Introduction to link definition

The definition of a link to a remote system consists of two basic parts:

  1. The definition of the remote system itself
  2. The definition of sessions with the remote system.

The remote system is defined by the DEFINE CONNECTION command. Each session, or group of parallel sessions, is defined by the DEFINE SESSIONS command. The definitions of the remote system and the sessions are always separate, and are not associated with each other until they are installed.

For single-session APPC terminals, an alternative method of definition, using DEFINE TERMINAL and DEFINE TYPETERM, is available.

If the remote system is CICS®, or any other system that uses resource definition to define intersystem sessions (for example, IMS™), the link definition must be matched by a compatible definition in the remote system. For remote systems with little or no flexibility in their session properties (for example, APPC terminals), the link definition must match the fixed attributes of the remote system concerned.

Naming the local CICS system

A CICS Transaction Server for z/OS® system can be known by more than one name:

All CICS systems have an applid and a sysidnt. A terminal-owning region that is a member of a VTAM generic resource group also has a VTAM generic resource name (VTAM generic resource names are described in Installation considerations for VTAM generic resources).

The applid of the local CICS system

The applid of a CICS system is the name by which it is known in the intercommunication network; that is, its netname.

For MRO, CICS uses the applid name to identify itself when it signs on to the CICS interregion SVC, either during startup or in response to a SET IRC OPEN master terminal command.

For ISC, the applid is used on a VTAM APPL statement, to identify CICS to VTAM.

You specify the applid on the APPLID system initialization parameter. The default value is DBDCCICS. This value can be overridden during CICS startup.

All applids in your intercommunication network should be unique.

Note:
CICS systems that use XRF have two applids, to distinguish between the active and alternate systems. This special case is described in Generic and specific applids for XRF.

The sysidnt of the local CICS system

The sysidnt of a CICS system is a name (1-4 characters) known only to the CICS system itself.

It is obtained (in order of priority) from:

  1. The startup override
  2. The SYSIDNT operand of the DFHSIT macro
  3. The default value CICS.
Note:
The sysidnt of your CICS system may also have to be specified in the DFHTCT TYPE=INITIAL macro if you are using macro-level resource definition. The only purpose of the SYSIDNT operand of DFHTCT TYPE=INITIAL is to control the assembly of local and remote terminal definitions in the terminal control table. (Terminal definition is described in Defining remote resources.) The sysidnt of a running CICS system is always the one specified by the system initialization parameters.

Related concepts
Multiregion operation
Installation considerations for multiregion operation
Intersystem communication
Installation considerations for intersystem communication
Generic and specific applids for XRF
Related tasks
Identifying remote systems
Defining links for multiregion operation
Defining links for use by the external CICS interfaceDefining APPC links
Defining logical unit type 6.1 links
Defining CICS-to-IMS LUTYPE6.1 links
Defining indirect links for transaction routing
Managing APPC links
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