{HEAD ~ The OLT} comprises an ingress module, {TAIL ~ egress module} and a network processor 
comprises
{ HEAD ~ The OLT } comprises an ingress module , { TAIL ~ egress module } and a network processor
HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH