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