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ISDN Service
ISDN SWITCHES
Figure 4-1. ISDN Devices and Reference Points
To use the ISDN, you must subscribe to a network service. The
available options depend on the carrier (telephone company),
but some generally available options are:
• Types of calls supported (voice, data, packetized data)
• Circuit-switched (dial-up) or permanent (nailed) lines
• One or two B-channels
• A telephone number for each B-channel, or one number for
both channels
The device controlling the ISDN line is the central office
switch. It is usually owned by the network provider (e.g., the
telephone company). Each switch has its own format and
procedures for the D-channel protocols used to establish and
control calls. (More on D-channel protocols later.) There are
three main ISDN switch standards used in North America:
AT&T, Northern Telecom (NTI), and NI-1. Their basic
functions are similar, but each has its own set of special
features and parameters.
Before using the TA, you must configure the unit for a switch
type. The TA will operate with AT&T, Northern Telecom
(NT), or any switch running National ISDN-1. Central Office
(CO) switches can be loaded with different software versions.
The TA supports AT&T switches running versions 5E4.2 and
later, and NT switches running versions BCS29 and later.
UTA220/UTA220k
ISDN
4-3
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