Chapter 3. I/O system structure 107
ports to support the ICB-2 connections. The STI-2 card converts the 2 GBps input into two
333 MBps ICB-2s. One ICB-2 feature is required for each end of the link. Each ICB-2 link at
the z990 end has a PCHID number. ICB-2 only support connection to 9672 G5/G6 servers.
The ICB-2 cable (feature code 0226) is a unique 10 meter (33 feet) 333 MB copper cable to
be used with ICB-2 links. Existing 10 meter 333 MB ICB-2 cables can be reused.
ICB-2 cables (feature code 0226) will be automatically ordered to match the quantity of
ICB-2s (feature code 0992) on order. Order one cable per connection, not per feature. The
quantity of ICB cables can be reduced, but cannot exceed the quantity of ICB features on
z990 ICB links summary
Table 3-12 shows a summary of all z990 Integrated Cluster Bus (ICB) link types, including
some of their characteristics.
Table 3-12 z990 ICB links summary
IC links
IC links are used when an ICF logical partition is on the same CPC as other system images
participating in the sysplex. An IC link is the fastest Coupling link, using just memory-to-
memory data transfers. IC links do not have PCHID number, but do require CHPIDs.
IC links require ICP channel path definition at the OS/390 or z/OS and the CF end of a
channel connection to operate in peer mode. They are always defined and connected in pairs.
3.4.6 External Time Reference (ETR) feature
The External Time Reference (ETR), feature code 6154, is an optional z990 feature.
Each ETR feature consists of one ETR card and each card has one port. When a quantity of
one is ordered, two features are shipped. The two ETR features are automatically ordered if
any coupling link feature (ISC-3, ICB-2, ICB-3 or ICB-4) is ordered.
These cards provide attachment to the Sysplex Timer in the CPC cage. Each ETR card
should connect to a different 9037 Sysplex Timer in an Expanded Availability configuration.
Each feature has a single port supporting an MT-RJ fiber optic connector to provide the
capability to attach to a Sysplex Timer Unit. The two ETR cards are supported in one CEC
cage card slot in the rear and provide attachment to a 9037 Sysplex Timer; it can be either a
9037 Model 1
or 9037 Model 2. The 9037 Sysplex Timer provides the synchronization for the
Time-of-Day (TOD) clocks of multiple CPCs, and thereby allows events started by different
CPCs to be properly sequenced in time. When multiple CPCs update the same database and
database reconstruction is necessary, all updates are required to be time-stamped in proper
ICB link type Feature
IOCP definition Bandwidth Intended
cable length
ICB-4 3393 CBP 2 GBps z990, z890 10 meters
ICB-3 0993 CBP 1 GBps z900, z800 10 meters
ICB-2 0992 CBS, CBR 333 MBps 9672 G5/G6 only 10 meters
Note that 9037-1 goes End of Service on Dec. 31, 2003.

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