Abstract: A ring network, which can reduce the amount of processing, deal with the occurrence of faults, and lighten the load on an operator, includes a plurality of transmission apparatuses each including a cross-connect function unit and a communication function unit for sending and receiving messages using the overhead of an SDH frame, and a master transmission apparatus to which a command is input for switching from a UPSR to BLSR mode including a path management database, a path decision unit, and an interchange decision unit. The master transmission apparatus to which the command is input collects and stores path setting information of all of the transmission apparatuses in the path management database and sequentially performs processing for deciding on and deleting a long path and processing for interchanging a path on a protection channel to an idle work channel by sending and receiving a message.

Abstract: A ring network, which can reduce the amount of processing, deal with the occurrence of faults, and lighten the load on an operator, comprised with a plurality of transmission apparatuses each including a cross-connect function unit and a communication function unit for sending and receiving messages using the overhead of an SDH frame, and a master transmission apparatus to which a command is input for switching from a UPSR to BLSR mode including a path management database, a path decision unit, and an interchange decision unit. The master transmission apparatus to which said command has been input for collecting and storing path setting information of all of the transmission apparatuses in the path management database and sequentially performing processing for deciding on and deleting a long path and processing for interchanging a path on a protection channel to an idle work channel by sending and receiving a message.

Abstract: Disclosed is a duplex system of transmission lines in a loop network applied, for example, to a local area network. To realize an autonomous recognition of transmission line faults by each communication node and to enable a rapid and automatic reconstruction of a network, each communication node comprises a loop back circuit for effecting a loop back operation in response to a predetermined state of signals received from two directions of the duplex loop lines, and a return indication circuit for adding, to a transmitted signal a return indication that a received signal was returned when the received signal could not be passed through the node.