Depending on the intended use and the configuration of computers and phone equipment at a particular site, there are several pieces of equipment needed to install ISDN.
Terminal Adapter – A terminal adapter (TA) is the ISDN equivalent of an analog modem. People often refer to TAs as ISDN modems, but that term isn't technically correct. Modems modulate and demodulate signals, and there's no modulation and demodulation necessary with the digital transmission used by ISDN. TAs let the computer talk to the ISDN circuit, control the calls, and manipulate the B channels for effective communication.
Network Terminator – Connecting ISDN to a personal computer requires a network terminator (NT1) and ISDN terminal adapter. The NT1 plugs into the two-wire line from the telephone company with an RJ-11 connector and provides output to the TA. Within the U.S., the NT1 is typically built into the TA, but in Europe and Japan, they are separate devices.
ISDN Router – An ISDN router is a device that enables several users on a network to access the Internet via ISDN. Also known as an ISDN LAN modem, it contains a BRI ISDN port and an Ethernet port. It may also provide several Ethernet ports, which lets it serve as a central Ethernet hub for a small workgroup. Access to the unit for configuration and monitoring is typically done via a Web browser.
For Internet access, the ISDN router supplies temporary IP addresses to each of the nodes through its DHCP capability. Routers may also provide analog phone support.