The Cisco 811 and 813 routers connect small professional offices or telecommuters over Integrated Services Digital Network (ISDN) Basic Rate Interface (BRI) lines to corporate local area networks (LANs) and the Internet. The routers offer multiprotocol routing between LAN and WAN ports.The ISDN BRI service provided by your telephone service provider offers two bearer channels (B channels) and one data channel (D channel). The B channel operates at 64 kbps and carries user data. The D channel operates at 16 kbps and carries control and signaling information, although it can support user data transmission under certain circumstances. The Cisco 811 and 813 routers include both the ISDN U and ISDN S/T ports. The ISDN U interface is a two-wire interface from the telephone switch that supports full-duplex data transfer over a single pair of wires. The Cisco 811 and 813 ISDN U interface supports the data service unit (DSU) feature that is integrated in the routers. The ISDN S/T interface is a four-wire interface from the telephone switch that supports full-duplex data transfer over two pairs of wires. Telephone service providers typically provide an ISDN S/T interface. The Cisco 811 and 813 ISDN S/T interface supports the connection to an external DSU, from which you can connect a digital telephone and other network devices. The Cisco 813 router supports data and voice applications. The data applications are implemented through the ISDN port. The voice applications are implemented with ISDN BRI and through the telephone ports.