Northern UTA220/UTA220k Manuel D’Utilisation

4-2

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 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.

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.