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