OPTICAL SUBSCRIBER NETWORK SYSTEM AND FAULT MONITOR METHOD IN ITS OPTICAL SUBSCRIBER NETWORK SYSTEM

PROBLEM TO BE SOLVED: To duplicate an optical transmission reception section or the like of an optical subscriber system, to specify a faulty point of a reception circuit of an optical transmission line/optical subscriber system and to ensure transmission of incoming data at a normal timing. SOLUTION: This network system adopts a passive optical network configuration where a station equipment 100 accommodates pluralities of subscriber equipments 1-n via an optical transmission line 60 by using a passive optical element 50. In this case, bypass transmission lines 1a-(n-1)a for mutual monitor control are provided among the subscriber equipments (1-n), a subscriber equipment mutual monitor control signal is sent/received among the subscriber equipments (1-n) via the bypass transmission lines 1a-(n-1)a, received subscriber equipment mutual monitor control information is sent to the station equipment 100 via the optical transmission line and the station equipment 100 monitors a fault.