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Re: [AVT] Fwd: I-D Action:draft-perkins-avt-rapid-rtp-sync-03.txt

Hi Ali,

Ali C. Begen (abegen) wrote:

Hi Colin,

I read the draft and I found it informative. The funny thing it shares a
similar title with our draft :)
I wonder whether we can come up with a better, non-colliding name for
any of the drafts. Furthermore, we are also defining control messages (3
for now), one of which is rapid (multicast) synch request (RMS-R).
Similar names can be confusing, IMO.
Actually, I do not really care about the naming, but I feel that what you are doing is more about rapid or fast tune-in than about synchronization which I personally connect with timing. Anyway, I would not mind to change the name of our draft and/or the message names. But I guess that can be "synchronized" once the drafts are accepted as WG items. 


Others comments:
- FYI: Section 3.1: reg. "next available FMT is 5?" We used 5, 6 and 7
in the our draft. Of course, it is not reserved yet.
- Could the draft also mention about the other useful properties of
having a sender report earlier? I also think a more appropriate name
could be found for this message.
As I said before, naming is not the problem. Which useful properties should be added here? 


- Section 4.2 says "The frequency of intersing ntp header exs is up to
the sender." Any guidance/constraints on this?
Guidelines would be helpful, but we didn't want to constraint this approach. I think it is clear the more often you insert them, the earlier you can, e.g., start the decoding order recovery. I think this is definitely depending on the application. What would you expect here? Do you think about guidance with respect to overhead against the time it takes to be synced? 


- There are a few inconsistent intra-document references.


Thanks, will check that.


Chairs:
I support this draft to become a WG item as it has two good solution for
(timestamp) synchronization for RTP flows.

-acbegen



Best regards,
Thomas


--
Thomas Schierl
--------------
Fraunhofer HHI




-----Original Message-----
From: avt-bounces at ietf.org [mailto:avt-bounces at ietf.org] On Behalf Of Colin Perkins 
Sent: Monday, March 09, 2009 12:43 PM
To: avt at ietf.org WG
Subject: [AVT] Fwd: I-D Action:draft-perkins-avt-rapid-rtp-sync-03.txt
The changes in this version are primarily editorial; we're aware that not all the open issues have been addressed yet. Any further comments are welcomed.
Chairs: we'd like this to be considered as an AVT working group draft, as indicated privately. 

Cheers,
Colin




Begin forwarded message:

From: Internet-Drafts at ietf.org
Date: 9 March 2009 17:15:02 GMT
To: i-d-announce at ietf.org
Subject: I-D Action:draft-perkins-avt-rapid-rtp-sync-03.txt
Reply-To: internet-drafts at 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-03.txt
	Pages           : 17
	Date            : 2009-03-09

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-03.txt 

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Audio/Video Transport Working Group
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