78 Author's Addresses...............................................78
Intellectual Property Statement..................................78 Intellectual Property Statement..................................78
Full Copyright Statement.........................................79 Full Copyright Statement.........................................79
Acknowledgment...................................................79 Acknowledgment...................................................79
1. Introduction 1. Introduction
skipping to change at page 8, line 28 skipping to change at page 8, line 28
+------------+ +------------+
| SDP o1 | | SDP o1 |
| (actual | | (actual |
| config | | config |
| |-+ Offer | |-+ Offer
+------------+ | -----> 3) Process offered configurations +------------+ | -----> 3) Process offered configurations
| SDP o2 | in order of preference indicated | SDP o2 | in order of preference indicated
| (potential | 4) Generate answer based on chosen | (potential | 4) Generate answer based on chosen
| config 1) |-+ configuration (e.g. o2), and | config 1) |-+ configuration (e.g. o2), and
inform +------------+ | inform offerer which one was
+------------+ | offerer which one was chosen | SDP o3 | chosen
| SDP o3 |
| (potential | | (potential |
| config 2) |-+ | config 2) |-+
+------------+ | +------------+ |
| SDP ... | | SDP ... |
: : : :
+------------+ +------------+
| SDP a1 | | SDP a1 |
Answer | (actual | Answer | (actual |
<----- | config,o2)| <----- | config,o2)|
skipping to change at page 10, line 40 skipping to change at page 10, line 37
o A new attribute ("a=tcap") that defines how to list transport o A new attribute ("a=tcap") that defines how to list transport
protocols (e.g. "RTP/AVP") as capabilities. protocols (e.g. "RTP/AVP") as capabilities.
o Two new attributes to negotiate configurations as follows: o Two new attributes to negotiate configurations as follows:
o A new attribute ("a=pcfg") that lists potential o A new attribute ("a=pcfg") that lists potential
configurations supported. This is done by reference to the configurations supported. This is done by reference to the
capabilities from the SDP in question. Extension capabilities capabilities from the SDP in question. Extension capabilities
can be defined and referenced in the potential can be defined and referenced in the potential
configurations. Alternative potential configurations have an configurations. Alternative potential configurations have an
explicit ordering associated with them. explicit ordering associated with them. Also, potential
configurations are preferred over the actual configuration
included in the "m=" line and its associated parameters.
o A new attribute ("a=acfg") to be used in an answer SDP. The o A new attribute ("a=acfg") to be used in an answer SDP. The
attribute identifies a potential configuration from an offer attribute identifies a potential configuration from an offer
SDP which was used as an actual configuration to form the SDP which was used as an actual configuration to form the
answer SDP. Extension capabilities can be included as well. answer SDP. Extension capabilities can be included as well.
o Extensions to the offer/answer model that allow for capabilities o Extensions to the offer/answer model that allow for capabilities
and potential configurations to be included in an offer. and potential configurations to be included in an offer.
Capabilities can be provided at the session level and the media Capabilities can be provided at the session level and the media
level. Potential configurations can be included at the media level. Potential configurations can be included at the media
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where Alice sends an offer to Bob: where Alice sends an offer to Bob:
Alice Bob Alice Bob
| (1) Offer (SRTP and RTP) | | (1) Offer (SRTP and RTP) |
|--------------------------------->| |--------------------------------->|
| | | |
| (2) Answer (SRTP) | | (2) Answer (SRTP) |
|<---------------------------------| |<---------------------------------|
| | | |
| (3) Offer (SRTP) |
|--------------------------------->|
| |
| (4) Answer (SRTP) |
|<---------------------------------|
| |
Alice's offer includes RTP and SRTP as alternatives. RTP is the Alice's offer includes RTP and SRTP as alternatives, where RTP is
default (actual configuration), but SRTP is the preferred one the default (actual configuration), but SRTP is the preferred one
(potential configuration): (potential configuration):
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
m=audio 53456 RTP/AVP 0 18 m=audio 53456 RTP/AVP 0 18
a=tcap:1 RTP/SAVP a=tcap:1 RTP/SAVP
a=acap:1 crypto:1 AES_CM_128_HMAC_SHA1_32 a=acap:1 crypto:1 AES_CM_128_HMAC_SHA1_80
inline:NzB4d1BINUAvLEw6UzF3WSJ+PSdFcGdUJShpX1Zj|2^20|1:32 inline:WVNfX19zZW1jdGwgKCkgewkyMjA7fQp9CnVubGVz|2^20|1:4
a=pcfg:1 t=1 a=1 a=pcfg:1 t=1 a=1
The "m=" line indicates that Alice is offering to use plain RTP with The "m=" line indicates that Alice is offering to use plain RTP with
PCMU or G.729. The capabilities are provided by the "a=tcap" and PCMU or G.729. The capabilities are provided by the "a=tcap" and
"a=acap" attributes. The transport capabilities ("a=tcap") indicate "a=acap" attributes. The transport capability attribute ("a=tcap")
that secure RTP under the AVP profile ("RTP/SAVP") is supported with indicates that secure RTP under the AVP profile ("RTP/SAVP") is
an associated transport capability handle of 1. The "acap" attribute supported with an associated transport capability handle of 1. The
provides an attribute capability with a handle of 1. The attribute "acap" attribute provides an attribute capability with a handle of
capability is a "crypto" attribute, which provides the keying 1. The attribute capability is a "crypto" attribute, which provides
material for SRTP using SDP security descriptions [RFC4568]. The the keying material for SRTP using SDP security descriptions
"a=pcfg" attribute provides the potential configuration included in [RFC4568]. The "a=pcfg" attribute provides the potential
the offer by reference to the capability parameters. One configuration included in the offer by reference to the capability
alternative is provided; it has a configuration number of 1 and it parameters. One alternative is provided; it has a configuration
consists of transport protocol capability 1 (i.e. the RTP/SAVP number of 1 and it consists of transport protocol capability 1
profile - secure RTP), and the attribute capability 1, i.e. the (i.e., the RTP/SAVP profile - secure RTP), and the attribute
crypto attribute provided. Potential configurations are preferred capability 1 (i.e., the crypto attribute provided). Potential
over the actual configuration included in the offer SDP, and hence configurations are preferred over the actual configuration included
Alice is expressing a preference for using secure RTP. in the offer SDP, and hence Alice is expressing a preference for
using secure RTP.
Bob receives the SDP offer from Alice. Bob supports SRTP and the SDP Bob receives the SDP offer from Alice. Bob supports SRTP and the SDP
Capability Negotiation framework, and hence he accepts the Capability Negotiation framework, and hence he accepts the
(preferred) potential configuration for Secure RTP provided by Alice (preferred) potential configuration for Secure RTP provided by Alice
and generates the following answer SDP: and generates the following answer SDP:
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
m=audio 54568 RTP/SAVP 0 18 m=audio 54568 RTP/SAVP 0 18
a=crypto:1 AES_CM_128_HMAC_SHA1_80 a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:PS1uQCVeeCFCanVmcjkpPywjNWhcYD0mXXtxaVBR|2^20|1:4 inline:PS1uQCVeeCFCanVmcjkpPywjNWhcYD0mXXtxaVBR|2^20|1:4
a=acfg:1 t=1 a=1 a=acfg:1 t=1 a=1
Bob includes the "a=acfg" attribute in the answer to inform Alice Bob includes the "a=acfg" attribute in the answer to inform Alice
that he based his answer on an offer containing the potential that he based his answer on an offer using potential configuration 1
configuration with transport protocol capability 1 and attribute with transport protocol capability 1 and attribute capability 1 from
capability 1 from the offer SDP (i.e. the RTP/SAVP profile using the the offer SDP (i.e., the RTP/SAVP profile using the keying material
keying material provided). Bob also includes his keying material in provided). Bob also includes his keying material in a "crypto"
a "crypto" attribute. If Bob supported one or more extensions to the attribute. If Bob supported one or more extensions to the capability
capability negotiation framework, he would have included option tags negotiation framework, he would have included option tags for those
for those in the answer as well (in an "a=csup" attribute). in the answer as well (in an "a=csup" attribute).
When Alice receives Bob's answer, session negotiation has completed,
however Alice nevertheless generates a new offer using the
negotiated configuration as the actual configuration. This is done
purely to assist any intermediaries that may reside between Alice
and Bob but do not support the SDP Capability Negotiation framework,
and hence may not understand the negotiation that just took place.
Alice's updated offer includes only SRTP, and it is not using the
SDP Capability Negotiation framework (Alice could have included the
capabilities as well is she wanted to):
v=0
o=- 25678 753850 IN IP4 192.0.2.1
s=
c=IN IP4 192.0.2.1
t=0 0
m=audio 53456 RTP/SAVP 0 18
a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:WVNfX19zZW1jdGwgKCkgewkyMjA7fQp9CnVubGVz|2^20|1:4
The "m=" line now indicates that Alice is offering to use secure RTP
with PCMU or G.729. The "crypto" attribute, which provides the SRTP
keying material, is included with the same value again.
Bob receives the SDP offer from Alice, which he accepts, and then
generates an answer to Alice:
v=0
o=- 24351 621815 IN IP4 192.0.2.2
s=
c=IN IP4 192.0.2.2
t=0 0
m=audio 54568 RTP/SAVP 0 18
a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:PS1uQCVeeCFCanVmcjkpPywjNWhcYD0mXXtxaVBR|2^20|1:4
Bob includes the same crypto attribute as before, and the session
proceeds without change. Although Bob did not include any
capabilities in his answer, he could have done so if he wanted to.
