Send/receive and bracket protocol

The change-direction indicator and bracket protocol, as defined by VTAM®, are used to specify the beginning and end of synchronous transmissions and to control the flow of such transmissions.

Because of its queued input and output processing, IMS does not support multiple related inputs or multiple related outputs. While in an in-brackets state, the following can occur:
  • One input message (coded BB/EB)
  • One output message (coded BB/EB)
  • One input message and an output reply (input coded BB/CD and output coded EB)
The input message and output reply are related only for:
  • Fast Path transactions
  • Terminal-response mode transactions
  • Conversational transactions

For other transaction types, the input message and output reply might or might not be related.