If at least one check node is unsatisfied, {TAIL ~ the decoder} reports {HEAD ~ a failure} 
If at least one check node is unsatisfied , { TAIL ~ the decoder } reports { HEAD ~ a failure }
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD