Telecommunication

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Telecommunication is the transmission of signals over a distance for the purpose of communication. Today this process almost always involves the sending of electromagnetic waves by electronic transmitters but in earlier years it may have involved the use of smoke signals, drums or semaphores. Today, telecommunication is widespread and devices that assist the process such as the television, radio and telephone are common in many parts of the world. There is also a vast array of networks that connect these devices, including computer networks, public telephone networks, radio networks and television networks. Computers communicating across the Internet is just one of many examples of telecommunication.

Technical foundations

The basic elements of a telecommunication system are:

1. a transmitter that takes information and converts it to a signal for tranmission
2. a transmission medium over which the signal is transmitted
3. a receiver that receives and converts the signal back into usable information

For example, consider a radio broadcast. In this case, the broadcast tower is the transmitter, the radio is the receiver and the transmission medium is free space. Often telecommunication systems are two-way and devices act as both a tranmitter and receiver or transceiver. For example, a mobile phone is a transceiver. Telecommunication over a phone line is called point-to-point communication because it is between one transmitter and one receiver, telecommunication through radio broadcasts is called broadcast communication because it is between one powerful transmitter and numerous receivers.^[2]

Signals can either be analogue or digital. In an analogue signal, the signal is varied continuously with respect to the information. In a digital signal, the information is encoded as a set of discrete values (e.g. 1's and 0's).^[3]

A collection of transmitters, receivers or transceivers that communicate with each other is known as a network. Digital networks may consist of one or more routers that route data to the correct user. An analogue network may consist of one or more switches that establish a connection between two or more users. For both types of network, a repeater may be necessary to amplify or recreate the signal when it is being transmitted over long distances. This is to combat noise which can corrupt the information carried by a signal.

A channel is a division in a tranmission medium so that it can be used to send multiple independent streams of data. For example, a radio station may broadcast at 96 MHz while another radio station may broadcast at 94.5 MHz. In this case the medium has been divided by frequency and each channel received a separate frequency to broadcast on. Alternatively one could allocate each channel a segment of time over which to broadcast.

The shaping of a signal to convey information is known as modulation. Modulation is a key concept in telecommunications and is frequently used to impose the information of one signal on another. Modulation is used to represent a digital message as an analogue waveform. This is known as keying and several keying techniques exist — these include phase-shift keying, amplitude-shift keying and minimum-shift keying. Bluetooth, for example, uses phase-shift keying for exchanges between devices (see note).

However, more relevant to earlier discussion, modulation is also used to boost the frequency of analogue signals. This is because a raw signal is often not suitable for tranmission over free space due to its low frequencies. Hence its information must be superimposed on a higher frequency signal (known as a carrier wave) before transmission. There are several different modulation schemes available to achieve this — some of the most basic being amplitude modulation and frequency modulation. An example of this process is a DJ's voice being superimposed on a 96 MHz carrier wave using frequency modulation (the voice would then be received on a radio as the channel “96 FM”).

History

Early telecommunications

Early forms of telecommunication include smoke signals and drums. Drums were used by natives in Africa, New Guinea and tropical America whereas smoke signals were used by natives in America and China. Contrary to what one might think, these systems were often used to do more than merely announce the presence of a camp.

In 1792, a French engineer, Claude Chappe built the first visual telegraphy (or semaphore) system between Lille and Paris. This was followed by a line from Strasbourg to Paris. In 1794, a Swedish engineer, Abraham Edelcrantz built a quite different system from Stockholm to Drottningholm. As opposed to Chappe's system which involved pulleys rotating beams of wood, Edelcrantz's system relied only upon shutters and was therefore faster.^[4] However semphore as a communication system suffered from the need for skilled operators and expensive towers often at intervals of only ten to thirty kilometres (six to nineteen miles). As a result, the last commercial line was abandoned in 1880.

Telegraph and telephone

The first commercial electrical telegraph was constructed by Sir Charles Wheatstone and Sir William Fothergill Cooke. It used the deflection of needles to represent messages and started operating over thirteen miles (twenty-one kilometres) of the Great Western Railway on 9 April 1839. Both Wheatstone and Cooke viewed their device as "an improvement to the [existing] electromagnetic telegraph" not as a new device.

On the other side of the Atlantic Ocean, Samuel Morse independently developed a version of the electrical telegraph that he unsuccessfully demonstrated on 2 September 1837. Soon after he was joined by Alfred Vail who developed the register — a telegraph terminal that integrated a logging device for recording messages to paper tape. This was demonstrated successfully over three miles (five kilometres) on 6 January 1838 and eventually over forty miles (64 kilometres) between Washington, DC and Baltimore on 24 May 1844. The patented invention proved lucrative and by 1851 telegraph lines in the United States spanned over 20,000 miles (32,000 kilometres).^[5]

The first transatlantic telegraph cable was successfully completed on 27 July 1866, allowing transatlantic telegraph communications for the first time. Earlier transatlantic cables installed in 1857 and 1858 only operated for a few days or weeks before they failed.^[6]

