The CC2420 radio stack provides CSMA and I assume other platforms provide a similar mechanism. So does TOSSIM (not sure if you are running your code on real motes or are simulating it). However the CSMA by nature is a best effort servcie in the sense that it tries to avoid collision by performing a carrier sense and implementing random back offs. This does not mean collision cannot take place.
There is also the case of the hidden terminal problem (for which you probably need something like an RTS/CTS scheme (CA) ) which could also induce collisions. So in short you need not do random back offs at the application layer, however you cannot do away with packet losses completely (even if you do random back offs) short of retransmitting the packets using acknowledgments. On 8/29/07, Ravi Prasad <[EMAIL PROTECTED]> wrote: > > > Hi, > > I am trying to implement a true mesh routing. I have > finished implementing an elementary routing layer > above the ActiveMessage layer. But I am facing a lot > of packet drops. This I guess is due to collision. I > added the packetacknowledgements to solve the problem > but still the case is same. I think MAC layer should > take care of link level collision avoidance. But it > seems it is not doing it efficeintly. > > My question is that when I call send of ActiveMessage > to send a packet, will it use proper CSMA/CA at MAC > level to avoid any collision and packet losses?? OR I > need to use a random delay to call send at application > level (i.e my routing layer)?? > > > Also if anyone can provide some guidelines about > avoiding packet losses in a multihop environment. > > > -Regards > > > > > > > > > > ____________________________________________________________________________________ > Sick sense of humor? Visit Yahoo! TV's > Comedy with an Edge to see what's on, when. > http://tv.yahoo.com/collections/222 > _______________________________________________ > Tinyos-help mailing list > [email protected] > https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help > -- Phd Dept. of Electrical Engineering University of Southern California http://www-scf.usc.edu/~asridhar
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