At time slot 0, {TAIL ~ the master} polls {HEAD ~ the slave} and the slave listens 
At time slot 0 , { TAIL ~ the master } polls { HEAD ~ the slave } and the slave listens
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH