a data determination unit determining, on the basis of all LINK IDs present in the data of at least one of the optical network units among the aforementioned optical network units, {HEAD ~ the data} requiring storage from among all data sent to {TAIL ~ the optical network unit} 
a data determination unit determining , on the basis of all LINK IDs present in the data of at least one of the optical network units among the aforementioned optical network units , { HEAD ~ the data } requiring storage from among all data sent to { TAIL ~ the optical network unit }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL