Guided vs Unguided 
  Guided - two or more devices physically connected.
    - requires physical access to link.
    - linking costly, hubs, wiring, etc.
    + more secure
    + power efficient
    + smart switching makes more efficient use of bandwidth

    Copper wire - fairly cheap, low distance.
      Requires a physical connection to each device.

    Optical - expensive, technically complex.
       Economical for high throughput over very long distances.
       Signals need to be converted back to electronic for switch or tap.

  Unguided - tends to use electromagnetic spectrum 
    infra-red, radio (WiFi, Bluetooth, WiMax), microwave, 
    satellite.

    + easily accessed.
    + easy to relocate endpoints, access while moving.
    - power hungry.
    - harder to secure.
    + cost effective to link many devices.
    - harder to efficiently use bandwidth (competition).

  Some implementations can be viewed as a cross between the two.

    Some microwave communication use guided transmission.
      Either focused beams.
      Or broadcast into metal pipes that can route the signal.

    Satellite - 
      down-link is broadcast.
      up-link is focused and pointed to satellite.