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The general aspects of timing and synchronization in digital communications networks are reviewed. The properties of the links and nodes carrying and switching time-multiplexed digital signals determine the throughput and performance of a network.The continuity and integrity conditions for the digital information flow, where timing faults cause errors and loss of information determine the requirements on accurate clock signal distribution.The dominant type of architecture for network synchronization is based on the master-slave hierarchy principle. In the future, dating and time-stamping of events will become feasible.

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A system of two coupled cavities is described replacing the single cavity of an NH3 maser. Using this system the curve of the oscillation frequency against cavity temperature presents a plateau, thus reducing considerably the "pulling" effects of the cavity.

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