Avinash,
thanks. Yes.. CC2420 should use CSMA/CA at MAC level as it is 802.15.4 radio. And the CA part in MAC is used to handle the hidden and exposed terminal problem. This all is what it _SHOULD_ do. But in my tossim simulation there is a huge loss in packets. Huge means >99% of data packets are lost. And many control(i.e. the control packets of routing layer I implemented) are also lost. When I used real motes the routing worked fine. And packet losses were very less!!! I am not able to understand this behavior. I want to use tossim as I need to check how the routing behaves in a large complex network with different type of traffic. But Tossim behaves totally different then real network in a simple 4 mote network!! Any ideas?? -regards --- Avinash Sridharan <[EMAIL PROTECTED]> wrote: > 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 > > Tinyos-help@Millennium.Berkeley.EDU > > > 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 > ____________________________________________________________________________________Ready for the edge of your seat? Check out tonight's top picks on Yahoo! TV. http://tv.yahoo.com/ _______________________________________________ Tinyos-help mailing list Tinyos-help@Millennium.Berkeley.EDU https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
