On Tue, May 13, 2008 at 11:59 AM, John Watlington <[EMAIL PROTECTED]> wrote:
> > 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 ? My definition, since I never found o good one in the literature. In a sparse mesh the number of active neighbors is smaller than your retry limit. So, in a sparse mesh your frame will never be discarded without being transmitted at least one time. In a dense mesh, there is a chance that a frame will reach the retry limit without being ever transmitted. So, 10 XOs in a room is a dense mesh (in that definition). I've done some tests in sparse topologies early in 2007. but I doubt they have any lasting values, after so many changes and fixes. Back there we were particularly interested in the hidden node problem and checked to see if RTS/CTS would help us (by the way it does not seem to help in multihop scenarios http://www.midiacom.uff.br/~schara/publications/SBrT2007.pdf)
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