When {HEAD ~ the known code portion} is not detected from {TAIL ~ the coded data}, the coded data will be decoded 
is not detected from
When { HEAD ~ the known code portion } is not detected from { TAIL ~ the coded data } , the coded data will be decoded
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH