[Tinyos-help] Random Backoff Delays in TinyOS 2.x Channel Access

[Anton]

Hello!

There is probable bug in the 
/tinyos-2.x/tos/chips/cc2420/csma/CC2420CsmaP.nc (lines 218 and 225)

Communicating wireless modules should wait some random delay before 
performing Clear Channel Assess.
According to the IEEE 802.15.4 standard, that delay should be   
random(2^BE-1)   backoff periods, where BE can vary from 3 to 5 (the 
default values macMinBE and macMaxBE, IEEE 802.15.4-2006, pages 
163-164). This means that for CC2420 the maximum backoff delay is 31*320 
= 9920 microseconds (when BE=5), and the maximum initial backoff delay 
is 7*320 = 2240 microseconds (since initially BE=3).

But according to CC2420CsmaP.nc file the maximum initial backoff delay 
can be around 9765 microseconds (line 218) and maximum congestion 
backoff delay can be around 2441 microseconds (line 225).
It seems that the ranges of these random delays are swapped. Even in 
TinyOS 1.x the range of the initial delay is smaller than that of 
congestion backoff delay 
(/tinyos-1.x/tos/lib/CC2420Radio/CC2420RadioM.nc, lines 745 and 752). In 
TinyOS 2.x this is conversely.

Also, according to the standard the range of the random delay should 
expand (by default BE should change from 3 to 5) each time the channel 
is sensed busy (CSMA/CA algorithm - page 172 of the standard). But the 
range of all random delays is constant both in TinyOS 1.x and TinyOS 2.x.

Please, tell whether it is bug or not.

Kind regards,

Anton.