I'd like to share some of my observations regarding the implementation of
IEEE
802.15.4 in ns-2. These observations are based on the results of running
the
script wpan_demo3.tcl in the directory
ns-allinone-2.33/ns-2.33/tcl/ex/wpan.
1. The effect of beacon order (BO)
wpan_demo3.tcl implicitly sets the beacon order to be the same as the
superframe order (SO), i.e., BO = SO = 3, thus resulting in only one beacon
slot in a superframe. Before the script is modified, all FFD nodes are
somehow
able to broadcast their beacons. When BO is set to 6 or above, no FFD nodes
are able to broadcast their beacons. I expected that when the number of
beacon
slots is increased, the chance of the FFDs broadcasting their beacons
increases, but this was not observed.
2. Sleeping in the inactive period/portion of a superframe
No sleeping by any node has been observed due to this conditional in the
file
p802_15_4mac.cc:
if ((backoffStatus!=99)
&& ((!capability.FFD)||(numberDeviceLink(&deviceLink1) == 0))
&& (NOW>phy->T_sleep_)) {
phy->putNodeToSleep();
...
because T_sleep_ is only initialized once to 10000. It seems like the
implementation does not make nodes sleep during inactive periods at all.
