Re: [MMUSIC] M-lines: Wikifying it - a=label

Paul Kyzivat <pkyzivat@alum.mit.edu> Mon, 03 December 2012 21:37 UTC

Return-Path: <pkyzivat@alum.mit.edu>
X-Original-To: mmusic@ietfa.amsl.com
Delivered-To: mmusic@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id B005E21F893A for <mmusic@ietfa.amsl.com>; Mon, 3 Dec 2012 13:37:54 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -0.06
X-Spam-Level:
X-Spam-Status: No, score=-0.06 tagged_above=-999 required=5 tests=[AWL=-0.223, BAYES_00=-2.599, FH_RELAY_NODNS=1.451, HELO_MISMATCH_NET=0.611, J_CHICKENPOX_15=0.6, RDNS_NONE=0.1]
Received: from mail.ietf.org ([64.170.98.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id A0hqdVSBltks for <mmusic@ietfa.amsl.com>; Mon, 3 Dec 2012 13:37:54 -0800 (PST)
Received: from qmta09.westchester.pa.mail.comcast.net (qmta09.westchester.pa.mail.comcast.net [IPv6:2001:558:fe14:43:76:96:62:96]) by ietfa.amsl.com (Postfix) with ESMTP id E64A621F85B8 for <mmusic@ietf.org>; Mon, 3 Dec 2012 13:37:53 -0800 (PST)
Received: from omta22.westchester.pa.mail.comcast.net ([76.96.62.73]) by qmta09.westchester.pa.mail.comcast.net with comcast id X0pQ1k0011ap0As599dtQe; Mon, 03 Dec 2012 21:37:53 +0000
Received: from Paul-Kyzivats-MacBook-Pro.local ([50.138.229.164]) by omta22.westchester.pa.mail.comcast.net with comcast id X9dt1k00E3ZTu2S3i9dtYk; Mon, 03 Dec 2012 21:37:53 +0000
Message-ID: <50BD1BB0.90307@alum.mit.edu>
Date: Mon, 03 Dec 2012 16:37:52 -0500
From: Paul Kyzivat <pkyzivat@alum.mit.edu>
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:17.0) Gecko/17.0 Thunderbird/17.0
MIME-Version: 1.0
To: mmusic@ietf.org
References: <50B624CC.4010501@alvestrand.no> <50B6704F.2000108@alum.mit.edu> <50BA1B90.2010905@alvestrand.no> <50BA6065.3090000@alum.mit.edu> <50BC87C6.9030600@alvestrand.no>
In-Reply-To: <50BC87C6.9030600@alvestrand.no>
Content-Type: text/plain; charset="ISO-8859-1"; format="flowed"
Content-Transfer-Encoding: 7bit
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=comcast.net; s=q20121106; t=1354570673; bh=aPN6hF0rEg/cpG9YDx1dwtzFs54yTLSlxKltv6S5Dt4=; h=Received:Received:Message-ID:Date:From:MIME-Version:To:Subject: Content-Type; b=nHW/6hvEcyTIHDNamzn2XCTNq5kQtb9b7P2qcwBn/Zm/9fgVOIE2D+aWANMJRpmNA REGCS1gprkGNCpI6JA8Z9PlfdkeUvc1/BEZ4VJp0D2EEW9VPMIhgz0zzkfXspG+/t8 +PvqMiZfew1Eu3RIpDOZ7HWg5QNZGvOe49QmEPcJN2zlPpUn9alOMd8rd+G8/oCoBH fiXBH8j835NYfZ8+bPkhLoi22kqMxte7jshHN5LVmJnKzQ4+aKf7HIRClhRkCBm1lv e4RJmm3uBraqW36PiO1AO5sUfQYDL4O/WPNAOT9R92xxxNFnsSltVxOi/62OTe8KHn AurjefU8hFKog==
Subject: Re: [MMUSIC] M-lines: Wikifying it - a=label
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: Mon, 03 Dec 2012 21:37:54 -0000

On 12/3/12 6:06 AM, Harald Alvestrand wrote:

>>>> Regarding a=label: This could be any of T/F/M, depending on
>>>> application use. I think we must assume T, and consider an alternative
>>>> for F. (And for M if we think it is needed.)
>>
>> I may have misunderstood your intended meaning for M. I assume you
>> meant all RTP streams of the same media type (audio or video) within a
>> single 5-tuple.
> I was thinking "same payload type", since the payload type is the
> distinguisher used for groups of flows that should have the same
> parameters in many cases.
>>
>>> The claim that a=label can be used to mark flows makes it F.
>>
>> a=label is a media-level attribute, so it is bound to an m-line.
>>
>> In the absence of bundle, regardless of whether the corresponding RTP
>> session has one or several flows. The m-line has a particular media
>> type, so I guess it could be viewed as either T or M.
> The reason why we're having the discussion is that we have two competing
> definitons of what an M-line should be, and need to choose one.
> So arguing from whether or not something associates with an M-line is
> not useful.
>>
>> Some applications of a=label may assume or require that the labeled
>> m-line contain only one RTP stream. If so, then perhaps the label
>> could be considered to be F. But we can't really know that.
> What applications of a=label do you know about?

I know of two: BFCP and SIPREC.

In BFCP the label is used to associate a bfcp floor with an m-line. I 
don't think it matters whether that m-line carries one or several RTP 
streams.

We can speculate how we would want this to work in the case that several 
media m-lines were bundled together. I don't know - too many hypotheticals.

In SIPREC, the label is used to associate an m-line with certain 
metadata that describes the source of the media being sent via that 
m-line. The siprec group has intentionally kept the question of whether 
the content in that m-line is a single RTP stream or if it can be 
several multiplexed together. There is nothing to forbid multiplexing, 
but no specification of what it means either.

SIPREC *might* have specified use of bundle, or explicitly specified 
multiplexing of RTP streams over a single m-line, if those things were 
better defined. But how it might eventually use bundle or mmt is again a 
hypothetical right now.

A problem for siprec is that it is recording media from existing sip 
sessions, without any knowledge of how they use SDP and RTP. We could 
find it recording a call initiated with RTCWEB that uses bundle or mmt. 
Most likely siprec will need to be extended to support that, though I 
wish that wasn't so.

	Thanks,
	Paul