ETO - Enhanced Terminal Option

Enhanced Definition

Enhanced Terminal Option (ETO) is a CICS feature that provides dynamic definition of CICS terminals and Logical Units (LUs) at sign-on or connection time. It eliminates the need for pre-defining every terminal in the CICS System Definition (CSD) file, significantly simplifying resource management in large and dynamic environments. Enhanced Terminal Option (ETO) is a CICS feature that allows for the dynamic definition of CICS terminals and Logical Units (LUs) at the time they attempt to connect to CICS. Instead of pre-defining every terminal in the CICS Resource Definition Online (RDO) files, ETO leverages VTAM definitions to create terminal control table entries dynamically, significantly reducing CICS startup time and storage consumption for large terminal networks.

Key Characteristics

- Dynamic Resource Creation: CICS dynamically builds the necessary terminal control blocks (TCTTEs) and associated resources when a terminal attempts to connect or a user signs on.
- Reduced CSD Maintenance: Drastically decreases the number of TERMINAL and LU resource definitions required in the CSD, saving storage and reducing CICS startup time.
- Model-Based Definitions: Relies on generic TYPETERM and PROFILE definitions (still defined in the CSD) to provide templates for the dynamically created terminal entries.
- Increased Flexibility: Allows terminals to connect from various network LUs without requiring specific CICS definitions for each, supporting fluctuating terminal populations.
- Security Integration: Often integrates with an external security manager (ESM) like RACF to authenticate users and authorize their use of specific TYPETERM and PROFILE models.
- Support for Various Terminal Types: Primarily used for LU 2 (3270 terminals) and LU 6.2 (APPC) sessions, as well as non-SNA terminals.

Use Cases

- Large-Scale 3270 Deployments: Managing thousands of 3270 terminals or 3270 emulator users where static CSD definitions would be impractical and burdensome.
- Dynamic Branch Office Connectivity: Supporting environments where the specific terminals connecting to CICS can change frequently, such as call centers or retail branches.
- Web-to-CICS Gateways: Facilitating connections from web applications that emulate 3270 sessions, allowing dynamic allocation of CICS terminal resources.
- Disaster Recovery Scenarios: Simplifying recovery by allowing terminals to reconnect to a backup CICS region without needing to replicate extensive terminal-specific CSD definitions.

Related Concepts

ETO is a core component of CICS Transaction Server's terminal control. It works in conjunction with the CICS System Definition (CSD) file, where generic TYPETERM and PROFILE definitions are still maintained. It relies on VTAM (Virtual Telecommunications Access Method) for network communication and often integrates with an external security manager like RACF for user authentication and authorization during the dynamic terminal creation process.

Best Practices:

Design Robust Models: Create well-defined and generic TYPETERM and PROFILE definitions in the CSD that can serve as templates for a wide range of dynamic terminals.
Implement Strong Security: Leverage RACF or another ESM to control which users can sign on and which TYPETERM and PROFILE models they are authorized to use, preventing unauthorized access.
Monitor Resource Consumption: Regularly monitor CICS storage and CPU usage related to ETO-defined terminals to ensure efficient operation and prevent resource exhaustion.
Configure Inactive Session Cleanup: Utilize CICS system initialization parameters (e.g., ICVTSD) to automatically purge inactive or disconnected ETO-defined terminals, freeing up valuable CICS resources.
Thorough Testing: Rigorously test ETO configurations, especially with new TYPETERM or PROFILE definitions, to ensure proper terminal functionality, security, and performance under load.