Subject: [MMUSIC] The future of initial offer

From: Christer Holmberg <[email-masked]>
Date: Wed, 20 Jun 2018 10:11:35 +0000

Hi,

As you may now, during the IESG review of BUNDLE an issue was raised regarding the “Initial offer” procedures that need to be in the SDP O/A procedures for new SDP attributes/features.

The problem is that, in some cases (RFC 3261) “initial offer” refers to the first SDP offer of a session. But, for new SDP attributes, “initial offer” refers (at least in my understanding) to the first offer where a SDP attribute is included in an offer (which may or may not be the first offer of the session).

I have been asked by the chairs to lead a discussion about this in Montreal, and to come up with a suggestion on how we could make things more clear.

Note that there is no draft e.g., at this point. Whether one will later be produced depends on the outcome of the discussions.

Now, in my opinion there are a few key background facts that we need to build the base upon:

  1.  We need to separate between an offer where an SDP attribute is first added to an m- line (note that SDP attributes may be added to different m- lines in different offers) and an offer where an attribute has previously been added to an m- section (currently called “subsequent offer”).
  2.  In the case where an attribute has previously been added to an m- section, when a subsequent offer is sent the attribute can be: unchanged, modified or removed.

In addition, we focus very much on SDP attributes, but perhaps we should talk more about features. Because, when a feature is added to an m- section, it may include multiple SDP attributes, other SDP information elements etc.

So, a suggestion for a new SDP O/A structure could look something like:

X. SDP Offer/Answer Considerations
X.1 Enabling feature X
X.1.1 Sending offer
X.1.2 Sending answer
X.1.3 Receiving answer
X.2 Maintain feature X //subsequent offer where attribute value is not changed
X.2.1 Sending offer
X.2.2 Sending answer
X.2.3 Receiving answer
X.3 Modify feature X //subsequent offer where attribute value is changed
X.3.1 Sending offer
X.3.2 Sending answer
X.3.3 Receiving answer
X.4 Remove feature X //subsequent offer where attribute value is removed (in case there is no default value defined)
X.4.1 Sending offer
X.4.2 Sending answer
X.4.3 Receiving answer

Regards,

Christer