Equipment needed to use ISDN

ISDN equipment varies for different applications, from ISDN telephone sets to videoconferencing units to routers. Most ISDN service providers deal primarily with ISDN basic rate terminal equipment for establishing wide-area network connections to personal computers, workstations, and Local Area Networks. This includes internal ISDN boards for the Macintosh and PC machines, stand-alone ISDN terminal adapters (TA) to connect to non-ISDN devices (such as analog telephones or a computer's serial port), and ISDN-capable routers.

AN NT1, or Network Termination-1, is required to connect ISDN terminal equipment to an ISDN line. the NT1 connects to the two-wire line (twisted-pair copper wiring) that your telephone company has assigned for your ISDN service. This two-wire interface is referred to as the 'U' interface or 'U' reference point, and is accessible via a modular RJ-11 or Rj-45 jack.

The connection point between the NT1 and terminal equipment is the 'S/T' interface, which defines a four-wire line with separate transmit and receive pairs (and additional pairs for powering when required). The S/T interface is accessible through Rj-45 jacks on the NT1 and terminal equipment. Some equipment, such as the 3Com Access Division's (formerly AccessWorks Communications) QuickAccess Remote or Adtran's ISU 128, incorporate the NT1 directorly, in which case the S/T interface is not accessible. While this approach does have advantages in cost and ease of installation, a separate NT1 permits the connection of more than one piece of equipment to the ISDN line (such as an ISDN telephone).

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