History of Integrated Services Digital Network (ISDN)

Before the coming of age of ISDN, original analogy telecommunication services, also known as Plain Old Telephone System (POTS) were the only source of telecommunication worldwide. POTS was the originally acronymic for Post Office Telephone Service/System but changed when post offices stopped offering telephone services. POTS comprised mainly of copper wires which linked the subscriber's home to the central switch office. This form of telecommunication had its limitations. Long distance calls had to be routed through operators and switchboards which made them highly unreliable and time consuming. There was also the issue of static inference known as line noise which disturbed communication.

In the 1960s, the telecommunication industry began working on converting its analogue systems to transmit 'packets' of digitized data by digital switching. The United Nations' International Telephone and Telegraph Consultative Committee (CCITT, French acronym), now known as International Telecommunications Union Telecommunications (ITU-T) actively pushed and encouraged the research for Integrated Services Digital Network (ISDN) by starting a movement to recommend and provide standards for international digitization of the telecommunication services. This was initiated in 1984.

Two major US networks, Northern Telecomm and AT&T took the first steps towards implementing ISDN, but it did not interoperate with existing equipments and software available to telecommunication networks, this led to a setback for ISDN worldwide. By 1990, due to a world wide effort, National ISDN 1 (NI-1) was made compatible with existing proprietary equipments for telecommunication services, this way people did not need to switch brand or buy software for the network. This set the standards and procedure for future digital telecommunication technology to be used by everyone.

ISDN has resulted in better voice quality and Internet access due to its packet-switch connection. With ISDN, voice and data are carried by a bearer channel (B channel) with a bandwidth of 64 kb/s, sometimes 56 kb/s as opposed to telephone line which carry 52 kb/s. A data channel (D channel) is used for controlling network services and signalling to construct, break connections and carry data over the bearer channels. This carries a bandwidth of 16 kb/s or 64 kb/s.

There are two services offered by ISDN. This is known as the BRI and PRI. BRI - Basic Rate Interface consists of two 64 kb/s bearer channels and one 16 kb/s data channel, totaling 144 kb/s; as the name implies, BRI usually has enough bandwidth for individual users. PRI - Primary Rate Interface is used for clients that require greater bandwidth. It usually comprised of 23 64 kb/s B channels and one 64 kb/s D channel, totaling 1.536 Mb/s. Sometimes, the PRI service can have 30 B channels and one D channel for a total of 1.984 Mb/s.

For now, the future of ISDN lies with Broadband ISDN (BISDN). This entails transferring data, voice and video all at the same time using fibre optic telephone line which can carry data rates from 155 Mb/s to 622 Mb/s and beyond. This is a major topic for research and development.

Article by Tola Fam.
Online marketing AT connect4free.co.uk
For more information on using ISDN for free and fast dial up internet access, visit us at http://www.connect4free.co.uk/.

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Brief History of the Telephone

In the last hundred years or so, the telephone has gone from an idea to one of the most ubiquitous appliances in households and businesses across the world, allowing human beings to communicate with each other for countless reasons across great distances. The origins of this device can be traced back to simple devices that transmit voice through tubes or some physical material. One of the most popular images of this sort of device is two tin cans linked by a taut piece of string; allowing sound waves to be transferred from one can to the other. Of course this simple device is considered in modern times to be more of a novelty rather than used for actual telecommunications.

Although it did not transmit voice, one of the precursors to the telephone as we know it today is the telegraph. Using what became known as "Morse Code", telegraphs were a way to transmit messages encoded into long and short beeps over fairly long distances. Someone on one end of the telegraph might converse with someone on the other end by tapping out the message on the device, modulating electrical current passing along the telegraph wire. This proved to be a time consuming and expensive way of sending messages, but was the fastest method at the time. Over time, there was a push to develop a system that functioned in much the same way but could transmit and receive voice.

Modern history frequently credits the invention of the telephone to Alexander Graham Bell, but who should actually be credited with the invention is still a matter of dispute. Antonio Meucci is credited with helping with the development of the telephone and German Johann Philipp Reis is widely seen as having come a long way in developing his own device, although he did not achieve a fully operable telephone. The general consensus regarding the inventor of the telephone is that rather than being the product of one person, it was the result of research and work done by these and a number of others. Perhaps the reason Bell is credited with its invention is due to his filing of a patent.

Alexander Graham Bell was also central in turning telephones and telephone service into a commercial venture, notorious for maintaining a monopoly in the telephone industry for decades. Originally each telephone had a battery but eventually power was carried along a single telephone line that served both telephone transmission and reception, the power being grounded in the earth rather than sent back on a return line. During this time, telephone users spoke into and listened with the same opening which was quite aggravating, as was the fact that consumers had to pay for lines to be run between a pair of telephones. This was before the concept of a switchboard was utilized, forcing lines to be constructed between each and every telephone pair.

Eventually switching technology came about which enabled callers to dial a particular number, first with a rotary dial and later a keypad. This was a major advancement because it didn't require operators to connect calls and greater facilitated long distance calls. Over time there was a push to break up the monopoly Bell had set up and in 1984 what had become the AT&T monopoly was broken up because of a federal mandate. What resulted was a number of smaller companies who then, theoretically, would compete in the marketplace and drive down the price of service for consumers. In the past two decades, however, traditional telephone service providers have had to compete with new cellular phone service providers and Voice over Internet Protocol (VOIP) service providers

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