Clock stability measures for the assessment of synchronization network performance

At present, one of the major open issues related to the implementation of SDH based transport networks is the design of a suitable synchronization network, required in order to exploit fully the capabilities offered by the new hierarchy. In fact, unacceptable signal degradation may result if too loose requirements are set in the specification of clocks and synchronization network architecture: hence the problem of characterizing synchronization network performance plays a central role in synchronization network design. In this paper, starting from a general model of timing signals generated by actual clocks, frequency and time domain quantities suitable for characterizing frequency and time stability are presented. Then the problem of assessing synchronization network performance is investigated, analysing with particular care the measurement configurations usable for the evaluation of the time domain quantities. Finally, results from computer based calculations performed to evaluate Allan variance behaviour in different measurement configurations are presented