Introduction to data and network communications

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• 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
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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

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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

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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

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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

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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

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• 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

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• 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.

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Morse telegraph circuit
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Data Communications Link
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Source Michael A. Miller Data and Network
Communications, Delmar-Thompson Publ 2000
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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

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Power of 2 value Binary form
0 1 00000000001
1 2 00000000010
2 4 00000000100
3 8 00000001000
4 16 00000010000
5 32 00000100000
6 64 00001000000
7 128 00010000000
8 256 00100000000
9 512 01000000000
10 1024 10000000000
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signal before and after quantization
time
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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

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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

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Frequencies 1Hz, 2, 10, 20 Hz
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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

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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

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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

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Spectrum Bandwidth

• Spectrum is the range of frequencies contained in
  signal
• DC Component
• Component of zero frequency

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Data Rate and Bandwidth

• Any transmission system has a limited band of
  frequencies
• This limits the data rate that can be carried

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