Patent ID: 7372807

Claim:
A multiplex transmission apparatus connected to a plurality of first communication lines each transmitting a signal comprising of an overhead and a payload according to the standard of SONET (Synchronous Optical Network) or SDH (Synchronous Digital Hierarchy) and to at least one second communication line capable of transmitting a signal according to the same standard as said first communication lines at a speed higher than that of each of said first communication lines, the multiplex transmission apparatus comprising: a plurality of first transceiver units each connected to one of said first communication lines for receiving a signal transferred on the first communication line and processing a first overhead extracted from the received signal; a multiplexing and conversion unit for multiplexing at least payload portions of a plurality of signals received from said first transceiver units to generate a payload of a signal to be transmitted to said second communication line; a second transceiver unit connected to said second communication line and said multiplexing and conversion unit for processing a second overhead to be transferred on the second communication line and transmitting a signal having the second overhead and the payload generated by said multiplexing and conversion unit to said second communication line; and a control unit for controlling the whole operation of the multiplex transmission apparatus, wherein said control unit instructs said second transceiver unit, when said first overhead received by one of said first transceiver units includes, at a predetermined location thereof, automatic protection switching (APS) bytes indicating that a failure occurs on one of said first communication lines, to add the alarm indication to said second overhead, said second transceiver unit inserts a bit pattern into a predetermined location of said second overhead in response to the instruction from said control unit and transmits a signal having the second overhead with said bit pattern to said second communication line, at least three low order bits of the bit pattern having an all “1” value, and said predetermined location being within a line overhead in the case of SONET and within an M section in the case of SDH, wherein said predetermined location of said second overhead where said bit pattern is inserted resides in an undefined area having no authorized definition with respect to information to be set therein according to said SONET and SDH standard.