OpenR2 is a library that implements the MFC/R2 signalling over E1 lines using
the Zapata Telephony interface (or DAHDI). The MF R2 tones required for the
signaling are generated by code borrowed from the LGPL library SpanDSP
written by Steve Underwood, the user has the option to provide a MF interface
to use his own MF R2 tone generation and detection so the library will use
them when needed, that's why this library does not depend directly on spandsp,
libteletone or zaptel for tone generation and detection (depends on zaptel
for CAS bits and general media transmission though)

WWW: https://libopenr2.org/