Northern UTA220/UTA220k manual Terminal Adapters, ISDN Basic Rate Interface Points, Isdn

ISDN

Basic Rate Interface

Several types of ISDN network services are available. The most common is Basic Rate Interface (BRI). BRI provides two B-channels (bearer channels) and one D-channel (used to place and release calls on the network).

B-channels, which operate at 64 kbps full-duplex, carry end- to-end data between network terminals. B-channels can be either circuit-switched (dial-up), allowing each call to be placed to different endpoints, or permanently connected (nailed) to a single endpoint. In some applications, B-channels can also be used to carry packet-switched data, where each frame of data can dynamically be sent to different network users. The TA does not support packet-switching on a B-channel.

The D-channel is primarily a control channel between the network and the terminal device (such as a TA).

Terminal Adapters

Terminal adapters attach standard data terminals and voice telephones to the ISDN, allowing them to send and receive calls and data via the ISDN. Some terminal adapters (but not the UTA220) support voice service, allowing a standard (analog) telephone set to be connected to the ISDN.

The UTA220 operates on the ISDN BRI. It provides circuit- switched data communications using circuit-switched B-channels for data, and uses the D-channel for signaling only.

ISDN Basic Rate Interface Points

BRI points and the associated devices found on customer premises are shown in Figure 4-1. The boxes in the diagram represent devices, and the vertical lines represent defined interface points. There are two types of DTEs represented in the diagram:

•TE1 devices have a built in ISDN interface.

•TE2 devices do not have a built in ISDN interface, and require a TA to interface with the ISDN.

The data terminal devices (DTEs) are located in the left of the diagram. The TA is connected to the ISDN at the U interface. An NT1 device is not required; the NT1 function is built into the UTA220.

4-2 UTA220/UTA220k