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