# Tpipes

Substation ES communicates with the OTMA server through a transaction pipe (Tpipe), similar to the way an LTERM communicates with IMS.

Tpipes are defined to IMS as destinations through the descriptor (D) control card of the IMS DFSYDTx PROCLIB member. The following are some of the characteristics of Tpipes and LTERMs:

- An LTERM or a Tpipe uses a queue where the transaction output is kept before it is returned to the requester.
- For each LTERM or Tpipe, IMS maintains a connection between the queue and the physical node that receives the output.
- Substation ES IMS Interface use Tpipes to associate its transactions with a transaction-pipe name.
- IMS uses the Tpipe name to associate all input and output with the particular Substation ES IMS interface. The association between the transaction output and its ultimate destination (the originating device) is not made within IMS, as is the case with LTERMs, but is handled by the Substation IMS Interface.
- When Substation ES uses a Tpipe, IMS does not know anything about the actual user of the transaction, who is often a user of the IMS application. Therefore, when a Tpipe comes into play:
  - Substation ES IMS Interface has complete control over the output of request or reply transactions.
  - For outbound requests, the IMS application must specify the same Tpipe name as that specified on Substation ES IMS Interface startup parameters.

Each Substation ES IMS interface uses at most two Tpipe names, one for request or reply requests and the other for triggered (IMS outbound) requests.

Tpipe names are supplied in the startup parameters for Substation ES. The names are also included in the message-control information segment of the OTMA message prefix for requests.

Substation ES IMS Interface supports both synchronized or unsynchronized Tpipes. For a synchronized Tpipe, all output messages are serialized through a single process and sequence numbers can be assigned to messages.

Copyright © TIBCO Software Inc. All rights reserved.