Note that in this particular example, the answerer supported the Note that in this particular example, the answerer supported the
capability negotiation extensions defined here. Had he not, he would capability negotiation extensions defined here. Had he not, he would
simply have ignored the new attributes and accepted the (actual simply have ignored the new attributes and accepted the (actual
configuration) offer to use normal RTP. In that case, the following configuration) offer to use normal RTP. In that case, the following
answer would have been generated instead: answer would have been generated instead:
v=0 v=0
o=- 24351 621814 IN IP4 192.0.2.2 o=- 24351 621814 IN IP4 192.0.2.2
s= s=
skipping to change at page 14, line 37 skipping to change at page 15, line 37
an offer that did not use the SDP Capability Negotiation an offer that did not use the SDP Capability Negotiation
framework. framework.
3.3.2. Required Capability Negotiation Extensions Attribute 3.3.2. Required Capability Negotiation Extensions Attribute
The Required Capability Negotiation Extensions attribute ("a=creq") The Required Capability Negotiation Extensions attribute ("a=creq")
contains a comma-separated list of option tags (see Section 3.3.1. ) contains a comma-separated list of option tags (see Section 3.3.1. )
specifying the SDP Capability Negotiation extensions that MUST be specifying the SDP Capability Negotiation extensions that MUST be
supported by the entity receiving the SDP, in order for that entity supported by the entity receiving the SDP, in order for that entity
to properly process the SDP Capability Negotiation attributes and to properly process the SDP Capability Negotiation attributes and
associated procedures. Support for the basic negotiation framework associated procedures. There is no need to include the base option-
is implied by the presence of an "a=pcfg" attribute (see Section tag ("cap-v0") with the "creq" attribute, since any entity that
3.5.1. ) and hence there is no need to include the "a=creq" supports the "creq" attribute in the first place also supports the
attribute with the base option-tag ("cap-v0"). Still, it is allowed base option-tag. Still, it is permissible to do so.
to do so.
Such functionality may be important if a future version of the
capability negotiation framework were not backwards compatible.
The attribute is defined as follows: The attribute is defined as follows:
a=creq: <option-tag-list> a=creq: <option-tag-list>
The "creq" attribute adheres to the RFC 4566 "attribute" production, The "creq" attribute adheres to the RFC 4566 "attribute" production,
with an att-value defined as follows: with an att-value defined as follows:
att-value = option-tag-list att-value = option-tag-list
The following examples illustrate use of the "a=creq" attribute with The following examples illustrate use of the "a=creq" attribute with
the "cap-v0" base option tag and two hypothetical option tags, "foo" the "cap-v0" base option tag and two hypothetical option tags, "foo"
and "bar" (note the lack of white space): and "bar" (note the lack of white space):
a=creq:cap-v0 a=creq:cap-v0
skipping to change at page 16, line 10 skipping to change at page 17, line 12
that SDP Capability Negotiation MUST NOT be performed at all. For that SDP Capability Negotiation MUST NOT be performed at all. For
non-supported extensions at the media-level, this implies that SDP non-supported extensions at the media-level, this implies that SDP
Capability Negotiation MUST NOT be performed for the media stream in Capability Negotiation MUST NOT be performed for the media stream in
question. question.
An entity that does not support the SDP Capability Negotiation An entity that does not support the SDP Capability Negotiation
framework at all, will ignore these attributes (as well as the framework at all, will ignore these attributes (as well as the
other SDP Capability Negotiation attributes) and not perform any other SDP Capability Negotiation attributes) and not perform any
SDP Capability Negotiation in the first place. SDP Capability Negotiation in the first place.
When an entity does not support one or more required SDP Capability When an SDP recipient does not support one or more required SDP
Negotiation extensions listed in the option tags, the entity MUST Capability Negotiation extensions listed in the option tags, the
proceed as if the SDP Capability Negotiation attributes were not recipient MUST proceed as if the SDP Capability Negotiation
included in the first place, i.e. all the capability negotiation attributes were not included in the first place, i.e. all the
attributes should be ignored. In that case, the entity SHOULD capability negotiation attributes should be ignored. If the SDP
include a "csup" attribute listing the SDP Capability Negotiation recipient is an SDP answerer [RFC3264], the recipient SHOULD include
extensions it actually supports. a "csup" attribute in the resulting SDP answer listing the SDP
Capability Negotiation extensions it actually supports.
This ensures that introduction of the SDP Capability Negotiation This ensures that introduction of the SDP Capability Negotiation
mechanism by itself does not lead to session failures. mechanism by itself does not lead to session failures.
3.4. Capability Attributes 3.4. Capability Attributes
In this section, we present the new attributes associated with In this section, we present the new attributes associated with
indicating the capabilities for use by the SDP Capability indicating the capabilities for use by the SDP Capability
Negotiation. Negotiation.
3.4.1. Attribute Capability Attribute 3.4.1. Attribute Capability Attribute
Attributes and their associated values can be expressed as Attributes and their associated values can be expressed as
capabilities by use of a new attribute capability attribute capabilities by use of a new attribute capability attribute
("a=acap"), which is defined as follows: ("a=acap"), which is defined as follows:
a=acap: <att-cap-num> <att-par> a=acap: <att-cap-num> <att-par>
where <att-cap-num> is an integer between 1 and 2^31-1 (both where <att-cap-num> is an integer between 1 and 2^31-1 (both
included) used to number the attribute capability and <att-par> is included) used to number the attribute capability and <att-par> is
an attribute ("a=") in its full '<type>=<value>' form (see an attribute ("a=") in its "<attribute>" or <attribute>:<value>"
[RFC4566]). form, i.e., excluding the "a=" part (see [RFC4566]).
The "acap" attribute adheres to the RFC 4566 "attribute" production, The "acap" attribute adheres to the RFC 4566 "attribute" production,
with an att-value defined as follows: with an att-value defined as follows:
att-value = att-cap-num 1*WSP att-par att-value = att-cap-num 1*WSP att-par
att-cap-num = 1*DIGIT ;defined in [RFC4234] att-cap-num = 1*DIGIT ;defined in [RFC4234]
att-par = attribute ;defined in RFC 4566 att-par = attribute ;defined in RFC 4566
Note that white space is not permitted before the att-cap-num.
Note that white-space is not permitted before the att-cap-num.
The "acap" attribute can be provided at the session level only when The "acap" attribute can be provided at the session level only when
the attribute capability contains session-level attributes, whereas the attribute capability contains session-level attributes, whereas
media level attributes can be provided in attribute capabilities at media level attributes can be provided in attribute capabilities at
either the media level or session-level. The base SDP Capability either the media level or session-level. The base SDP Capability
Negotiation framework however only defines procedures for use of Negotiation framework however only defines procedures for use of
media-level attribute capabilities at the media level (extensions media-level attribute capabilities at the media level (extensions
may define use at the session level). may define use at the session level).
Each occurrence of the "acap" attribute in the entire session Each occurrence of the "acap" attribute in the entire session
description MUST use a different value of <att-cap-num>. description MUST use a different value of <att-cap-num>.
Consecutive numbering of the <att-cap-num> values is not required.
There is a need to be able to reference both session-level and There is a need to be able to reference both session-level and
media-level attributes in potential configurations at the media media-level attributes in potential configurations at the media
level, and this provides for a simple solution to avoiding overlap level, and this provides for a simple solution to avoiding overlap
between the references (handles) to each attribute capability. between the references (handles) to each attribute capability.
The <att-cap-num> values provided are independent of similar <cap- The <att-cap-num> values provided are independent of similar <cap-
num> values provided for other types of capabilities, i.e., they num> values provided for other types of capabilities, i.e., they
form a separate name-space for attribute capabilities. form a separate name-space for attribute capabilities.
skipping to change at page 18, line 27 skipping to change at page 19, line 34
reference, and <proto-list> is one or more <proto>, separated by reference, and <proto-list> is one or more <proto>, separated by
white space, as defined in the SDP "m=" line. white space, as defined in the SDP "m=" line.
The "tcap" attribute adheres to the RFC 4566 "attribute" production, The "tcap" attribute adheres to the RFC 4566 "attribute" production,
with an att-value defined as follows: with an att-value defined as follows:
att-value = trpr-cap-num 1*WSP proto-list att-value = trpr-cap-num 1*WSP proto-list
trpr-cap-num = 1*DIGIT ;defined in [RFC4234] trpr-cap-num = 1*DIGIT ;defined in [RFC4234]
proto-list = proto *(1*WSP proto) ; defined in RFC 4566 proto-list = proto *(1*WSP proto) ; defined in RFC 4566
Note that white-space is not permitted before the trpr-cap-num. Note that white space is not permitted before the trpr-cap-num.
The "tcap" attribute can be provided at the session-level and the The "tcap" attribute can be provided at the session-level and the
media-level. There can be at most one "a=tcap" attribute at the media-level. There can be at most one "a=tcap" attribute at the
session-level and at most one at the media-level (one per media session-level and at most one at the media-level (one per media
description in the latter case). Each occurrence of the "tcap" description in the latter case). Each occurrence of the "tcap"
attribute in the entire session description MUST use a different attribute in the entire session description MUST use a different
value of <trpr-cap-num>. When multiple <proto> values are provided, value of <trpr-cap-num>. When multiple <proto> values are provided,
the first one is associated with the value <trpr-cap-num>, the the first one is associated with the value <trpr-cap-num>, the
second one with the value one higher, etc. There MUST NOT be any second one with the value one higher, etc. There MUST NOT be any
capability number overlap between different "tcap" attributes in the capability number overlap between different "tcap" attributes in the
entire SDP. The <trpr-cap-num> values provided are independent of entire SDP. The <trpr-cap-num> values provided are independent of
similar <cap-num> values provided for other capability attributes, similar <cap-num> values provided for other capability attributes,
i.e., they form a separate name-space for transport protocol i.e., they form a separate name-space for transport protocol
capabilities. capabilities. Consecutive numbering of the <trpr-cap-num> values in
different "tcap" attributes is not required.
Below, we provide examples of the "a=tcap" attribute: Below, we provide examples of the "a=tcap" attribute:
a=tcap:1 RTP/AVP a=tcap:1 RTP/AVP
a=tcap:2 RTP/AVPF a=tcap:2 RTP/AVPF
a=tcap:3 RTP/SAVP RTP/SAVPF a=tcap:3 RTP/SAVP RTP/SAVPF
The first one provides a capability for the "RTP/AVP" profile The first one provides a capability for the "RTP/AVP" profile
defined in [RFC3551] and the second one provides a capability for defined in [RFC3551] and the second one provides a capability for
the RTP with RTCP-Based Feedback profile defined in [RFC4585]. The the RTP with RTCP-Based Feedback profile defined in [RFC4585]. The
third one provides capabilities for the "RTP/SAVP" (transport third one provides capabilities for the "RTP/SAVP" (transport
capability number 3) and "RTP/SAVPF" profiles (transport protocol capability number 3) and "RTP/SAVPF" profiles (transport protocol
capability number 4). capability number 4).
Transport capabilities are inherently included in the "m=" line, The ability to use a particular transport protocol is inherently
however they still need to be specified explicitly in a "tcap" implied by including it in the "m=" line, regardless of whether it
attribute if they are to be used as a capability. is provided in a "tcap" attribute or not. However, if a potential
configuration needs to reference that transport protocol as a
capability, the transport protocol MUST be included explicitly in a
"tcap" attribute.
This may seem redundant (and indeed it is from the offerer's point This may seem redundant (and indeed it is from the offerer's point
of view), however it is done to protect against intermediaries of view), however it is done to protect against intermediaries
(e.g. middle-boxes) that may modify "m=" lines while passing (e.g. middle-boxes) that may modify "m=" lines while passing
unknown attributes through. If an implicit transport capability unknown attributes through. If an implicit transport capability
were used instead (e.g. a reserved transport capability number were used instead (e.g. a reserved transport capability number
could be used to refer to the transport protocol in the "m=" could be used to refer to the transport protocol in the "m="
line), and an intermediary were to modify the transport protocol line), and an intermediary were to modify the transport protocol
in the "m=" line (e.g. to translate between plain RTP and secure in the "m=" line (e.g. to translate between plain RTP and secure
RTP), then the potential configuration referencing that implicit RTP), then the potential configuration referencing that implicit
transport capability may no longer be correct. With explicit transport capability may no longer be correct. With explicit
capabilities, we avoid this pitfall; however, the potential capabilities, we avoid this pitfall; however, the potential
configuration preference (see Section 3.5.1. ) may not reflect configuration preference (see Section 3.5.1. ) may not reflect
that of the intermediary (which some may view as a feature). that of the intermediary (which some may view as a feature).
Note that a transport protocol capability may be provided,
irrespective of whether it is referenced in a potential
configuration or not (just like any other capability).
3.4.3. Extension Capability Attributes 3.4.3. Extension Capability Attributes
The SDP Capability Negotiation framework allows for new types of The SDP Capability Negotiation framework allows for new types of
capabilities to be defined as extensions and used with the general capabilities to be defined as extensions and used with the general
capability negotiation framework. The syntax and semantics of such capability negotiation framework. The syntax and semantics of such
new capability attributes are not defined here, however in order to new capability attributes are not defined here, however in order to
be used with potential configurations, they SHOULD allow for a be used with potential configurations, they SHOULD allow for a
numeric handle to be associated with each capability. This handle numeric handle to be associated with each capability. This handle
can be used as a reference within the potential and actual can be used as a reference within the potential and actual
configuration attributes (see Section 3.5.1. and 3.5.2. ). The configuration attributes (see Section 3.5.1. and 3.5.2. ). The
skipping to change at page 20, line 20 skipping to change at page 21, line 34
The "pcfg" attribute adheres to the RFC 4566 "attribute" production, The "pcfg" attribute adheres to the RFC 4566 "attribute" production,
with an att-value defined as follows: with an att-value defined as follows:
att-value = config-number [1*WSP pot-cfg-list] att-value = config-number [1*WSP pot-cfg-list]
config-number = 1*DIGIT ;defined in [RFC4234] config-number = 1*DIGIT ;defined in [RFC4234]
pot-cfg-list = pot-config *(1*WSP pot-config) pot-cfg-list = pot-config *(1*WSP pot-config)
pot-config = attribute-config-list / pot-config = attribute-config-list /
transport-protocol-config-list / transport-protocol-config-list /
extension-config-list extension-config-list
The missing productions are defined below. Note that white-space is The missing productions are defined below. Note that white space is
not permitted before the config-number. not permitted before the config-number.
The potential configuration attribute can be provided at the media- The potential configuration attribute can be provided at the media-
level only and there can be multiple instances of it within a given level only and there can be multiple instances of it within a given
media description. The attribute includes a configuration number, media description. The attribute includes a configuration number,
which is an integer between 1 and 2^31-1 (both included). The which is an integer between 1 and 2^31-1 (both included). The
configuration number MUST be unique within the media description configuration number MUST be unique within the media description
(i.e. it has media level scope only). The configuration number also (i.e. it has media level scope only). The configuration number also
indicates the relative preference of potential configurations; lower indicates the relative preference of potential configurations; lower
numbers are preferred over higher numbers. numbers are preferred over higher numbers. Consecutive numbering of
the configuration numbers in different "pcfg" attributes in a media
description is not required.
A potential configuration list is normally provided after the A potential configuration list is normally provided after the
configuration number. When the potential configuration list is configuration number. When the potential configuration list is
omitted, the potential configuration equals the actual omitted, the potential configuration equals the actual
configuration. The potential configuration list contains one or more configuration. The potential configuration list contains one or more
of attribute, transport and extension configuration lists. The of attribute, transport and extension configuration lists. A
configuration lists generally reference one or more capabilities potential configuration may for example include attribute
capabilities and transport capabilities, transport capabilities
only, or some other combination of capabilities.
The configuration lists generally reference one or more capabilities
(extension configuration lists MAY use a different format). Those (extension configuration lists MAY use a different format). Those
capabilities are (conceptually) used to construct a new internal capabilities are (conceptually) used to construct a new internal
version of the SDP by use of purely syntactic add and (possibly) version of the SDP by use of purely syntactic add and (possibly)
delete operations on the original SDP (actual configuration). This delete operations on the original SDP (actual configuration). This
provides an alternative potential configuration SDP that can be used provides an alternative potential configuration SDP that can be used
by conventional SDP and offer/answer procedures if selected. by conventional SDP and offer/answer procedures if selected.
This document defines attribute configuration lists and transport This document defines attribute configuration lists and transport
protocol configuration lists. Each of these MUST NOT be present protocol configuration lists. Each of these MUST NOT be present
more than once in a particular potential configuration attribute. more than once in a particular potential configuration attribute.
skipping to change at page 22, line 43 skipping to change at page 24, line 18
and each list contains one or more attribute capabilities separated and each list contains one or more attribute capabilities separated
by commas (","). The attribute capabilities are either mandatory or by commas (","). The attribute capabilities are either mandatory or
optional. Mandatory attribute capabilities MUST be supported in optional. Mandatory attribute capabilities MUST be supported in
order to use the potential configuration, whereas optional attribute order to use the potential configuration, whereas optional attribute
capabilities MAY be supported in order to use the potential capabilities MAY be supported in order to use the potential
configuration. configuration.
Within each attribute capability list, all the mandatory attribute Within each attribute capability list, all the mandatory attribute
capabilities (if any) are listed first, and all the optional capabilities (if any) are listed first, and all the optional
attribute capabilities (if any) are listed last. The optional attribute capabilities (if any) are listed last. The optional
attribute capabilities are contained within a pair of angle brackets attribute capabilities are contained within a pair of square
("[" and "]"). Each attribute capability is merely an attribute brackets ("[" and "]"). Each attribute capability is merely an
capability number (att-cap-num) that identifies a particular attribute capability number (att-cap-num) that identifies a
attribute capability by referring to attribute capability numbers particular attribute capability by referring to attribute capability
defined above and hence MUST be between 1 and 2^31-1 (both numbers defined above and hence MUST be between 1 and 2^31-1 (both
included). The following example illustrates the above: included). The following example illustrates the above:
a=pcfg:1 a=-m:1,2,[3,4]|1,7,[5] a=pcfg:1 a=-m:1,2,[3,4]|1,7,[5]
where where
o "a=-m:1,2,[3,4]|1,7,[5]" is the attribute configuration list o "a=-m:1,2,[3,4]|1,7,[5]" is the attribute configuration list
o "-m" is the delete-attributes o "-m" indicates to delete all attributes from the media
description of the actual configuration
o "1,2,[3,4]" and "1,7,[5]" are both attribute capability lists. o "1,2,[3,4]" and "1,7,[5]" are both attribute capability lists.
The two lists are alternatives, since they are separated by a The two lists are alternatives, since they are separated by a
vertical bar above vertical bar above
o "1", "2" and "7" are mandatory attribute capabilities o "1", "2" and "7" are mandatory attribute capabilities
o "3", "4" and "5" are optional attribute capabilities o "3", "4" and "5" are optional attribute capabilities
Note that in the example above, we have a single handle ("1") for Note that in the example above, we have a single handle ("1") for
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configuration are supported with the attribute values provided. configuration are supported with the attribute values provided.
