Subject: others cretaria in MANET routing protocol

From: MEDDOUR Djamal Eddine thesard FTRD/DAC/LAN <[email-masked]>
Date: Tue, 19 Feb 2002 09:57:27 +0100

Hi all<?xml:namespace prefix = o ns =
"urn:schemas-microsoft-com:office:office" /> 

The criteria of the choice of the optimal route is the number of hops, do
you think that it's sufficient? Why don't take in consideration some other
criteria like traffic load around node, node energy, node capacity, ...

Any comments

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From: "David Simplot" <[email-masked]>
Date: Mon, 25 Feb 2002 08:36:49 +0100

You are right: perhaps we can consider the "robustness" of the generated
route... The definition of "robustness" could be the probability that
the route stays valid during a given time without route maintenance.
Notice that, in the general case, an optimal route (number of hops) is
not a robust one.
David.
--
David SIMPLOT
CNRS UPRESA 8022 - LIFL Univ. Lille 1 / IUP MIAGE Formation Continue
http://www.lifl.fr/~simplot 

-----Message d'origine-----
De : [email-masked] [mailto:[email-masked]]
De la part de MEDDOUR Djamal Eddine thesard FTRD/DAC/LAN
Envoyé : mardi 19 février 2002 09:57
À : [email-masked]
Objet : others cretaria in MANET routing protocol

Hi all 

The criteria of the choice of the optimal route is the number of hops,
do you think that it's sufficient? Why don't take in consideration some
other criteria like traffic load around node, node energy, node
capacity, ...

Any comments

---

From: Dave Johnson <[email-masked]>
Date: Mon, 25 Feb 2002 05:22:06 -0600

The real problem is actually fairly complex.  Suggesting that
robustness may be more important than minimal hop count -- that you
care more that a route remains valid during a given time without need
for route maintenance -- seems to imply that route maintenance has
some significant harmful effect to a route in use, more so than the
extra overhead and latency and battery consumption caused by sending
packets over routes that involve more hops than are otherwise
necessary.  If, instead, route maintenance can be done quickly and
effeciently when needed, without significant disturbance to the flow
of packets from that source to that destination, then perhaps this
definition of robustness is less important.  I don't at all mean to
suggest that robustness actually is not important, but there are many
factors that affect the "optimal" choice of routes that any given
sender may want to use for any given type of traffic.

In our paper "Caching Strategies in On-Demand Routing Protocols for
Wireless Ad Hoc Network" at MobiCom 2000, one of our results was a
new route caching strategy in which a sending node selects from its
cache the route that it knows with minimum hop count to the
destination, but among those with that same hop count, it selects
the one that it believes will remain valid for the longest period
of time, based on its past observations of links involving the
nodes along that route.  This caching strategy, which we call
Link-MaxLife, performed overall better than other caches we
studied.  This cache is also the recommended cache in the DSR
Internet-Draft.  This MobiCom paper is available from our web site
at http://www.monarch.cs.rice.edu/monarch-papers/mobicom2000.pdf.

					Dave

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From: Fred Baker <[email-masked]>
Date: Mon, 25 Feb 2002 17:16:58 -0800

At 03:22 AM 2/25/2002, Dave Johnson wrote:
>one of our results was a new route caching strategy in which a sending 
>node selects from its cache the route that it knows with minimum hop count 
>to the destination, but among those with that same hop count, it selects 
>the one that it believes will remain valid for the longest period of time, 
>based on its past observations of links involving the nodes along that route.

I'll argue that hop count in and of itself is a poor indicator.  Consider 
the following

         A--------------------->B
          ---------->C--------->

B and C can both hear A; C hears A with an excellent S/N Ratio and B hears 
A with a poor signal to noise ratio, such that a small percentage of 
packets (less than some threshold measured in percent) can actually 
traverse A->B. I will argue that A->C->B is much kinder to the application 
than A->B, so adding a hop creates a significantly improved route even 
though the smaller hop count would be nice.

It seems to me that hop count might be a tie-breaker amount routes of equal 
robustness, not the other way around.

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From: Kwan-Wu Chin <[email-masked]>
Date: Tue, 26 Feb 2002 13:35:11 +1100

Hi All,

> robustness, not the other way around.

I agree with this argument.   We found this to be true on our testbed,
especially in indoor environments where multipath fading is severe.
We found that the link between A and B comes up and
down frequently, causing routing protocols (based on hop count) to
construct - deconstruct - construct ........ route continuosly over the link
since A and B think they have a 1-hop route each other.    When we
add more nodes (i.e., topology with more unreliable links), we found that
hop-based
MANET routing protocols spend most of their time trying to establish a route and
little
packets get through.   So, hop count is a poor metric, and we feel a combination
of
metrics such as link lifetimes (from radio and mobility perspectives), etc will be
more
suitable.

cheers,
kwan-wu

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From: Laurent Viennot <[email-masked]>
Date: Tue, 26 Feb 2002 11:26:22 +0100

This is where link hysteresis comes up. It allows to detect dangling
links and to ignore them so that hop count becomes a rather good metric.
See the advanced neighbor sensing section of OLSR draft for a short
description of link hysteresis.

laurent

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From: Kwan-Wu Chin <[email-masked]>
Date: Wed, 27 Feb 2002 08:28:31 +1100

Hi laurent,

   Exactly.  We ended up doing hysterisis as well, but in our
implementation the routing protocol was oblivious to the
existence of the hysterisis.

   I'll look at the indicated section in the OLSR draft, thanks for
   the info.

cheers,
kwan-wu