This is the non beacon-enabled mode.
No architecture, radio always in reception except when transmitting.
You can't have large and mobile networks with the beacon-enabled mode of
IEEE 802.15.4. It was not designed for that.
Have a look at the example network, create your own from that. And then
change one thing after the other (begin by ini parameters and then maybe
modifying the ned models if needed) and look at how this impacts the
results.
Jérôme