basic rate interface (ISDN) (BRI)
The basic access (BaAS) provides the ISDN subscriber with two separate, simultaneously usable channels at the S0 interface. The basic access is made via the copper twisted pair of the normal telephone connection. In addition to the two basic channels, the B channels with a data rate of 64 kbit/s, the subscriber also has a data channel, the D channel, with 16 kbit/s at his disposal.
The ISDN basic access essentially consists of a passive bus that is connected to the DIVO digitallocal exchange via a network termination( NT). The International Telecommunication Union( ITU) has defined this interface under I.420.
The range of the passive bus can be up to 200 m. Up to 8 terminals can be connected to one ISDN basic rate interface.
In terms of configuration, a distinction is made between four different basic connections, the short passive bus with network termination at the end of the bus, the short passive bus with network termination between the connection boxes, the point-to-point configuration and the remote passive bus.
The different configurations have different ranges; these are between 200 m (passive bus) and 1,000 m for the point-to-point connection. Such a configuration exists, for example, when a single terminal device is connected at a distance of 1,000 m from the network termination and a small PBX is connected to the base port. With the remote passive bus, up to 4 terminal devices can be connected at a maximum distance of 500 m from the network termination. All terminals on a basic access can have the same ISDN address as well as be specifically addressed using the terminal equipment selection digit(EAZ).