CCP - Communication Control Program

Enhanced Definition

The Communication Control Program (CCP) is a fundamental internal component of IBM's CICS (Customer Information Control System) that is responsible for managing all terminal and network input/output (I/O) operations. It acts as the interface between CICS application programs and the underlying z/OS communication access methods, enabling CICS to interact with terminals and other systems.

Key Characteristics

- CICS Internal Component: The CCP is not a standalone product but an integral, core part of the CICS Transaction Server architecture.
- Terminal Management: It handles the receipt of input from terminals (e.g., 3270 devices, emulators) and the transmission of output back to them.
- Network Interface: The CCP interfaces directly with z/OS communication access methods, primarily VTAM (now part of z/OS Communications Server), to establish and manage network sessions.
- Asynchronous Processing: It manages the asynchronous nature of terminal I/O, allowing CICS to handle multiple concurrent transactions efficiently.
- Resource Management: The CCP manages communication-related control blocks, buffers, and queues within the CICS region.
- High Performance: Designed for high-volume, high-performance online transaction processing (OLTP) environments, ensuring rapid response times for terminal users.

Use Cases

- Online Transaction Processing (OLTP): Facilitates user interaction with CICS applications via terminals for tasks like order entry, customer service, and financial transactions.
- Data Entry and Retrieval: Enables users to input data into or retrieve information from databases (e.g., DB2, IMS) through CICS-based screens.
- Terminal Emulation: Underpins the communication for modern terminal emulators (e.g., PCOMM, RUMBA) connecting to CICS regions over TCP/IP.
- Message Routing: Directs incoming messages from terminals to the correct CICS transaction programs for processing and delivers responses back to the originating terminal.

Related Concepts

The CCP is inextricably linked to CICS, serving as its primary communication engine. It relies on VTAM (or z/OS Communications Server) to establish the underlying network connections, and it uses CICS Resource Definition Online (RDO) definitions for terminals (TYPETERM, TERMINAL) to understand the characteristics of connected devices. The CCP delivers input to and receives output from CICS transaction programs (often written in COBOL), acting as the crucial intermediary between the user and the application logic.

Best Practices:

Optimize RDO Definitions: Ensure that CICS TYPETERM and TERMINAL definitions are accurately configured and optimized for the types and numbers of terminals connecting to the CICS region.
Monitor Performance: Regularly monitor CICS statistics and performance metrics related to communication (e.g., terminal I/O rates, buffer usage) to identify and address potential bottlenecks.
Buffer Pool Tuning: Properly size and tune CICS communication buffer pools to minimize I/O waits and improve throughput for terminal operations.
Implement Security: Enforce robust security measures (e.g., using RACF or ACF2) for terminal access and CICS transactions to prevent unauthorized access.
Error Handling in Applications: Design CICS application programs to gracefully handle communication errors, timeouts, and unexpected terminal disconnections to maintain system stability and user experience.