Re: [B.A.T.M.A.N.] TTL yes, TTL no

[Antonio Quartulli <ordex@autistici.org>]

Hello,

On sab, mar 26, 2011 at 04:31:42 +0100, Marek Lindner wrote:
> 
> Hi,
> 
> > In these days I was wondering whether the TTL field in the OGM packet is
> > really useful or not...Due to hop_penalty an OGM will be discarded as
> > soon as the TQ will reach 0 (which is a sort of TTL mechanism itself).
> > At this point why is the TTL field needed?
> 
> uhm.., you probably are right. As long as there is a hop penalty it also 
> functions as a TTL. Keep in mind that it is possible to set the hop penalty to 
> zero. With the current default hop penalty of 10 the maximum number of hops is 
> limited to 25.

I think it is wrong: TQ is not decremented by hop_penalty each time, but it is
multiplied by (TQ_MAX-hop_penalty/TQ_MAX), then the number of hops is
bigger than what you said. With hop_penalty = 10 we can probably reach
~135 hops (raw calculus 255*(TQ_MAX-hop_penalty/TQ_MAX)^135) =~ 0)

> 
> 
> > Someone could probably say that a node far at least TTL hops will never
> > be reached by a unicast packet, then it is meaningless to let it know
> > about me. But then it could be possible to recalibrate the TTL such that
> > it has to be equal to the maximum length in number of hops of the longest
> > path the OGM can traverse.
> 
> Not quite sure what you are proposing. A TTL of TQ_MAX / hop penalty ?
> 

Looking at the calculus above, I'm proposing to use TTL = ~135

Bye!

-- 
Antonio Quartulli

..each of us alone is worth nothing..
Ernesto "Che" Guevara