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