The egress module is configured to transmit data to {HEAD ~ the ONU} over {TAIL ~ the optical line} 
The egress module is configured to transmit data to { HEAD ~ the ONU } over { TAIL ~ the optical line }
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL