An Introduction to ISDN

by Aeyne Schriber on February 11, 2012 in Internet Access

ISDN is another form of Internet connectivity that allows you to run applications such as videoconferencing, video streaming programs like online movies, and other applications that require a high speed connection.  ISDN is much faster than a dial-up connection and is less expensive to install however, recently it has been largely replaced by Digital Subscriber Lines (DSL) and Asymmetrical Digital Subscriber Lines which are easier to install and meet the necessary requirements for most of today’s business applications.

Definition of ISDN

Integrated Digital Services Network (ISDN) transmits both voice and data over a telephone line using a defined series of digital transmission protocols.  These standards are set by the International Standards Body for Telecommunications which is an accepted protocol for telecommunications carriers across the globe.

An ISDN connection utilizes an existing telephone line and allows for multiplexing of a single telephone which allows voice and data transmission to occur simultaneously and without interference.  Where a conventional telephone line is analog an ISDN connection makes it digital to enable information packets to travel in bits instead of waves.

ISDN is capable of separating bandwidth into three different channels which make up the total bandwidth of ISDN.  Typically the setup is 64 Kbps (kilobits per second) for the first two channels with one channel running at 16 Kbps.  The first two channels we mentioned run at a higher data transfer rate which makes the connection capable of handling data, video, and voice.  The third channel runs at a slower data transfer rate making it capable of handling single bits of information.  PCs which are connected with an ISDN line can function on all channels provided by this type of connection.

How ISDN Works

When ISDN is used in a business setting it is capable of supporting multiple devices on the same line as well as a high number of telephone numbers.  The devices include telephones, fax machines, and PCs which can all function independently on a basic rate ISDN.  For example, if you want to place multiple telephone calls, send a fax, and run a PC connection this can be accomplished simultaneously on an ISDN line.

Using a digital ISDN connection you can also call a telephone which is analog regardless of the fact your telephone is digital and the analog telephone can call your telephone which is connected via ISDN.  The two different types of networks are connected by a switch operated by a public telephone network.  When you make calls the difference in the connection (analog or digital) is not apparent to the caller since is handled through the public telephone network.

Basic Rate ISDN vs. Primary Rate ISDN

There are two different types of ISDN connections which include the Basic Rate and the Primary Rate.  Basic Rate is a slower connection operating at approximately 146,000 bits per second where the Primary Rate operates at about 2,000,000 bits per second.  Basic Rate provides two user channels and is typically implemented for small business and personal use.  Primary Rate can offer up to 30 user channels and is installed in larger businesses and commercial enterprises.

Although there are two basic types of ISDN it is possible for ISDN service providers to implement a service where there are unused channels included in the service.  This allows a business to pay only for the channels they use and the unused channels allow for future expansion.  This concept is also known as fractional ISDN.

The Difference between ISDN and DSL

Telephone companies and Internet Service Providers use ISDN and DSL (Digital Subscriber Line) connections.  These two types of connections do have common features however; there is a difference between an ISDN connection and DSL.

First, DSL is less expensive to install and provides an ‘always-on’ connection.  ISDN is more expensive to install and sometimes requires PC users to login in to establish a connection to the Internet.  DSL is also more commonly available for personal use than an ISDN lines which tends to be implemented in commercial environments.  If ISDN is used by an Internet Service Provider then the service can be made available in the home environment.

In terms of the data transfer rate a Digital Subscriber Line is much faster and more efficient than an ISDN connection.  Depending upon the DSL service the maximum data transfer rate can be as high as 1.5Mbps.  If you connect with ISDN the data transfer rate is limited to speeds which are lower than a DSL connection.  Despite the difference in the data transfer rate both connections are capable of supporting voice, data, video, and high speed Internet connectivity.

ISDN tends to be more consistent with data transmission speeds where DSL may vary according to the number of devices connecting to the network simultaneously.  However, the digital clarity when used for voice can be considerably less than a DSL connection.  ISDN connections are also typically farther away from the central switching station than a Digital Subscriber Line which is why digital clarity comes at an extra cost during installation.  For this reason, DSL has widely replaced business communications as the connection of choice due to a higher rate of data transfer, clarity and cost effective installation.

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