# Constraints

Note the constraints of Substation ES IMS Interface.

The following are a few constraints of Substation ES IMS Interface:

## IBM OTMA API

Substation ES Interface does not use the standard IBM supplied OTMA API, primarily because OTMA Callable Interface (C/I) does not support the commit-then-send option and resynchronization feature of the IMS OTMA protocol.

## IMS DFS$$TOQ

Starting with IMS 11, timeout queues are now supported for outbound Tpipe messages. The default timeout queue is DFS$$TOQ.

Substation ES does not use this Tpipe, so you might have to create procedures to handle messages that might end up on the DFS$$TOQ queue.

## Substation ES IMS Interface

Note the software requirements, naming conventions, and restrictions of Substation ES IMS Interface:

- Software requirements

  To initialize and install Substation ES IMS Interface, you must have z/OS 2.1 or above and IMS 13.1 or above installed.

  To use request/reply transactions, which require the IMS synchronous callout (ICAL) feature, IMS 10 or above is required. Note that IMS 10 might also require implementation PTFs.

- Naming conventions

  OTMA places a restriction on the naming of clients and transaction pipes. For a list of the naming conventions you must adhere to, see IMS Communications and Connections.

- Restrictions
  Currently, the following restrictions apply for all versions of Substation ES IMS Interface, unless otherwise noted:
  - The commit-then-send option of IMS OTMA is not supported.
  - The message resynchronization feature of IMS OTMA is not supported.
  - Beginning with Substation ES 2.7, IMS outbound messages might now be multi-segmented.

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