Subject: [manet] marginal utility of retransmitting pkt after retry timeout

From: Jim Kaba <[email-masked]>
Date: Mon, 12 Aug 2002 13:34:23 -0400

All,
  Does anyone have any simulation results that show the expected
performance benefit (e.g. in % PDR increase) that can be gained when a Link
Layer notifies the higher layers of a transmission time-out  (e.g. when the
number of RTS retries have expired)???

  In other words, what performance gain should be expected when the routing
layer has the ability to "invalidate a route" based on feedback from the
link layer that a neighbor has moved (as inferred from the inability to
complete a single unicast transmission  -- not from some more extensive
"neighbor location" facility)???

  Also, what is the additional benefit of being able to retransmit the
packet that prompted the feedback to begin with?  A big gain would be
expected by invalidating the route, but how much more could be expected by
not dropping that first packet?

  I expect the answers are protocol, mobility, and load dependent...so if
you have any insight as to *why* your particular protocol behaves so well
or poorly under the circumstances, I'd appreciate hearing your thoughts.

  The issue here is that not all link layers and device drivers support
this kind of feedback, and those that do often don't indicate *which*
packet was dropped...

Jim

-- 
--------------------------------------------------------------
James T. Kaba                   
Sarnoff Corporation      Time flies like an arrow...
[email-masked]                ...Fruit flies like a banana!
609-734-2246

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