Clock Stability Characterization and Measurement in Telecommunications

Clock stability characterization and measurement for telecommunications pose peculiar issues and requirements. This paper aims to provide an overview on this subject. After briefly recalling the background work, the key features and issues of clock stability characterization and measurement in telecommunications are described. The timing signal reference model and the stability quantities adopted in the new international standards are introduced and the impact of the measurement configuration and of the time error sampling period on their behavior are elucidated. The measurement of clock stability in telecommunications is then addressed, and a standard practical measurement procedure is outlined. Several measurement results are provided to support the concepts expounded with experimental evidence. The results shown have been chosen among those obtained throughout the last three years by testing clocks of digital switching exchanges, clocks for synchronous digital hierarchy (SDH) equipment, and state-of-the-art stand-alone slave clocks for synchronization networks. They thus represent a survey of the actual performance of clocks currently deployed in telecommunications networks.