Four (4) span digital T1/E1/J1/PRI PCI-Express x1 card and hardware echo cancellation (VPM128). Digium TE435F is designed to provide optimal voice quality for Asterisk-based systems. This digital PCI Express card features echo cancellation to improve audio quality. The four interfaces can support up to 96 simultaneous calls through T1, or 120 simultaneous calls through E1.