Re: [rtcweb] JSEP: Relaxing SDP O/A rules?

Martin Thomson <martin.thomson@gmail.com> Tue, 02 October 2012 18:59 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 C3CD921F8587 for <rtcweb@ietfa.amsl.com>; Tue, 2 Oct 2012 11:59:56 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -3.699
X-Spam-Level:
X-Spam-Status: No, score=-3.699 tagged_above=-999 required=5 tests=[AWL=-0.100, BAYES_00=-2.599, RCVD_IN_DNSWL_LOW=-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 ACfPRf9NsPqE for <rtcweb@ietfa.amsl.com>; Tue, 2 Oct 2012 11:59:56 -0700 (PDT)
Received: from mail-lb0-f172.google.com (mail-lb0-f172.google.com [209.85.217.172]) by ietfa.amsl.com (Postfix) with ESMTP id E6E8021F850D for <rtcweb@ietf.org>; Tue, 2 Oct 2012 11:59:55 -0700 (PDT)
Received: by lbok13 with SMTP id k13so6091989lbo.31 for <rtcweb@ietf.org>; Tue, 02 Oct 2012 11:59:55 -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=HDxAxkZ8NYtQogdysfvyg4pf3k+wfs5Uv5ShYiLsmdA=; b=tB/f9pGM8lJZ7IZi+VcKo+spvmW+GuFGEWXXMhoOFYKjdOXnaNH2DpcZv+Nu/cwddE tMie1As992z9/GiJw34xP4aSWZaQD+nsmC48YNIU3BpK9rDNFHsnkdB1X1DnZrwTGr+J qsV8qlto+Y+057dXrgN9DyXvKfxRRzRBh8ZDtfcFq31T08GJbcwI3avopHWW84wYUL07 cfFYl4+Rg3MVro+bAVNnyYY1oKcM6eWE4+YrUusq2xHUkJIk9Aur7G1g9sSMagh0LeEs mih3EnryIF5e3HnFsA1LXaZfPWIP9rzcV0RXcfvHdP081+FTBkj0JLaXlEe3qpUsc4R/ DaHA==
MIME-Version: 1.0
Received: by 10.152.106.81 with SMTP id gs17mr15407290lab.2.1349204394815; Tue, 02 Oct 2012 11:59:54 -0700 (PDT)
Received: by 10.112.83.2 with HTTP; Tue, 2 Oct 2012 11:59:54 -0700 (PDT)
In-Reply-To: <7F2072F1E0DE894DA4B517B93C6A0585340A1E3AB1@ESESSCMS0356.eemea.ericsson.se>
References: <7F2072F1E0DE894DA4B517B93C6A0585340A1E3AB1@ESESSCMS0356.eemea.ericsson.se>
Date: Tue, 02 Oct 2012 11:59:54 -0700
Message-ID: <CABkgnnUFvw_J2+tvVBoHrzR9ZRkPT-6LhXvbaz_U1P7gqtJ4xw@mail.gmail.com>
From: Martin Thomson <martin.thomson@gmail.com>
To: Christer Holmberg <christer.holmberg@ericsson.com>
Content-Type: text/plain; charset="UTF-8"
Cc: "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] JSEP: Relaxing SDP O/A rules?
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, 02 Oct 2012 18:59:56 -0000

On 2 October 2012 11:00, Christer Holmberg
<christer.holmberg@ericsson.com> wrote:
> There has also been ideas about JSEP "relaxing" the SDP O/A rules.

JSEP already does that.

PRANSWER is probably the most obvious diversion, but it goes deeper.

There's a simple view of what JSEP is and it goes a little like this:

 - SDP provides a description of the session that you are going to create [1]

 - You need two SDP blobs so that you can get all the non-negotiated
parameters like crypto and candidate attributes

 - setLocalDescription and setRemoteDescription provide a way of
matching up two SDP blobs into a complete session description

 - negotiation is performed outside this machine, and the browser can
help you with that in two ways: providing createOffer and createAnswer
to build the SDP; and by nudging you with a negotiatedneeded event
when it learns of things that necessitate changes.

Obviously, it's a little more nuanced than that, but if you take this
view, you are more likely to get something to work.

--Martin

[1] Caveat: PRANSWER adds a layer of complexity to this by shifting
part of the session description to the offer rather than the answer