IBM eServer zSeries 900 Technical Guide

Chapter 3. Connectivity 143

3.8.1 Connectivity

This section describes the ETR connectivity of the z900 server.

OSC/ETR

Two OSC/ETR cards are standard on the z900 server. These cards provide the main

oscillator for the z900 server, including the Self Timed Interface (STI), reference, and Memory

Bus Adapter (MBA) clocks. They also provide the I/O for the External Time Reference

connection to one or two 9037 Sysplex Timer Units.

The two standard OSC/ETR cards are located in the CPC cage of the z900 server. Each card

has a single port supporting an MT-RJ fiber optic connector to provide the capability to attach

to a 9037 Sysplex Timer Unit. The MT-RJ is an industry standard connector which has a

much smaller profile compared with the original ESCON Duplex connector supported on the

ETR ports of G5/G6 and earlier servers. The 9037 Sysplex Timer Unit has an optical

transceiver that supports an ESCON Duplex connector.

An MT-RJ/ESCON Conversion Kit (feature code 2325) supplies two 62.5 micron multimode

conversion cables. The conversion cable is two meters (6.5 feet) in length and is terminated at

one end with an MT-RJ connector and at the opposite end with an ESCON Duplex receptacle

to attach to the under floor cabling. This conversion kit is used on the z900 server with the

16-port ESCON feature (feature code 2323) or ETR when reusing existing 62.5 micron

multimode fiber optic cables terminated with ESCON Duplex connectors.

9037 Sysplex Timer models

There are two models of the IBM 9037 Sysplex Timer Unit: Model 1 and Model 2. IBM 9037

Model 1 has been withdrawn from marketing and is no longer available. Refer to the IBM

Redbook

S/390 Timer Management and IBM 9037 Sysplex Timer,

SG24-2070, for more

information on the IBM 9037 Model 1.

The z900 server can attach to either a 9037 Model 1 or Model 2 Sysplex Timer Unit. Both

Sysplex Timer Unit models support:

򐂰 Basic configuration

򐂰 Expanded availability configuration

Sysplex Timer expanded availability configuration is the recommended configuration in a

Parallel Sysplex environment. This configuration is fault-tolerant to single points of failure, and

minimizes the possibility that a failure can cause a loss of time synchronization information to

the attached servers.

Sysplex Timer basic configuration

The IBM 9037 Model 2 basic configuration is shown in Figure 3-29 on page 144. The basic

configuration is not recommended in a Parallel Sysplex environment because of the limited

fault tolerance it provides. It can be used for applications when setting and maintaining the

time of multiple servers to the same external time reference is desirable. When the IBM 9037

provides this time reference, the user does not need to manually set the TOD clock at

operating system IPL.

Note: The OSC/ETR card does not support a multimode fiber optic cable terminated with

an ESCON Duplex connector.

However, 62.5 micron multimode ESCON Duplex jumper cables can be reused to

connect to the OSC/ETR card. This is done by installing an MT-RJ/ESCON Conversion

kit between the OSC/ETR card MT-RJ port and the ESCON Duplex jumper cable.