Subject: [Sip] Open Issue #370: RTT estimates for 2xx retransmits

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 02 Jan 2002 01:05:52 -0500

Section 13.3.1.4 talks about how the uas core retransmits the 2xx with 
intervals
that start at t1 and double until t2. These timers should ideally be 
rtt-tuned,
but they are NOT the same measurements as the ones used for sending 
requests.
The reason is that these are almost always through intermediaries, so 
the rtt
estimate is from uas to uac through N proxies. It could be done by 
including a
Timestamp in the 2xx, which is mirrored in the ACK. However, its not 
clear how
to scope that measurement. Note that a similar thing exists for 1xx/PRACK.

Should we say anything about this?

My proposal is NO, since I think that any such estimation is impossible 
to be done usefully.

-Jonathan R.
-- 
Jonathan D. Rosenberg, Ph.D.            72 Eagle Rock Avenue
Chief Scientist                         First Floor
dynamicsoft                             East Hanover, NJ 07936
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From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 10 Jan 2002 13:32:05 -0500

There were no comments on this, so I will assume consensus is to accept 
the proposal, and make no changes to the text as it stands.

-Jonathan R.