Re: [AVTCORE] RFC3550: RTP Jitter value calculation

Kevin Gross <kevin.gross@avanw.com> Thu, 27 March 2014 21:37 UTC

Return-Path: <kevin.gross@avanw.com>
X-Original-To: avt@ietfa.amsl.com
Delivered-To: avt@ietfa.amsl.com
Received: from localhost (ietfa.amsl.com [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 19C541A06A8 for <avt@ietfa.amsl.com>; Thu, 27 Mar 2014 14:37:59 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -0.498
X-Spam-Level:
X-Spam-Status: No, score=-0.498 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, FM_FORGED_GMAIL=0.622, HTML_MESSAGE=0.001, SPF_NEUTRAL=0.779] autolearn=no
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 VeAuokMYgK8M for <avt@ietfa.amsl.com>; Thu, 27 Mar 2014 14:37:57 -0700 (PDT)
Received: from qmta14.emeryville.ca.mail.comcast.net (qmta14.emeryville.ca.mail.comcast.net [IPv6:2001:558:fe2d:44:76:96:27:212]) by ietfa.amsl.com (Postfix) with ESMTP id A45EB1A03F6 for <avt@ietf.org>; Thu, 27 Mar 2014 14:37:57 -0700 (PDT)
Received: from omta23.emeryville.ca.mail.comcast.net ([76.96.30.90]) by qmta14.emeryville.ca.mail.comcast.net with comcast id iisX1n0031wfjNsAEldwyL; Thu, 27 Mar 2014 21:37:56 +0000
Received: from mail-yk0-f177.google.com ([209.85.160.177]) by omta23.emeryville.ca.mail.comcast.net with comcast id ilbv1n0043pwec18jlbvwJ; Thu, 27 Mar 2014 21:35:55 +0000
Received: by mail-yk0-f177.google.com with SMTP id q200so2933889ykb.22 for <avt@ietf.org>; Thu, 27 Mar 2014 14:35:54 -0700 (PDT)
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=6wH5XRKVOjyy91KZ8x8sYlaMeEH6MfvF71nPvPUNia0=; b=fW/wKyMPQBh1Yqd6HXcqLOPandgqPCRCLIywas3DcQadc9LQoKfVZPxb9xa3nvMPFm Se3eRw7YVmMo1YPZ6uoeRJwyKS/MO+hUiQLtYCZpnpfdeCn7DtjvqAJlMBrdO/aTqRuW Py+awDA4m3hpB97RXtaXggEeMM9EWxg3plXbNAs8PWsOTdYWCSRYOlGpMgwBKkx3mzIy lQQw8mL7XBOP24d5d6j/MHU4p9ir5UE0rqEJvXMi4Gg9V/jM9rSFV6P/fXWfk2hPDlw3 +72CMtbJSPIJluiqOGvzcv9Gobu9mZv0IAh3S36/Epl7KS29LLBBPZe0U+CREXTb0qhN 0tAA==
MIME-Version: 1.0
X-Received: by 10.236.139.70 with SMTP id b46mr5743024yhj.63.1395956154960; Thu, 27 Mar 2014 14:35:54 -0700 (PDT)
Received: by 10.170.216.197 with HTTP; Thu, 27 Mar 2014 14:35:54 -0700 (PDT)
In-Reply-To: <alpine.BSF.2.00.1403261007240.74781@hsa.packetdesign.com>
References: <349A84ECFABF2A4F98D9102C4AFD83FA55D63BAF@IL-EXCH-01.dspg.com> <CALw1_Q0wpm==DwcK7pfBfUccWZeyoiDS9bPO6-y3XomVhXHc5g@mail.gmail.com> <349A84ECFABF2A4F98D9102C4AFD83FA55D63D91@IL-EXCH-01.dspg.com> <alpine.BSF.2.00.1403261007240.74781@hsa.packetdesign.com>
Date: Thu, 27 Mar 2014 15:35:54 -0600
Message-ID: <CALw1_Q3phK9p+gRwcpg_tzUYs_b80pnNY8wULH-Vh+F53+qaTw@mail.gmail.com>
From: Kevin Gross <kevin.gross@avanw.com>
To: Stephen Casner <casner@acm.org>
Content-Type: multipart/alternative; boundary="20cf303dd434bd11ba04f59d5e3b"
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=comcast.net; s=q20140121; t=1395956276; bh=6wH5XRKVOjyy91KZ8x8sYlaMeEH6MfvF71nPvPUNia0=; h=Received:Received:Received:MIME-Version:Received:Date:Message-ID: Subject:From:To:Content-Type; b=eNsrTMlXuXrsNWt+Kohvy20xZjjs26ZGeoS3KheferZONHxJBuXafFdr8AQ5PCkl4 TETJnEl/2t0d8rVCPbRW8X8NKgQg+44x8yoCPqKKlhlUKpkmslzwdACDi6Qx05zvA5 5AlISVnSFkJ29hrtkFb2uGvS8n1EofSxbE2DFm0a+6hOLzdHj1RF46aKUT2slZ6UCR jj8OfMFeMMBcPu62yjPnDdtOIGnXUx/E8cifB8AqnJnBNv8g4l+5MFFLlapnYEfWUV lCGgLxbi1okb/eq/uVjul1SoFeDBtpLF7X7WxsFYD7acOgzgWrurlJbilwIK/XMEd1 a0so25jH7az9g==
Archived-At: http://mailarchive.ietf.org/arch/msg/avt/9u91wZ6Fvlew9n8yLBp3Ijbhu0g
Cc: Nataraja Hosahalli <Nataraja.Hosahalli@dspg.com>, "avt@ietf.org" <avt@ietf.org>
Subject: Re: [AVTCORE] RFC3550: RTP Jitter value calculation
X-BeenThere: avt@ietf.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: Audio/Video Transport Core Maintenance <avt.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/avt>, <mailto:avt-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/avt/>
List-Post: <mailto:avt@ietf.org>
List-Help: <mailto:avt-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/avt>, <mailto:avt-request@ietf.org?subject=subscribe>
X-List-Received-Date: Thu, 27 Mar 2014 21:37:59 -0000

For the purpose of comparing reports from multiple receivers, you want the
receivers to be using the same formula. The way it is currently specified,
integer and floating point implementations will give approximately the same
answer. My proposed "improvement" would produce different answers for
integer implementations. We don't want to do this.

Kevin Gross - AVA Networks


On Wed, Mar 26, 2014 at 11:26 AM, Stephen Casner <casner@acm.org> wrote:

> On Wed, 26 Mar 2014, Nataraja Hosahalli wrote:
>
> > Hi Kevin,
> >
> > Yes you are right. I ran both the formulae and also your improved
> > formula for 500 times with constant d value, the value rr->jitter is
> > converging near to average delay d after couple of iterations (~100
> > for d=2 for example).
> > However your new formula below is resulting to more accurate average.
> > rr->jitter = (s->jitter + 8) >> 4;
> > Older formula is almost always lagging by nearly 1 ms (0.5 ms
> > floating value) with the average delay.
> >
> > May be your new formula can be updated in RFC.
>
> That difference in accuracy is unimportant because the value is not
> intended to be interpreted quantitatively.  This is an important
> paragraph from RFC 3550:
>
>    The interarrival jitter field provides a second short-term measure of
>    network congestion.  Packet loss tracks persistent congestion while
>    the jitter measure tracks transient congestion.  The jitter measure
>    may indicate congestion before it leads to packet loss.  The
>    interarrival jitter field is only a snapshot of the jitter at the
>    time of a report and is not intended to be taken quantitatively.
>    Rather, it is intended for comparison across a number of reports from
>    one receiver over time or from multiple receivers, e.g., within a
>    single network, at the same time.  To allow comparison across
>    receivers, it is important the the jitter be calculated according to
>    the same formula by all receivers.
>
> The integer calculation was kept as simple as possible for use in
> environments with constrained processing power.  In a modern DSP with
> fast floating point calculations, this is not an issue, but 30-40
> years ago we had to use fixed-point arithmetic in our array processors
> and early DSPs.  The jitter calculation using a scaled value is an
> example of that.
>
>                                                         -- Steve
>