IBM 990 - Manual (Page 172)

160 IBM
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zSeries 990 Technical Guide
Even though multiple servers can connect to only one Sysplex Timer unit, the typical
configuration is usually connected to two different Sysplex Timer units called an Expanded
Availability configuration. Refer to IBM
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zSeries Connectivity Handbook,
SG24-5444, for IBM 9037 Sysplex Timer connectivity information.
External Reference ID
A Sysplex Timer unit is assigned a unique two-digit ID at installation time, called a Unit ID.
This Unit ID is referenced as an External Time Reference ID (ETR ID) in the output of the
z/OS command D ETR and Support Element panels.
A function is introduced with the z990 server, 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 function checks that the ETR
Network ID being received in the timing signals via each of the server's two ETR ports
matches the ETR Network ID manually set in the server's Support Element (SE).
Up to two Sysplex Timer units can be configured in an Expanded Availability configuration,
each one with a unique ETR ID. When in Expanded Availability configuration, a network ID
(Net ID) is also assigned at installation time to identify that these two Sysplex Timer units
belong to the same Sysplex Timer configuration.
The z990 requires that the ETR Network ID of the attached Sysplex Timers be entered in a
panel on the Support Element (SE). As part of the installation of a Sysplex Timer in either
Basic or Expanded Availability configuration, each IBM 9037 Sysplex Timer Unit is assigned
an ETR Network ID (0 to 31 decimal) and an ETR Unit ID (0 to 31 decimal). Within the valid
range, the ETR Network ID and ETR Unit ID values are arbitrary and can be chosen by the
customer to uniquely identify an ETR network and a unique ETR unit (Sysplex Timer) within
the ETR network.
In addition, on the same panel, the ETR ports have to be enabled for stepping the TOD. This
function checks that the ETR Network ID being received in the timing signals via each of the
two ETR ports matches the ETR Network ID manually set in the z990 Support Element. This
provides greater checking, helping eliminate cabling errors where a z990 ETR port may be
incorrectly connected to a Sysplex Timer Unit in an incorrect Sysplex Timer ETR network,
and allows verification of cabling connectivity from the Sysplex Timer to the z990 server prior
to IPLing z/OS or OS/390.
To get the appropriate SE panel, log on to the SE directly or via the HMC single object
operations task. Navigate to the CPC Configuration task list and invoke the System Complex
(Sysplex) Timer task. Once this task is invoked, a notebook is displayed with two panels. The
first panel contains configuration information, as shown in Figure 7-2 on page 161; the ETR
Network ID (0-31) is entered on this configuration panel.