Data and Computer Communications

Data and Computer Communications

1. Data Transmission

2. Transmission Terminology

   • data transmission occurs between a transmitter & receiver via some medium
   • guided medium
   • unguided / wireless medium
   • direct link
   • point-to-point
   • multi-point
   • simplex
   • half duplex
   • full duplex

3. Frequency, Spectrum and Bandwidth

   • analog signal
   • digital signal
   • aperiodic signal
   • aperiodic signal

4. Sine Wave

   • peak amplitude (A)
   • frequency (f)
   • phase

5. Wavelength

   • is distance occupied by one cycle

6. Frequency Domain Concepts

   • signal are made up of many frequencies

7. Spectrum & Bandwidth

   • spectrum
   • absolute bandwidth
   • effective bandwidth
   • DC Component

8. Data Rate and Bandwidth

   • any transmission system has a limited band of frequencies

9. Analog and Digital Data Transmission

   • data
   • signals & signalling
   • transmission

10. SIgnals

    • Audio Signals
    • Video Signals
    • Analog Signals
    • Digital Signals
      • Advantages & Disadvantages of Digital Signals
        • cheaper
        • less susceptible to noise
        • but greater attenuation
        • digital now preferred choice
        • digital preferred Method
          • Technology support of VLSI
          • Security (Encryption)
          • Integration (data, audio, video)

11. Digital Data

    • has two dc components
    • bandwidth depends on data rate

12. Transmission Impairments

    • signal received may differ from signal transmitted causing
      • analog
      • digital
    • most significant impairments
      • attenuation and attenuation distortion
      • delay distortion
      • noise

13. Attenuation

    • depends on medium
    • where signal strength falls off with distance
    • increase strength using amplifiers/repeaters

14. Delay Distortion

    • only occurs in guided media
    • propagation velocity varies with frequency
    • particularly critical for digital data

15. Noise

    • additional signals inserted between transmitter and receiver
    • thermal
    • intermodulation
    • impulse
    • crosstalk

16. Channel Capacity

    • limitations due to physical properties
    • s a function of
      • data rate
      • bandwidth
      • noise
      • error rate
    • max possible data rate on comms channel
    • want most efficient use of capacity

17. Nyquist Bandwidth

    • consider noise free channels
    • can increase rate by using M signal levels
    • for binary signals, 2B bps needs bandwidth B Hz