Network Termination Unit (NTU)

Network Termination Unit is a device for connecting digital ISDN customer premises equipment to ISDN lines allows customer premises equipment to be connected to the switching equipment at the telco’s central office. Read the full article.

What is NTU (Network Termination Unit)?

A device for connecting digital Integrated Services Digital Network (ISDN) customer premises equipment to ISDN lines. The Network Termination Unit (NTU) allows customer premises equipment to be connected to the switching equipment at the telco’s central office (CO).

How It Works

Digital ISDN customer premises equipment such as routers and ISDN phones usually have an ISDN S/T interface, while the ISDN termination at the customer end of the local loop usually has a U interface using an RJ-45 connector. The NTU converts the U termination of the ISDN line to one or more standard coding S/T interfaces that are suitable for connecting digital ISDN-ready phones, routers, and other devices to an ISDN line. NTUs work differently than ISDN terminal adapters, which allow you to connect analog telephones, faxes, and similar equipment to your ISDN line. NTUs typically support either point-to-point or multipoint connections over distances of up to 5.4 kilometers on 26 AWG copper twisted-pair cabling.

NOTE

Some newer ISDN-enabled devices have a built-in U interface, making an NTU unnecessary. The following table shows the differences between the Basic Rate ISDN U and S/T interfaces.


Basic Rate ISDN U Interfaces vs. Basic Rate ISDN S/T Interfaces

Property U Interface S/T Interface
Number of wires
2
4
Connector
RJ-45
RJ-45
Zero-to-peak voltage
2.5 V
0.75 V
Line coding
2B1Q (or 4B3T in Europe)
ASI (Alternate Space Inversion)

See also