Each communication message from the driver is initiated by a special header message, which must be read with a separate FGET. This header is to be kept and sent unchanged as a separate message (the first message) when responding to the SAP driver (FPUT header).

The driver report begins communication with an SAP logon message (CONN message) when logging on to to another SAP system. If the application addressed is not a SAP system, then this logon must be acknowledged by the message 'APPCCPIC1 '. This logon can be suppressed from 5.0E if user and password are not specified when creating the queue.

Then the driver sends the first message of the first LUW (that has not yet been completely dispatched) and waits for an acknowledgement of receipt. Each message received with a length greater than zero is taken to be an acknowledgement. However, it has become customary to use the character string ‘OK’ for an acknowledgement. If there are other messages, the driver now sends the next message. When all the messages of an LUW have been sent and individually acknowledged by the partner system, the LUW in the file DOUT is deleted. If there is another LUW available, transfer is continued with the first data record of the next LUW.

The following diagram illustrates the communication process asynchronous driver - receiving program.