IFREQ - Interface Request

Enhanced Definition

IFREQ (Interface Request) is a CICS command used to initiate a program link to a program residing in a *different* CICS region. It is a fundamental component of CICS Multi-Region Operation (MRO) and Inter-Region Communication (IRC), enabling distributed transaction processing and workload balancing across multiple CICS systems.

Key Characteristics

- Cross-Region Program Link: Specifically designed for invoking programs in a *remote* CICS region, unlike the LINK command which defaults to local execution.
- Requires SYSID: The SYSID option is mandatory, specifying the 4-character system identifier of the target CICS region where the remote program resides.
- Uses CICS MRO/IRC: Relies on CICS's underlying Multi-Region Operation (MRO) or Inter-Region Communication (IRC) facilities to establish and manage the communication link between regions.
- Passes Data: Data can be passed to the remote program using a COMMAREA (Communication Area) or CHANNEL/CONTAINER mechanism, similar to local LINK commands.
- Error Handling: Provides RESP and RESP2 fields to indicate the success or failure of the remote program invocation, including communication errors or remote program abends.
- Synchronous Operation: By default, IFREQ operates synchronously, meaning the calling program waits for the remote program to complete and return control.

Use Cases

- Distributed Transaction Processing: A CICS application in one region needs to invoke specific business logic or access data managed by a program in another CICS region (e.g., an order entry system calling an inventory management system).
- Workload Balancing: Distributing processing load for specific functions across multiple CICS regions, allowing for better resource utilization and scalability.
- Accessing Specialized Services: A CICS region acting as a front-end might use IFREQ to access back-end services or data residing in a dedicated CICS region (e.g., a security validation service or a legacy data access program).
- System Integration: Integrating different CICS applications or subsystems that are logically separated into distinct CICS regions for modularity or administrative reasons.

Related Concepts

IFREQ is tightly coupled with CICS Multi-Region Operation (MRO) and Inter-Region Communication (IRC), which provide the underlying infrastructure for cross-region communication. It is conceptually similar to the LINK command but specifically targets remote programs, requiring a CONNECTION definition to the target SYSID. It often works in conjunction with PROGRAM resource definitions, where a remote program entry points to the actual program in another region, and TRANSACTION definitions if the remote program is to be initiated under a specific transaction ID.

Best Practices:

Robust Error Handling: Always check the RESP and RESP2 values after an IFREQ command to handle potential communication failures, remote program abends, or logical errors gracefully.
Optimize COMMAREA Size: Keep COMMAREA sizes as small as possible to minimize network overhead, especially for high-volume transactions. Consider using CHANNEL/CONTAINER for larger or more complex data structures.
Secure Remote Access: Ensure that CONNECTION and PROGRAM resource definitions for remote access are properly secured using CICS security mechanisms (e.g., RACF) to prevent unauthorized access.
Monitor Performance: Regularly monitor the performance of IFREQ calls, including response times and network utilization, to identify and address potential bottlenecks in MRO/IRC links.
Design for Idempotency: If possible, design remote programs invoked via IFREQ