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1、湖南城市学院教师备课纸 第 次课题：Telecommunication Step I what is telecommunication The word telecommunication derives from the Greek word tele, meaning over a distance, plus the word communication. Thus, putting the two parts together, you get telecommunication- communication that spans a distance. An ancient exa
2、mple of telecommunication is the use of fire signals on hilltops those miles apart. These days, modern telecommunications is a vast field that encompasses everything from broadcasting to telephone technology to computer networks. TelecommunicationVoice Video DataWireline wireless wireline wireless w
3、ireline wireless Local+long cellular telephony video broadcast TV computers RF networksDistance conferencingTelephony digital cable radio broadcasting desktop video over networks satellite feeds LANs paging Intercom wireless local+long distance telephony cable TV WANs point-to-point services closed
4、circuit TV The internet Figure 1. Telecommunication services Three categories of telecommunication are: voice, video and data. Voice telecommunication refers to any means of using electrical signals to transmit human voice across a distance, such as telephone and audio broadcasts. Video telecommunic
5、ation refers to the electrically-based transmission of moving pictures and sound across a distance , such as TV broadcasting or distributing live feeds of an event to the screen of networked computers. Data telecommunication refers to use of electrical signals to exchange encoded information between
6、 computerized devices across a distance. Sending an e-mail to a colleague, retrieving a spread-sheet from your computers hard disk, and sending a message to your spouses pager are all examples of data telecommunications. Voice, video and data telecommunications all belong to the larger “data telecom
7、munication” categories that they rely on electrical signals. Step II Evolution of telecommunication networks The first phase The first phase in the evolution of communication networks is dominated by the wide spread of telephony and covers over 90 years. However, the telegraph preceded the telephone
8、 by more than 30 years and the teletypewriter by half a century. In 1844, Samuel Morse, the telegraphs inventor, sent the first telegraph message from Washington D.C, to his colleague Alfred Vail in Baltimore, Maryland. Shortly after the invention of the telephone by Alexander Grahan Bell in 1876, i
9、t was realized that telephone wires had to converge on central points where telephone-to-telephone connections could be made. These points were manual switch-boards, staffed by operators. 1889, Almond B. Strowger invented the first two-motion step-by-step switch. 1932, the first crossbar switch was
10、used in Sweden. 1938, the Bell System introduced the NO.1Crossbar switch. In the mid 1930s, analog point-to-point radio relay transmission was possible by extending high-frequency (HF) communication technology into the very-high-frequency range. During the World War 2, the operating bands of the analogue radio relay systems were extended into the ultra-high- frequency(UHF) range. The first link with over 100 repeater station was placed into commercial service in 1951 between New York and San Francisco, operating in the 4GHz band with a 20MHz band. By the 1980s, quadrature amplitude mod
