R2 MFC, Multi Frequency Compelled, is a widely spread signalling system. It has got its roots in the analog telecommunications world as it was developed for more than 30 years ago.
Due to its reliable operation and flexibility, it has been developed for both national and international usage. The signals are used to transfer the B-number as well as the category of the calling subscriber to the other exchange. In some cases, also the A-number is transferred. The R2 MFC signals code senders and code receivers to transfer the information between exchanges in the form of tones.
The 5 or 6 different tones frequencies are used. By combining these tones two and two can 10-15 different signals be coded.