Precision time-transfer in transport networks using digital cross-connect systems

A technique for precise synchronization of the time-of-day clocks in networks of digital cross-connect systems (DCSs) is described. This method is intended to enhance the performance of reconfigurable transport networks and is specifically devised to exploit the fine time resolution of the carrier signals to which a DCS has direct access. The resulting scheme is a master-slave, multisite, implicitly delay compensated, nonhierarchical time-transfer method with a theoretical precision of one bit time at the carrier rate. In practice, precision is limited by transmission span delay asymmetries but residual time errors of under 1 μs are predicted. The method is intended for n/ n space-switching DCS, but other DCS properties can be accommodated. Requirements for DCS equipment design are given, including a generic circuit module for DCS hardware support of the time transfer function. The proposed method applies to DS-3 networks or synchronous optical networks and requires no change in the standards. Measurement or improved estimation of characteristic span delay asymmetries is recommended to refine the preliminary performance estimate