Configuring the Link3270 bridge

The 3270 bridge provides an interface so that you can run 3270-based CICS® transactions without a 3270 terminal. The 3270 bridge mechanism simulates the presence of a real 3270 by providing internal interfaces for a virtual 3270, known as the bridge facility. The bridge facility is created by DFHL3270 when it receives a single transaction mode request or a session mode request to allocate a bridge facility. You do not provide a TERMINAL resource definition for the bridge facility, but you can control the terminal properties used by providing a 3270 TERMINAL resource definition to be used as a template. This TERMINAL definition is known as the facilitylike.

However, once the bridge facility has been defined, its facilitylike template cannot be changed. Therefore, if the bridge facility is reused in session mode, CICS ignores the facilitylike value passed in subsequent calls.

Typically, CICS defines all bridge facilities automatically. However, you can write a user replaceable module to control the autoinstallation of bridge facilities if required.

Procedure

Defining Link3270 system initialization parameters

Optional: Define Link3270 system initialization parameters to help manage the Link3270 bridge.
- In the bridge router region, define the AIBRIDGE system initialization parameter to specify whether the autoinstall user replaceable module (URM) is called when bridge facilities are created and deleted.
- Define the SPCTR and STNTR system initialization parameters if you want standard and special tracing for the bridge (BR) and partner (PT) domains.
- The Link3270 bridge runs under CSMI by default. If you want to use a transaction ID other than CSMI for the Link3270 bridge, specify an INITPARM system initialization parameter for program DFHL3270, as follows:
```
INITPARM=(DFHL3270='tttt'),
```
  where tttt is the desired transaction ID. The definition of your transaction tttt must be a copy of the definition of CSMI, so that the initial program is DFHMIRS and the profile is the same as that used by CSMI.
You have configured CICS to use a URM to install bridge facilities and added tracing.

Defining the bridge facility

You can use a real TERMINAL resource definition as a template for some of the properties of the bridge facility. Use the name of this TERMINAL definition as the FACILITYLIKE value. It can be passed to CICS in one of three ways (the first non-blank value found is used):
- From the BRIH-FACILITYLIKE parameter in the Link3270 call.
- From the PROFILE resource definition for the user transaction.
- The default definition CBRF, supplied by CICS in group DFHTERM, to support the bridge.
Note: If you are running in a CICS system started with the VTAM=NO system initialization parameter, the resource definition specified by facilitylike must be defined as REMOTE. CBRF is defined as REMOTE.
VTAM® is now z/OS® Communications Server.
Create and define the bridge facility namespace allocation file DFHBRNSF to CICS in the Link3270 router regions.
See Creating and defining the bridge facility namespace allocation file DFHBRNSF.

What to do next

The bridge facility can have a Terminal Control Table User Area (TCTUA), which can be accessed by EXEC CICS ADDRESS TCTUA in the normal way. The TCTUA is initialized to nulls when the bridge facility is created. The global user exit XFAINTU is called when a bridge facility is created and discarded. XFAINTU is passed the address of the TCTUA, so you can use this exit to initialize the TCTUA.