The IBM External Time Reference (ETR) architecture facilitates the synchronization of server time-of-day (TOD) clocks to ensure consistent time stamp data across multiple servers and operating systems. The ETR architecture provides a means of synchronizing TOD clocks in different servers with a centralized time reference, which in turn can be set accurately on the basis of an international time standard (External Time Source). The architecture defines a time-signal protocol and a distribution network (called the ETR network) that permits accurate setting, maintenance, and consistency of TOD clocks.

A new function is introduced with the IBM eServer zSeries 990, implemented in the server's Support Element code, which now requires the ETR Network ID of the attached Sysplex Timer Network to be manually set in the Support Element at installation time. This new function checks that the ETR Network ID being received in the timing signals through each of the server's two ETR ports matches the ETR Network ID manually set in the server's Support Element (SE).

Sysplex Timer

ETR Network ID setup during z990 installation

Changing the ETR Network ID