Output bracketing protocol

For output messages, IMS specifies begin-bracket and end-bracket on single-segment output messages and on the first transmission of a multi-segment message.

If the input message specified begin-bracket and change-direction, the next output IMS sends specifies only end-bracket. If IMS detects an error when receiving chained input on which only begin-bracket is specified, it returns end-bracket and an IMS error message.

In the case of Fast Path, conversational, or response-mode transactions, the output message is the reply to the previous input message. In other cases, the output message might or might not be related to the previous input message.

IMS sends an only-in-chain output message (no FM header and data length=0), requesting exception DR2, and indicating FM header end-bracket when no other output is immediately available. This occurs in the following situations:

An input message from a workstation defined to IMS as negated terminal-response mode specifies begin-bracket and change-direction.
An input message from a workstation defined to IMS as forced terminal-response mode specifies begin-bracket and change-direction and is not an IMS transaction.
An input message from a workstation defined to IMS as transaction-dependent terminal-response mode specifies begin-bracket and change-direction and is not a response-mode transaction.

After receiving exception-response sense codes 0811 and 0812, IMS also sends an only-in-chain output message (no FM header and data length=0), requesting exception DR2, and indicating FM header begin-bracket/end-bracket when no other output is immediately available.