Additive time synchronous system in existing SDH networks

A simplified SDW (synchronous digital hierarchy)-based time synchronous system that does not need modification of existing SDH transmission equipment (STE) and clock supply equipment (CSE) is proposed. The system has auxiliary time synchronizing equipment attached to existing STE and CSE, where frequency and time are separately synchronized, and which enables us to partially time-synchronize an SDH network or to introduce a time synchronous system locally. Experimental time synchronizing devices using a data communication channel (DCC) in the section overhead (SOH) showed potentially satisfactory performance; synchronization errors of a 4-link system are of the order of sub-microseconds.