Abstract: The optical communication system employs PON system. An office device includes a pair of an optical transmitting/receiving devices. A subscriber line, which is a single core optical fiber, is connected to the optical transmitting/receiving devices at each terminal to form a loop network. Subscriber devices are connected to the network via passive optical branching/coupling elements. When the office device transmits a test signal, the subscriber devices transmit response signals corresponding to the test signal. The office device specifies fault point based on the response signals received by the optical transmitting/receiving devices.

Abstract: The high performance multiplexed transmission system of this invention is configured by a sound coding unit for coding voice input information by separating it into a core information part for assuring the minimum acceptable sound quality and a supplementary information part discardable in stages per the transmission priorities. There is a silent section detecting unit for detecting silent sections of voice input information. In addition, there is a multiplexing unit for multiplexing only the information synchronizing with the correspondent's coder for the voice channels from which no sound is detected, or first the core information part and second the supplementary information part from the ones with the highest priorities in stages in fixed length frames, for discarding the supplementary information parts, which cannot be multiplexed because of a band deficiency.

Abstract: A diagnostic expert system is set up with a first diagnostic subsystem based on a maintenance technician's knowledge and a second diagnostic subsystem based on a design engineer's knowledge. If a fault cannot be located under the first diagnostic subsystem, the second diagnostic subsystem, which operates by using the result obtained from the first diagnostic subsystem is started so as to determine the location of the fault.