Transport protocol configuration lists are included in a potential Transport protocol configuration lists are included in a potential
configuration by use of the transport-protocol-config-list configuration by use of the transport-protocol-config-list
parameter, which is defined by the following ABNF: parameter, which is defined by the following ABNF:
transport-protocol-config-list = transport-protocol-config-list =
"t=" trpr-cap-num *(BAR trpr-cap-num) "t=" trpr-cap-num *(BAR trpr-cap-num)
trpr-cap-num = 1*DIGIT ; defined in [RFC4234] trpr-cap-num = 1*DIGIT ; defined in [RFC4234]
Note that white-space is not permitted within this production. Note that white space is not permitted within this production.
The trpr-cap-num refers to transport protocol capability numbers The trpr-cap-num refers to transport protocol capability numbers
defined above and hence MUST be between 1 and 2^31-1 (both defined above and hence MUST be between 1 and 2^31-1 (both
included). Alternative transport protocol capabilities are separated included). Alternative transport protocol capabilities are separated
by a vertical bar ("|"). The alternatives are ordered by preference by a vertical bar ("|"). The alternatives are ordered by preference
with the most preferred listed first. If there are no transport with the most preferred listed first. If there are no transport
protocol capabilities included in a potential configuration at the protocol capabilities included in a potential configuration at the
media level, the transport protocol information from the associated media level, the transport protocol information from the associated
"m=" line MUST be used. In order for a recipient of the SDP (e.g., "m=" line MUST be used. In order for a recipient of the SDP (e.g.,
an answerer receiving this in an offer) to use this potential an answerer receiving this in an offer) to use this potential
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Extension capabilities can be included in a potential configuration Extension capabilities can be included in a potential configuration
as well by use of extension configuration lists. Such extension as well by use of extension configuration lists. Such extension
configuration lists MUST adhere to the following ABNF: configuration lists MUST adhere to the following ABNF:
extension-config-list= ["+"] ext-cap-name "=" extension-config-list= ["+"] ext-cap-name "="
ext-cap-list ext-cap-list
ext-cap-name = 1*(ALPHA / DIGIT) ext-cap-name = 1*(ALPHA / DIGIT)
ext-cap-list = 1*VCHAR ; defined in [RFC4234] ext-cap-list = 1*VCHAR ; defined in [RFC4234]
Note that white-space is not permitted within this production. Note that white space is not permitted within this production.
The ext-cap-name refers to the name of the extension capability and The ext-cap-name refers to the name of the extension capability and
the ext-cap-list is here merely defined as a sequence of visible the ext-cap-list is here merely defined as a sequence of visible
characters. The actual extension supported MUST refine both of these characters. The actual extension supported MUST refine both of these
further. For extension capabilities that merely need to be further. For extension capabilities that merely need to be
referenced by a capability number, it is RECOMMENDED to follow a referenced by a capability number, it is RECOMMENDED to follow a
structure similar to what has been specified above. Unsupported or structure similar to what has been specified above. Unsupported or
unknown potential extension configuration lists in a potential unknown potential extension configuration lists in a potential
configuration attribute MUST be ignored, unless they are prefixed configuration attribute MUST be ignored, unless they are prefixed
with the plus ("+") sign, which indicates that the extension is with the plus ("+") sign, which indicates that the extension is
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attributes: attributes:
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
m=audio 53456 RTP/AVPF 0 18 m=audio 53456 RTP/AVPF 0 18
a=acap:1 crypto:1 AES_CM_128_HMAC_SHA1_32 a=acap:1 crypto:1 AES_CM_128_HMAC_SHA1_32
inline:NzB4d1BINUAvLEw6UzF3WSJ+PSdFcGdUJShpX1Zj|2^20|1:32 inline:NzB4d1BINUAvLEw6UzF3WSJ+PSdFcGdUJShpX1Zj|2^20|1:32
a=tcap:1 RTP/AVPF RTP/AVP a=tcap:1 RTP/AVPF RTP/AVP RTP/SAVP RTP/SAVPF
a=tcap:3 RTP/SAVP RTP/SAVPF
a=pcfg:1 t=4|3 a=1 a=pcfg:1 t=4|3 a=1
a=pcfg:8 t=1|2 a=pcfg:8 t=1|2
We have two potential configuration attributes listed here. The We have two potential configuration attributes listed here. The
first one (and most preferred, since its configuration number is first one (and most preferred, since its configuration number is
"1") indicates that either of the profiles RTP/SAVPF or RTP/SAVP "1") indicates that either of the profiles RTP/SAVPF or RTP/SAVP
(specified by the transport protocol capability numbers 4 and 3) can (specified by the transport protocol capability numbers 4 and 3) can
be supported with attribute capability 1 (the "crypto" attribute); be supported with attribute capability 1 (the "crypto" attribute);
RTP/SAVPF is preferred over RTP/SAVP since its capability number (4) RTP/SAVPF is preferred over RTP/SAVP since its capability number (4)
is listed first in the preferred potential configuration. Note that is listed first in the preferred potential configuration. Note that
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3.5.2. Actual Configuration Attribute 3.5.2. Actual Configuration Attribute
The actual configuration attribute identifies which of the potential The actual configuration attribute identifies which of the potential
configurations from an offer SDP was selected and used as the actual configurations from an offer SDP was selected and used as the actual
configuration to generate an answer SDP. This is done by including configuration to generate an answer SDP. This is done by including
the configuration number and the configuration lists (if any) from the configuration number and the configuration lists (if any) from
the offer that were selected and used by the answerer in his the offer that were selected and used by the answerer in his
offer/answer procedure as follows: offer/answer procedure as follows:
o A selected attribute configuration MUST include the delete- o A selected attribute configuration MUST include the delete-
attributes and the selected alternative mo-att-cap-list (i.e., attributes and the known and supported parameters from the
containing all mandatory and optional capability numbers from the selected alternative mo-att-cap-list (i.e., containing all
potential configuration, irrespective of whether the optional mandatory and all known and supported optional capability numbers
ones were supported or not). If delete-attributes were not from the potential configuration). If delete-attributes were not
included in the potential configuration, they will of course not included in the potential configuration, they will of course not
be present here either. be present here either.
o A selected transport protocol configuration MUST include the o A selected transport protocol configuration MUST include the
selected transport protocol capability number. selected transport protocol capability number.
o A selected potential extension configuration MUST include the o A selected potential extension configuration MUST include the
selected extension configuration parameters as specified for that selected extension configuration parameters as specified for that
particular extension. particular extension.
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sel-attribute-config = sel-attribute-config =
"a=" [delete-attributes ":"] mo-att-cap-list "a=" [delete-attributes ":"] mo-att-cap-list
; defined in Section 3.5.1. ; defined in Section 3.5.1.
sel-transport-protocol-config = sel-transport-protocol-config =
"t=" trpr-cap-num ; defined in Section 3.5.1. "t=" trpr-cap-num ; defined in Section 3.5.1.
sel-extension-config = sel-extension-config =
ext-cap-name "=" 1*VCHAR ; defined in Section 3.5.1. ext-cap-name "=" 1*VCHAR ; defined in Section 3.5.1.
Note that white-space is not permitted before the config-number. Note that white space is not permitted before the config-number.
The actual configuration ("a=acfg") attribute can be provided at the The actual configuration ("a=acfg") attribute can be provided at the
media-level only. There MUST NOT be more than one occurrence of an media-level only. There MUST NOT be more than one occurrence of an
actual configuration attribute within a given media description. actual configuration attribute within a given media description.
Below, we provide an example of the "a=acfg" attribute (building on Below, we provide an example of the "a=acfg" attribute (building on
the previous example with the potential configuration attribute): the previous example with the potential configuration attribute):
v=0 v=0
o=- 24351 621814 IN IP4 192.0.2.2 o=- 24351 621814 IN IP4 192.0.2.2
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configuration(s) included in the "m=" line(s). configuration(s) included in the "m=" line(s).
The procedures defined in the following subsections apply to both The procedures defined in the following subsections apply to both
unicast and multicast streams. unicast and multicast streams.
3.6.1. Generating the Initial Offer 3.6.1. Generating the Initial Offer
An offerer that wants to use the SDP Capability Negotiation defined An offerer that wants to use the SDP Capability Negotiation defined
in this document MUST include the following in the offer: in this document MUST include the following in the offer:
o An attribute capability attribute ("a=acap") as defined in o Zero or more attribute capability attributes. There MUST be an
Section 3.4.1. for each attribute name and associated value (if attribute capability attribute ("a=acap") as defined in Section
any) that needs to be indicated as a capability in the offer. 3.4.1. for each attribute name and associated value (if any) that
needs to be indicated as a capability in the offer. Attribute
capabilities may be included irrespective of whether they are
referenced by a potential configuration or not.
Session-level attributes and associated values MUST be provided Session-level attributes and associated values MUST be provided
in attribute capabilities at the session-level only, whereas in attribute capabilities at the session-level only, whereas
media-level attributes and associated values can be provided in media-level attributes and associated values can be provided in
attribute capabilities at either the media-level or session- attribute capabilities at either the media-level or session-
level. Attributes that are allowed at either the session- or level. Attributes that are allowed at either the session- or
media-level can be provided in attribute capabilities at either media-level can be provided in attribute capabilities at either
level. If there is no need to indicate any attributes as level.
attribute capabilities, then there will not be any "a=acap"
attributes either. o Zero or more transport protocol capability attributes. There MUST
be transport protocol capabilities as defined in Section 3.4.2.
with values for each transport protocol that needs to be
indicated as a capability in the offer. Transport protocol
capabilities may be included irrespective of whether they are
referenced by a potential configuration or not.
o One or more transport protocol capability attributes ("a=tcap")
as defined in Section 3.4.2. with values for each transport
protocol that needs to be indicated as a capability in the offer.
