As more and more traffic is being delivered in Ethernet format, carriers are realizing the
advantages to converging on a pure Ethernet infrastructure, but are not able to do so with
Ethernet as presently defined. New ITU-T Recommendations, such as Y.1731 for
Ethernet OAM and G.8031 for Ethernet protection switching, provide features essential
for operational maintenance of Ethernet networks. Recently proposed mechanisms for
configuring point-to-point connections in Ethernet networks close another gap between
and SONET/SDH networks.
The final difference between conventional TDM-based networks and Ethernet is that the
former also transport frequency information, needed for some applications, while
Ethernet does not. Numerous methods have been suggested for augmenting Ethernet to
distribute frequency and/or timing information, such as IEEE 1588, IETF’s NTP, and
methods developed for use of TDM pseudowires.
In this article I will talk another method for transport of synchronization over Ethernet
networks, for those applications that need it. This method locks the timing of the Ethernet
physical layer, much the same way that SONET/SDH does. This enables simple recovery
of the physical layer timing, which can be used directly by locking downstream networks
and applications, or indirectly by using the physical layer timing as a common reference.