Hi Urs, During the random back-off time we do nothing. After the timer expires, then we do CCA and if the channel is free, then we send the message. If the channel is busy, then we go another round of random back-off (congested). On the TelosB the random back-off time was up to 8 ms the last time I have checked. IRIS uses 4 ms now.
Best, Miklos On Thu, Dec 9, 2010 at 9:42 AM, Urs Hunkeler <[email protected]> wrote: > Hi, > > My bad, I mixed CCA (clear channel assessment) up with random back-off > time. I think that the original question was rather about the random > back-off time (used for the CSMA in the default MAC protocol used by > TinyOS), during which (please correct me if I'm wrong here) the channel > is continuously checked to see whether it is busy, and if so, the timer > for the random back-off is suspended while the channel is sensed to be busy. > > Cheers, > Urs > > On 12/09/2010 09:20 AM, Miklos Maroti wrote: >> Hi Guys! >> >> On the RF230 we perform an instantaneous RSSI based CCA check, but you >> can enable the hardware CCA which takes around 16 microseconds. >> >> Miklos >> >> On Thu, Dec 9, 2010 at 7:55 AM, Urs Hunkeler<[email protected]> wrote: >>> From my tests on a TelosB (CC2420 radio) it varies linearly between 1ms >>> and 10ms (when the channel is free, in principle the radio is already in >>> receive mode while the message is being copied to the radio's memory, >>> but I don't think this is used as the CCA). The duration on an Iris mote >>> (RF230 radio) is shorter, but I haven't measured the details. >>> >>> The duration of the CCA is definitely configured by TinyOS, as I managed >>> to shorten it. You might have to dig into the lower levels of the radio >>> interface. >>> >>> Cheers, >>> Urs >>> >>> >>> >>> On 12/08/2010 10:46 PM, TheMrOrange wrote: >>>> from my tests cc2420 is in rx mode for 8msec if the channel is empty >>>> >>>> Davide >>>> >>>> On 08/dic/10, at 20:53, Eric Decker wrote: >>>> >>>>> >>>>> >>>>> On Wed, Dec 8, 2010 at 12:27 PM, wasif masood<[email protected] >>>>> <mailto:[email protected]>> wrote: >>>>> >>>>> >>>>> Hi all, >>>>> >>>>> can anyone tell me how long does a sender sense(in msec) the >>>>> channel if I use CCA enabled transmission? is this mention anywhere? >>>>> >>>>> >>>>> I think that is buried down in the radio h/w but I am not sure. You >>>>> might want to take a look at the h/w specs for the radio you are >>>>> using. >>>>> >>>>> eric > _______________________________________________ > 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
