IBM Z10 EC - Manual (Page 54)

The following STP enhancements are available on System
z10 and System z9 servers.
The STP feature and the latest Machine Change Levels are
required.
Enhanced Network Time Protocol (NTP) client support:
This enhancement addresses the requirements for those
who need to provide the same accurate time across het-
erogeneous platforms in an enterprise.
The STP design has been enhanced to include support
for a Simple Network Time Protocol (SNTP) client on the
Support Element. By confi guring an NTP server as the
STP External Time Source (ETS), the time of an STP-only
Coordinated Timing Network (CTN) can track to the time
provided by the NTP server, and maintain a time accuracy
of 100 milliseconds.
Note: NTP client support has been available since October
2007.
Enhanced accuracy to an External Time Source: The
time accuracy of an STP-only CTN has been improved by
adding the capability to confi gure an NTP server that has
a pulse per second (PPS) output signal as the ETS device.
This type of ETS device is available worldwide from sev-
eral vendors that provide network timing solutions.
STP has been designed to track to the highly stable,
accurate PPS signal from the NTP server, and maintain
an accuracy of 10 microseconds as measured at the PPS
input of the System z server. A number of variables such
as accuracy of the NTP server to its time source (GPS,
radio signals for example), and cable used to connect the
PPS signal will determine the ultimate accuracy of STP to
Coordinated Universal Time (UTC).
In comparison, the IBM Sysplex Timer is designed to
maintain an accuracy of 100 microseconds when attached
to an ETS with a PPS output. If STP is confi gured to use
a dial-out time service or an NTP server without PPS, it is
designed to provide a time accuracy of 100 milliseconds
to the ETS device.
For this enhancement, the NTP output of the NTP server
has to be connected to the Support Element (SE) LAN,
and the PPS output of the same NTP server has to be con-
nected to the PPS input provided on the External Time
Reference (ETR) feature of the System z10 or System z9
server.
Continuous availability of NTP servers used as Exter-
nal Time Source: Improved External Time Source (ETS)
availability can now be provided if you confi gure different
NTP servers for the Preferred Time Server (PTS) and the
Backup Time Server (BTS). Only the PTS or the BTS can
be the Current Time Server (CTS) in an STP-only CTN.
Prior to this enhancement, only the CTS calculated the
time adjustments necessary to maintain time accuracy.
With this enhancement, if the PTS/CTS cannot access the
NTP server or the pulse per second (PPS) signal from the
NTP server, the BTS, if confi gured to a different NTP server,
may be able to calculate the adjustment required and
propagate it to the PTS/CTS. The PTS/CTS in turn will per-
form the necessary time adjustment steering.
This avoids a manual reconfi guration of the BTS to be the
CTS, if the PTS/CTS is not able to access its ETS. In an
ETR network when the primary Sysplex Timer is not able
to access the ETS device, the secondary Sysplex Timer
takes over the role of the primary - a recovery action not
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