# ISDN Software configurations

ISDN Software allows you to write NaturalAccess applications that communicate with BRI, T1, or E1 trunks to perform voice processing functions and call control using ISDN common channel signaling protocols.

ISDN Software uses one or more digital trunk interface boards as the physical interface to trunk lines. In addition to line interfaces, these boards also feature on-board digital signal processing (DSP) resources that can handle most of the call control and voice processing tasks.