IETF Logo Mail Archive

Re: [rtcweb] A problem with both A and B

Martin Thomson <martin.thomson@gmail.com> Tue, 21 May 2013 22:03 UTC

Return-Path: <martin.thomson@gmail.com>
X-Original-To: rtcweb@ietfa.amsl.com
Delivered-To: rtcweb@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 722011F0D3A for <rtcweb@ietfa.amsl.com>; Tue, 21 May 2013 15:03:01 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.6
X-Spam-Level:
X-Spam-Status: No, score=-2.6 tagged_above=-999 required=5 tests=[BAYES_00=-2.599, NO_RELAYS=-0.001]
Received: from mail.ietf.org ([12.22.58.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 0gPx2rGCbPxU for <rtcweb@ietfa.amsl.com>; Tue, 21 May 2013 15:03:01 -0700 (PDT)
Received: from mail-la0-x232.google.com (mail-la0-x232.google.com [IPv6:2a00:1450:4010:c03::232]) by ietfa.amsl.com (Postfix) with ESMTP id A68D21F0D37 for <rtcweb@ietf.org>; Tue, 21 May 2013 15:03:00 -0700 (PDT)
Received: by mail-la0-f50.google.com with SMTP id ed20so1290060lab.9 for <rtcweb@ietf.org>; Tue, 21 May 2013 15:02:59 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=mGxwBbJH5ur0kIjT9acILwKNl+VXTnBHZcqq+35ShnU=; b=xiRb5unxX+IydqwZhIOELNSQVfrjdlhXmIBU8wvQg6fRVwZMYw8wcBOoiLJlbX7UcM 42Pnc7rmCM13HUrwQ9HpqPThYhG8mnzBQhiwBs8QatomES2jlr9vWRX+84B/lRzM7bEh uwN0LM14IFs1gxL0cEKtVI8xnUgc+e3OIm/C0jgCQD/h4PGo6GIpKQKVqpyqgJP1/6b8 4GrE4gUG9JbAzzTxq7t0JBxKPY0MxjF70NfXTCihiFwM7vuZ0op28IVSUWu0Hmf+58GO 7lJi1Rh/EcIx7iQeALSrfBL2iemEWsUSjWHnA9vVfoEh+VXT3nA16nh4qlpcmhacf1sm WAtQ==
MIME-Version: 1.0
X-Received: by 10.112.204.194 with SMTP id la2mr2671582lbc.38.1369173779568; Tue, 21 May 2013 15:02:59 -0700 (PDT)
Received: by 10.112.235.233 with HTTP; Tue, 21 May 2013 15:02:59 -0700 (PDT)
In-Reply-To: <519BD580.7080205@alum.mit.edu>
References: <BLU403-EAS40305B2D015B786CC67EB9293AC0@phx.gbl> <CABkgnnXX3zoeKqjFxjsfMgaGGRM0JzymaeWfA13LEjUZ4tGF9Q@mail.gmail.com> <7594FB04B1934943A5C02806D1A2204B1C373EF0@ESESSMB209.ericsson.se> <519A4C9A.6020501@alum.mit.edu> <7594FB04B1934943A5C02806D1A2204B1C374F13@ESESSMB209.ericsson.se> <519BD580.7080205@alum.mit.edu>
Date: Tue, 21 May 2013 15:02:59 -0700
Message-ID: <CABkgnnVcQgK4OwqRb5iFUhQE_obuBh+wFrnYjRz4iK=r5gRY1A@mail.gmail.com>
From: Martin Thomson <martin.thomson@gmail.com>
To: Paul Kyzivat <pkyzivat@alum.mit.edu>
Content-Type: text/plain; charset="UTF-8"
Cc: "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] A problem with both A and B
X-BeenThere: rtcweb@ietf.org
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: Real-Time Communication in WEB-browsers working group list <rtcweb.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/rtcweb>, <mailto:rtcweb-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/rtcweb>
List-Post: <mailto:rtcweb@ietf.org>
List-Help: <mailto:rtcweb-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/rtcweb>, <mailto:rtcweb-request@ietf.org?subject=subscribe>
X-List-Received-Date: Tue, 21 May 2013 22:03:01 -0000

This is an excellent summary.

On 21 May 2013 13:13, Paul Kyzivat <pkyzivat@alum.mit.edu> wrote:
> AFAIK there is wide agreement that an RTP *session* can carry multiple RTP
> streams.
>
> An SDP O/A exchange negotiating an RTP m-line pair establishes an RTP
> session. There is disagreement whether it is permissible for the resulting
> RTP session to carry multiple RTP streams.

Nitpick:

As I understand it, there's a disagreement whether O/A allows for
creating multiple streams *in each negotiated direction*... as
determined by a=sendrecv/sendonly/recvonly/inactive.

In the Plan A view, there are 0 or 1 streams in the each "negotiated
open" direction.  The SSRC might change over time, but it maps to the
same rendering.

In the Plan B view, there are 0 or more streams in the each
"negotiated open" direction.  I believe that the assumption is that
every SSRC is a different rendering (in the absence of a=ssrc:...
previous-ssrc:...).

> The specs are ambiguous on this
> point. Clearly there are well identified cases where they do, and we aren't
> likely to rule those incorrect. Its also clear that some of these cases
> start out sending a single SSRC, and then later "add" another. (It may
> actually be a substitution.)

v2.23.0 | Report a Bug | By Email