Dual-stage clock recovery for TDM in packet networks

Clock recovery for TDM service in a packet network is inherently different from its circuit-switched counterpart. There are two generic approaches, namely, non-synchronous methods which rely on packet jitter filter and synchronous methods which use a common reference clock. A new TDM service clock recovery in packet networks with dual-stage structure which combines the merits of those approaches mentioned above is presented in this paper. In the first-stage of this structure, a reference clock created at the destination through a non-synchronous method can follow the origin reference clock as closely as possible, and a service clock can be recovered using synchronous methods like SRTS (synchronous residual time stamp) in the second-stage. Theory analysis and practical measurement results are used to validate the scheme.