[rtcweb] Adding previously "discarded" codecs in SDP renegotiation

Iñaki Baz Castillo <ibc@aliax.net> Mon, 28 March 2016 21:26 UTC

Return-Path: <ibc@aliax.net>
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 3B67712D0C1 for <rtcweb@ietfa.amsl.com>; Mon, 28 Mar 2016 14:26:17 -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=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, RCVD_IN_DNSWL_LOW=-0.7] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=aliax-net.20150623.gappssmtp.com
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id w8boSmg7j6Ew for <rtcweb@ietfa.amsl.com>; Mon, 28 Mar 2016 14:26:14 -0700 (PDT)
Received: from mail-qk0-x236.google.com (mail-qk0-x236.google.com [IPv6:2607:f8b0:400d:c09::236]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 85D6612D97B for <rtcweb@ietf.org>; Mon, 28 Mar 2016 14:26:08 -0700 (PDT)
Received: by mail-qk0-x236.google.com with SMTP id i4so91752720qkc.3 for <rtcweb@ietf.org>; Mon, 28 Mar 2016 14:26:08 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=aliax-net.20150623.gappssmtp.com; s=20150623; h=mime-version:from:date:message-id:subject:to :content-transfer-encoding; bh=VqtrDDYvd2NTuFxeF2LP+I9B7CNzo2Iqekta15bZKlQ=; b=WT41laBGlyNFsbhCvG9kEpXg0o0oTd8+ZrRNLuxK0SOVZmtV23CsvLiy12qMpZq9s7 CgL5vJ3abWZ0iNiPKk9PbV3Ojz2kRsVH1rGwnZEcdL9chA/DkzvbJvSY6Wm7YibNLv3y g3zO37OvM5cdFkLo4N8BJ+eHu9S9CtqGJgBqnUJXxmg+10meiztORWw86ZIUnXY93Gnb 2Eln1tOpUbaXjdQIEftaxJj/UjVac4dXbE/JzW5vRpr6ivvRVTMJ0MBdM9BcS0/Z1ZFg Jg7RXiQG5SNV/adHj+FNixil867RchdAFoTHWNIvOW0TwvMf8sNtvLl6d/5gGYe3j4y1 FJdg==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:from:date:message-id:subject:to :content-transfer-encoding; bh=VqtrDDYvd2NTuFxeF2LP+I9B7CNzo2Iqekta15bZKlQ=; b=EJhydLmIwQ5BsohUFbLntWejBBrD48DJ4ZefVB4BmsJm8Tt32o+n2BnJk9O+e7WN3z 75aNX5AgqHI489KIFA6LkhK1fwBZp6eo5Ak7rWxarrUQFxfzX+Znq6zUEKLcONkSvQU7 +ixP532gORF8MQojdFECvmeX2mSaC04tMo02ZMhPMbo9uK9SWw2HLQ70GbB9s0cmMh/7 /vLgauXsU12DKjm5NAQzS8ew8PpLkFe3Ef+ymwUbQjHWjgw+HtYjZwYbdisgJHocX3GZ vD2lQzm71qCLahHvzQTtI/AB+2iO3VtCdrvN57NrdpEsze5S2hZjp4N48bbYfFRu6Sau IVSQ==
X-Gm-Message-State: AD7BkJIV/SoDebSFnOJotKFp+9ITqymIVV697Um00T4iHgIpBQBlq+od8/+g/2SCKB9K3Ede8GhClMdfAiMUtQ==
X-Received: by 10.37.92.215 with SMTP id q206mr14407527ybb.172.1459200367566; Mon, 28 Mar 2016 14:26:07 -0700 (PDT)
MIME-Version: 1.0
Received: by 10.37.201.132 with HTTP; Mon, 28 Mar 2016 14:25:48 -0700 (PDT)
From: Iñaki Baz Castillo <ibc@aliax.net>
Date: Mon, 28 Mar 2016 23:25:48 +0200
Message-ID: <CALiegfmxG-NFoQdQ0HZi80kB4J4_G0YnYXbCYxwz6TPEg8+ACA@mail.gmail.com>
To: "rtcweb@ietf.org" <rtcweb@ietf.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Archived-At: <http://mailarchive.ietf.org/arch/msg/rtcweb/4yA3J7fgOmzFuy-TH192o2--zBA>
Subject: [rtcweb] Adding previously "discarded" codecs in SDP renegotiation
X-BeenThere: rtcweb@ietf.org
X-Mailman-Version: 2.1.17
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: <https://mailarchive.ietf.org/arch/browse/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: Mon, 28 Mar 2016 21:26:17 -0000

Hi, the scenario is the following:

- Alice sends SDP offer to Bob by offering VP8 (PT 100) and H264
packetization-mode=1 (PT 101).

- Bob answers with just VP8 (let's say it sets PT 110) in the m= line,
regardless he also supports H264.

At this time Alice must send VP8 (PT 110) to Bob, and Bob must send
VP8 (PT 100) to Alice. Fine.

Later Bob wants to change to H264, so he sends a SDP reoffer to Alice
by just offering H264 packetization-mode=1 (PT 111).

Assuming this is valid (re-enabling a previously discarded codec),
Alice answers the reoffer with just H264 (PT 101).


Is this valid? And a more pragmatic questions: should I assume that
current WebRTC implementations would support this scenario?

Thanks a lot.


-- 
Iñaki Baz Castillo
<ibc@aliax.net>