Patent ID: 7372804

Claim:
A line switching system in a multiplex communication system, comprising a plurality of terminal devices and a plurality of line switching devices, wherein: at least one terminal device is connected to one line switching device and one line switching device is connected to another line switching device via a present line and a standby line; one terminal device is connected to another terminal device prescribed beforehand to be capable of communication via a line switching device and a present line so that communication is achieved using a protocol without a line switching function; and the standby line is a line replaceable with the present line, wherein: the line switching device comprises: a fault detection unit for detecting generation of a fault through checking whether or not a recognizable signal is detected from a line within a prescribed time; a fault notification unit for notifying generation of fault to another line switching device when the generation of fault is detected in the fault detection unit; and a line switching unit for, when the fault detection unit detects generation of a fault in the present line, switching the present line with the fault detected by the fault detection unit to the standby line which can be replaced with the present line thereby to perform communication between the terminal device and another terminal device prescribed beforehand, wherein the line switching unit switches the line after a switching protection time has passed from the detection of a fault by the fault detection unit, wherein the fault notification unit comprises a function of notifying a fault by periodically repeating interruption of signal output and transmission of a link down pattern for downing the link in a protocol, and wherein in a period in the periodical repeat, time for transmitting the link down pattern is set longer than time for interrupting output.