Tips and Training >> Definitions >> NT1

What is an NT1?

An NT1 is a network interface that converts a Basic Rate ISDN network interface from a telephone provider to a form that is suitable for ISDN equipment such as an ISDN telephone or an ISDN capable video conferencing system. The term "NT1" refers to the location in an ISDN network where this device is located and it may be thought of as the first point of customer/telephone provider connection. Basic Rate ISDN can economically provide up to two 64Kbps channels of bandwidth on one telephone line.

A common mistake in understanding is to consider an NT1 to include only one network interface. In fact, the NT1 is a functional point of connection and it can include a number of network connections. Commonly referred to as an NT1, these networking devices routinely include from one to four network connections to telephone equipment and from one to eight network connections to customer equipment. Some suppliers use the term NT1, NT3 and NT4 to indicate the number of connections that are available on this device to connect to the telco provider jacks.

This designation of NT1, NT3 or NT4, although technically not correct topographically in an ISDN network do serve to ensure that the right number of ports are available for connection to source network. For this reason, NT1, NT3 and NT4 as product descriptions do serve a valuable nomenclature purpose and these terms are widely used in Telco networking parlance.

Why do I need an NT1, NT3 or NT4?

The NT1 functionally converts a 2-wire telco interface called a "U" interface to an "S/T" interface. Most ISDN devices require a connection interface of S/T and telco equipment generally does not provide this type of connection. The S/T interface is a both a physical and logical interface and it even has some available options (such as whether this interface provides power to user equipment). In general, however an S/T interface from a user perspective is a 4-wire connection that connects to user equipment. An RJ-45 network jack straight through networking cable is suitable for this connection.

Can I connect more than one piece of equipment to an NT1?

Connecting multiple pieces of equipment to an ISDN network line is possible with a correctly configured ISDN line and NT1. Basic Rate ISDN is a loop technology that allows users to connect several devices to a single ISDN telephone line. In practice, however, most users connect at most two devices (such as telephones) to an ISDN line. Another common use for Basic Rate ISDN lines is to connect multiple lines to a video conferencing system. Users often install three or even four Basic Rate ISDN (BRI Lines) and they then make two connections for each BRI Line to their equipment. This configuration would require an NT3 or an NT4 and it would enable from 6 to 8 channels of 64Kbps bandwidth for a video conferencing system.

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