The Session Description Protocol (SDP) Content Attribute
RFC 4796

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: 'The SDP (Session Description 
         Protocol) Content Attribute' to Proposed Standard 

The IESG has approved the following document:

- 'The SDP (Session Description Protocol) Content Attribute '
   <draft-ietf-mmusic-sdp-media-content-07.txt> as a Proposed Standard

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

The IESG contact persons are Cullen Jennings and Jon Peterson.

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

Technical Summary

This document defines a new Session Description Protocol (SDP) 
media-level attribute, 'content'. The 'content' attribute defines the
content of the media stream in more detailed level than the media
description line. The sender of an SDP session description can
attach the 'content' attribute to one or more media streams. The
receiving application can then treat each media stream differently
(e.g., show it on a big screen or small screen) based on its 
content.

Working Group Summary

The draft is a product of the MMUSIC working group.

Protocol Quality

The draft received thorough review by Tom Taylor. The draft was 
brought to the attention of the ietf-types list, which raised no concerns.







Note to RFC Editor
 
OLD
   The 'content' attribute contains a token, which MAY be attached to a
   media stream by a sending application.  An application MAY attach a
   content attribute to any media stream it describes.  That attribute
   contains one or more tokens describing the content of the transmitted
   media stream to the receiving application.

NEW
   The 'content' attribute contains one or more tokens, 
   which MAY be attached to a
   media stream by a sending application.  An application MAY attach a
   content attribute to any media stream it describes.  

OLD:
Since the 'content' attribute does not have to be understood, an SDP
answer MAY contain 'content' attributes even if none were present in
the offer.  Similarly, the answer MAY contain no 'content' attributes
even if they were present in the offer.  Furthermore, the values of
'content' attributes does not need to match in an offer and an
answer.
NEW:
The 'content' attribute describes the data the application generating the
SDP session description intends to send over a particular media stream.
The 'content' values for both directions of a media stream do not need to
be the same. Therefore, an SDP answer MAY contain 'content' attributes
even if none were present in the offer.  Similarly, the answer MAY contain
no 'content' attributes even if they were present in the offer. 
Furthermore, the values of 'content' attributes does not need to match in
an offer and an answer.

OLD:

All these values can be used with any media type.  The application
can make decisions on how to handle a single media stream based on
both the media type and the value of the 'content' attribute.
Therefore the situation where one value of 'content' attribute occurs
more than once in a single session descriptor is not problematic.

NEW:

All these values can be used with any media type. We chose not to
restrict each value to a particular set of media types in order not to
prevent applications from using innovative combinations of a given value
with different media types.

The application can make decisions on how to handle a single media
stream based on both the media type and the value of the 'content'
attribute. If the application does not implement any special logic for
the handling of a given media type and 'content' value combination, it
applies the application's default handling for the media type.

Note that the same 'content' attribute value can occur more than once in
a single session description.