Then, {HEAD ~ the feedback frame} is transmitted from the reception side to {TAIL ~ the transmission side} 
is transmitted to
Then , { HEAD ~ the feedback frame } is transmitted from the reception side to { TAIL ~ the transmission side }
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL