{HEAD ~ The ingress module} is configured to receive data from {TAIL ~ the ONU} over the optical line 
{ HEAD ~ The ingress module } is configured to receive data from { TAIL ~ the ONU } over the optical line
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH