libpri is a C implementation of the Primary Rate ISDN specification.
It was based on the Bellcore specification SR-NWT-002343 for National
ISDN.  As of May 12, 2001, it has been tested work with NI-2, Nortel
DMS-100, and Lucent 5E Custom protocols on switches from Nortel and
Lucent.

Please note that there are no man pages and precious little documentation
for this library.  The build is simple and straight forward though.