Synchronization Techniques for Digital Networks

A fault-tolerant network clock regenerator (NCR) will be analyzed, which consists of two digital phase-locked loops (DPLL), and which allows a dynamical configuration control and thus is able to meet CCITT\´s Recommendations concerning permissible slip rates, frequency inaccuracy, as well as phase jitter and wander. The network synchronization scheme will conform to the master-slave principle, in the course of which the reference clock is derived from a national caesium atomic oscillator as master. The NCR\´s mentioned before serve as slaves which are equipped with highly precise voltage-controlled crystal oscillators and proportional-integral working DPLL\´s. The results of a field trial in the long-distance communications network of the "Deutsche Bundespost (FRG)" are given and interpreted by a Random Walk Model which describes the time interval errors appearing. For future digital exchanges, an NCR with intelligent configuration control is introduced, which consists of two microprocessor-controlled digital phase-locked loops (MCDPLL) and which has comparable time stability characteristics as the double-DPLL mentioned above at half the circuit volume. Finally, the dominant advantages are shown which result from synchronizing broad-band services by intelligent NCR techniques.