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Re: [manet] Default metric in OLSRv2



Am Fri October 16 2009 12:03:58 schrieb Philippe Jacquet:
> Hello, Henning,
>
> I would add two points to the discussion which is interesting and
> important.
>
> First point: there are many ways to have a MANET/OLSR not working
> well: bugs, badly tuned parameters. The main source of trouble is in
> general how neighbor sensing asserts the quality of a link in order to
> accept it or reject it, and I agree that using a metric will greatly
> help.
>
> Anyhow RFC 3626 was not excluding the use of link quality in neighbor
> sensing, and was suggesting some. The hop count should not be problem
> as long as the links that are on the path are good links. In other
> words I would see the use of path quality as a minor improvement over
> the use link quality in neighbor sensing. Anyhow this would help
> traffic engineering.
I don't agree.

In practice it's very difficult to decide if a link is "good" or "bad" as a 
binary decission. Maybe the bad link is really important for another node, 
maybe it is not.

Link sensing and hysteresis, even with a local metric, is no replacement for a 
good additive routing metric used for the dijkstra algorithm in global 
routing.

> Second point: adding a default link quality in OLSRv2 may be as
> complicated as inserting general metric in OLSv2, eg in MPR selection,
> so we might be careful if we hurry too much.
If we put only hop count metric into the main document that's what most 
research projects will be using as a comparision. And you will hear things 
like "yes, AODV has lot's of delay for route creation, but OLSR has 30% packet 
loss".

It's more a matter of perception. People will use "Core RFC OLSR without 
extensions" and will get bad results from it.

Henning Rogge

-- 
Diplom-Informatiker Henning Rogge , Fraunhofer-Institut für
Kommunikation, Informationsverarbeitung und Ergonomie FKIE
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