SONET/SDH adaptive threshold pointer processor clocking strategies

Pointer processors in synchronous optical networks (SONET)/synchronous digital hierarchy networks (SDH) consist of three fundamental types: traditional fixed threshold pointer processors, uniform pointer processors, and adaptive threshold pointer processors. Uniform pointer processors and adaptive threshold pointer processors produce less network jitter than traditional pointer processors. This has created much interest in these advanced pointer processing algorithms. The theory behind adaptive threshold pointer processors is similar to that of sigma delta modulators with important distinctions which include the clocking opportunities for updating the algorithms. The SONET/SDH requirement that pointers must be spaced by at least 4 multiframes imposes a novel requirement that is not present in a standard sigma delta modulator. This paper compares the jitter which results from three different adaptive threshold pointer processor clocking strategies: uniform sampling, state-dependent feedback and non-uniform sampling. Simulation results show that, of these three different clocking strategies, uniform sampling is best.