In the broad sense, clock synchronization includes frequency synchronization and time synchronization. Generally, clock synchronization refers to frequency synchronization. Clock synchronization is a basic condition of synchronous digital communication.

For transport networks, clock synchronization must be implemented to accurately sample digital signals transmitted over the network and therefor minimizes the impact of the slips, burst bit errors, phase jumps, jitters, and wanders on digital communication systems.
From group: Transport&Access Network

