Re: [AVT] I-D Action:draft-perkins-avt-rapid-rtp-sync-02.txt

Hi

I have read the draft and I believe it is a good collection of
solutions. 

Medium comments: 
Section 4.2, page 13. "The frequency of inserting NTP header extensions
in the RTP flows is up to the sender". It is here perhaps worth to
consider the possible impact on header compression algorithms such as
RoHC. Depending on profile used the toggling of the X bit may increase
the packet overhead by 3-5 bytes for a number of packets. This is likely
no big issue for transmission of video but may have an impact for e.g
audio. Anyway, this is not a very impotant issue but I just wanted to
bring this up.

Minor comments(nits):
Section 3
  "repid" -> "rapid"

Section 3.1
  "constraints of RTCP the early..." -> "constraints of the RTCP
early..."

Section 4.1 
  "are not send.." -> "are not sent.."

  "If synchronously in all flows inserting header extensions as defined
in..." -> "If header extensions are synchronously inserted in all flows
as defined in..." 

  "trasnported" -> "transported"

Section 4.2 
   last paragraph: "Such an NTP header extension insertion is only...."
Confusing, is something missing in the end of the sentence?

Regards
Ingemar

> -----Original Message-----
> From: avt-bounces@ietf.org [mailto:avt-bounces@ietf.org] On 
> Behalf Of avt-request@ietf.org
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> Subject: avt Digest, Vol 58, Issue 8
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> Today's Topics:
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>    1. Fwd: I-D Action:draft-perkins-avt-rapid-rtp-sync-02.txt
>       (Colin Perkins)
> 
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Fri, 13 Feb 2009 17:38:50 +0000
> From: Colin Perkins <csp@csperkins.org>
> Subject: [AVT] Fwd: I-D Action:draft-perkins-avt-rapid-rtp-sync-02.txt
> To: IETF AVT WG <avt@ietf.org>
> Message-ID: <C31AC42F-0694-4B91-96AC-939FA0B64539@csperkins.org>
> Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed
> 
> This draft is a merger between draft-perkins-avt-rapid-rtp- 
> sync-01.txt and draft-schierl-avt-rtp-ntp-for-layered-codecs-00.txt.
> 
> Please send any comments to the list. We'd like this to be 
> considered for adoption as an AVT working group draft.
> 
> Colin
> 
> 
> 
> Begin forwarded message:
> > From: Internet-Drafts@ietf.org
> > Date: 13 February 2009 14:45:01 GMT
> > To: i-d-announce@ietf.org
> > Subject: I-D Action:draft-perkins-avt-rapid-rtp-sync-02.txt
> > Reply-To: internet-drafts@ietf.org
> >
> > A New Internet-Draft is available from the on-line Internet-Drafts 
> > directories.
> >
> > 	Title           : Rapid Synchronisation of RTP Flows
> > 	Author(s)       : C. Perkins, T. Schierl
> > 	Filename        : draft-perkins-avt-rapid-rtp-sync-02.txt
> > 	Pages           : 18
> > 	Date            : 2009-02-13
> >
> > This memo outlines how RTP multimedia sessions are 
> synchronised, and 
> > discusses how rapidly such synchronisation can occur.  We show that 
> > most RTP sessions can be synchronised immediately, but that 
> the use of 
> > video switching multipoint conference units (MCUs) or large source 
> > specific multicast (SSM) groups can greatly increase the initial 
> > synchronisation delay.  This increase in delay can be 
> unacceptable to 
> > some applications that use layered and/or multi-description codecs.
> >
> > This memo updates the RTP Control Protocol (RTCP) timing rules to 
> > reduce the initial synchronisation delay for SSM sessions.  A new 
> > feedback packet is defined for use with the Extended RTP 
> Profile for 
> > RTCP-based Feedback (RTP/AVPF), allowing video switching MCUs to 
> > rapidly request resynchronisation.  Two new RTP header 
> extensions are 
> > defined to allow rapid synchronisation of late joiners, and 
> guarantee 
> > correct timestamp based decoding order recovery for layered 
> codecs in 
> > the presence of clock skew.
> >
> > A URL for this Internet-Draft is:
> > http://www.ietf.org/internet-drafts/draft-perkins-avt-rapid-rtp-
> > sync-02.txt
> 
> 
> 
> -- 
> Colin Perkins
> http://csperkins.org/
> 
> 
> 
> 
> 
> ------------------------------
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