Customer expectations regarding the performance of intelligent digital networks can be met only if careful consideration is given to synchronization at every level in the network. This includes synchronization of the public switched and private networks, and performance of the clocks that control customer premises equipment (CPE). Poor synchronization planning at the public or private network level, as well as poor CPE clock performance can degrade customer applications such as video, facsimile, digital data, encryption, voice‐band data, and voice transmission. In this paper, we consider the synchronization philosophies and implementation of both AT&T's national telecommunications network and private customer‐owned networks. We will also discuss the performance of typical CPE clocking systems and describe the synchronization systems used in AT&T's line of Definity® business communications systems.