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