Overview of ISC TCP/IP support

ISC TCP/IP does not use SNA VTAM® or the protocols, commands, headers, and so forth, that are used with VTAM. However, for consistency, some VTAM terms are used in an ISC TCP/IP context where the meaning is the same.

Otherwise, from an operational, application programming, and high-level configuration perspective, ISC TCP/IP communication and ISC VTAM communication are generally the same.

You use the same IMS commands to control the ISC sessions from IMS. IMS applications programs do not need to be sensitive to the use of either ISC TCP/IP or ISC VTAM. Statically defined ISC LU 6.1 terminals are defined with the same IMS stage-1 system definition macros, and dynamically defined terminals use similar ETO logon descriptors.

Statically defined ISC LU 6.1 terminals and dynamically defined ISC nodes can use TCP/IP to connect to CICS subsystems.

If you use dynamically defined terminals, the Extended Terminal Option (ETO) is required.

The following figure shows the main components that support ISC TCP/IP communication between IMS and CICS: the Structured Call Interface (SCI) for communication between IMS and IMS Connect, and IMS Connect for communication with CICS over TCP/IP.

The figure compares these components with the main components that support ISC VTAM communication. The primary difference between the two communication types is that for ISC TCP/IP the path between IMS and CICS is provided by SCI, IMS Connect, and TCP/IP. For ISC VTAM, the path between IMS and CICS is provided by VTAM only.

Both communication types support input that originates from either an IMS user or a CICS user. In either case, the input is sent to the partner subsystem, which processes the transaction and returns a reply.