Telefax Telefax Gr 4 Digital Subscriber Line ISDN = Integrated Services AM radio FM radio Stereo radio Digital radio Digital Network Radio Color TV Stereo TV Digital TV AM = Amplitude Modulation Telephone FM = Frequency Modulation Cellular Telephone Mobile IP = Internet Protocol Paging Digital CS = Circuit Switched Cellular Telephone Mobile PS = Packet Switched VoD = Video on Demand Time/year Figure 1.2 Development of telecommunications systems and services. 1800-1837 Preliminary developments: Volta discovers the primary battery; Fourier and Laplace present mathematical treatises; Ampere, Faraday, and Henry conduct experiments on electricity and magnetism; Ohm's law (1826); Gauss, Weber, and Wheat- stone develop early telegraph systems. 1838-1866 Telegraphy: Morse perfects his system; Steinhill finds that the earth can be used for a current path; commercial service is ini- tiated (1844); multiplexing techniques are devised; William Thomson calculates the pulse response of a telegraph line (1855); transatlantic cables are installed. Kirchoff's circuit laws. Maxwell's equations predict electromagnetic radiation. 1876-1899 Telephony: Alexander Graham Bell perfects acoustic trans- ducer; first telephony exchange with eight lines; Edison's carbon-button transducer; cable circuits are introduced; Strowger devises automatic step-by-step switching (1887); Pupin presents the theory of loading. 1887-1907 Wireless telegraphy: Heinrich Hertz verifies Maxwell's theory; demonstrations by Marconi and Popov; Marconi patents com- plete wireless telegraph system (1897); commercial service begins, including ship-to-shore and transatlantic systems. Introduction to Telecommunications 1904-1920 Communication electronics: Lee De Forest invents the Audion (triode) based on Fleming's diode; basic filter types devised; experiments with AM radio broadcasting; the Bell System completes the transcontinental telephone line with electronic repeaters (1915); multiplexed carrier telephony is introduced: H.C. Armstrong perfects the superheterodyn