[MMUSIC] Protocol Action: RTCP attribute in SDP to Proposed Standard

The IESG has approved the Internet-Draft 'RTCP attribute in SDP'
<draft-ietf-mmusic-sdp4nat-05.txt> as a Proposed Standard. This
document is the product of the Multiparty Multimedia Session Control
Working Group. The IESG contact persons are Allison Mankin and Jon
Peterson.

Technical Summary

The new version of RTP (draft-ietf-avt-rtp-new-12) relaxes the requirement
in 1889 that the port number used for the Real Time Control Protocol (RTCP)
must be one port number higher than the port chosen for an RTP stream.
Because of this, protocols like the Session Description Protocol which use
RTP now need a way to explicitly specify the port that will be used for an
RTCP stream corresponding to an RTP stream; previously, SDP had no need for
this capability since implementations just assumed that RTP/RTCP used
consecutive numbers.

So, this document proposes a new SDP attribute (a=rtcp:<port>) that allows
this change in RTP, and the proposed change to SDP, RTCP had a great deal of
trouble traversing NATs in SDP-based applications (like SIP). The document
therefore considers NAT traversal as a motivating case for the addition of
this attribute. The use of this new attribute to facilitate NAT traversal is
intended to be used in concert with STUN (RFC 3489).

Working Group Summary

The MMUSIC WG supported the advancement of this document.

Protocol Quality

Jon Peterson reviewed this specification for the IESG.

RFC Editor Note:

2.1 The RTCP attribute
last paragraph

OLD:

The RTCP attribute MAY be used as a media level attribute; it MUST NOT be
used as a session level attribute.

NEW:

The RTCP attribute MAY be used as a media level attribute; it MUST NOT be
used as a session level attribute. Though the examples below relate to a
method that will return only unicast addresses, both unicast and multicast
values are valid.
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