Table of Contents

• Information Transmission
• Problem: Making it faster
• Methods
• Modulation
• Faster/more efficient Transmission
• Bands
• Noise
• Shannon "Capacity Limit"
• Encoding
• Mapping bit patterns
• Media: Copper
• Why does it matter?
• Antenna Problem
• UTP cables

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Slides: Topic #1, #2

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Information Transmission

• A real link faces problems

Problem: Making it faster

• Narrow vs long pulses

• Can't be too small (dim)

• Analog/digital -> Digital is powerful, easy to replicate, regenerate and manipulate

Methods

• Faster via narrower pulses -> No
• Faster via different height pulses, info per pulse and colours/sounds -> Yes

Modulation

• Modulation -> TUrning information bits into analogue signals
• Demodulation -> Turning analogue signals into information bits

Faster/more efficient Transmission

• More data per "cycle"

  • Multi-level AM -> Amplitude Shift Keying (ASK)
  • Multi-level PM = Phase Shift Keying (PSK)
  • Multi-level FM = Frequency Shift Keying (FSK)

• Symbol (baud) rate != bitrate

• 1 symbol/second >> 1 bit/second

• Both sides must use the same approach

Bands

• Band -> A special range of frequences
• Base band -> A single carrier
• Pass bond -> Frequency relatve to work
• Broad-bank - Multiple frequency carriers across a ranch

Noise

• Having too much means signals become distorted and unreadable
• Fixes
  • Decrease symbol rate (Average longer)
  • Decrease # of levels
  • Put more energy into signal (uses more energy)

Shannon "Capacity Limit"

• Reliable Capacity = Baudrate * $log_2$(1 + Signal/Noise)

• SNR in deciBels = $10 * log_10$(Signal/Noise)

Encoding

Mapping bit patterns

• e.g. 4b/5b -> For every 4 bits, there are 5 bits, adding in resilience and a clear + distinct transition every 5 bits

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Media: Copper

Why does it matter?

• Many failure modes
• Weird behaviours in the physical media
• Costs
• Maintenance, power
• Benefits, risks

Antenna Problem

• Can avoid shielding by sending the signal + the inverse then subtracting them. Can twist them together to ensure any noise affects both cables equally.

UTP cables

• Unshielded Twisted Pairs