Re: [rtcweb] Clarification on offer/answer in jsep-01

Kaiduan Xie <kaiduanx@gmail.com> Wed, 29 August 2012 13:58 UTC

Return-Path: <kaiduanx@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 5520E11E80D1 for <rtcweb@ietfa.amsl.com>; Wed, 29 Aug 2012 06:58:31 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -3.599
X-Spam-Level:
X-Spam-Status: No, score=-3.599 tagged_above=-999 required=5 tests=[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 uiePIHwPGcdn for <rtcweb@ietfa.amsl.com>; Wed, 29 Aug 2012 06:58:29 -0700 (PDT)
Received: from mail-ob0-f172.google.com (mail-ob0-f172.google.com [209.85.214.172]) by ietfa.amsl.com (Postfix) with ESMTP id 92F6011E808E for <rtcweb@ietf.org>; Wed, 29 Aug 2012 06:58:29 -0700 (PDT)
Received: by obbwc20 with SMTP id wc20so1195811obb.31 for <rtcweb@ietf.org>; Wed, 29 Aug 2012 06:58:29 -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=PsVr8Sxm5ISSI8FQilW8Z5dYoSLtBZQKnoqK7EuSsRo=; b=cLWt6glMyjk9uKNZQ2M+wA8mf6Ol4UGQPRpCfRp3Hy9pJBhu+mMNELCxSV3/6RYleE x+LLrbeicl0SOZdwP+MmGbFNSLrrDLsYn/K0+QQxYfnVfoVTf6PpA6ImPojjdtLHDhdd ZLBlVAX9/BU0dAZvOv2G09ZNZPZYZPvRY+OeFrDbR19hYwLGhyeAT1Mt6WoS0ZYY1EGS g1N/6dxVxCq4gXj7eVzlWu8cZ5mxoECBbtoCp2j+CpFCfd3Czv5yxc65Cq6XZpW1B8gu 5WtB+DqRTVkV31w8yKLvK9lEmsXxx4I9NrWDAgZc4moEyzDbqr6lJqur5YPTjHrtCLnc 6hjA==
MIME-Version: 1.0
Received: by 10.60.171.174 with SMTP id av14mr1295100oec.61.1346248709252; Wed, 29 Aug 2012 06:58:29 -0700 (PDT)
Received: by 10.76.23.129 with HTTP; Wed, 29 Aug 2012 06:58:29 -0700 (PDT)
In-Reply-To: <DA165A8A2929C6429CAB403A76B573A514697939@szxeml534-mbx.china.huawei.com>
References: <CACKRbQfXam_QqsUdMif-zR0uuiM6VFwP-VDy0q7f_r6gdV_-VQ@mail.gmail.com> <A9BAC738-4077-450F-ACC4-DD246292A2EF@microsoft.com> <AB704ACB-877F-4F55-B806-AF4EA771EDD3@iii.ca> <DA165A8A2929C6429CAB403A76B573A514697939@szxeml534-mbx.china.huawei.com>
Date: Wed, 29 Aug 2012 09:58:29 -0400
Message-ID: <CACKRbQcP=LDvTuAz50ucoB9Ocb09-9kXKfDwvY8R-Fqw-yu9fA@mail.gmail.com>
From: Kaiduan Xie <kaiduanx@gmail.com>
To: Lishitao <lishitao@huawei.com>
Content-Type: text/plain; charset=ISO-8859-1
Cc: "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] Clarification on offer/answer in jsep-01
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: Wed, 29 Aug 2012 13:58:31 -0000

> The next sentence just after this one
> " The answerer can send back zero or more
>    provisional answers, and finally end the offer-answer exchange by
>    sending a final answer."
> does not describe quite well either, right?
>
> AFAIK , the answerer can send back zero or more provisional answers, but they are not all SDP answers,

If we look the Section 12.1.1 of RFC5245 (ICE),

  "If an offer is received in an INVITE request, the answerer SHOULD
   begin to gather its candidates on receipt of the offer and then
   generate an answer in a provisional response once it has completed
   that process.  ICE requires that a provisional response with an SDP
   be transmitted reliably.  This can be done through the existing
   Provisional Response Acknowledgment (PRACK) mechanism [RFC3262] or
   through an optimization that is specific to ICE ..."

Here provisional response carriers answer, but the offer/answer
exchange is completed. Offerer can send PRACK with SDP to updates the
offer, and the answerer replies answer in 200 of PRACK, but this is a
new round of offer/answer exchange.

Also from the RFC 6337 (Session Initiation Protocol (SIP) Usage of the
Offer/Answer Model
), we can't find the case where the answerer sends multiple different
answers for one offer.

So it seems that we also need clarification on the following,

"The answerer can send back zero or more provisional answers, and
finally end the offer-answer exchange by
  sending a final answer."

/Kaiduan

On Tue, Aug 28, 2012 at 10:50 PM, Lishitao <lishitao@huawei.com> wrote:
>
>
>> -----Original Message-----
>> From: rtcweb-bounces@ietf.org [mailto:rtcweb-bounces@ietf.org] On Behalf
>> Of Cullen Jennings
>> Sent: Tuesday, August 28, 2012 8:58 PM
>> To: Francois Audet
>> Cc: rtcweb@ietf.org
>> Subject: Re: [rtcweb] Clarification on offer/answer in jsep-01
>>
>>
>> On Aug 27, 2012, at 10:48 PM, Francois Audet <francois.audet@skype.net>
>> wrote:
>>
>> >> "As in [RFC3264], an offerer can send an offer, and update it as long
>> >> as it has not been answered."
>>
>> yah that won't work or all the reasons mentioned before and in my opinion does
>> not represent the WG consensus. BTW - that was added in the -01 version of
>> the draft and submitted without me ever seeing it - I'd be happy to fix it but I
>> don't have the source for the draft. Chairs?
>>
>
> The next sentence just after this one
> " The answerer can send back zero or more
>    provisional answers, and finally end the offer-answer exchange by
>    sending a final answer."
> does not describe quite well either, right?
>
> AFAIK , the answerer can send back zero or more provisional answers, but they are not all SDP answers,
>
> and I don't find any place in RFC 3264 has the definition about "final answer".
>
> shitao
> _______________________________________________
> rtcweb mailing list
> rtcweb@ietf.org
> https://www.ietf.org/mailman/listinfo/rtcweb