Re: [B.A.T.M.A.N.] [PATCH 5/5] batman-adv: avoid temporary routing loops by being strict on forwarded OGMs

Marek Lindner
2012-03-12T08:36:17Z

On Monday, March 12, 2012 16:23:30 Daniele Furlan wrote:
> 2012/3/12 Marek Lindner <lindner_marek@yahoo.de>:
> > On Monday, March 12, 2012 15:49:26 Daniele Furlan wrote:
> >> > I don't quite understand what you are proposing. Are you saying
> >> > removing the averaging mechanism makes this patch obsolete and allows
> >> > replacing the TTL/TQ values as the code does now (without the patch)
> >> > ?
> >>
> >> No no this patch is good, the removing of TQ average can be a following
> >> step as now average is not forwarded anymore, but only used as a
> >> comparative value between path in another point of the source code.
> >
> > This follow-up step needs a volunteer. It is a bigger operation to remove
> > the averaging and ensure everything still works. :-)
>
> I can try to send some patch next week to start this operation.. :)

Wow - cool!

> > Do you mind explaining in simple words how the averaging could cause
> > routing havoc together with the strict OGM forwarding patch ? I did not
> > understand. Or are you in favor of removing the averaging for style /
> > performance reasons?
>
> Actually the average as it is calculated in the current version
> (without "considering" lost OGMs) is not monotonically decreasing. This
> cause routing loops when it is forwarded so with this patch the problem does
> not happen.

That is what I thought. This patch also enforces monotonicity, thereby
eliminating the loop "potential" created by averaging the TQ.

> Also maintaing only the latest TQ guarantee to have a more updated
> information about the path. Furthermore an average is already done at
> every link TQ calculation so it is superfluous to have another window.
> This reduce also memory and computational requirements.

Full agreement on this part.
At the moment, I was more worried about temporary loops which seems to be
addressed with this patch.

Thanks for all your feedback!

Cheers,
Marek