Subject: Route Reply generation in AODV

From: George Aggelou <[email-masked]>
Date: Sat, 10 Oct 1998 17:29:29 +0100

Hi Charlie/Elizabeth,

I have two questions on AODV algorithm:

i. AODV Draft does not discuss the case where a node receives a RREQ
(Route Request) with the same <src, dest, seq_no> but smaller metric to
src of RREQ.
I guess that in this case the node should proceed and re-broadcast it,
in order to reflect a smaller route to src. Is that correct? 

ii. In AODV (applies to DSR as well), if a node receives a RREQ for a
destination (dst) and has a "fresh enough" route to dst, the node
generates a RREP (Route Reply) message.  Under what terms, a route is
considered as as "fresh"? For instance, one may assume that a fresh
route in a node's routing table may well be one with remaining Lifetime
that is equal or smaller than Route_Timeout/2 in order to be considered 
as a fresh.... What concept AODV is using to calculate the freshness of
a route?

Regards,
George A.
-- 
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George Aggelou			     	
Centre for Communications Systems Research   
Mobile Communications Research Group      		
University of Surrey  		     

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From: Charles Perkins <[email-masked]>
Date: Sat, 10 Oct 1998 09:38:32 -0700 (PDT)

George,

> in order to reflect a smaller route to src. Is that correct?

The current specification is that the packet should not be re-broadcast.
But, the node _should_ use the information to update the appropriate
information in its reverse route.  This will lead to the case where
the hop count is inconsistent along a route, but that's not horrid.
And, we could repair it later by a fairly trivial unicast repair RREP
if it turns out to be advantageous.
 
> as a fresh.... What concept AODV is using to calculate the freshness of

AODV has destination sequence numbers, which operate the same way
as in DSDV.  The remaining route lifetime is never used for this
determination.  Link breakages cause triggered updates which include
artificially generated destination sequence numbers, just as with DSDV.

Regards,
Charlie P.