CMA - Communications Management Application

Enhanced Definition

CMA, or Communications Management Application, is a key component of the Network Control Program (NCP) that runs on an IBM Communication Controller (e.g., 3745/3746). Its primary purpose in the mainframe/z/OS context is to manage communication resources, establish and terminate sessions, and control data flow for applications accessing the host via an SNA network. It offloads significant communication processing from the mainframe CPU. CMA (Communications Management Application) is a user-written program on z/OS designed to manage and control network communications, often acting as an intermediary between end-user terminals or other applications and backend transaction processing systems like CICS or IMS. Its primary purpose is to handle the complexities of network protocols and session management, providing a simplified and controlled interface for business applications.

Key Characteristics

- NCP Component: CMA is an integral part of the Network Control Program (NCP), which executes on a dedicated Communication Controller, not directly on the z/OS host.
- Session Management: It is responsible for managing logical unit (LU) to application program (APPLID) sessions, including session establishment, termination, and recovery within the SNA network.
- Resource Control: CMA controls and manages physical communication resources such as lines, modems, and physical units (PUs) connected to the communication controller.
- SNA Architecture: Operates strictly within the Systems Network Architecture (SNA) framework, handling various SNA protocols and functions like pacing and data link control.
- VTAM Interface: It works in close conjunction with VTAM (Virtual Telecommunications Access Method) on the z/OS host, acting as the front-end processor for network traffic.
- Offloads Host CPU: By handling low-level communication tasks, CMA significantly reduces the processing overhead on the mainframe's CPU, allowing it to focus on application execution.

Use Cases

- 3270 Terminal Access: Facilitating connections for 3270 terminals (or emulators) to access mainframe applications like CICS, IMS, or TSO via the communication controller.
- Remote Site Connectivity: Managing communication links and sessions for remote branch offices or distributed systems connecting to the central z/OS mainframe.
- Application-to-Application Communication: Supporting SNA LU 6.2 sessions for program-to-program communication between distributed applications and mainframe applications (e.g., CICS-to-CICS, CICS-to-DB2).
- Network Resource Sharing: Enabling multiple host applications to efficiently share common communication lines and communication controllers, optimizing network infrastructure.

Related Concepts

CMA is fundamental to SNA (Systems Network Architecture) and operates within the NCP (Network Control Program), which runs on a dedicated Communication Controller. It serves as the bridge between the physical network and VTAM (Virtual Telecommunications Access Method) on the z/OS host. VTAM, in turn, provides network access to mainframe applications such as CICS, IMS, and TSO. CMA offloads the intricate details of session management and data link control from VTAM and the mainframe CPU, allowing for more efficient processing of application workloads.

Best Practices:

NCP Generation Planning: Carefully plan and generate the NCP configuration, including CMA parameters, to accurately reflect the network topology and optimize resource allocation and performance.
Performance Monitoring and Tuning: Regularly monitor CMA statistics (e.g., buffer utilization, session counts) and tune parameters like buffer sizes, pacing values, and queue depths to ensure optimal data flow and minimize network response times.
High Availability: Implement redundant communication controllers and NCP configurations with CMA to provide failover capabilities and ensure continuous network availability for critical mainframe applications.
Security Configuration: Ensure that CMA and NCP configurations include appropriate security measures, such as access controls for LUs and APPLIDs, to protect network resources and prevent unauthorized access.
Version Management: Keep the NCP microcode and CMA definitions updated to leverage the latest features, performance enhancements, and security fixes provided by IBM.