C4

• Guided medium

  Visible form of physical wire or cable

  
• Unguided medium

  Wireless transmission like air or the vacuum of space

  
• Twisted Pair Cable

  • Consists of two separate insulated twisted copper wires
  • Each wire is coated with plastic
  • Electromagnetic field is generated when electricity flows
  • Twisted wire creates less energy and is less susceptible to interference from other wires
  • Each pair of wire is considered as a single communication line

  
• Unshielded Twisted Pair (UTP)

  • Lacks the wire wrapping
  • More prone to interference
  • Suitable for voice transmission, telephone system at home or office
• Shielded Twisted Pair (STP)


  • Covered with metallic shield which has thin wires to absorb interference
  • Has another plastic outer shell
  • Often used when many wires are packed together
  • Reliable for transmission of high-interference area

  
• Twisted Pair Cable Categories

  
• Coaxial Cable (coax)

  • A high-frequency transmission cable
  • Replaces the multiples wires of telephone lines with a single solid-copper wire
  • Composed of a single copper wire covered by a shell
  • The shell is covered by a second conductor (braided) for more electromagnetic protection
  • The entire cable is surrounded by a plastic outer shell or jacket
  • Transmit data over longer distance and less susceptible to interference

  
• Baseband transmission (digital)

  • One channel on one cable
  • Used in computer networks

  
• Broadband transmission (analog)

  • Many channels on one physical cable
  • Cable TV

  
• Fiber-Optic Cable

  • Transmit digital data by using light pulses to presents binary digits
  • The core is composed of one or more thin strands of pure glass or plastic, called optical fiber
  • They are bundled together and each surrounded by a reflective buffer
  • Fiber optic uses LED (light-emitting diode) or laser to send pulses
  • Using lights results faster transmission speed

  
• Advantages of Fiber-Optic Cable

  • Speed
  • Security
  • Immunity to electrical interference

  
• Disadvantages of Fiber-Optic Cable

  • Fragility. Glass fiber is more easily broken than wire
  • Cost. This cable is very expensive, because the density of the core must be very precise and a laser light source is also costly
  • Installation/maintenance. Any cracking to the core will diffuses light and alters the signal. All core must be maintain and be polishes

  
• Ground propagation

  • Radio waves travel through the lowest portion of the atmosphere, hugging the earth
  • The low frequency signal follow the curvature of the planet
  • Distance depends on the amount of the power

  
• Sky propagation

  • Higher frequency radio radiate upward into the ionosphere where they are reflected back to the earth
  • Sky propagation allow for greater distance with lower power output

  
• Line-of-sight propagation

  • Very high frequency signals are transmitted in straight lines directly from antenna to antenna
  • Antennas must be directional, facing each other and close enough together not to be affected by the curvature of the earth

  
• Radio wave

  • A type of electromagnetic radiation with a much longer wavelength than visible light
  • Transmit data signal through the air with a frequency range of 500 kHz to 300 MHz
  • Used by AM and FM radio stations, shortwave, and various high-frequency television transmissions
  • Broadcast is omnidirectional (receiving or sending radio waves equally well in all directions omnidirectional antenna)
  • Different broadcast signals use different ranges of frequency spectrum. Example: AM radio is transmitted using a lower frequency while FM radio uses a higher frequency
• Microwave

  • 3000 MHz to 30 GHz
  • Super-high frequency signals
  • Short wavelength

  
• Terrestrial Microwave

  • To transmit data between microwave station on earth
  • Transmit data at line-of-sight
  • For long distance communications
• Satellite Microwave

  • Transmit data between 2 or more earth-based microwave stations and a satellite
  • Geosynchronous Earth orbiting satellite (GEOS): in the fixed position over the earth
  • Satellite footprint: Coverage area of reception and transmission covers several countries, only the station within footprint can receive signal from that satellite
  • Transponder: to transmit the signal
  • Uplinks: to send signal from earth to the transponder
  • Downlinks: to retransmit the signal back to earth station
  • Uplink and downlink use different frequency to avoid interference
  • May cause Propagation delay: solve by equalizer
• Infrared

  • Light signals sent at a frequency that cannot be seen
  • Used in remote control products
  • Transmit signals at line-of-sight
  • Cover 30 to 80 feet of area
  • IrDA ports used in wireless products with printers, keyboards, mouse
  • LANs for wireless transmission

  
• Factors to consider when selecting communication media

  • Cost
  • Speed
  • Rate of Errors
  • Security
• UTP is the least expensive communication medium
• Fiber optic cable is the fastest communication medium
• Twisted pair and coaxial cable are easy to tap on, making them less secure
• Transmission via air waves is less secure, so data needs to be encrypted