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