This section provides a short introduction to MFC-R2 register signaling according to CCITT. For detailed information, refer to CCITT Recommendation Q.440 or to the guidelines published by the individual administrative authorities.

The MFC register signals are exchanged between the registers of the originating and terminal exchanges (end-to-end) in compelled inband signaling. There is a distinction made between the two different signal directions: forward (originating exchange to terminal exchange) and backward signals (terminal exchange to originating exchange). They are used for exchanging information when setting up a connection.

The forward signals are the dialing information (digits), type and origin of the connection, and others. Each signal (1...15) consists of two frequencies (2 of 6). To differentiate between the directions, there is an upper frequency group (1380...1980 Hz, at intervals of 120Hz intervals) for the forward signals and a lower frequency group.

The backward signals are retrieval, status of the user connections, user class of service, and others. The backward signals use the lower frequency group (1140...540 Hz, at intervals of 120 Hz).

There are administrative authorities that use only the signals 1...10 for the PBX connections. This can save on configurations (2 of 5 instead of 2 of 6 code). The OpenScape 4000 SIU can always handle the entire range of signals (2 of 6). You can filter out signals 11 ... 15 by choosing the appropriate configurations (MFCTA, MFC conversion table).

The introduction of MFC-R2 register signaling according to CCITT Q.440 also included the implementation of signaling according to SOCOTEL (for France) and IBERCOM (for Spain). These types of signaling are not discussed here.