Messages are commonly used for communicating between an OpenTP1 and a non-OpenTP1 system. An OpenTP1 system that can send or receive messages in real time is said to have an MCF message-exchange configuration. The message control facilities, which are usually abbreviated to MCF, manage an MCF message-exchange system. The message control facilities are provided by the software products TP1/Message Control, TP1/NET/Library, and the products that correspond to the relevant communication protocol.

Figure 3-26 illustrates the above example of MCF message exchange.

Figure 3-26 Overview of sending and receiving a message by using MCF