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Establish

Enhanced Definition

In the context of IBM z/OS and enterprise computing, to **establish** typically refers to the process of initiating and setting up a logical connection or session between two communicating entities. This involves a series of protocol-driven handshakes and exchanges to create a stable, often stateful, communication path for data transfer between applications, terminals, or systems.

Key Characteristics

- Protocol-driven: Establishment adheres to specific communication protocols, such as SNA (Systems Network Architecture) for VTAM sessions or TCP/IP for network connections, which dictate the sequence of steps.
- Resource Allocation: During the establishment phase, system resources like control blocks, buffers, and unique identifiers (e.g., session IDs, port numbers) are allocated on both ends of the communication.
- Stateful Nature: Once established, a connection or session maintains a defined state, enabling subsequent data transfers to occur efficiently without repeated negotiation until it is explicitly terminated.
- Security Integration: Authentication and authorization processes are frequently integrated into or immediately follow connection establishment to verify the identity and permissions of the communicating parties.
- Bidirectional Capability: Most established connections are designed to support two-way data flow, allowing both participating entities to send and receive information concurrently.

Use Cases

- Terminal User Access: A user performing a LOGON to TSO/ISPF, CICS, or IMS from a 3270 terminal or emulator, which involves VTAM establishing an SNA session.
- Distributed Application Connectivity: A client application (on or off-mainframe) establishing a TCP/IP connection to a z/OS-based server, such as a DB2 database, a CICS region acting as a web service provider, or an MQ queue manager.
- Inter-System Communication: Two CICS regions establishing MRO (Multi-Region Operation) or ISC (Inter-System Communication) sessions to route transactions, exchange data, or share resources.
- Batch Job External Access: A JCL batch job using utilities or custom programs to establish a connection