Problems with jitter measurement in PDH/SDH-based digital telecommunication systems

The present paper arises from criticisms, originated by telecommunication factories, concerning some problems experienced during production tests of digital telecommunication apparatuses. The faultfinding mainly concerns test equipment as well as recommendations actually in force for generating and measuring timing jitter in telecommunication systems based on both (PDH) plesiochronous and (SDH) synchronous digital hierarchies. In the paper, the aforementioned problems are first discussed in detail and then confirmed by some experiments carried out at the laboratories of a great Italian factory. To meet the request of production managers, a novel, more accurate method for measuring jitter in PDH/SDH-based systems is proposed. Thanks to a suitable digital signal-processing solution, the method no longer needs timing recovery circuitry, and shows itself insensitive to non-rectangular pulse shapes. The results obtained from the application of the method to the same data signals analyzed at the aforementioned factory finally assess its reliability and efficacy.