Method and apparatus for the mutual synchronization of the exchange clock pulse oscillators in switching systems of a PCM time division multiplex telecommunication network

摘要

A method and apparatus for synchronizing clock oscillators in each of the exchange installations (network nodes) of a PCM/TDM telecommunication network is described. A frequency divider in each network node receives pulses from a clock generator at that node, and frequency dividers are provided for receiving clock pulses from other exchangers on incoming trunks. The incoming trunk frequency dividers are caused to operate with a phase displacement of 180° relative to the clock generator in the exchange. The outputs from the incoming trunk frequency dividers and the exchange clock frequency divider are coupled to phase discriminators. The phase discriminator outputs are coupled through a sum or mean value producing element to produce a control signal for adjusting the frequency of the exchange clock oscillator. Reference phase regeneration is initiated as a result of frequency drift from the oscillator no-load frequency, which drift exceeds a predetermined value.