Transmission of data.
  Analog on analog:
    Radio - music and voice transmitted via radio waves.

  Analog on digital:
    Movies on dvd, on-line radio - analog data sampled.

  Digital on analog:
    28K modems on computers, internet via satellite.

  Digital on digital:
    Local area networks, fiber optics, high speed internet.

Problems with sending information over a distance.
  As a signal is sent over a distance, signal is distorted.

    Resistance - signal fades over distance.

    Impedance - form of resistance related to changing electrical fields.

    Inductance - tendency of changing signal to induce itself into 
      adjacent lines.

    Attenuation - tendency of signal to fade by becoming flatter and 
      spread out.  

    Introduction of garbage - static.

Solutions
  Analog carrier.
    Amplify signal. 

    However any distortion or static also amplified.

  Digital carrier. 
    Repeater - something like an amplifier.

    Signal sampled and if caught before completely distorted,
      New exact copy of digital value regenerated.

Unguided vs Guided
  Unguided - tends to use electromagnetic spectrum 
    infra-red, microwave, satellite (borders on guided).

  Guided - two or more devices physically connected.
    Twisted pair - phone, local area networks.  1 Mbit/sec 

      For short distances (50 feet) - 10 MBit/sec or even 100 MBit
   
      Newer cabling (cat 5 or 6) has increased this.

      Tend to be sensitive to RFI, EMI interference and attenuation.

    Coaxial - shielded cable - up to 45 Mbits/sec.

      Tend to be sensitive to attenuation.

      Large (1/4") and stiff.
  
    Optical -  very high speeds > 100 Mbit ranges.

      Much lower attenuation, immune to RFI and EMI.

      Small and lightweight.

      However, fragile and requires highly skilled technicians.

      More expensive (but at Gb speeds, costs break even)

Connection styles
  Point to point vs broadcast.

  Point to point:
    Two and only two devices are connected via a single connection.
 
    Some handshaking required.
  
    No addressing needed, although software port ids may be used.

    Sequencing handled by devices, usually automatic, and straight forward.

    Between your pc and your internet provider.

    Between nodes on the internet.
 
    Simpler and cheaper for very long distances.

  Broadcast - multiple devices connected via a single connection bus.

    Handshaking, addressing, and mediation.

    Sequencing may have to be encoded in data.
      Greater chance of lost packets.

    Local area networks, old fashion party line telephone systems.