If there is no substantial transmission data to be transported by the feedback frame on the reception side, then {TAIL ~ the feedback frame} is arranged such that data unrelated to feedback information including at least the transmission data length, the transmission data and the data frame number within the feedback frame, is substituted with a predetermined fixed pattern, and {HEAD ~ thereafter an error} detecting code for all the data is added thereto 
If there is no substantial transmission data to be transported by the feedback frame on the reception side , then { TAIL ~ the feedback frame } is arranged such that data unrelated to feedback information including at least the transmission data length , the transmission data and the data frame number within the feedback frame , is substituted with a predetermined fixed pattern , and { HEAD ~ thereafter an error } detecting code for all the data is added thereto
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH