Re: [xrblock] Fw: I-D Action: draft-ietf-xrblock-rtcp-xr-jb-08.txt

Kevin Gross <kevin.gross@avanw.com> Sun, 03 March 2013 22:13 UTC

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Date: Sun, 3 Mar 2013 15:13:13 -0700
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From: Kevin Gross <kevin.gross@avanw.com>
To: Qin Wu <bill.wu@huawei.com>
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Cc: xrblock@ietf.org
Subject: Re: [xrblock] Fw: I-D Action: draft-ietf-xrblock-rtcp-xr-jb-08.txt
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I'm afraid we're still not there. There is trouble in section 3:

   The jitter buffer can be considered as a time window with one side
   (the early window) aligned with the delay corresponding to the
   earliest arriving packet and the other side (the late window)
   representing the maximum permissible delay before a late arriving
   packet would be discarded.  The delay applied to packets that arrive
   at their expected time is known as the Nominal Delay and this is
   equivalent to the late window.

   The "expected arrival time" is the time that a packet would arrive if
   there was no delay variation.  If all packets arrived at their
   expected arrival time then every packet would be delayed by exactly
   the Nominal Delay.  Early packets arrive before their expected
   arrival time and late packets arrive after.  The reference for the
   expected arrival time may, for example, be the first packet in the
   session or the running average delay.

Nominal delay is defined in the first paragraph as the delay inserted for
the latest arriving playable packet. I believe this is a reasonable
definition. The definition of expected arrival time is in error. If there
is no delay variation, there are no late packets and everything should
arrive before the expected arrival time and most likely at early window.
I suggest expected arrival time should be the same as late window. I also
find the "window", "early window", "late window" terminology unclear. Early
window and late window are actually the edges of a single receive buffering
"window".

I have not done a comprehensive re-review. There are possibly other
problems in this short draft.

Kevin Gross
+1-303-447-0517
Media Network Consultant
AVA Networks - www.AVAnw.com <http://www.avanw.com/>, www.X192.org


On Sun, Feb 24, 2013 at 6:28 PM, Qin Wu <bill.wu@huawei.com> wrote:

> On 23 February , 2012 10:40 PM, Internet-Drafts@ietf.org wrote:
>
> > A New Internet-Draft is available from the on-line Internet-Drafts
> directories.
> > This draft is a work item of the Metric Blocks for use with RTCP's
> Extended Report Framework Working Group of the IETF.
> >
> > Title           : RTP Control Protocol (RTCP) Extended Report (XR) Block
> for Jitter Buffer Metric Reporting
> > Author(s)       : Alan Clark
> >                          Varun Singh
> >                          Qin Wu
> > Filename        : draft-ietf-xrblock-rtcp-xr-jb-08.txt
> > Pages           : 17
> > Date            : 2013-02-23
> >
> > Abstract:
> >   This document defines an RTP Control Protocol (RTCP) Extended Report
> >   (XR) Block that allows the reporting of Jitter Buffer metrics for a
> >   range of RTP applications.
> >
> >
> > The IETF datatracker status page for this draft is:
> > https://datatracker.ietf.org/doc/draft-ietf-xrblock-rtcp-xr-jb
> >
> > There's also a htmlized version available at:
> > http://tools.ietf.org/html/draft-ietf-xrblock-rtcp-xr-jb-08
> >
> > A diff from the previous version is available at:
> > http://www.ietf.org/rfcdiff?url2=draft-ietf-xrblock-rtcp-xr-jb-08
>
> [Qin]: Here is our another update to JB draft. In this version (-08),
> We rewrote descriptive text and definitions for clarification, thanks for
> Alan's proposed text change.
>
> Kevin: Would you like to take a look this version and see if your comments
> are addressed.