Then {TAIL ~ the FEC processor} computes {HEAD ~ an FEC value} 515 data block 500A and appends it to the data block 500A 
Then { TAIL ~ the FEC processor } computes { HEAD ~ an FEC value } 515 data block 500A and appends it to the data block 500A
OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH