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