Subject: [AVT] IESG comments on draft-ietf-avr-rtp-retransmission-11.txt - Issue 2: packet reordering

From: "Jose Rey" <[email-masked]>
Date: Wed, 25 May 2005 12:33:27 +0200

Mark,

Issue 2: Mark says "If packet reordering is determined to be extremely
rare (e. g., essentially never - perhaps due to the underlying datalink
preventing misordering) then the optimum delay here could in fact be
zero except in the rarest of cases. I'm afraid that an implementor might
take this too literally and always include some minimum delay,
inhibiting performance for no good reason. Perhaps it should be pointed
out that "some delay" may in fact be zero in some cases." Also, the best
"possible reorder delay" algorithm may not actually be time based, but
packet based....."
Answer: basically agree with all. Very helpful comment!

OLD:

   The receiver should not send a retransmission request as soon as 
   it detects a missing sequence number but should add some extra 
   delay to compensate for packet reordering.  This extra delay may, 
   for example, be based on past observations of the experienced 
   packet reordering.

NEW:

   The receiver should not send a retransmission request as soon as 
   it detects a missing sequence number but should add some extra 
   delay to compensate for packet reordering.  This extra delay may, 
   for example, be based on past observations of the experienced 
   packet reordering.  It should be noted that, in environments where
   packet reordering is rare or does not take place, e. g., if the 
   underlying datalink layer affords ordered delivery, the delay may 
   be extremely low or even take the value zero. In such cases, an 
   appropriate "reorder delay" algorithm may not actually be 
   timer-based, but packet-based. E. g., if n number of packets are
   received after a gap is detected, then it should be assumed 
   that the packet was truly lost rather than out of order. This may 
   turn out to be far easier to code on some platforms as a very 
   short fixed FIFO packet buffer as opposed to the timer-based
mechanism.

(I shamelessly lent much of the new text from Mark :)

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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