Physical layer clock synchronization means that devices restore the clock frequency from physical signals to achieve frequency synchronization between upstream and downstream devices.
1588v2, SMPTE-2059-2 and G.8275.1 are all time synchronization protocols. 1588v2 is defined by IEEE, SMPTE-2059-2 is an IEEE 1588-based standard used to allow time synchronization for video devices over an IP network and G.8275.1 is defined by ITU-T for telecom applications. This section describes 1588v2, SMPTE-2059-2 and G.8275.1.