The TPs that make up an APPC cooperative processing application communicate through a conversation that takes place across a standard interface, just as people communicate through a conversation over the telephone. One partner calls the other, identifying it in a way that the system recognizes; the system makes the connection and the partner accepts the conversation. The conversation follows a protocol, with statements dictated by sequence and the state of the conversation. For example, one partner talks (sends data) while the other listens (receives data). They take turns sending and receiving data until one of them ends the conversation.

APPC conversations follow a half-duplex protocol. That means data can be transmitted back and forth between partners, but only in one direction at a time. To make sure that partners do not get out of sequence or both try to communicate at the same time, APPC enforces conversation states.