ISDN (Integrated Services Digital Network) is a telephone network system that makes it possible to transmit, at high rates, more data and information than the traditional phone line. Whereas before phones could only send out voice, now it is possible to transmit out video, images, and other data types; being digital, the quality is superior to analog devices.

An Overview of the ISDN Infrastructure

The ISDN utilizes two channels for transmitting the data it receives, channel B and channel D.

Channel B, or the Bearer Channel, is used for the actual sending out of the information while the Delta Channel (channel D) is mainly for control and signal operations. However, depending on the configuration, it can also be used for sending out data.

The interface of the network is composed of two elements, the Basic Rate Interface (BRI) and the Primary Rate Interface. They are also known as Basic Rate Access and Primary Rate Access.

The Basic Rate Interface

The BRI consists of two Bearer channels with a bandwidth capable of transmitting data up to 64 bits/s, and a Delta channel with a 16bit/s. The BRI is also referred to as 2B+D.

Some of the most common features of a BRI interface include the following: the U interface, which marks the NTU (Network Terminating Unit). This is used mostly in Europe. The T serial interface that lies between an adapter and a computer device, and is very similar in function to the modem. The S interface (bus, 4 way) is where an ISDN device is connected to, while the R interface marks the area between a non ISDN device and the terminal adapter.

The Primary Rate Interface

The Primary Rate Interface is made up of several Bearer channels, the number depending on the network system and how it is arranged. It also has a Delta channel with a bandwidth of 64 bits/s the size of the B channel in the BRI. In the United States the PRI can be designated as 23B+D, although in some countries in will vary depending on the channels and bandwidth.

How ISDN Works

ISDN functions in different ways, but one of the most popular is through the bipolar eight zero substitution. Basically what it does is to have the data placed in the B channels exclusively, while the D channel is utilized to install and handle the streaming data. The more channels there are, the greater the number of possible data.

Benefits of ISDN

For the ordinary user, the advantages of an ISDN line is that it will provide for much faster Internet connections, allowing for quicker downloading of software, video and access to information.

For the communications industry itself, ISDN presents a viable alternative, because it can relay messages at a more rapid pace. ISDN is also being utilized in some PSTN (public switched telephone network) systems, because it allows for the use of high quality digital services, and at the same time it can function as a backup device in case of circuit failure or it encounters an error.