Re: [xrblock] I-D Action: draft-ietf-xrblock-rtcp-xr-discard-05.txt

Colin Perkins <csp@csperkins.org> Wed, 25 July 2012 07:58 UTC

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From: Colin Perkins <csp@csperkins.org>
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Date: Wed, 25 Jul 2012 08:58:48 +0100
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To: Qin Wu <bill.wu@huawei.com>
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Subject: Re: [xrblock] I-D Action: draft-ietf-xrblock-rtcp-xr-discard-05.txt
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On 25 Jul 2012, at 07:49, Qin Wu wrote:
> Based on Alan's proposal to the open issue mentioed below, we like to add one new section after SDP signaling section as follows:
> "
> 6. Consideration for duplicate packets discards
> 
> Early/ late discards are usually regarded as a symptom of PDV due to congestion (or route changes) however duplicate packets discards have quite different causes.
> 
> (a) A few duplicate packets can indicate some form of Layer 1/2 LAN problem. This would not need to be an accurate measure - more of a general barometer.
> 
> (b) If the number of duplicate packets is very high then this may be due to RTP replication - and if this is the case then you would want to compare the number of duplicate packets to the number of received packets in the same time interval. If the duplicate packet count is X% of the received packet count, this indicates that a (100-X)% packet loss rate is being "hidden" by the replicated packets, and  it is very useful to know the actual loss rate(useful to indicate that replication should be kept "on" and helpful to know that there are some network issues that need to be investigated).
> "

Duplicating RTP packets in this way for robustness is a very bad idea, since - as you note - it disrupts all the RTCP statistics. If you need to send duplicate streams, draft-ietf-avtext-rtp-duplication-00 describes how to do it without breakage. If you are going to mention duplication, I'd recommend including a reference to the working group draft to show how to do it right.

-- 
Colin Perkins
http://csperkins.org/