Writing programs for APPC basic conversations

These topics describe the CICS® APIs available for DTP programming using APPC basic conversations.

Conversation initiation
The front-end transaction is responsible for acquiring a session, specifying the conversation characteristics, and requesting the startup of the back-end transaction in the partner system.
Back-end transaction initiation
A back-end transaction is initiated as a result of the front end’s GDS CONNECT PROCESS command.
What happens if the back-end transaction fails to start
It is possible that the back-end transaction fails to start. However, because of the transmission delay mechanism in APPC, the front-end transaction is not informed of this fact until the conversation has been active long enough for responses from the back-end system to be received.
Sending data to the partner transaction
To send data on an APPC basic conversation, an application must format the data into generalized data stream (GDS) records.
Receiving data from the partner transaction
The GDS RECEIVE command is used to receive data from the connected partner transaction.
Communicating errors across a conversation
The APPC basic API provides commands to enable transactions to pass error notification across a conversation. There are three commands depending on the severity of the error.
Safeguarding data integrity
If it is important to safeguard data integrity across connected transactions, then the CICS synchronization commands are available.
Ending the conversation
These topics describe the different ways a conversation can end, either unexpectedly or under transaction control.
Checking the outcome of GDS commands
The CICS exec interface block (EIB) is not affected by EXEC CICS GDS commands, and no CICS conditions can be raised when EXEC CICS GDS commands are executed. Instead, you must provide data areas in your application to receive return codes and session status information.
Summary of commands for APPC basic conversations
The CICS application programming interface provides a set of commands for use in APPC basic conversations.
State transitions in APPC basic conversations
These topics show how the state changes when GDS commands are issued in APPC basic conversations.

Parent topic: Developing distributed applications