Hi, That's great. Finally a paper which actually describes what is implemented in tinyOS 2.1. At the first scan of the paper, it seems that what is implemented is similar to Box-MAC2, but I will read it more carefully and check the implementation again..
Thank you, Alban 2009/9/9 Razvan Musaloiu-E. <[email protected]>: > Hi! > > On Wed, 9 Sep 2009, Alban Hessler wrote: > >> Hi, >> >> In the LPL stack, in the PowerCycleP file: >> >> I don't understand why it is needed to probe 400 times >> (MAX_LPL_CCA_CHECKS) the signal strength to detect if there is >> currently a transmission. The sender on the other side sends >> continuously, there is just a bit of radio silence between two >> duplicates. >> >> 400 times is like 50ms (according to another post), which is a lot. > > The check is actually much smaller, around 16.5ms on TelosB. Figure 7 and > Table 1 from here shows this: > http://cs.jhu.edu/~razvanm/ipsn2008koala.pdf > >> Finally, if you put a node to sleep 100 ms, then it's actually with >> the radio on for half of the time (!) >> >> Then, if I decrease this MAX_LPL_CCA_CHECKS to 80, then I get about >> 50-60 percent packet losses. (LPL with receive sleep between 100ms and >> 300ms). Whereas with the value set to 400, I have a residual 1 % >> packet loss. >> >> Can somebody explain me the reason behind this 400 value? Why is it so >> large? Why is for example 80 not enough? > > As far as I know the value of 400 for the number o checks was picked > because, as you also noticed, it is giving better performance than a small > one. :-) It would be nice to investigate more the behavior of the CCA pin > when a stream of packets are received. > > A good paper that talks about the LPL from TinyOS is this one: > http://sing.stanford.edu/pubs/sing-08-00.pdf > > -- > Razvan ME > >> The nodes are close to each other and send at 0 dbm, so I don't expect the >> CCA threshold to be an issue. The CC2420 spec says that the RSSI prob is >> +-6db, but I expect the RSSI to be anyway 12db more than the CCA threshold. >> >> That question was already asked in the following post, but remained >> unanswered: >> >> >> http://mail.millennium.berkeley.edu/pipermail/tinyos-help/2009-February/038272.html >> >> Thanks for any help, >> >> Best regards, >> >> Alban >> _______________________________________________ >> Tinyos-help mailing list >> [email protected] >> https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help >> > _______________________________________________ Tinyos-help mailing list [email protected] https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
