[MMUSIC] SCTP question: Where does it multiplex?

Harald Alvestrand <harald@alvestrand.no> Fri, 02 November 2012 10:39 UTC

Return-Path: <harald@alvestrand.no>
X-Original-To: mmusic@ietfa.amsl.com
Delivered-To: mmusic@ietfa.amsl.com
Received: from localhost (localhost []) by ietfa.amsl.com (Postfix) with ESMTP id 940CC21F93A7 for <mmusic@ietfa.amsl.com>; Fri, 2 Nov 2012 03:39:11 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -110.599
X-Spam-Status: No, score=-110.599 tagged_above=-999 required=5 tests=[BAYES_00=-2.599, RCVD_IN_DNSWL_HI=-8, USER_IN_WHITELIST=-100]
Received: from mail.ietf.org ([]) by localhost (ietfa.amsl.com []) (amavisd-new, port 10024) with ESMTP id vdOcAgClYpbz for <mmusic@ietfa.amsl.com>; Fri, 2 Nov 2012 03:39:10 -0700 (PDT)
Received: from eikenes.alvestrand.no (eikenes.alvestrand.no []) by ietfa.amsl.com (Postfix) with ESMTP id 4911621F9395 for <mmusic@ietf.org>; Fri, 2 Nov 2012 03:39:08 -0700 (PDT)
Received: from localhost (localhost []) by eikenes.alvestrand.no (Postfix) with ESMTP id 7432E39E173 for <mmusic@ietf.org>; Fri, 2 Nov 2012 11:39:06 +0100 (CET)
X-Virus-Scanned: Debian amavisd-new at eikenes.alvestrand.no
Received: from eikenes.alvestrand.no ([]) by localhost (eikenes.alvestrand.no []) (amavisd-new, port 10024) with ESMTP id iUekpUzIvQ7a for <mmusic@ietf.org>; Fri, 2 Nov 2012 11:39:05 +0100 (CET)
Received: from [] (unknown []) by eikenes.alvestrand.no (Postfix) with ESMTPSA id 9A6E039E020 for <mmusic@ietf.org>; Fri, 2 Nov 2012 11:39:05 +0100 (CET)
Message-ID: <5093A2C9.9040001@alvestrand.no>
Date: Fri, 02 Nov 2012 11:39:05 +0100
From: Harald Alvestrand <harald@alvestrand.no>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121011 Thunderbird/16.0.1
MIME-Version: 1.0
To: mmusic <mmusic@ietf.org>
Content-Type: text/plain; charset="ISO-8859-1"; format="flowed"
Content-Transfer-Encoding: 7bit
Subject: [MMUSIC] SCTP question: Where does it multiplex?
X-BeenThere: mmusic@ietf.org
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: Multiparty Multimedia Session Control Working Group <mmusic.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/mmusic>, <mailto:mmusic-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/mmusic>
List-Post: <mailto:mmusic@ietf.org>
List-Help: <mailto:mmusic-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/mmusic>, <mailto:mmusic-request@ietf.org?subject=subscribe>
X-List-Received-Date: Fri, 02 Nov 2012 10:39:11 -0000

As currently specified, the DTLS/SCTP protocol is carefully specified in 
such a way that it can ride on the same 5-tuple as an SRTP session. I'd 
like to keep that property when we SDP-negotiate it.

The proposed syntax for DTLS/SCTP seems to be

m=<something, likely application> <port number> DTLS/SCTP <fmt data, 
mostly meaningless>

I see two ways to define this as a multiplex:

- Give the same port number as another m= line in the same SDP session
- Give a meaningless port number, and use the a=group:BUNDLE (of 
whatever flavor) to give which port number it's actually multiplexed 
together with.

The best way to do this may be obvious after the BUNDLE discussion, but 
in case there are other considerations .... are there thoughts?