Technical Summary
This specification defines a new Session Description Protocol (SDP)
media-level attribute: "label". The "label" attribute carries a
pointer to a media stream in the context of an arbitrary network
application that uses SDP. The sender of the SDP document can attach
the "label" attribute to a particular media stream or streams. The
application can then use the provided pointer to refer to each or all
of the media in its particular context.
SDP is a body or document used by other protocols. It is left to the using
applications to manage the "label" attribute. However an important
user of the attribute is identified, the XCON framework. The
SIP conferencing package, in review at the same time as this
specification, is another important using protocol.
Working Group Summary
The document carefully reviews why other SDP attributes or functionality which
to provide this labeling function were not chosen. The working group had
raised each of the alternatives and discussed the points through to consensus.
Before working group last call, there was a thorough document review by
Magnus Westerlund, and the specification revised for small issues from that
was supported for advancement.
Protocol Quality
Allison Mankin has reviewed the specification for the IESG.
Note(s) to the RFC Editor
Replace normative reference to RFC 2234 with normative reference
to draft-crocker-abnf-rfc2234bis-00.txt
[DS in RFC Editor Queue]
Section 1. Add a sentence at the end of the second paragraph.
OLD:
[...]
media stream's role in the conference) about it.
NEW:
[...]
media stream's role in the conference) about it. The SIP Event
Package for Conference State [Informative refence to
draft-ietf-sipping-conference-package] defines and uses a concrete
format for such external documents.
Section 4: extend the ABNF as follows:
OLD:
Its formatting in SDP is described by the following BNF
[2]:
label-attribute = "a=label:" pointer
pointer = token
NEW:
Its formatting in SDP is described by the following ABNF
[normative reference to draft-crocker-abnf-rfc2234bis-00.txt]:
label-attribute = "a=label:" pointer
pointer = token
token-char = %x21 / %x23-27 / %x2A-2B / %x2D-2E / %x30-39
/ %x41-5A / %x5E-7E
token = 1*(token-char)
The token-char and token elements are defined in [give a Normative
reference to draft-ietf-mmusic-sdp-new-24.txt] but included here to
provide support for the implementor of this SDP feature.
Section 6: addition of an 'i' line to the example:
OLD:
v=0
o=bob 280744730 28977631 IN IP4 host.example.com
s=
c=IN IP4 192.0.2.2
t=0 0
m=audio 6886 RTP/AVP 0
a=label:1
m=audio 22334 RTP/AVP 0
a=label:2
NEW
v=0
o=bob 280744730 28977631 IN IP4 host.example.com
s=
i=A Seminar on the session description protocol
c=IN IP4 192.0.2.2
t=0 0
m=audio 6886 RTP/AVP 0
a=label:1
m=audio 22334 RTP/AVP 0
a=label:2
Add to the beginning of Section 8 -
Upon approval of this specification, IANA is requested to register
the following new SDP attribute: