Frequency and time synchronization over a network are key requirements for precise timekeeping. Synchronous Ethernet (SyncE) is a physical layer technology that supports frequency transfer from hop to hop that can be made traceable to an external source such as a network clock. It distributes synchronization over the physical layer.
Although SyncE can deliver stable frequency synchronization, it cannot deliver time or phase synchronization. A separate protocol is required for delivery of time or phase synchronization.
SyncE uses the physical layer (Ethernet interfaces) to distribute frequency from the primary reference clock (PRC) to downstream devices. It supports frequency transfer from hop to hop and is used to provide frequency synchronization in networks. Because SyncE operates at the physical level, all Ethernet devices along the synchronization path must be SyncE-capable.
The advantage of SyncE for network synchronization over PTPv2 is that it provides high-quality frequency synchronization irrespective of the network load. When SyncE is enabled on the physical Ethernet interface and switch, frequency recovery from the received signal on the physical line occurs, and frequency synchronization is performed in the hardware.
SyncE uses the Synchronization Status Message (SSM) and the Ethernet Synchronization Message Channel (ESMC) for clock selection, traceability, and failover.