e radio receiver (1918); first commercial broadcasting station. 1920-1928 Carson, Nyquist, Johnson, and Hartley present their transmis- sion theory. 1923-1938 Television: Mechanical image-formation system demonstrated; theoretical analysis of bandwidth requirements; DuMont and others perfect vacuum cathode-ray tubes; field tests and experi- mental broadcasting begin. Teletypewriter service initiated. H.S. Black develops the negative feedback amplifier. Armstrong's paper states the case of frequency modulation (FM) radio. Alec Reeves conceives pulse code modulation (PCM). 1938-1945 Radar and microwave systems developed during World War II; FM used extensively for military communications; hard- ware, electronics, and theory are improved in all areas. 1944-1947 Mathematical representations of noise developed; statistical methods for signal detection developed. 1948-1950 C. E. Shannon publishes the founding papers on information theory. 1948-1951 Transistor devices are invented. Time-division multiplexing (TDM) is applied to telephony. Hamming presents the first error correction codes. Color TV standards are established in the United States. J.R. Pierce proposes satellite communication systems. Long-distance data transmission system is developed for mili- tary purposes. Maiman demonstrates the first laser. Integrated circuits are applied to commercial production. Satellite communication begins with Telstar I. Introduction to Telecommunications Network Engineering 1962-1966 Data transmission service offered commercially; PCM proves feasible for voice and TV transmission; theory for digital trans- mission is developed; Viterbi presents new error-correcting schemes; adaptive equalization is developed. Fully electronic telephone switching system is put into service. Mariner IV transmits pictures from Mars to Earth. 1966-1975 Commercial satellite relay becomes available; optical links using lasers and fiber optics are introduced; ARPANET is cre- ated (1969) followed by international computer networks. Ethernet LAN invente