The ONU is connected with an aggregating ONU in the PON through {HEAD ~ an alternate connection} separate from {TAIL ~ the PON} 
The ONU is connected with an aggregating ONU in the PON through { HEAD ~ an alternate connection } separate from { TAIL ~ the PON }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL