[MEDIACTRL] ISSUE 17 - Control Framework - Transaction-Timeout

Chris Boulton <chris@ns-technologies.com> Wed, 04 August 2010 13:46 UTC

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Date: Wed, 04 Aug 2010 14:47:05 +0100
From: Chris Boulton <chris@ns-technologies.com>
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Cc: draft-ietf-mediactrl-sip-control-framework@tools.ietf.org, mediactrl-chairs@tools.ietf.org, gonzalo.camarillo@ericsson.com
Subject: [MEDIACTRL] ISSUE 17 - Control Framework - Transaction-Timeout
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As part of our IESG review the following has been identified:


 > Transaction-Timeout: The maximum allowed time between a Control

 > Client or Server issuing a framework message and receiving a

 > corresponding response. The value for 'Transaction-Timeout' is 5

 > seconds.

ISSUE 17 - DISCUSS: As I understand it, Transaction-Timeout has two 
meanings. For
clients, it's the **minimum** amount of time they need to wait for the
server to respond. For the server, it's the amount of time after which
they should let the client know that processing will take longer. The
mechanism as described isn't very robust. First, 5 seconds is not
sufficiently larger than some Internet RTTs, which may cause spurious
transaction failures even under normal operating conditions. Second,
clients and servers use the same value, which means that if there is
any delay spike or congestion along the path, a spurious transaction
failures will occur.

The Transaction-Timeout set to 5 seconds does not seem appropriate for 
the job.  Firstly we need to take realistic (internet)
RTT time into consideration.  Proposal is that we assert a RTT time of 
10 seconds for the mediactrl framework. Thoughts?

We also need to construct more robust timeout rules for client and 
server.  The proposal is that:

- client sets Transaction-Timeout to be 2*RTT on issuing a request.
- server sets Transaction-Timeout to be 1*RTT on receiving a request.


Chris Boulton
CTO & Co-founder
NS-Technologies <http://www.ns-technologies.com>
m: +44.7876.476681