Transmission device with data channel failure notification function during control channel failure

摘要

The present invention provides a transmission network system, which can discover the location of a failure of a data channel during a control channel failure. When a first transmission device located at a downstream side of a working path detects a failure of a working data channel for transmitting data signals to be input to the first transmission device along the working path during a control channel failure, it notifies the failure of the working channel to a second transmission device located at an upstream side of the working path via a bypass control channel. The second transmission device judges the location of the failure based on positional relationship between the second and first transmission devices, and based on presence of a failure of a working data channel for transmitting data signals to be input to the second transmission device along the working path.