# Overview

TIBCO messaging applications are normally the source of the external messages and requests that are received by Substation ES. Substation ES-to-Substation ES communication through the messaging layer can be another source for messages.

ESB Interface transforms TIBCO messaging application requests into a buffer and forwards the buffer to Substation ES IMS Interface, which, in turn, attaches the buffer to an Open Transaction Manager Access (OTMA) header and passes the message through OTMA to IMS applications.

TIBCO clients can publish requests that initiate IMS transactions. Alternatively, IMS applications can publish events, messages, or requests/replies (synchronous callouts) from 3270 applications or from within Batch Message Program (BMP) or Message Processing Program (MPP) regions to TIBCO messaging applications that are listening to those events.

Communication between Substation ES IMS Interface and IMS is handled by the Substation ES OTMA Interface with the OTMA facility.

The preferred manner of defining OTMA destinations is using the IMS PROCLIB member DFSYDTx using the D control card. However, the previous method of using the OTMA Prerouting exit routine (DFSYPRX0) and Destination Resolution exit routine (DFSYDRU0) on M control cards is still supported.

Substation ES IMS Interface performs the following key tasks:

- Extracts the details of OTMA and IBM cross-system coupling facility (XCF).
- Submits IMS transactions and commands and receives IMS replies.
- Provides connectivity and conversations from programs that run on non-IBM platforms and other z/OS subsystems to multiple IMS servers or regions.

Substation ES IMS Interface has the following advantages:

- Flexible, scalable, and easy to install and operate, and includes implemented applications that use this facility.
- No coding (nonintrusive) is necessary or only minor changes (intrusive) are required to activate and use the interface with existing applications.
- The most direct and fastest method to add bidirectional IMS transactional information to the ESB, so that the information can be used by all SOA processes. The synchronous IMS request/reply support in Substation ES makes it even easier for IMS transactions to make requests across the ESB and have the ability to receive data.

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