Chapter 1. What are MFC/R2 and the MFC/R2 protocol module for Unicall

MFC/R2 is a telephony signaling protocol, which dates back over 50 years. Its full name is the Multifrequency Compelled R2 Signaling System. It was originally used to provide register to register (i.e. switch to switch) signaling over analogue copper pair wiring at a higher speed than had been possible with pulse dialing. It was widely used for international circuits, and many national ones. Later, with the advent of E1 PCM trunks, MFC/R2 was adapted for use over this new medium. Though seemingly a relic from the past at a time when SS7 and ISDN are widely deployed, digital MFC/R2 over E1 trunks is still heavily used in many countries.

This MFC/R2 software is implemented as a protocol module within the Unicall framework. Unicall is a unified call processing API, allowing multiple telephony signalling protocols to be used by the same applications source code.

The MFC/R2 protocol module for Unicall supports the MFC/R2 variants used in most parts of the world. Additional variants may be added in a simple manner. Quite a few installations currently use this software, some with very heavy call volumes. However, each country as its own variant of MFC/R2, and these variants sometimes vary a little within country. Some variants have received much more thorough testing than others.