SUBSIDARY ROUTE SWITCHING SYSTEM FOR NETWORK SYNCHRONIZING DEVICE

PURPOSE:To prevent the frequency abnormality of a subsidary destination route from exerting an influence in a clock synchronizing network by providing a switching means for a subsidary destination clock and a means which detects a slip generated in each link. CONSTITUTION:Clock extracting circuits 2A-2C extract clock signals from a PCM multiplex communication line and supply extracted reference clock signals to the network synchronizing device 4. Further, slip detecting circuits 3A-3C detect slips generated owing to a frequency difference between an input PCM signal and a clock signal to an exchange and inform a common controller 5 of their detection results. Then if serious slip trouble occurs to a link having a ratio exceeding a previously specified standard value among links other than subsidary routes, the common controller 5 decides the frequency abnormality of the subsidary route being selected currently. Then an instruction is sent to a changeover switch 6 to perform switching to a stand-by subsidary route.