A Few Fluffy But Necessary Issues

• What is information? $\rightarrow$ A measure of how surprised you are
• What is a channel? $\rightarrow$ Something which corrupts your information and makes the recipient have to guess exactly what the surprise is
• What is a medium Electro/optic:
• Wires $\rightarrow$ 100kHz
• Coax $\rightarrow$ 1GHz
• Waveguide $\rightarrow$ 100GHz
• Fiber optics $\rightarrow$ 1000THz
in increasing order of ``capacity''






Neat idea: Load a truck with tapes and drive it from point A to point B. Divide the number of bits by the time taken to deliver the tapes. This is a high speed communication channel too! (though essentially useless)

• What is corruption? (did you ever think you'd have to LEARN what corruption is?)

Noise! Also multipath issues raise their ugly heads! (ghosts on your TV, echos on your phone line). FADING! Storage Channel: tape irregularities (bouncing tape heads make hiss), spontaneous damage (gamma rays, heat, etc.)

PUNCHLINE:

• Any communication medium suffers from ``impairments'' such as multipath, attenuation, noise, etc.
• What you use depends on the situation
• We need a methodology which can handle everything - otherwise we chase perpetual motion 

1999-01-20