IBM System z10 EC Reference Manual page 41

Server Time Protocol (STP)
Server Time Protocol (STP) is designed to provide the
capability for multiple servers and Coupling Facilities to
maintain time synchronization with each other, without
requiring an IBM Sysplex Timer.
Server Time Protocol is designed to help:
• Reduce cost
• Simplify your infrastructure
• Improve systems management
• Improve support for Geographically Dispersed Parallel
Sysplex (GDPS )
™ ®
• Improve time synchronization
• Accommodate concurrent migration
• Coexist with Sysplex Timer based timing network
The Server Time Protocol (STP) feature is designed to be
the supported method for maintaining time synchronization
between IBM System z10, System z9, z990, z890 servers
and Coupling Facilities (CFs). To enable these servers and
CFs for STP, the STP feature—Licensed Internal Code—
must be installed and enabled.
STP supports the ability to:
• Initialize the time either manually or by using an External
Time Source (ETS). The ETS can be a dial out time ser-
vice or a connection to a Network Time Protocol (NTP)
server. Accessing an ETS allows the time of the STP net-
work to be set to an international time standard such as
Coordinated Universal Time (UTC).
• Initialize the Time Zone offset, Daylight Savings Time
(DST) offset and Leap seconds offset.
• Schedule periodic dial-outs to a time service to maintain
accurate time. If an NTP server is used as the ETS, no
scheduling is required because STP will periodically
access the NTP server to maintain accurate time.
• Adjust time by up to +/- 60 seconds. This improves upon
the Sysplex Timer's capability of adjusting time by up to
+/- 4.999 seconds.
Prior to the introduction of STP, a Sysplex Timer was used
to synchronize the time of attached servers in an External
Time Reference (ETR) network. STP can help provide
functional and economic benefits when compared to the
Sysplex Timer. The possible benefits provided by STP are:
• Help eliminate infrastructure requirements, such as
energy consumption and floor space, needed to support
the Sysplex Timers
• Help eliminate maintenance costs associated with the
Sysplex Timers
• Help reduce the fiber optic infrastructure requirements
in a multi-site configuration. Dedicated links may not be
required to transmit timing information as they are with
Sysplex Timers. STP can use existing Coupling links.
• STP supports a multi-site timing network of up to 100
km without requiring an intermediate site. Previously, an
intermediate site was recommended to locate one of
the Sysplex Timers when the multi-site sysplex distance
exceeded 40 km (25 miles).
• Allow more stringent synchronization between servers
and CFs using short communication links, compared
to servers and CFs using long distance communication
links
• Help improve systems management by providing auto-
matic adjustment of Daylight Saving Time offset
The STP design introduces a new concept called Coordi-
nated Timing Network (CTN). A CTN is a collection of serv-
ers and Coupling Facilities that are time synchronized to a
time value called Coordinated Server Time. The CTN con-
cept was introduced to help meet two key goals of existing
IBM System z environments: Concurrent migration from an
existing ETR network to a timing network using STP and
the ability of servers and CFs that cannot support STP to
be synchronized in the same network as servers that sup-
port STP (z10 EC, z9 EC, z9 BC, z990, and z890).
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