Using Link3270 bridge load balancing

The Link3270 bridge mechanism extends the dynamic routing capability of base CICS® to support dynamic routing of 3270 bridge transactions. Figure 13 shows that the DPL request from the Link3270 bridge program to a remote user transaction can be sent to any of a number of AORs where the user transaction is enabled.

The dynamic transaction routing user replaceable program (URM) is called when DFHL3270 needs to identify the AOR to which an eligible transaction should be routed. New parameters on the interface allow the dynamic transaction routing program to identify Link3270 bridge requests and obtain the names of the target transaction and the bridge facility token. You can write your own transaction routing program to exploit these new parameters, use the CICS supplied dynamic routing program (DFHDYP), or use workload balancing services provided by CICSPlex® SM.

Figure 13. Link3270 load balancing
  Link3270 load balancing described in the preceding text.

Using the dynamic transaction routing program with Link3270

When the dynamic transaction routing user replaceable program is called in the Link3270 bridge environment, the following input parameters are set:

DYRTYPE
8
DYRBRTK
bridge facilitytoken
DYRTRAN
name of user transaction as known in the router region

When a client links to the bridge routing program (DFHL3270) with the first application transaction for that facility and that transaction is defined as dynamic, the dynamic transaction routing program is called to determine if the request should be routed (using DPL) to another server region. The dynamic transaction routing program is passed the transaction id in the message, and determines the sysid of the region (AOR) where the user transaction will be started.

The dynamic transaction routing program is only called if the transaction is defined as DYNAMIC(YES).

Once a bridge transaction has been routed successfully to an AOR, all transactions executing with the same FACILITYTOKEN are routed to the same AOR. This affinity continues until the bridge facility is deleted in the AOR.

In session mode, subsequent transactions that are defined as dynamic will cause a notify call to the dynamic transaction routing program, informing the routing program that the transaction request is being routed to a specific region.

See the CICS Customization Guide for information about using a dynamic routing program.

Related concepts
The Link3270 bridge mechanism
The bridge facility
Related tasks
Defining Link3270 SIT parameters
Using Link3270 session mode
Managing Link3270 bridge resources
Writing the Link3270 client
Related reference
Link3270 message formats
Link3270 diagnostics
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