Re: [rtcweb] An input for discussing congestion control (Fwd: New Version Notification for draft-alvestrand-rtcweb-congestion-00.txt)

Soo-Hyun Choi <soohyun.choi@cl.cam.ac.uk> Tue, 20 September 2011 12:34 UTC

Return-Path: <s.choi@daemon.or.kr>
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 C96FC21F8C71 for <rtcweb@ietfa.amsl.com>; Tue, 20 Sep 2011 05:34:23 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.977
X-Spam-Level:
X-Spam-Status: No, score=-2.977 tagged_above=-999 required=5 tests=[AWL=0.000, BAYES_00=-2.599, FM_FORGED_GMAIL=0.622, RCVD_IN_DNSWL_LOW=-1]
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 PRDL2FPTSlx0 for <rtcweb@ietfa.amsl.com>; Tue, 20 Sep 2011 05:34:22 -0700 (PDT)
Received: from mail-fx0-f44.google.com (mail-fx0-f44.google.com [209.85.161.44]) by ietfa.amsl.com (Postfix) with ESMTP id 6A74A21F8C6C for <rtcweb@ietf.org>; Tue, 20 Sep 2011 05:34:22 -0700 (PDT)
Received: by fxd18 with SMTP id 18so550598fxd.31 for <rtcweb@ietf.org>; Tue, 20 Sep 2011 05:36:46 -0700 (PDT)
Received: by 10.223.38.196 with SMTP id c4mr1275962fae.32.1316522206351; Tue, 20 Sep 2011 05:36:46 -0700 (PDT)
Received: from mail-bw0-f44.google.com (mail-bw0-f44.google.com [209.85.214.44]) by mx.google.com with ESMTPS id f10sm1332381fac.14.2011.09.20.05.36.44 (version=SSLv3 cipher=OTHER); Tue, 20 Sep 2011 05:36:45 -0700 (PDT)
Received: by bkaq10 with SMTP id q10so529445bka.31 for <rtcweb@ietf.org>; Tue, 20 Sep 2011 05:36:44 -0700 (PDT)
Received: by 10.204.130.130 with SMTP id t2mr532489bks.223.1316522204221; Tue, 20 Sep 2011 05:36:44 -0700 (PDT)
MIME-Version: 1.0
Received: by 10.205.81.10 with HTTP; Tue, 20 Sep 2011 05:36:24 -0700 (PDT)
In-Reply-To: <4E787D56.8060106@alvestrand.no>
References: <4E649FBD.1090001@alvestrand.no> <4E734E89.5010105@ericsson.com> <4E766C4C.2020201@jesup.org> <CAEdus3LcjV9x+gLdZm5vwKhh-ge6xzfWSEB_NxcHe1Gz_5DZ8g@mail.gmail.com> <CAOhzyf=MqsgsGUi521oJ5N6+T+K1N01MjeHYPpX_VZK8uyQksw@mail.gmail.com> <CAKkvrEkx0mqnDWqNYse3r9WUMbYKNZhrBqQ0SPUAnTtKrA5bLg@mail.gmail.com> <CAOhzyf=_n3VhNi1GgxdKJpyzEMLORcKX2499+YZHQnGqYURxjg@mail.gmail.com> <CAKkvrEnXxoiJZJ3a3eg_Ybz0POCM+UTxU7nnWCf8Xt331jiXLA@mail.gmail.com> <4E787D56.8060106@alvestrand.no>
From: Soo-Hyun Choi <soohyun.choi@cl.cam.ac.uk>
Date: Tue, 20 Sep 2011 21:36:24 +0900
Message-ID: <CAKkvrEnpMusPu8py2-98NffDY493z=tA_giW9X-p6c1LtgL+XA@mail.gmail.com>
To: Harald Alvestrand <harald@alvestrand.no>
Content-Type: text/plain; charset=ISO-8859-1
Cc: rtcweb@ietf.org
Subject: Re: [rtcweb] An input for discussing congestion control (Fwd: New Version Notification for draft-alvestrand-rtcweb-congestion-00.txt)
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, 20 Sep 2011 12:34:23 -0000

Harald,

On Tue, Sep 20, 2011 at 20:47, Harald Alvestrand <harald@alvestrand.no> wrote:
>
> let's avoid unquantifiable terms in our discussions. "A little more careful"
> is an unquantifiable term.
>
> If we want to say "I think the algorithm must guarantee that the bandwidth
> estimate is updated within 1.5 seconds when the available bandwidth changes
> from 2 Mbit/sec to 1 Mbit/sec", let's say something like that - focus on
> what the requirements are.
>
> We can always be a little more careful. But it doesn't tell us when we're
> close enough.
>

Sorry if my previous email looked that way to you (of course, I didn't
mean to just pray for the mere hope). I was talking about some general
CC principles in the high level for real-time interactive multimedia
applications, like some of us did too in this thread.

One of the critical metrics of a delay-based CC algo is an accurate
measurement of inter-packet interval (IPI) and timely report of IPI to
the sender so it can update the send rate correctly, which we all
agreed in this email thread. Although everyone in this list seemed to
aware of this, I have highlighted again that the relatively
course-grained RTCP carrying the IPI measurement data can cause
instability at the encoder's output bitrate due to the following
reason.


> I.e., Inaccurate BW estimation could lead into providing inaccurate
> information about the available BW to the upper layer, which
> eventually result in instability at the codec's encoding rate.


So, my original question/suggestion was why not use AVPF (which is
smaller packet than the standard RTCP) to generate/report more
frequently to the sender in your algorithm. Or alternatively, I have
already designed a window-version's of TFRC that re-introduces a
TCP-like Ack-clocking, so-called TFWC (TCP-Friendly Window-based CC),
which performs reasonably well (as good as TFRC) for the similar
situations (RTC environment).

I would like to ask to this list (or Harald) if suggesting alternative
CC algo idea could fit into the RTCWEB Charter's scope - if so, I
could elaborate more by writing an I-D or so. In the mean time, you
could check my document at http://tfwc.hackerslab.eu/ if you are
interested.

Kind regards,
Soo-Hyun