A communications channel comprises {HEAD ~ a buffer} that receives user data that includes a plurality of {TAIL ~ m bit symbols} 
A communications channel comprises { HEAD ~ a buffer } that receives user data that includes a plurality of { TAIL ~ m bit symbols }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL