Subject: Destination sequence number

From: SSDP143 <[email-masked]>
Date: Mon, 3 Jul 2000 18:29:10 +0300 (EEST)

Dear all,
         We are a goroup of students at the Information Technology
Institute Egypt we are currently implementing the AODV deamon for linux,
We have a question : what is meant by "Distination sequence number " in
all packets ( RREQ, RREP, RERR,.)?and when any node needs to update this
sequence(increment or .........)? 

                                         Best regards
                                           Azza
                                           Hany
                                           Morcos

---

From: "Charles E. Perkins" <[email-masked]>
Date: Mon, 03 Jul 2000 10:22:08 -0700

Hello folks,

The destination sequence number is a monotonically increasing
number maintained by a node in the ad hoc network.  Each node
keeps its own destination sequence number, and uses it to
ensure freshness for RREP messages.  Each other node that
receives a RREP is required by protocol to keep track of the
destination sequence number for the associated IP address
representing the destination.  A destination sequence number
can only be incremented by the destination, except in one
circumstance which has the effect of invalidating routes
towards that destination.  So, the destination has to be
considered the _authority_ for any transactions involving
that number.  Other nodes offering routes to that destination
will have the validity of their offer judged based on the
value of the sequence number.  A higher destination sequence
number can invalidate any route towards that destination
that is tagged with a lower destination sequence number.

The destination increments the sequence number whenever
it notices a change in its neighborhood topology.  It is
possible for the destination sequence number to be incremented
by an intermediate node, but ONLY by one, and ONLY if that
intermediate node then reports a metric of infinity.
Then any sequence number reported by the destination
will result in a route update that replaces the
pseudo-route-entry represented by the infinite metric.

I hope that is a sufficiently clear, if long, explanation
for an idea that is basically very simple.  However, this
simple idea lies at the very heart of the protocol.  It
is what makes AODV loop-free at all instants.

Regards,
Charlie P.