Networking Wireless

The Electromagnetic Spectrum

The foundations of wireless data transmission.

The Electromagnetic Spectrum

  • The electromagnetic spectrum encompasses all frequencies of electromagnetic radiation, from radio waves to gamma rays
  • In networking, we primarily work with radio frequency (RF) and infrared portions of the spectrum
  • Key principle: Higher frequencies carry more data but travel shorter distances and penetrate obstacles poorly

RF Spectrum Allocation for Networking

  • 2.4 GHz ISM Band: 2.400-2.485 GHz (unlicensed)

    • Used by 802.11b/g/n WiFi, Bluetooth, microwave ovens
    • Crowded spectrum leads to interference issues
    • Longer wavelength = better building penetration

  • 5 GHz ISM Band: 5.150-5.825 GHz (unlicensed)

    • Used by 802.11a/n/ac/ax WiFi
    • More channels available (reduces interference)
    • Higher frequency = more capacity but shorter range

  • 6 GHz Band: 5.925-7.125 GHz (newly available)

    • Used by WiFi 6E (802.11ax extended)
    • Clean spectrum with minimal interference
    • Requires compatible hardware

Frequency vs Wavelength Relationship

Property Low Frequency High Frequency
Wavelength Long Short
Penetration Better through walls Poor through obstacles
Range Longer distance Shorter distance
Data Capacity Lower Higher
Example 2.4 GHz WiFi 5/6 GHz WiFi

Practical Wireless Considerations

  • Path Loss: Signal strength decreases with distance (inverse square law)

    • Doubling distance reduces signal power by 75%
    • Higher frequencies experience greater path loss

  • Absorption: Different materials affect different frequencies

    • Water absorbs 2.4 GHz readily (why microwaves work)
    • Metal reflects RF signals (creates dead zones)

  • Reflection and Multipath: Signals bounce off surfaces

    • Can cause constructive or destructive interference
    • Modern WiFi uses MIMO to exploit multipath

Vocabulary

  • ISM Band: Industrial, Scientific, Medical - unlicensed spectrum portions
  • Path Loss: Signal attenuation over distance in free space
  • Multipath: Multiple signal paths between transmitter and receiver
  • MIMO: Multiple Input, Multiple Output - uses multiple antennas
  • dBm: Decibel-milliwatts, logarithmic power measurement scale

Notes

  • Remember: Unlicensed bands mean no coordination between users - interference is expected and must be managed
  • When designing wireless networks, always consider frequency selection based on environment (dense urban vs rural)
  • Higher frequencies aren’t always better - 2.4 GHz still preferred for IoT devices due to better penetration and lower power requirements
  • Spectrum analyzers help identify interference sources (use show dot11 associations on Cisco APs for client info)
  • Regulatory domains vary by country - ensure equipment is configured for local regulations (FCC in US, ETSI in Europe)