Digital Data System: Network Synchronization
Burton R. Saltzberg, H. M. Zydney · Bell System Technical Journal · 1975
The Digital Data System is synchronized by means of a network in the form of a master-slave tree. Functioning data links are used for distribution of synchronization signals and timing is recovered from the data stream. The master timing supply sets the frequency for the entire network. Each major node contains a nodal timing supply with an extremely long time constant, which phase-locks to the incoming data signal. The nodal timing supply contains frequency memory and sufficient accuracy to free run satisfactorily for several days if its inputs fail. A local or secondary timing supply is designed for operation in distant nodes of the tree. Each timing supply provides common clock signals to all DDS equipment in the office in which it is installed. All timing supply designs include a high degree of redundancy for reliability purposes.