In-band communication of alarm status information in a synchronous transport communication system

Techniques are disclosed for in-band communication of alarm status information or other information between physical layer devices comprising a working device and a protection device in a network-based communication system. In one aspect, a protection receive signal is monitored in the protection device for the presence of alarm status information. The protection device encodes alarm status information extracted from the protection receive signal, and inserts the encoded alarm status information into one or more designated portions of a protection loop-back signal supplied from the protection device to the working device. The protection loop-back signal is monitored in the working device and the encoded alarm status information therein is decoded and utilized by the working device to initiate a protection switching operation.