Subject: [AVT] IESG comments on draft-ietf-avr-rtp-retransmission-11.txt - Issue 3: retransmission request timer value

From: "Jose Rey" <[email-masked]>
Date: Wed, 25 May 2005 12:33:33 +0200

Mark,

Issue 3: "simply stating that the retransmission request timer should
rely on a timer is not enough, should it be based on RTT?  Should it be
static or dynamic?"
Answer: Yes, the timer should be based in the observed RTT. For a start,
I would leave it static, since experience is needed to find a meaningful
description/value of an adaptive mechanism. BTW, just to check, with
"part of the algorithm for when to send multiple retransmissions" in
your orginal comment, I guess you mean some adaptive algorithm that
adjusts the timer for each subsequent request?

OLD:
   To increase the robustness to the loss of a NACK or of a 
   retransmission packet, a receiver may send a new NACK for the same 
   packet.  This is referred to as multiple retransmissions.  Before 
   sending a new NACK for a missing packet, the receiver should rely 
   on a timer to be reasonably sure that the previous retransmission 
   attempt has failed in to avoid unnecessary retransmissions. 

NEW:

   To increase the robustness to the loss of a NACK or of a 
   retransmission packet, a receiver may send a new NACK for the same 
   packet.  This is referred to as multiple retransmissions.  Before 
   sending a new NACK for a missing packet, the receiver should rely 
   on a timer to be reasonably sure that the previous retransmission 
   attempt has failed and so avoid unnecessary retransmissions.  
   The timer value shall be based on the observed round-trip time.
Both, a static
   or an adaptive value MAY be used.  

   An adaptive timer could be one that changes its value with 
   every new request for the same packet.  This document 
   does not provide any guidelines as to how this adaptive value should
   be calculated because no experiments have been done to find this out.

Cheers,

---------------------------------------------
Jose Rey     mailto:[email-masked]
P R D C G - Panasonic R&D Center Germany GmbH
Phone/Fax: +49(0)6103766-134/166
--------------------------------------------- 

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