On May 12, 2008, at 3:31 PM, Ricardo Carrano wrote: > > > 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.
Certainly an interesting question. But is your answer really true ? I'd argue that very little, if any, testing has been done of the "large, yet sparse" mesh. Certainly none by OLPC. Our problems certainly come from "large" meshes (more than 10-15 laptops in the mesh). What is your definition of sparse ? > 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. ;-) One interesting note is that the suggested routing algorithm for 802.11s is a combination of reactive and proactive routing (unlike our current one, which is solely reactive). Perhaps that provides the adaptation necessary for the mesh to work ? wad _______________________________________________ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel