Telecommunications

I

Introduction

Telecommunications, communications over a distance using technology to overcome that distance. It usually means the transmission of words, sounds, pictures, or data in the form of electronic signals or impulses, sent either as an individual message between two parties or as a broadcast to be received at many locations. While broadcasting is far removed from private communications, a new range of one-to-one communication services (including video-on-demand, and other personal information and entertainment services provided over cable networks and so-called “Webcasting” over the Internet) will blur the current clear distinction between the two, assisted by a move towards replacing conventional standalone televisions with integrated “media centre” computers or “infotainment machines” that are used for entertainment as well as computing, messaging, and other information processing.

Since its invention in the 1860s and 1870s by Alexander Graham Bell and others, the telephone has become the most familiar form of telecommunications. More recently, voice telephony has been supplemented by a range of computer-based telecommunication services. These have become popular through the Internet and World Wide Web—vast computer networks that provide many people with the means to exchange information. With low-cost broadband connections reaching ever more homes and offices, this delivery mechanism is beginning to offer not only high-speed Internet service but new premium (paid-for) content including streamed video and audio programmes (so-called narrowcasting), educational resources, online sophisticated shopping and banking facilities, gaming and personal dating services, online access to archived films and television programmes, and much more yet to be devised.

II

History

It is now taken for granted in developed nations that by pressing a few buttons people can talk to family, friends, or business associates across the world—and at a readily affordable price. The technology that led to one of the most complex creations of the 20th century—the telephone network—has evolved over the past hundred years or so.

The first electrical means of communication was not the telephone, however, but the telegraph, which allowed messages sent in code (usually Morse Code) to be received and printed at a distant location. The age of commercial telegraphy dawned in 1839 when the British pioneers William Fothergill Cooke and Charles Wheatstone opened their line alongside the main railway route running west from London. A technically simpler system of telegraphy was devised in 1843 by Samuel Morse, and after this the spread of telegraph networks was rapid, with routes spreading across most of the countries of the Old and New Worlds and then beneath the oceans that separated them. By 1930 nearly 650,000 km (400,000 mi) of undersea cables had been laid, linking the economic, political, military, and cultural institutions of the world.

An even greater breakthrough was made in 1876, when Alexander Graham Bell made the first telephone call to his assistant with the words “Mr Watson, come here, I want you”. Bell’s invention sparked a series of innovations, ultimately culminating in today’s information superhighway. Key steps along the way were:

In 1889 Almon Strowger developed an automatic switching system that could set up a telephone call without intervention by a human operator. Strowger’s motivation for this invention was to prevent his calls being diverted to a business competitor by his local operator. The impact of the invention was much wider as it provided the basis for the current telephone network.

In 1901 Guglielmo Marconi demonstrated that radio waves could be used to transmit information over long distances when he sent a radio message across the Atlantic. Radio is still one of the key transmission media today, and is the basis of many mobile services.

In 1947 William Shockley, John Bardeen, and Walter Brattain invented the transistor. This enabled the electronics revolution to take place and provided the basis for a computerized, rather than mechanical, telecommunications network.

In 1965 Charles Kao put forward the theory that information could be carried using optical fibres. These have subsequently been developed to provide a means of carrying huge amounts of information at very high speed. Optical fibres form the backbone of the global transmission network (see Fibre Optics).

The modern telephone network can be viewed as a globally distributed machine that operates as a single resource. Much of it uses interconnected computers. The network that most people use to carry voice traffic can also be used to transfer data in the form of pictures, text, and video images.

III

Networks

Despite being very complex, global telecommunications service is comprised of a few basic network components, which are: (1) user equipment—telephones, computers, and all the other devices that provide a means of accessing the network; (2) the access network—users are connected to the main network by wireline or radio links; (3) the main network—copper wire, microwave radio, and optical fibre cables connecting all the nodes of the global network; (4) transmission equipment—the means by which huge volumes of information (there are many millions of telephone and data calls made every second) are carried over the network; and (5) switching equipment—the hierarchy of local, national, and international switches that allow any user of the network to connect to any other user. Most of these networks are to some degree integrated (multifunctional), made up from narrowband and broadband elements, some of which are dedicated to particular types of calls or “traffic”. This situation is changing, as we shall see in Section VI, meaning that we must consider both the existing networks and those that will soon succeed them. Old or new, each of these components is made up of a combination of hardware and software.

A

Hardware

This usually covers items such as telephones, transmitters, cables, interface devices, switches, and computers. In the past, telecommunications have relied heavily on hardware, such as dedicated switching elements, and on the logic providing its control functions. A situation is now developing in which more of the system relies on elements operating under computer (software) control. Because this software can be upgraded, this makes it easy to add new, enhanced functionality later.