The need for synchronization, one of the key mechanisms required by telecommunication systems, emerged with the introduction of digital communication systems. Synchronization requirements have been evolving with technology and adapting to the needs of networks. Networks were originally designed to primarily carry voice calls; whereas today most traffic is data. The tremendous increase of data traffic has triggered the migration from time division multiplexing (TDM) networks to packet networks, in particular Ethernet. This change has provided a cost efficient means for handling rapidly increasing data loads, but Ethernet is asynchronous in nature and some network services require some form of synchronization. New standards have been developed that enable synchronization in packet networks.
One of these standards is Synchronous Ethernet (SyncE) that enables physical layer frequency synchronization for the Ethernet network. SyncE requires hardware support along the whole path of frequency synchronization transfer. Another standard is precision time protocol (PTP) defined by IEEE 1588 that enables frequency, phase and time synchronization through any packet network. Hardware support is not required from a packet network to carry PTP timing, however using PTP aware devices, such as transparent clocks and boundary clocks, may be necessary to achieve required synchronization accuracy.