Using Advanced Program-to-Program Communication › Advanced Program-to-Program Communication (APPC) › APPC Conversations

APPC Conversations

NCL procedures (and transaction programs in general) communicate by establishing a communication path called a conversation. Conversations use LU6.2 sessions to exchange data and protocols between the communicating procedures. All conversations consist of three main phases:

• Conversation initiation (allocation and attach processing)
• Data exchange (sending and receiving data operations)
• Conversation termination (deallocation processing)

Once a conversation is allocated to a session, a send-receive relationship is established between the participating programs. Initially, the procedure that requested the conversation is allowed to issue send data verbs while the other procedure issues receive data verbs. This send-receive relationship can change many times during the life of the conversation.

To terminate the conversation the procedures request deallocation processing, by issuing the appropriate deallocate verb. The following sections give a detailed description of the conversation phases and the associated verbs.

Note: This implementation of APPC enables NCL procedures on the same system to communicate without the need to use SNA sessions. This is a highly effective means of data transfer between NCL processes.