SYNCHRONOUS TECHNIQUES FOR TIMING RECOVERY IN BISDN

Timing recovery for an ATM network is inherently different from its ci rcuit-switched counterpart, There are two generic approaches to ATM ti ming recovery, namely, nonsynchronous methods which rely on cell jitte r filtering and synchronous methods which use a common reference clock . The latter approach has better jitter/wander performance, This is pa rticularly significant for circuit emulation of existing hierarchical signals (e.g. DSn signals), which have stringent jitter/wander require ments. This paper compares several methods for timing recovery network environment and discusses concept, implementation, and performance of three synchronous techniques: Synchronous Frequency Encoding Techniqu e (SFET), Time Stamp (TS), and Synchronous Residual Time Stamp (SRTS). Among these methods, it is concluded that the SETS method, invented b y the authors, is the most efficient, SETS has been accepted by ITU-T as the timing recovery standard for AAL-1 (ATM Adaptation Layer - Circ uit Emulation). Practical implementation considerations of the SRTS te chnique and its robustness against cell loss are also examined in this paper, In addition, it is shown that a strong analogy can be drawn be tween SRTS and conventional pulse stuffing synchronization techniques so that the jitter performance for SRTS is comparable to that of the c ircuit-switched network.