Support for Robbed Bit Signaling (RBS), Basic Rate ISDN (BRI) and Primary Rate ISDN (PRI) lines are provided by Digium’s series of digital telephony cards. The digital cards are provided in one (1), two (2), and four (4) port varieties for both PCI and PCI-Express slot types. An optional DSP module provides hardware-based echo cancellation for Digium’s digital PRI cards; digital BRI cards include on-board DSP-based echo cancellation [9].