Cisco Single-port WAN Interface Card (WIC)
Single-port, four-wire, WIC-1DSU-56K4 card combines a DSU/CSU into a single card with 64-kbps maximum throughput speed. DSU/CSU interface devices are always required to interface between the synchronous serial ports of a router and the telco/Post, Telephone, and Telegraph (PTT)-supplied data communications circuit. A DSU is a device used in digital transmission for connecting data terminal equipment to a digital transmission service. A CSU is a digital interface device that connects end-user equipment to a local digital telephone loop .