System configuration for standardizing SDH-based time and frequency transfer

By using the Network Node Interface (NNI) and User-Network Interface (UNI) in the Synchronous Digital Hierarchy (SDH), time and frequency transfer can be realized. The transfer system uses a bi-directional transmission medium instead of the conventional uni-directional medium for reference signal distribution, and can use the information channel called Section OverHead (SOH) to transfer time and frequency without interfering with B-ISDN services. The combination of a single fiber cable and the wavelength division multiplex method, which can be applied between network nodes, permits accurate time dissemination of the order of subnano seconds.