The conventional telephone was invented by Alexander Bell in 1857. Although in 1849 Antonio Meucci invented a device that allowed the electrical tranmission of voice over a line. Meucci's device depended upon the electrophonic effect and was of little practical value because it required users to place the receiver in their mouth to “hear” what was being said.^[7]

The first commercial telephone services were set-up in 1878 and 1879 on both sides of the Atlantic in the cities of New Haven and London. Bell held patents needed for such services in both countries. The technology grew quickly from this point, with inter-city lines being built and exchanges in every major city of the United States by the mid-1880's. Switching technology also improved.^{[8] [9]} Despite this, transatlantic communication remained impossible for customers until January 7 1927 when a connection was esablished using radio. However no cable connection existed until TAT-1 was inaugerated on September 25, 1956 providing 36 telephone circuits. ^[10]

Radio and television

In 1832, James Lindsay gave a classroom demonstration of wireless telegraphy to his students. By 1854 he was able to demonstrate a transmission across the Firth of Tay from Dundee to Woodhaven, a distance of two miles, using water as the tranmission medium.^[11]

Addressing the Franklin Institute in 1893, Nikola Tesla described and demonstrated in detail the principles of wireless telegraphy. The apparatus that he used contained all the elements that were incorporated into radio systems before the development of the vacuum tube. However it was not until 1900, that Reginald Fessenden was able to wirelessly transmit a human voice. In December 1901, Guglielmo Marconi established wireless communication between Britain and the United States earning him the Nobel Prize in physics in 1909 (which he shared with Karl Braun).^[12]

On March 25, 1925, John Logie Baird was able to demonstrate the tranmission of moving pictures at the London department store Selfridges. However his device did not adaquately display halftones and thus only presented a silhouette of the recorded image. This problem was rectified in October of that year leading to a public demonstration of the improved device on 26 January, 1926 again at Selfridges. Baird's device relied upon the Nipkow disk and thus became known as the mechanical television. It formed the basis of experimental broadcasts done by the British Broadcasting Corporation beginning September 30, 1929.^[13]

However for most of the twentieth century televisions depended upon the cathode ray tube invented by Karl Braun. The first working version of such a television was produced by Philo Farnsworth and demonstrated to his family on September 7, 1927. Farnsworth's device would compete with the work of Vladimir Zworykin who also produced a working electronic television in 1929. Zworykin's device had the backing of the influential Radio Corporation of America (RCA) however eventually court action between Farnsworth and the RCA would resolve in Farnsworth's favour.^[14]

Computer networks and the Internet

On September 11, 1940 George Stibitz was able to transmit problems using teletype to his Complex Number Calculator in New York and receive the computed results back at Dartmouth College in New Hampshire.^[15] This configuration of a centralized computer or mainframe with remote dumb terminals remained popular throughout the 1950's. However it was not until the 1960's that researchers started to investigate packet switching — a technology that would allow chunks of data to be sent to different computers without first passing through a centralized mainframe. A four-node network emerged on December 5, 1969 between the University of California, Los Angeles, the Stanford Research Institute, the University of Utah and the University of California, Santa Barbara. This network would become ARPANET, which by 1981 would consist of 213 nodes.^[16] In June 1973, the first non-US node was added to the network belonging to Norway's NORSAR project. This was shortly followed by a node in London.^[17]

ARPANET's development centred around the Request for Comment process and on April 7, 1969, RFC 1 was published. This process is important because ARPANET would eventually merge with other networks to form the Internet and many of the protocols the Internet relies upon today were specified through this process. In September 1981, RFC 791 introduced the Internet Protocol v4 (IPv4) and RFC 793 introduced the Transmission Control Protocol (TCP) — thus creating the TCP/IP protocol that much of the Internet relies upon today. A more relaxed transport protocol that, unlike TCP, did not guarantee the orderly delivery of packets called the User Datagram Protocol (UDP) was submitted on 28 August, 1980 as RFC 768. An e-mail protocol, SMTP, was introduced in August 1982 by RFC 821 and HTTP/1.0 a protocol that would make the hyperlinked Internet possible was introduced on May 1996 by RFC 1945.

However not all important developments were made through the Request for Comment process. Two popular link protocols for local area networks (LANs) also appeared in the 1970's. A patent for the token ring protocol was filed by Olof Soderblom on October 29, 1974.^[18] And a paper on the ethernet protocol was published by Robert Metcalfe and David Boggs in the July 1976 issue of Communications of the ACM.^[19] From the late 1980's until the late 1990's both protocols would have success in the LAN market with the token ring protocol fiercely promoted by IBM. But ultimately the majority of LANs would settle on the ethernet protocol by the start of the twenty-first century.

