Principles of Synchronous Digital Hierarchy

165Synchronization

The master clock supplies the timing to the SSU, which in turn supplies

timings to the actual nodes and the local clocks at the nodes, which are called

“SEC.” All these clocks have been dened in ITU-T recommendations G.811,

G.812, and G.813. (For details of the clock accuracies, please see Section 5.5.)

7.8 Types of Network Synchronization

Depending upon the method of implementation, synchronization may be

categorized as follows:

(i) Master–slave synchronization

(a) Using primary and secondary reference clocks

(b) Timing distribution through GPS

(ii) Mutual synchronization

(iii) Plesiochronous synchronization

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