B-4-g WIRE & WIRELESS COMMUNICATIONS
In 1837, Samuel Morse perfected the telegraph, which was a painter. With the words "What has God wrought," transmitted by Morse's electric telegraph between Washington D.C., and Baltimore, Maryland, in 1844, a completely revolutionary means of real-time, long-distance communications was triggered.
The telegraph is the forerunner of digital communications in that the Morse code is a variable-length ternary code using an alphabet of four symbols: a dot, a dash, a letter space, and a word space; short sequences represent frequent letters, whereas long sequences represent infrequent letters.
In 1864, James Clerk Maxwell formulated the electromagnetic theory of light and predicted the existence of radio waves.
Heinrich Hertz established the existence of radio waves experimentally in 1887.
In 1894, Oliver Lodge demonstrated wireless communication over a relatively short distance (150 yards). Then, on December 12, 1901, Guglielmo Marconi received a radio signal at Signal Hill in Newfoundland; the radio signal had originated in Cornwall, England, 1700 miles away across the Atlantic. The way was thereby opened toward a tremendous broadening of the scope of communications.
In 1905, Reginald Fessenden demonstrated wireless telephony by transmitting speech and music over a radio channel.
In 1875, the telephone was invented by Alexander Graham Bell, a teacher of the deaf. The first version of the telephone was crude and weak, enabling people to talk over short distances only. When telephone service was only a few years old, interest developed in automating it.
Notably, in 1897, A. B. Strowger, an undertaker from Kansas City, Missouri, devised the automatic step-by-step switch that bears his name; of all the electromechanical switches devised over the years, the Strowger switch was the most popular and widely used.
In 1904, John Ambrose Fleming invented the vacuum-tube diode, which paved the way for the invention of the vacuum-tube triode by Lee de Forest in 1906.
The discovery of the triode was instrumental in the development of transcontinental telephony in 1913 and signaled the dawn of wireless voice communications. Indeed, until the invention and perfection of the transistor, the triode was the supreme device for the design of electronic amplifiers.
In 1918, Edwin H. Armstrong invented the super heterodyne radio receiver; even to this day, almost all radio receivers are of this type.
Then, in 1933, Armstrong demonstrated another revolutionary concept, namely, a modulation scheme that he called frequency modulation (FM). Philo T. Farnsworth demonstrated the first all-electronic television system in 1928. By 1939, the British Broadcasting Corporation (BBC) was broadcasting television on a commercial basis.
In 1937, Alec Reeves invented pulse-code modulation (PCM) for the digital encoding of speech signals. The technique was developed during World War II to enable the encryption of speech signals. However, PCM had to wait the discovery of the transistor and the subsequent development of large-scale integration of circuits for its commercial exploitation.
In 1948, Claude Shannon laid the theoretical foundations of digital communications. In the same year, Walter H. Britain, John Bardeen, and William Shockley at Bell Laboratories invented the transistor. The invention of the transistor spurred the application of electronics to switching and digital communications. The motivation was to improve reliability, increase capacity, and reduce cost.
The first call through a stored-program system was placed in March 1958 at Bell Laboratories; and the first commercial telephone service with digital switching began in Morris, Illinois, in June 1960.
Bell Laboratories in the United States installed the first T-1 digital carrier system transmission in 1962.
The first silicon integrated circuit (IC) was produced in 1958 through Robert Noyce.
These landmark innovations in solid-state devices and integrated circuits led to the development of very-large-scale integrated (VLSI) circuits and single-chip microprocessors, and with them the nature of the telecommunications industry changed forever.
During the period 1943 to 1946, the first electronic digital computer, called the ENIAC, was built at the Moore School of Electrical Engineering of the University of Pennsylvania.
Computers and terminals started communication with each other over long distances in the early 1950s.
The links used were initially voice-grade telephone channels operating at low speeds (300 to1200 b/s). Various factors have contributed to a dramatic increase in data transmission rates; notable among them are the idea of adaptive equalization, pioneered by Robert Lucky in 1965, and efficient modulation techniques, pioneered by G. Ungerboeck in 1982.
Another idea widely employed in computer communications is that of automatic repeat-request (ARQ) for error correction.
The ARQ method was originally devised by H.C.A. van Duuren during World War II and published in 1946. ARQ was used to improve radiotelephony for telex transmission over long distances.
During 1950-1970, various studies were made on computer networks. However, the most significant of them in terms of impact on computer communications was the Advanced Research Project Agency Network (ARPANET), first put into service in 1971, which was the origin of the Internet.