Circuit Emulation Services (CES) is an essential technology to ease the migration towards Ethernet/IP/MPLS networks by protecting the investment made in equipment having TDM interfaces. Therefore the first to realize the need for a cost-effective sync over packet solution were the Metro Ethernet and the Pseudo Wire equipment vendors requiring the clock synchronization performance to meet ITU-T G.823 and ITU-T G.824 clock synchronization standards.

CES packets can be used both for in-band clock synchronization where the CES packet stream serves for data and clock recovery or as out-of-band clock recovery whereas the CES packets are used for clock recovery only. However, it was found that the inherent packet network impairments severely degraded clock synchronization performance.

Packet network impairments include:

A new approach for clock synchronization over packet was taken separating the data processing and clock synchronization into two independent entities to allow new clock synchronization technologies for handling the inherent packet network impairments in order to meet the ITU-T G.823, ITU-T G.824, and ITU-T G.8261 clock synchronization standards.