Highly accurate time synchronization over switched Ethernet

In the automation world the intelligent electrical devices need to be accurately synchronized for time stamping of data and motion control. We discuss how to achieve precise time synchronization over switched Ethernet networks in a generic way. The addressed synchronization requirements relate to substation automation, which is associated with five levels of synchronization accuracy defined as the IEC 61850 classes T1 to T5. The paper challenges the hardest requirements and presents general solutions for IEC classes T4/T5 (4 /spl mu/s/1 /spl mu/s) and IEC class 3 (25 /spl mu/s) in multi-traffic LAN environments. The classes T4/T5 solution is based on an Ethernet switch from OnTime Networks, while the class T3 solution relies on standard Ethernet switches. Common for both solutions is that they adhere to a low-level time stamp implementation of the Simple Network Time Protocol.