JPH035699B

PURPOSE:To supervise all systems of the U-shaped optical bus network by providing a supervisory device supervising a transmission line and each transmission/reception unit to the end of the open side of the optical transmission line. CONSTITUTION:An optical signal from a generic transmission system 11 is reflected on a half mirror 3C, transmitted through a half mirror 3D via an optical fiber 5, propagated along the progressing direction 7 of the generic transmission system optical signal, reflected on a half mirror 3B and then received by the generic transmission system 21 of the transmisstion/reception unit B2. Moreover, the optical signal from an RAS system 12 is reflected on the half mirror 3C, reflected on a half mirror 3A via the optical fiber 5 and the supervisory device 4, progressed along the progressing direction 6 of the RAS syste optical signal and received by the RAS system 12 of the transmisstion/reception unit 1. Thus, the RAS supervision is attained independently of the state of the generic transmission line.