The digital data comprises a preamble field followed by {HEAD ~ a sync mark} followed by {TAIL ~ a data field} 
The digital data comprises a preamble field followed by { HEAD ~ a sync mark } followed by { TAIL ~ a data field }
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL