The ABAP communications interface (based on the CPI-C Starter Set) has no explicit functions for synchronization of both partners. The Advanced Function Calls CMCFM/CMCFMD are not implemented in ABAP.

Both communications partners must perform the synchronization with send and receive commands on the application level.

Synchronization is necessary because a send request does not necessarily trigger the immediate sending of data.

Different communications subsystems buffer data first and only send it physically when certain bufer limits are exceeded, a status change is made or the connection is closed.

Synchronization means:

• Sending as yet unsent data to the partner (flush)
• Requesting an acknowledgement from the partner
• The partner sending an acknowledgement
• Waiting for the acknowledgement to be received

The easiest method involves passing the send authorization to the partner program after sending one or more data blocks in order to request an acknowledgement. It is recommendable to use a RECEIVE call after no more than 7 SEND calls. The larger the data blocks, the less SEND calls you should use before the next RECEIVE call. The partner can return the send authorization (acknowledgement) immediately. In addition, a response (data) can be sent in order to differentiate between positive and negative acknowledgements.

Certain restrictions apply for setting up communication via LU6.2 from IMS (up to Version 3.1).

When changing from COMMUNICATION SEND to COMMUNICATION RECEIVE, any unsent data is transferred to the communications partner.

For each COMMUNICATION SEND there must be at least one COMMUNICATION RECEIVE in the partner system.