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