Transport protocol capabilities that apply to multiple media Transport protocol capabilities that apply to multiple media
descriptions SHOULD be provided at the session-level whereas descriptions SHOULD be provided at the session-level whereas
transport protocol capabilities that apply to a specific media transport protocol capabilities that apply to a specific media
description ("m=" line) only, SHOULD be provided within that description ("m=" line) only, SHOULD be provided within that
particular media description. In either case, there MUST NOT be particular media description. In either case, there MUST NOT be
more than a single "a=tcap" attribute at the session-level and a more than a single "a=tcap" attribute at the session-level and a
single "a=tcap" attribute in each media description. If there is single "a=tcap" attribute in each media description.
no need to indicate any transport protocols as transport protocol
capabilities, then there will not be any "a=tcap" attributes
either.
o One or more extension capability attributes (as outlined in o Zero or more extension capability attributes. There MUST be one
Section 3.4.3. ) for each extension capability that is referenced or more extension capability attributes (as outlined in Section
by a potential configuration. Extension capability attributes 3.4.3. ) for each extension capability that is referenced by a
that are not referenced by a potential configuration MAY be potential configuration. Extension capability attributes that are
provided as well. not referenced by a potential configuration can be provided as
well.
o One or more potential configuration attributes ("a=pcfg"), as o Zero or more potential configuration attributes. There MUST be
one or more potential configuration attributes ("a=pcfg"), as
defined in Section 3.5.1. , in each media description where defined in Section 3.5.1. , in each media description where
alternative potential configurations are to be negotiated. Each alternative potential configurations are to be negotiated. Each
potential configuration attribute MUST adhere to the rules potential configuration attribute MUST adhere to the rules
provided in Section 3.5.1. and the additional rules provided provided in Section 3.5.1. and the additional rules provided
below. below.
If the offerer requires support for more or extensions (besides the If the offerer requires support for more or extensions (besides the
base protocol defined here), then the offerer MUST include one or base protocol defined here), then the offerer MUST include one or
more "a=creq" attribute as follows: more "a=creq" attributes as follows:
o If support for one or more capability negotiation extensions is o If support for one or more capability negotiation extensions is
required for the entire session description, then option tags for required for the entire session description, then option tags for
those extensions MUST be included in a single session-level those extensions MUST be included in a single session-level
"creq" attribute. "creq" attribute.
o For each media description that requires support for one or more o For each media description that requires support for one or more
capability negotiation extensions not listed at the session- capability negotiation extensions not listed at the session-
level, a single "creq" attribute containing all the required level, a single "creq" attribute containing all the required
extensions for that media description MUST be included within the extensions for that media description MUST be included within the
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deleted, e.g. rtpmaps). deleted, e.g. rtpmaps).
Please refer to Section 3.6.2.1. for examples of how the answerer Please refer to Section 3.6.2.1. for examples of how the answerer
may conceptually "see" the resulting offered alternative potential may conceptually "see" the resulting offered alternative potential
configurations. configurations.
The answerer MUST check that he supports all mandatory attribute The answerer MUST check that he supports all mandatory attribute
capabilities from the potential configuration (if any), the capabilities from the potential configuration (if any), the
transport protocol capability (if any) from the potential transport protocol capability (if any) from the potential
configuration, and all mandatory extension capabilities from the configuration, and all mandatory extension capabilities from the
potential configuration (if any) in accordance with the rules potential configuration (if any). If he does not, the answerer MUST
provided for these. If he does not, the answerer MUST proceed to the proceed to the second-most preferred valid potential configuration
second-most preferred valid potential configuration for the media for the media description, etc.
description, etc. In the case of attribute capabilities, support
implies that the attribute name contained in the capability is o In the case of attribute capabilities, support implies that the
supported and it can (and will) be used successfully in the attribute name contained in the capability is supported and it
negotiation process with the value provided. This does not can (and will) be negotiated successfully in the offer/answer
necessarily imply that the value provided is supported in its exchange with the value provided. This does not necessarily imply
entirety. For example, the "a=fmtp" parameter is often provided with that the value provided is supported in its entirety. For
one or more values in a list, where the offerer and answerer example, the "a=fmtp" parameter is often provided with one or
negotiate use of some subset of the values provided. Other more values in a list, where the offerer and answerer negotiate
attributes may include mandatory and optional parts to their values; use of some subset of the values provided. Other attributes may
support for the mandatory part is all that is required here. include mandatory and optional parts to their values; support for
the mandatory part is all that is required here.
A side-effect of the above rule is that whenever an "fmtp" or A side-effect of the above rule is that whenever an "fmtp" or
"rtpmap" parameter is provided as a mandatory attribute "rtpmap" parameter is provided as a mandatory attribute
capability, the corresponding media format (codec) must be capability, the corresponding media format (codec) must be
supported and use of it negotiated successfully. If this is not supported and use of it negotiated successfully. If this is
the offerer's intent, the corresponding attribute capabilities not the offerer's intent, the corresponding attribute
must be listed as optional instead. capabilities must be listed as optional instead.
o In the case of transport protocol capabilities, support implies
that the transport protocol contained in the capability is
supported and the transport protocol can (and will) be negotiated
successfully in the offer/answer exchange.
o In the case of extension capabilities, the extension MUST define
the rules for when the extension capability is considered
supported and those rules MUST be satisfied.
If the answerer has exhausted all potential configurations for the If the answerer has exhausted all potential configurations for the
media description, without finding a valid one that is also media description, without finding a valid one that is also
supported, then the answerer MUST process the offered media stream supported, then the answerer MUST process the offered media stream
based on the actual configuration plus any session-level attributes based on the actual configuration plus any session-level attributes
added by a valid and supported potential configuration from another added by a valid and supported potential configuration from another
media description in the offered SDP. media description in the offered SDP.
The above process describes potential configuration selection as a The above process describes potential configuration selection as a
per media stream process. Inter-media stream coordination of per media stream process. Inter-media stream coordination of
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o The offerer MUST now process the answer in accordance with the o The offerer MUST now process the answer in accordance with the
rules in [RFC3264], except that it must be done as if the offer rules in [RFC3264], except that it must be done as if the offer
consisted of the selected potential configuration instead of the consisted of the selected potential configuration instead of the
original actual configuration, including any transport protocol original actual configuration, including any transport protocol
changes in the media ("m=") line(s), attributes added and deleted changes in the media ("m=") line(s), attributes added and deleted
by the potential configuration at the media and session level, by the potential configuration at the media and session level,
and any extensions used. and any extensions used.
If the offer/answer exchange was successful, and if the answerer If the offer/answer exchange was successful, and if the answerer
selected one of the potential configurations from the offer as the selected one of the potential configurations from the offer as the
actual configuration, then the offerer MAY perform another actual configuration, and the selected potential configuration
offer/answer exchange: This new offer SHOULD contain the selected differs from the actual configuration in the offer (the "m=", "a=",
potential configuration as the actual configuration, i.e., with the etc. lines), then the offerer SHOULD initiate another offer/answer
actual configuration used in the "m=" line and any other relevant exchange. This second offer/answer exchange will not modify the
attributes and extensions. This second offer/answer exchange will session in any way, however it will help intermediaries (e.g.
not modify the session in any way, however it will help middleboxes), that look at the SDP but do not support the capability
intermediaries (e.g. middleboxes) that look at the SDP, but do not negotiation extensions, understand the details of the media
understand or support the capability negotiation extensions, to stream(s) that were actually negotiated. This new offer MUST contain
understand the details of the media stream(s) that were actually the selected potential configuration as the actual configuration,
negotiated. If it is known or suspected that one or more such i.e., with the actual configuration used in the "m=" line and any
intermediaries exist, then this second offer/answer SHOULD be other relevant attributes, bandwidth parameters, etc.
performed (this is already done when using Interactive Connectivity
Establishment [ICE], and in those cases, there will not be a need Note that, per normal offer/answer rules, the second offer/answer
for a third offer/answer exchange). Note that, per normal exchange still needs to update the version number in the "o=" line
offer/answer rules, the second offer/answer exchange still needs to ((<sess-version> in [RFC4566]). Attribute lines carrying keying
update the version number in the "o=" line ((<sess-version> in material SHOULD repeat the keys from the previous offer, unless re-
[RFC4566]). Attribute lines carrying keying material SHOULD repeat keying is necessary, e.g. due to a previously forked SIP INVITE
the keys from the previous offer, unless re-keying is necessary, request. Please refer to Section 3.12. for additional considerations
e.g. due to a previously forked SIP INVITE request. Please refer to related to intermediaries.
Section 3.12. for additional considerations related to
intermediaries.
3.6.4. Modifying the Session 3.6.4. Modifying the Session
Capabilities and potential configurations may be included in Capabilities and potential configurations may be included in
subsequent offers as defined in [RFC3264], Section 8. The procedure subsequent offers as defined in [RFC3264], Section 8. The procedure
for doing so is similar to that described above with the answer for doing so is similar to that described above with the answer
including an indication of the actual selected configuration used by including an indication of the actual selected configuration used by
the answerer. the answerer.
If the answer indicates use of a potential configuration from the If the answer indicates use of a potential configuration from the
skipping to change at page 43, line 22 skipping to change at page 45, line 9
candidate attributes can be defined as attribute capabilities and candidate attributes can be defined as attribute capabilities and
the relevant ones should then be included in the proper potential the relevant ones should then be included in the proper potential
configurations (for example candidate attributes for UDP only for configurations (for example candidate attributes for UDP only for
potential configurations that are restricted to UDP, whereas there potential configurations that are restricted to UDP, whereas there
could be candidate attributes for UDP, TCP, and TCP/TLS for could be candidate attributes for UDP, TCP, and TCP/TLS for
potential configurations that can use all three). Furthermore, use potential configurations that can use all three). Furthermore, use
of the delete-attributes in a potential configuration can be used to of the delete-attributes in a potential configuration can be used to
ensure that ICE will not end up using a transport protocol that is ensure that ICE will not end up using a transport protocol that is
not desired for a particular configuration. not desired for a particular configuration.
SDP Capability Negotiation recommends use of a second offer/answer
exchange when the negotiated actual configuration was one of the
potential configurations from the offer. Similarly, ICE requires use
of a second offer/answer exchange if the chosen candidate is not the
same as the one in the m/c-line from the offer. When ICE and
capability negotiation are used at the same time, the two secondary
offer/answer exchanges should be combined to a single one.
3.8. Interactions with SIP Option Tags 3.8. Interactions with SIP Option Tags
SIP [RFC3261] allows for SIP extensions to define a SIP option tag SIP [RFC3261] allows for SIP extensions to define a SIP option tag
that identifies the SIP extension. Support for one or more such that identifies the SIP extension. Support for one or more such
extensions can be indicated by use of the SIP Supported header, and extensions can be indicated by use of the SIP Supported header, and
required support for one or more such extensions can be indicated by required support for one or more such extensions can be indicated by
use of the SIP Require header. The "a=csup" and "a=creq" attributes use of the SIP Require header. The "a=csup" and "a=creq" attributes
defined by the SDP Capability Negotiation framework are similar, defined by the SDP Capability Negotiation framework are similar,
except that support for these two attributes by themselves cannot be except that support for these two attributes by themselves cannot be
guaranteed (since they are specified as extensions to the SDP guaranteed (since they are specified as extensions to the SDP
skipping to change at page 45, line 15 skipping to change at page 47, line 12
here does not include the ability to do so, however extensions that here does not include the ability to do so, however extensions that
enable that may be defined. enable that may be defined.
3.10. Indicating Bandwidth Usage 3.10. Indicating Bandwidth Usage
The amount of bandwidth to use for a particular media stream depends The amount of bandwidth to use for a particular media stream depends
on the codecs, transport protocol and other parameters being used. on the codecs, transport protocol and other parameters being used.
For example use of Secure RTP [RFC3711] with integrity protection For example use of Secure RTP [RFC3711] with integrity protection
requires more bandwidth than plain RTP [RFC3551]. SDP defines the requires more bandwidth than plain RTP [RFC3551]. SDP defines the
bandwidth ("b=") parameter to indicate the proposed bandwidth for bandwidth ("b=") parameter to indicate the proposed bandwidth for
the session or media stream,. the session or media stream.
In current SDP, each media description contains one transport In current SDP, each media description contains one transport
protocol and one or more codecs. When specifying the proposed protocol and one or more codecs. When specifying the proposed
bandwidth, the worst case scenario must be taken into account, i.e., bandwidth, the worst case scenario must be taken into account, i.e.,
use of the highest bandwidth codec provided, the transport protocol use of the highest bandwidth codec provided, the transport protocol
indicated, and the worst case (bandwidth-wise) parameters that can indicated, and the worst case (bandwidth-wise) parameters that can
be negotiated (e.g., a 32-bit HMAC or an 80-bit HMAC). be negotiated (e.g., a 32-bit HMAC or an 80-bit HMAC).
The core SDP capability negotiation framework does not provide a way The core SDP capability negotiation framework does not provide a way
to negotiate bandwidth parameters. The issue thus remains, however to negotiate bandwidth parameters. The issue thus remains, however
skipping to change at page 46, line 38 skipping to change at page 48, line 32
configuration for a single media stream. Adding an extension configuration for a single media stream. Adding an extension
capability with just two alternatives for each would double that capability with just two alternatives for each would double that
number (to 10), and doing the equivalent with two media streams number (to 10), and doing the equivalent with two media streams
would again double that number (to 20). While it is easy (and would again double that number (to 20). While it is easy (and
inexpensive) for the offerer to generate such offers, processing inexpensive) for the offerer to generate such offers, processing
them at the answering side may not be. Consequently, it is them at the answering side may not be. Consequently, it is
RECOMMENDED that offerers do not create offers with unnecessarily RECOMMENDED that offerers do not create offers with unnecessarily
large number of potential configurations in them. large number of potential configurations in them.
On the answering side, implementers MUST take care to avoid On the answering side, implementers MUST take care to avoid
excessive memory and CPU consumption. For example, a na excessive memory and CPU consumption. For example, a naive
implementation that first generates all the valid potential implementation that first generates all the valid potential
configuration SDPs internally, could find itself being memory configuration SDPs internally, could find itself being memory
exhausted, especially if it supports a large number of endpoints. exhausted, especially if it supports a large number of endpoints.
Similarly, a na implementation that simply performs iterative Similarly, a naive implementation that simply performs iterative
trial-and-error processing on each possible potential configuration trial-and-error processing on each possible potential configuration
SDP (in the preference order specified) could find itself being CPU SDP (in the preference order specified) could find itself being CPU
constrained. An alternative strategy is to prune the search space constrained. An alternative strategy is to prune the search space
first by discarding the set of offered potential configurations first by discarding the set of offered potential configurations
where the transport protocol indicated (if any) is not supported, where the transport protocol indicated (if any) is not supported,
and/or one or more mandatory attribute capabilities (if any) are and/or one or more mandatory attribute capabilities (if any) are
either not supported or not valid. Potential configurations with either not supported or not valid. Potential configurations with
unsupported mandatory extension configurations in them can be unsupported mandatory extension configurations in them can be
discarded as well. discarded as well.
skipping to change at page 50, line 37 skipping to change at page 52, line 34
RFC 3407 implementations is desired, implementations MAY include RFC 3407 implementations is desired, implementations MAY include
both RFC 3407 capability descriptions and capabilities defined by both RFC 3407 capability descriptions and capabilities defined by
this document. The offer/answer negotiation procedures defined in this document. The offer/answer negotiation procedures defined in
this document will not use the RFC 3407 capability descriptions. this document will not use the RFC 3407 capability descriptions.
4. Examples 4. Examples
In this section, we provide examples showing how to use the SDP In this section, we provide examples showing how to use the SDP
Capability Negotiation. Capability Negotiation.
4.1. Best-Effort Secure RTP 4.1. Multiple Transport Protocols
The following example illustrates how to use the SDP Capability
Negotiation extensions to support so-called Best-Effort Secure RTP.
In that scenario, the offerer supports both RTP and Secure RTP. If
the answerer does not support secure RTP (or the SDP Capability
Negotiation extensions), an RTP session will be established.
However, if the answerer supports Secure RTP and the SDP Capability
Negotiation extensions, a Secure RTP session will be established.
The best-effort Secure RTP negotiation is illustrated by the
offer/answer exchange below, where Alice sends an offer to Bob:
Alice Bob
| (1) Offer (SRTP and RTP) |
|--------------------------------->|
| |
| (2) Answer (SRTP) |
|<---------------------------------|
| |
| (3) Offer (SRTP) |
|--------------------------------->|
| |
| (4) Answer (SRTP) |
|<---------------------------------|
| |
Alice's offer includes RTP and SRTP as alternatives. RTP is the
default, but SRTP is the preferred one:
v=0
o=- 25678 753849 IN IP4 192.0.2.1
s=
c=IN IP4 192.0.2.1
t=0 0
m=audio 53456 RTP/AVP 0 18
a=tcap:1 RTP/SAVP RTP/AVP
a=acap:1 crypto:1 AES_CM_128_HMAC_SHA1_80
inline:WVNfX19zZW1jdGwgKCkgewkyMjA7fQp9CnVubGVz|2^20|1:4
FEC_ORDER=FEC_SRTP
a=pcfg:1 t=1 a=1
The "m=" line indicates that Alice is offering to use plain RTP with
PCMU or G.729. The capabilities are provided by the "a=tcap" and
"a=acap" attributes. The "tcap" capability indicates that both
Secure RTP and normal RTP are supported. The "acap" attribute
provides an attribute capability with a handle of 1. The capability
is a "crypto" attribute, which provides the keying material for SRTP
using SDP security descriptions [RFC4568]. The "a=pcfg" attribute
provides the potential configurations included in the offer by
reference to the capabilities. A single potential configuration
with a configuration number of "1" is provided. It includes the
transport protocol capability 1 (RTP/SAVP, i.e. secure RTP) together
with the attribute capability 1, i.e. the crypto attribute provided.
Note that attribute capability 1 is mandatory, and hence it must be
supported in order for the potential configuration to be used.
Bob receives the SDP offer from Alice. Bob supports SRTP and the SDP
Capability Negotiation framework, and hence he accepts the potential
configuration for Secure RTP provided by Alice:
v=0
o=- 24351 621814 IN IP4 192.0.2.2
s=
c=IN IP4 192.0.2.2
t=0 0
m=audio 54568 RTP/SAVP 0 18
a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:PS1uQCVeeCFCanVmcjkpPywjNWhcYD0mXXtxaVBR|2^20|1:4
a=acfg:1 t=1 a=1
Bob includes the "a=acfg" attribute in the answer to inform Alice
that he based his answer on an offer containing the potential
configuration with transport protocol capability 1 and attribute
capability 1 from the offer SDP (i.e. the RTP/SAVP profile using the
keying material provided). Bob also includes his keying material in
a crypto attribute.
When Alice receives Bob's answer, session negotiation has completed,
however Alice nevertheless chooses to generate a new offer using the
actual configuration. This is done purely to assist any
intermediaries that may reside between Alice and Bob but do not
support the SDP Capability Negotiation framework (and hence may not
understand the negotiation that just took place):
Alice's updated offer includes only SRTP, and it is not using the
SDP Capability Negotiation framework (Alice could have included the
capabilities as well is she wanted to):
v=0
o=- 25678 753850 IN IP4 192.0.2.1
s=
c=IN IP4 192.0.2.1
t=0 0
m=audio 53456 RTP/SAVP 0 18
a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:WVNfX19zZW1jdGwgKCkgewkyMjA7fQp9CnVubGVz|2^20|1:4
FEC_ORDER=FEC_SRTP
The "m=" line now indicates that Alice is offering to use secure RTP
with PCMU or G.729. The "crypto" attribute, which provides the SRTP
keying material, is included with the same value again.
Bob receives the SDP offer from Alice, which he accepts, and then
generates an answer to Alice:
v=0
o=- 24351 621815 IN IP4 192.0.2.2
s=
c=IN IP4 192.0.2.2
t=0 0
m=audio 54568 RTP/SAVP 0 18
a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:PS1uQCVeeCFCanVmcjkpPywjNWhcYD0mXXtxaVBR|2^20|1:4
Bob includes the same crypto attribute as before, and the session
proceeds without change. Although Bob did not include any
capabilities in his answer, he could have done so if he wanted to.
Note that in this particular example, the answerer supported the SDP
Capability Negotiation framework, and hence the attributes and
procedures defined here, however had he not, the answerer would
simply have ignored the new attributes received in step 1 and
accepted the offer to use normal RTP. In that case, the following
answer would have been generated in step 2 instead:
v=0
o=- 24351 621814 IN IP4 192.0.2.2
s=
c=IN IP4 192.0.2.2
t=0 0
m=audio 54568 RTP/AVP 0 18
4.2. Multiple Transport Protocols
The following example illustrates how to use the SDP Capability The following example illustrates how to use the SDP Capability
Negotiation extensions to negotiate use of one out of several Negotiation extensions to negotiate use of one out of several
possible transport protocols. As in the previous example, the possible transport protocols. The offerer uses the expected least-
offerer uses the expected least-common-denominator (plain RTP) as common-denominator (plain RTP) as the actual configuration, and the
the actual configuration, and the alternative transport protocols as alternative transport protocols as the potential configurations.
the potential configurations.
The example is illustrated by the offer/answer exchange below, where The example is illustrated by the offer/answer exchange below, where
Alice sends an offer to Bob: Alice sends an offer to Bob:
Alice Bob Alice Bob
| (1) Offer (RTP/[S]AVP[F]) | | (1) Offer (RTP/[S]AVP[F]) |
|--------------------------------->| |--------------------------------->|
| | | |
| (2) Answer (RTP/AVPF) | | (2) Answer (RTP/AVPF) |
skipping to change at page 57, line 12 skipping to change at page 56, line 12
accepted the offer to use normal RTP. In that case, the following accepted the offer to use normal RTP. In that case, the following
answer would have been generated in step 2 instead: answer would have been generated in step 2 instead:
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
m=audio 54568 RTP/AVP 0 18 m=audio 54568 RTP/AVP 0 18
4.3. Best-Effort SRTP with Session-Level MIKEY and Media Level Security 4.2. Best-Effort SRTP with Session-Level MIKEY and Media Level Security
Descriptions Descriptions
The following example illustrates how to use the SDP Capability The following example illustrates how to use the SDP Capability
Negotiation extensions to support so-called Best-Effort Secure RTP Negotiation extensions to support so-called Best-Effort Secure RTP
as well as alternative keying mechanisms, more specifically MIKEY as well as alternative keying mechanisms, more specifically MIKEY
[RFC3830] and SDP Security Descriptions. The offerer (Alice) wants [RFC3830] and SDP Security Descriptions. The offerer (Alice) wants
to establish an audio and video session. Alice prefers to use to establish an audio and video session. Alice prefers to use
session-level MIKEY as the key management protocol, but supports SDP session-level MIKEY as the key management protocol, but supports SDP
security descriptions as well. security descriptions as well.
skipping to change at page 62, line 5 skipping to change at page 61, line 5
It should be noted, that although Bob could have chosen session- It should be noted, that although Bob could have chosen session-
level MIKEY for one media stream, and SDP Security Descriptions for level MIKEY for one media stream, and SDP Security Descriptions for
another media stream, there are no well-defined offerer processing another media stream, there are no well-defined offerer processing
rules of the resulting answer for this, and hence the offerer may rules of the resulting answer for this, and hence the offerer may
incorrectly assume use of MIKEY for both streams. To avoid this, if incorrectly assume use of MIKEY for both streams. To avoid this, if
the answerer chooses session-level MIKEY, then all secure RTP based the answerer chooses session-level MIKEY, then all secure RTP based
media streams SHOULD use MIKEY (this applies irrespective of whether media streams SHOULD use MIKEY (this applies irrespective of whether
SDP Capability Negotiation is being used or not). Use of media-level SDP Capability Negotiation is being used or not). Use of media-level
MIKEY does not have a similar constraint. MIKEY does not have a similar constraint.
4.4. SRTP with Session-Level MIKEY and Media Level Security 4.3. SRTP with Session-Level MIKEY and Media Level Security
Descriptions as Alternatives Descriptions as Alternatives
The following example illustrates how to use the SDP Capability The following example illustrates how to use the SDP Capability
Negotiation framework to negotiate use of either MIKEY or SDP Negotiation framework to negotiate use of either MIKEY or SDP
Security Descriptions, when one of them is included as part of the Security Descriptions, when one of them is included as part of the
actual configuration, and the other one is being selected. The actual configuration, and the other one is being selected. The
offerer (Alice) wants to establish an audio and video session. Alice offerer (Alice) wants to establish an audio and video session. Alice
prefers to use session-level MIKEY as the key management protocol, prefers to use session-level MIKEY as the key management protocol,
but supports SDP security descriptions as well. but supports SDP security descriptions as well.
skipping to change at page 69, line 29 skipping to change at page 68, line 29
Section 3.5.1. and 3.5.2. Associated with each registration MUST be Section 3.5.1. and 3.5.2. Associated with each registration MUST be
the encoding name for the parameter as well as a short descriptive the encoding name for the parameter as well as a short descriptive
name for it. name for it.
The potential configuration parameters "a" for "attribute" and "t" The potential configuration parameters "a" for "attribute" and "t"
for "transport protocol" are defined in this document and the IANA for "transport protocol" are defined in this document and the IANA
is hereby requested to register these. is hereby requested to register these.
7. Acknowledgments 7. Acknowledgments
This document is heavily influenced by the discussions and work done The SDP Capability Negotiation solution defined in this document
by the SDP Capability Negotiation Design team. The following people draws on the overall capability negotiation framework that was
in particular provided useful comments and suggestions to either the defined by [SDPng]. Also, the SDP Capability Negotiation solution is
heavily influenced by the discussions and work done by the SDP
Capability Negotiation Design Team. The following people in
particular provided useful comments and suggestions to either the
document itself or the overall direction of the solution defined in document itself or the overall direction of the solution defined in
here: Francois Audet, John Elwell, Roni Even, Robert Gilman, Cullen here: Francois Audet, John Elwell, Roni Even, Robert Gilman, Cullen
Jennings, Jonathan Lennox, Matt Lepinski, Joerg Ott, Colin Perkins, Jennings, Jonathan Lennox, Matt Lepinski, Joerg Ott, Colin Perkins,
Jonathan Rosenberg, Thomas Stach, and Dan Wing. Jonathan Rosenberg, Thomas Stach, and Dan Wing.
8. Change Log 8. Change Log
8.1. draft-ietf-mmusic-sdp-capability-negotiation-07 8.1. draft-ietf-mmusic-sdp-capability-negotiation-08
Incorporated Working Group Last Call comments as follows:
o Added second offer/answer exchange to introductory example, fixed
minor error in that example, and deleted similar example in the
Examples Section.
o Fixed "type=value" semantic error in the attribute capability
definition.
o Clarified that consecutive numbering of capabilities and
potential configurations is not required.
o Fixed inconsistency for which parameters to include in the "acfg"
attribute.
o Changed second offer/answer exchange from MAY to SHOULD strength.
o Clarified there should be a combined second offer/exchange when
using ICE.
o Moved RFC 3407 to informative references.
o Various editorial clarifications.
8.2. draft-ietf-mmusic-sdp-capability-negotiation-07
o Removed the ability to have attribute capabilities provide o Removed the ability to have attribute capabilities provide
attribute names without values, when those attributes otherwise attribute names without values, when those attributes otherwise
require an associated value. require an associated value.
o Document no longer obsoletes RFC 3407 but instead recommends that o Document no longer obsoletes RFC 3407 but instead recommends that
it is being used instead of RFC 3407. it is being used instead of RFC 3407.
o Added ability to specific that specific extensions in a potential o Added ability to specific that specific extensions in a potential
configuration are mandatory. configuration are mandatory.
skipping to change at page 70, line 18 skipping to change at page 70, line 5
o Removed the redundant "a=" part of attribute capabilities. o Removed the redundant "a=" part of attribute capabilities.
o Clarified what it means to support an attribute capability in the o Clarified what it means to support an attribute capability in the
offer/answer procedures. offer/answer procedures.
o Changed "a=acap" attribute and offer/answer procedures to include o Changed "a=acap" attribute and offer/answer procedures to include
only the known and supported attribute capabilities. only the known and supported attribute capabilities.
o Added new section on indicating bandwidth usage. o Added new section on indicating bandwidth usage.
