Server Time Protocol (STP) is a server-wide facility that provides capability for multiple z/OS systems to maintain TOD synchronization with each other and form a Coordinated Timing Network (CTN), that is, a collection of z/OS systems that are time synchronized to a time value.
The External Time Reference (ETR) connections will be replaced over time by the implementation of Server Time Protocol (STP), which makes use of coupling links to pass timing messages to the servers. Transition to STP makes it possible to have a Mixed Coordinated Network configuration. The Sysplex Timer provides the timekeeping information in a Mixed CTN. Once an STP-only configuration is established, the ETR connections are no longer needed. STP allows coexistence with Sysplex Timer in mixed configurations. The Sysplex Timer console is replaced by an HMC screen for each possible time zone.