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