A path error monitoring method is provided for monitoring for an error in a communication
path in a synchronous network by using an error detection code inserted into a
first predetermined byte in the overhead of transmitted information. The method
includes the steps of: performing an error detection code operation for a predetermined
range of the transmitted information in a sender side; inserting the obtained error
detection code into a second predetermined byte different from the first predetermined
byte in the overhead of the transmitted information and sending the inserted transmitted
information; performing an error detection code operation for a predetermined range
of the inserted transmitted information received in a receiver side; and monitoring
for an error in a communication path between the sender side and the receiver side
by comparing the obtained error detection code with the second predetermined byte
in the inserted transmitted information. Accordingly, even if a redundant communication
path is provided in the middle of a communication path, it is possible to determine
whether or not there arises an error with respect to only the redundant communication
path. As a result, it is possible to avoid an unnecessary path switching operation
due to an error in the upper stream to the redundant communication path.
