[Olsr-dev] invalidate node links

[Henning Rogge]

On Fri, 30 Sep 2011 10:49:53 Giovanni Di Stasi wrote:
>  Hi everyone,
> 
> I would like to receive some advices regarding an experiment we are
> currently performing aboud channel assignment algorithms. The scenario is
> multi-radio.
> 
> The channel assignment algorithm (centralized) triggers at a certain point
> the change of channels of most of the interfaces of nodes. It may happen
> that a neighbor which was reachable through one interface, after the
> change,  becomes reachable through another interface [1]. The experiment
> we are doing shows an interruption of approximately one minute before the
> TCP connections we had established are able to return to their full speed.
> This is due (I noticed that by taking a look at the Olsrd logs) to the
> time Olsrd needs to drop the old route (on the old interface) and use the
> new one (on the new interface). We would like to speed up things a little
> bit. The first attempt we think  to do is to reduce the Hello and TC
> Intervals. This would speed up the change but will imply greater overhead.
> First results however show no improvements. A different solution would be
> to discard all the links departing from the interface of which we have
> changed channel. If we change the channel of an interface, it means that
> all the links departing from that interface are (probably) no longer good,
> so it is good to drop them and start using new links (possibly just after
> the first hello packet is seen, so to regain rapidly connectivity). Do you
> agree on this solution?   If that's the case, how can I tell to Olsrd to
> drop all the links from a certain interface?

We have some "quick shotdown" feature for OLSR that uses something that might 
work for you. You can invalidate a link by sending a Hello with the 
corresponding connections marked as state "dropped".

Look into main.c, line 725 to 735.

olsr_reset_all_links() sets ALL links to state dropped (you need a version 
that only does this for a single link).

olsr_shutdown_messages() sends out a hello and TC for all links (again you 
need a limited one).

> Thanks a lot,
> Giovanni
> 
> 
> [1] suppose two nodes each with two interfaces, the one set on channel 1
> and the other on channel 2. After the channel change the first node starts
> using channels 3 and 4 and the second channels 4 and 3.


Henning Rogge
-- 
Diplom-Informatiker Henning Rogge , Fraunhofer-Institut für
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