Modern operation

Telephone

Today, the fixed-line telephone systems in most residential homes remain analogue and, although short-distance calls may be handled from end-to-end as analogue signals, increasingly telephone service providers are transparently converting signals to digital before, if necessary, coverting them back to analogue for reception. Mobile phones have had a dramatic impact on telephone service providers. Mobile phone subscriptions now outnumber fixed line subscriptions in many markets. Sales of mobile phones in 2005 totalled 816.6 million with that figure being almost equally shared amongst the markets of Asia/Pacific (204m), Western Europe (164m), CEMEA (Central Europe, the Middle East and Africa) (153.5m), North America (148m) and Latin America (102m).^[20] In terms of new subscriptions over the five years from 1999, Africa has outpaced other markets with 58.2% growth compared to the next largest market, Asia, which boasted 34.3% growth.^[21] Increasingly these phones are being serviced by digital systems such as GSM or W-CDMA with many markets chosing to depreciate analogue systems such as AMPS.^[22]

However there have been equally drastic changes in telephone communication behind the scenes. Starting with the operation of TAT-8 in 1988, the 1990's saw the widespread adoption of systems based around optic fibres. The benefit of communicating with optic fibres is that they offer a drastic increase in data capacity. TAT-8 itself was able to carry to carry 10 times as many telephone calls as the last copper cable laid at that time and today's optic fibre cables are able to carry 25 times as many telephone calls as TAT-8.^[23] This rapid increase in data capacity is due to several factors. Firstly, optic fibres are physically much smaller than competing technologies. Secondly, they do not suffer from crosstalk which means several hundred of them can be easily bundled together in a single cable.^[24] Lastly, improvements in multiplexing have lead to an exponential growth in the data capacity of a single fibre. This is due to technologies such as dense wavelength-division multiplexing, which at its most basic level is building multiple channels based upon frequency division as discussed in the Technical foundations section.^[25] However despite the advances of technologies such as dense wavelength-division multiplexing, technologies based around building multiple channels based upon time division such as synchronous optical networking and synchronous digital hierarchy remain dominant.^[26]

Assisting communication across these networks is a protocol known as Asynchronous Transfer Mode (ATM). As a technology, ATM arose in the 1980's and was envisioned to be part of the Broadband Integrated Services Digital Network. The network ultimately failed but the technology gave birth to the ATM Forum which in 1992 published its first standard.^[27] Today, despite competitors such as Multiprotocol Label Switching, ATM remains the protocol of choice for most major long-distance optical networks. The importance of the ATM protocol was chiefly in its notion of establishing pathways for data through the network and associating a traffic contract with these pathways. The traffic contract was essentially an agreement between the client and the network about how the network was to handle the data. This was important because telephone calls could negotiate a contract so as to guarantee themselves a constant bit rate, something that was essential to ensure the call could take place without a caller's voice being delayed in parts or cut-off completely.^[28]

Radio and television

The broadcast media industry is also at a critical junction in its development, with the many countries starting to move from from analogue to digital broadcasts. The chief advantage of digital broadcasts is that they prevent a number of complaints with traditional analogue broadcasts. For television, this includes the elimination of a host of problems such as snowy pictures, ghosting or other distortion. These occur because noise distorts the analogue signal that contains the television transmission. Digital transmission overcomes these problems because digital signals are reduced to binary data upon reception and hence small perturbations to the digital signal do not affect output. In a simplified example, if a binary message 1011 was transmitted with signal amplitudes [ 1.0 0.0 1.0 1.0 ] and received with signal amplitudes [ 0.9 0.2 1.1 0.9 ] it would still decode to the binary message 1011 — a perfect reproduction of what was sent. From this example, a problem with digital transmissions can also be seen in that if the noise is great enough it can significantly alter the decoded message. Using forward error correction a reciever can correct a handful of bit errors in the resulting message but too much noise will lead to block errors, skipped frames or, at worse, a complete loss in transmission. Where as an analogue transmission might be able to provide an outline of the picture in very noisy conditions digital transmissions have a tendency to break down completely. For this reason digital broadcasting is sometimes referred to as being an “all or nothing” game.^[29]

To further elaborate on the above points, the modulation scheme widely used by digital broadcasts outside of North America is called orthogonal frequency-division multiplexing and has inherent protections against multipath interference that specifically target the problem of ghosting.

The Internet

Today an estimated 15.7% of the world population has access to the Internet with the highest penetration in North America (68.6%), Ocenia/Australia (52.6%) and Europe (36.1%).^[30] In terms of broaband access, countries such as Iceland (26.7 per 100), South Korea (25.4 per 100) and the Netherlands (25.3 per 100) lead the world.^[31] The International Telecommunication Union uses this information to compile a Digital Access Index that measures the overall ability of citizens to access and use information and communication technologies. Using this measure, countries such as Sweden, Denmark and Iceland receive the highest ranking while African countries such as Niger, Burkina Faso and Mali receive the lowest.^[32]

Local area networks

See also

• History of the Internet
• History of radio
• History of television
• Information theory
• International Telecommunication Union
• Radio
• Telephone
• Television

References

External links

• International Telecommunication Union
• Federal Communications Commission
• IEEE Communications Society
• Telecommunications Industry Association (TIA)
• Read Congressional Research Service (CRS) Reports regarding Telecommunications
• Aronsson's Telecom History Timeline
• Alcatel Telecommunications Review Telecom magazine published since 1922
• Ericsson's Understanding Telecommunications at archive.org (Ericsson removed the book from their site in Sep 2005)
• Voice Over Internet Protocol