A Transport Independent Bandwidth Modifier for the Session Description Protocol (SDP)
RFC 3890

Approval announcement
Draft of message to be sent after approval:

From: The IESG <iesg-secretary@ietf.org>
To: IETF-Announce <ietf-announce@ietf.org>
Cc: Internet Architecture Board <iab@iab.org>,
    RFC Editor <rfc-editor@rfc-editor.org>, 
    mmusic mailing list <mmusic@ietf.org>, 
    mmusic chair <mmusic-chairs@tools.ietf.org>
Subject: Protocol Action: 'A Transport Independent Bandwidth 
         Modifier for the Session Description Protocol (SDP)' to Proposed 
         Standard 

The IESG has approved the following document:

- 'A Transport Independent Bandwidth Modifier for the Session Description 
   Protocol (SDP) '
   <draft-ietf-mmusic-sdp-bwparam-07.txt> as a Proposed Standard

This document is the product of the Multiparty Multimedia Session Control 
Working Group. 

The IESG contact persons are Jon Peterson and Cullen Jennings.

A URL of this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-ietf-mmusic-sdp-bwparam-07.txt

Technical Summary
 
Although the Session Description Protocol (SDP) already has a "bandwidth" 
parameter(the b= line) to characterize the amount of bandwidth a particular 
session will require, it is difficult for the receiver of an SDP message to 
know what values the creator of SDP used to factor the overhead into the 
total session bandwidth value. This becomes especially problematic in the 
presence of middleboxes that convert between IPv4 and IPv6. The use of 
session header compression (such as cRTP) on a per-hop basis at the sender 
side can also confuse recipients of SDP, since the assessment of total 
bandwidth on the sender side will assume header compression that probably 
isn't available at the receiver side. Similar problems exist for calculating 
RTCP bandwidth.

Accordingly, this document defines a Transport Independent Application 
Specific Maximum (TIAS) bandwidith modifier that can appear in the b= line o
SDP, and a new attribute, "maxrate", that is correlated with SDP media (m=) 
lines. Together, these two parameters enable recipients of SDP to make a muc
more exact and universal assessment of the bandwidth that a session will 
require.
 
Working Group Summary
 
This MMUSIC Working Group supported the advancement of this specification.
 
Protocol Quality
 
This document has been reviewed for the IESG by Jon Peterson.