The method 5, wherein the grant specifies a transmission window on the optical line during which only the ONU can transmit {HEAD ~ data} to {TAIL ~ the OLT} 
The method 5 , wherein the grant specifies a transmission window on the optical line during which only the ONU can transmit { HEAD ~ data } to { TAIL ~ the OLT }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL