1. Introduction to data and network communications  History of telecommunications  Data communication systems  Data communications links  Some hardware facts  Analog and digital data  Codes: binary, ASCII  Digital data rates  Data formats Required textbook for this course: Michael A. Miller: Data and Network Communications, Delmar-Thompson Learning, 2000

2. Milestones in history of telecom 1832 Morse code 1874 teletype 1876 Telephone 1881 Long distance line Boston-Providence 1898 Marconi wireless telegraph 1921 first radio broadcast 1934 FCC formed

3. Milestones continued 1940 first computers: ENIAC, MARK I, II 1947 transistor invented 1956 TDM – time division multiplexing 1958 first coast-to-coast microwave 1959 first integrated circuits 1965 Intelsat 1 1966 fiber optic cable

4. Milestones 1969 packet-switched network ARPANET 1969 UNIX operating system 1972 first e-mail 1974 –1976 TCP/IP Ethernet LAN 1978 Hayes 300-bps modem 1981 IBM PC

5. Milestones 1982 Internet term coined 1983 first cellular phones 1987 NSFNET 1988 CERT formed 1990 Frame relay, commercial dial-up 1991 ATM, first wireless LAN 1992 HTML

6. Milestones 1993 MOSAIC 1994 Netscape 1995 JAVA, 6 million Internet users 1997 Telecommunications reform act 1998 E-commerce takes off 1999 Y2K fears 2000 Wide spread of wireless communications

7. Telegraph Facts A telegraph works by sending pulses of current through a (long) wire to a remote location. At the remote location, the received pulses are converted into a form that can be interpreted by a human operator. The transmitter is just a switch that allows the flow of current when the switch is pressed. There are three types of symbols: off (space) -no pulse is transmitted short (.) a short pulse is transmitted long (-) a long pulse is sent

8. Morse Code A.- B -... C -.-. D -.. E. F..-. G --. H.... I.. J.--- K -.- L.-.. M -- N -. O --- P.--. Q --.- R.-. S... T - U..- V...- W.-- X -..- Y -.-- Z --.. If the duration of a dot is taken to be one unit then that of dash is three units. The space between the components of one character is one unit, between characters is three units and between words seven units.

9. Morse telegraph circuit

10. Data Communications Link

11. Source: Michael A. Miller: Data and Network Communications, Delmar-Thompson Publ 2000

12. Elements of a data comm link End stations (primary, remote) LCU – line control unit: parallel data coming out of the processor UART: universal asynchronous receiver transmitter: converts parallel data into serial DCE: data communications equipment i.e. modem (modulator-demodulator) Transmission medium: telephone line, coax cable, fiber cable, wireless, microwave, satellite link

15. Power of 2 value Binary form 0100000000001 1200000000010 2400000000100 3800000001000 41600000010000 53200000100000 66400001000000 712800010000000 825600100000000 951201000000000 10102410000000000

21. signal before and after quantization time

22. Digitized signal each bar corresponds to a binary number the sequence of binary numbers is transmitted through the communications link as a sequence of symbols the time intervals between the samples are used to transmit signals of other users (this is called multiplexing) In digital telephone system the speech signal is sampled 8,000 per second

23. Frequency, bandwidth IEEE defines frequency as “the number of complete cycles of sinusoidal variation per unit time” (or sinusoidal oscillation) 1 Cycle per second = 1 Hertz = 1 Hz 1000 cycles per second = 1000 Hz = 1kHz 1,000,000 cycles per second = 1 MHz 1,000,000,000 Hz = 1 GHz

24. Frequencies 1Hz, 2, 10, 20 Hz

25. Sine Functions Amplitude –maximum strength of signal Frequency –Rate of change of signal: cycles per second –Period = time for one repetition (T) –T = 1/f, where f is frequency Phase –Relative position in angle

26. Frequencies: examples Acoustic frequencies: human speech: 100 Hz to 7 kHz ultrasounds: above 20 Khz to 1 MHz Electromagnetic carrier frequencies: AM radio broadcast (example) 710 kHz FM broadcast 89 MHz- 108 MHz TV broadcasting 150 MHz- 900 MHz Cellular telephony ~ 1 GHz

27. Frequency Domain Concepts Signal has many frequencies Components are sine functions Fourier analysis shows that any signal is made up of component sine waves Frequency domain functions can be plotted as “spectrum”

28. Spectrum & Bandwidth Spectrum is the range of frequencies contained in signal DC Component –Component of zero frequency

29. Data Rate and Bandwidth Any transmission system has a limited band of frequencies This limits the data rate that can be carried

30. Source: Michael A. Miller: Data and Network Communications, Delmar-Thompson Publ 2000