[Tinyos-help] influence congestionbackoff

[Ruben Catteeuw]

Hi all,


I have been thinking about this for a very long time, but couldn't formulate an answer, so I ask my question to this community:

My application exists of 41 telosbmotes, 40 of them send 1 request (20 bytes) at a random time in every 1-second interval to the 41sth mote who functions as a controller.
Upon receiving a request, the controller waits 200ms and sends a reply (100 bytes) back. The succesrate of the whole application is about 89% (so of all requests 89% are responded to with a reply)

Since the 40 requesters are in contention, the backoff-windows are expected to have influence on this succesrate.
The initialbackoff should have no influence, since the motes allready send at a random time and random+random=random.

The congestionbackoff however also seems to have no influence.
For each packet, I choose, a random value from [0...congestionwindow] like this:

async event void RadioBackoff.requestCongestionBackoff(message_t *msg){

        if(useCustomBackoffs==TRUE) call RadioBackoff.setCongestionBackoff((call bRand.rand16())%congestionWindow); 

    }

this window is changed from 5 to 200 (ticks of a 32kHz timer), but the succesrate of the application does not change, I have no answer for this behaviour



Anyone who could have an anwser to this, please respond, you could be a great help to me.

thanks a lot for your time

Ruben

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