8.2. draft-ietf-mmusic-sdp-capability-negotiation-06 8.3. draft-ietf-mmusic-sdp-capability-negotiation-06
o Added additional background text on terminology used, and a new o Added additional background text on terminology used, and a new
section on the negotiation model. section on the negotiation model.
o Allowed for session-level attribute capabilities to contain o Allowed for session-level attribute capabilities to contain
media-level only attributes, albeit the base framework does not media-level only attributes, albeit the base framework does not
define (or allow) them to be used in a potential configuration define (or allow) them to be used in a potential configuration
(extensions may change that) (extensions may change that)
o Disallowing multiple "a=tcap" attributes at the session-level o Disallowing multiple "a=tcap" attributes at the session-level
skipping to change at page 71, line 40 skipping to change at page 71, line 23
o Updated examples in accordance with other changes and to o Updated examples in accordance with other changes and to
illustrate use of mandatory and optional attribute capabilities illustrate use of mandatory and optional attribute capabilities
in a potential configuration. in a potential configuration.
o Updated security considerations to address potential denial of o Updated security considerations to address potential denial of
service attack caused by large number of potential service attack caused by large number of potential
configurations. configurations.
o Various editorial updates throughout. o Various editorial updates throughout.
8.3. draft-ietf-mmusic-sdp-capability-negotiation-05 8.4. draft-ietf-mmusic-sdp-capability-negotiation-05
o Allowed for '<type>=<value>' attributes to be listed as attribute o Allowed for '<type>=<value>' attributes to be listed as attribute
capabilities the attribute name only. capabilities the attribute name only.
o Changed IP-address to conform to RFC 3330 guidelines. o Changed IP-address to conform to RFC 3330 guidelines.
o Added section on relationship to RFC 3407 and "Obsoletes: 3407" o Added section on relationship to RFC 3407 and "Obsoletes: 3407"
in the front. in the front.
o Disallowed use of white space in a number of places for more o Disallowed use of white space in a number of places for more
skipping to change at page 72, line 45 skipping to change at page 72, line 27
o Updated rtpmap and fmtp section to allow potential configurations o Updated rtpmap and fmtp section to allow potential configurations
to use remapped payload types in attribute capabilities for to use remapped payload types in attribute capabilities for
rtpmaps and fmtp parameters. rtpmaps and fmtp parameters.
o Added section on direction attributes. o Added section on direction attributes.
o Added another example showing SRTP with session-level MIKEY and o Added another example showing SRTP with session-level MIKEY and
SDP Security Descriptions using the attribute capability DELETE SDP Security Descriptions using the attribute capability DELETE
operator. operator.
8.4. draft-ietf-mmusic-sdp-capability-negotiation-04 8.5. draft-ietf-mmusic-sdp-capability-negotiation-04
The following are the major changes compared to version -03: The following are the major changes compared to version -03:
o Added explicit ordering rules for attributes added by potential o Added explicit ordering rules for attributes added by potential
configurations. configurations.
o Noted that ICE interaction issues (ice-tcp specifically) may not o Noted that ICE interaction issues (ice-tcp specifically) may not
be as clear as originally thought. be as clear as originally thought.
o Added considerations on using rtpmap and fmtp attributes as o Added considerations on using rtpmap and fmtp attributes as
attribute capabilities. attribute capabilities.
o Added multiple transport protocol example. o Added multiple transport protocol example.
o Added session-level MIKEY and media level security descriptions o Added session-level MIKEY and media level security descriptions
example. example.
8.5. draft-ietf-mmusic-sdp-capability-negotiation-03 8.6. draft-ietf-mmusic-sdp-capability-negotiation-03
The following are the major changes compared to version -02: The following are the major changes compared to version -02:
o Base option tag name changed from "v0" to "cap-v0". o Base option tag name changed from "v0" to "cap-v0".
o Added new section on extension capability attributes o Added new section on extension capability attributes
o Firmed up offer/answer procedures. o Firmed up offer/answer procedures.
o Added security considerations o Added security considerations
o Added IANA considerations o Added IANA considerations
8.6. draft-ietf-mmusic-sdp-capability-negotiation-02 8.7. draft-ietf-mmusic-sdp-capability-negotiation-02
The following are the major changes compared to version -01: The following are the major changes compared to version -01:
o Potential configurations are no longer allowed at the session o Potential configurations are no longer allowed at the session
level level
o Renamed capability attributes ("capar" to "acap" and "ctrpr" to o Renamed capability attributes ("capar" to "acap" and "ctrpr" to
"tcap") "tcap")
o Changed name and semantics of the initial number (now called o Changed name and semantics of the initial number (now called
skipping to change at page 74, line 16 skipping to change at page 73, line 46
selected a potential configuration selected a potential configuration
o Updated rules (and added restrictions) for referencing media- and o Updated rules (and added restrictions) for referencing media- and
session-level capabilities in potential configurations (at the session-level capabilities in potential configurations (at the
media level) media level)
o Added initial section on ICE interactions o Added initial section on ICE interactions
o Added initial section on receiving media before answer o Added initial section on receiving media before answer
8.7. draft-ietf-mmusic-sdp-capability-negotiation-01 8.8. draft-ietf-mmusic-sdp-capability-negotiation-01
The following are the major changes compared to version -00: The following are the major changes compared to version -00:
o Media capabilities are no longer considered a core capability and o Media capabilities are no longer considered a core capability and
hence have been removed. This leaves transport protocols and hence have been removed. This leaves transport protocols and
attributes as the only capabilities defined by the core. attributes as the only capabilities defined by the core.
o Version attribute has been removed and an option tag to indicate o Version attribute has been removed and an option tag to indicate
the actual version has been defined instead. the actual version has been defined instead.
skipping to change at page 75, line 5 skipping to change at page 74, line 33
configuration attributes. configuration attributes.
o Potential configurations at the session level now limited to o Potential configurations at the session level now limited to
indicate latent capability configurations. Consequently, an indicate latent capability configurations. Consequently, an
actual configuration attribute can no longer be provided at the actual configuration attribute can no longer be provided at the
session level. session level.
o Cleaned up capability and potential configuration terminology - o Cleaned up capability and potential configuration terminology -
they are now two clearly different things. they are now two clearly different things.
8.8. draft-ietf-mmusic-sdp-capability-negotiation-00 8.9. draft-ietf-mmusic-sdp-capability-negotiation-00
Version 00 is the initial version. The solution provided in this Version 00 is the initial version. The solution provided in this
initial version is based on an earlier (individual submission) initial version is based on an earlier (individual submission)
version of [SDPCapNeg]. The following are the major changes compared version of [SDPCapNeg]. The following are the major changes compared
to that document: to that document:
o Solution no longer based on RFC 3407, but defines a set of o Solution no longer based on RFC 3407, but defines a set of
similar attributes (with some differences). similar attributes (with some differences).
o Various minor changes to the previously defined attributes. o Various minor changes to the previously defined attributes.
skipping to change at page 76, line 20 skipping to change at page 76, line 20
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434, IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998. October 1998.
[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, June with Session Description Protocol (SDP)", RFC 3264, June
2002. 2002.
[RFC3407] F. Andreasen, "Session Description Protocol (SDP) Simple
Capability Declaration", RFC 3407, October 2002.
[RFC4234] Crocker, D., and P. Overell, "Augmented BNF for Syntax [RFC4234] Crocker, D., and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005. Specifications: ABNF", RFC 4234, October 2005.
[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.
9.2. Informative References 9.2. Informative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002. June 2002.
[RFC3312] G. Camarillo, W. Marshall, and J. Rosenberg, "Integration [RFC3312] G. Camarillo, W. Marshall, and J. Rosenberg, "Integration
of Resource Management and Session Initiatio Protocol of Resource Management and Session Initiation Protocol
(SIP)", RFC 3312, October 2002. (SIP)", RFC 3312, October 2002.
[RFC3262] J. Rosenberg, and H. Schulzrinne, "Reliability of [RFC3262] J. Rosenberg, and H. Schulzrinne, "Reliability of
Provisional Responses in Session Initiation Protocol Provisional Responses in Session Initiation Protocol
(SIP)", RFC 3262, June 2002. (SIP)", RFC 3262, June 2002.
[RFC3388] Camarillo, G., Eriksson, G., Holler, J., and H. [RFC3388] Camarillo, G., Eriksson, G., Holler, J., and H.
Schulzrinne, "Grouping of Media Lines in the Session Schulzrinne, "Grouping of Media Lines in the Session
Description Protocol (SDP)", RFC 3388, December 2002. Description Protocol (SDP)", RFC 3388, December 2002.
[RFC3407] F. Andreasen, "Session Description Protocol (SDP) Simple
Capability Declaration", RFC 3407, October 2002.
[RFC3551] Schulzrinne, H., and S. Casner, "RTP Profile for Audio and [RFC3551] Schulzrinne, H., and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", RFC 3551, July Video Conferences with Minimal Control", RFC 3551, July
2003. 2003.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol Norrman, "The Secure Real-time Transport Protocol
(SRTP).", RFC 3711, March 2004. (SRTP).", RFC 3711, March 2004.
[RFC3830] J. Arkko, E. Carrara, F. Lindholm, M. Naslund, and K. [RFC3830] J. Arkko, E. Carrara, F. Lindholm, M. Naslund, and K.
Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830, Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830,
 End of changes. 64 change blocks. 
338 lines changed or deleted 316 lines changed or added

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