Hi, i don't know much about the wireless data link layer but this drew my attention a couple of months before: http://www.wi-fi.org/news_articles.php?f=media_news&news_id=909
maybe it makes thinks easier? :) On 10 March 2010 17:01, Korvin <[email protected]> wrote: > Hello guys, I have some info/ideas here that need to be discussed. > > Some time ago I wrote an article at some of russian IT community sites > (habrahabr.ru), which caused a lot of response. > > One of commentars was quite sceptic about actual possibility of widespread > mesh newtork. He provided two interesting links as a proof: > > 1) > http://www.strixsystems.com/products/datasheets/StrixWhitepaper_Multihop.pdf > 2) http://www.belairnetworks.com/resources/pdfs/Mesh_Capacity_BDMC00040- > C02.pdf > > These papers are analyzing current wireless technologies in terms of mesh > networking. Authors are saying, that modern single channel AP's are almost > unusable in large scale networks, as latency/bandwidth degradation gets more > and more valuable. They said that even 5 hops may kill the idea (huh?) even on > almost noise-clean environment. > > Their main argument is half duplex nature of modern WiFi and need of backhaul > traffic forwarding along with the user one. Authors conclude that mesh > networks > may exist only with respect to separation of user/backhaul traffic > frequencies/channels. > > Could you please give a feedback/comment about it? > > ----- > > Anyway, whether this is true or not, I may suggest some ideas which probably > may be taken in mind: > > Overpopulated regions with many WiFi hotspots may experience problems with the > lack of free channels. Overinterference may cause major slowdown of the whole > thing. > > If we'll try to consciously distribute the channels on our network things may > change. My suggestion is to use some kind of map colouring algorithm. > > Look at the picture on the page > http://en.wikipedia.org/wiki/Four_color_theorem Suppose that different colors > are representing different channels of WiFi, and different shapes reflecting > radiowave interference on the urban relief. > > Because we know the placement and interconnection of our own spots, we may > select the frequencies in a way to minimize interference with other networks, > yet achieving good connectivity of our own. Of course this is almost opposite > poles and improvement of one will lead to other's degradation. > > The key may be in multi channel spanning of the network, which needed to be > handled by Netsukuku protocols. > > Suppose we have two nodes: > ((( A ))) [[[ B ]]] > A operates on channel 6 and B on channel 10. In the current design different > channels are treated as completely different networks which may not be aware > of > each other. Netsukuku daemons running on both nodes could not see each other, > thus could not take this into account. > > Now we adding two more WiFi spots: A2 and B2 linked to their companion by > ethernet cable. Operating channels are reversed: > [( (A)<-->[A2] )] <~~link~~> [( [B] <--> (B2) )] > > Now all four nodes may be interconnected into one subnet. Of course, this may > be done without any protocol updates. But if nodes will be aware of channels, > they may intentionally select the operating channel to increase overall > span/quality. On a heavy loaded environment we may intentionally create > several layers of Netsukuku using the colouring method described above. > > By analyzing current state and channel utilization, nodes may vote and decide > to migrate to another channel if it will improve the overall quality. On the > other hand, such migration may lead to a network split if there are no border > nodes linked to a previous channel and fallback internet tunnels are also > unavailable. > > > > > P.S. I was told that recent Linksys APs have two or even three independent > transcievers builtin. Such APs may operate on many channels at once and thus > may be used as such ‘supernode’. (actually I don't know whether such devices > are really exist. maybe this is not true) > > > _______________________________________________ > Netsukuku mailing list > [email protected] > http://lists.dyne.org/mailman/listinfo/netsukuku > _______________________________________________ Netsukuku mailing list [email protected] http://lists.dyne.org/mailman/listinfo/netsukuku
