The Link3270 bridge mechanism

The client application uses the Link3270 bridge to run 3270 transactions by linking to the DFHL3270 program in the router region and passing a COMMAREA that identifies the transaction to be run and contains the data used by the user application.

The response contains the 3270 screen data reply. If the target application used BMS, this is presented in the form of an application data structure (ADS) , another name for the symbolic map that is generated by the BMS macros used to define the mapping of the 3270 screen.

The Link3270 bridge is called in the same way for all request mechanisms of the interface: EXEC CICS® LINK, the EXternal CICS Interface (EXCI), and the CICS External Call Interface (ECI).

The following flow describing the Link3270 mechanism is shown also in Figure 1 :

1. The client application creates a Link3270 request message.
2. The client application issues an appropriate link request (ECI, EXCI or LINK) to the CICS router program DFHL3270, passing the Link3270 message as a COMMAREA. Note that CICS takes care of the code page conversion if necessary.
3. DFHL3270 dynamically routes the request to the bridge driver task, which may be in the same or another CICS region. Load balancing can be implemented in this step.
4. The driver starts the user application ( the target 3270 transaction), running in a bridge environment.
5. The response Link3270 message is returned to the client as a COMMAREA.
6. The client application processes the outbound message .

The Link3270 mechanism supports non-conversational, pseudoconversational and conversational applications.