65-node simple mesh test (and counting... ;-)

Ricardo Carrano carrano at laptop.org
Mon May 12 15:31:04 EDT 2008

> > How does the collision model/scheme change between AP mode and
> > ad-hoc/mesh modes?
> As far as I can tell, it doesn't.  802.11s is interoperable with
> 802.11abg, which means that the same media access algorithms are used.
>  At least part of our problem might be in the synchronized transmits
> occurring in our present 802.11s implementation of broadcast, which
> are probably killing whatever CA scheme 802.11abg dictate.  See:
> http://wiki.laptop.org/go/Path_Discovery_Mechanism:Sanity#Question_.232_-_Does_PDM_traffic_self-interfere.3F
> which is trying to deal with low-level path discovery requests, which
> also use the broadcast mechanism.
>  --scott

Yes, it is the same 802.11 DCF for both scenarios (infra and mesh).

I would like to add to this discussion that sparse and dense mesh are too
completely different animals. Most of the problems that we are trying to
address now, are associated to the latter.

The more we dig into this, the more clear it gets that we need to "adapt".

Everything we do to increase coverage in a sparse mesh hurt us in a dense
cloud. One example: broadcasting or multicasting at 1 or 2Mbps.

Likewise, what we do to increase reliability, might actually decrease it.
One example: the verbosity or redundancy of some of our protocols. And
that's one of the strengths of Cerebro (less is more).

So, as a side note: Treating the two animals as different will avoid some
bites and scratches. ;-)

Ricardo Carrano
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