Then, the output signal is outputted by {TAIL ~ the output end} of {HEAD ~ the buffer} 20; and 
Then , the output signal is outputted by { TAIL ~ the output end } of { HEAD ~ the buffer } 20 ; and
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH