Networking Wireless

802.11

The wifi spectrum.

Overview

  • 802.11 is the IEEE standard family for wireless local area networks (WLANs)
  • Operates in unlicensed spectrum bands (2.4 GHz and 5 GHz primarily)
  • Uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) instead of CSMA/CD
  • Cannot detect collisions like Ethernet - wireless is half-duplex by nature
  • Access Points (APs) bridge wireless clients to wired infrastructure

802.11 Standards Evolution

Standard Year Frequency Max Speed Range Key Features
802.11 1997 2.4 GHz 2 Mbps ~20m indoor Original standard
802.11b 1999 2.4 GHz 11 Mbps ~35m indoor First widespread adoption
802.11a 1999 5 GHz 54 Mbps ~25m indoor Less congestion, shorter range
802.11g 2003 2.4 GHz 54 Mbps ~35m indoor Backward compatible with 11b
802.11n 2009 2.4/5 GHz 600 Mbps ~50m indoor MIMO, channel bonding
802.11ac 2013 5 GHz only 6.93 Gbps ~35m indoor MU-MIMO, wider channels
802.11ax (Wi-Fi 6) 2019 2.4/5 GHz 9.6 Gbps ~30m indoor OFDMA, improved efficiency

Frequency Bands and Channels

2.4 GHz Band

  • Only 3 non-overlapping channels in North America: 1, 6, 11
  • Channel width: 20 MHz (22 MHz with guard bands)
  • More congested due to ISM devices (microwaves, Bluetooth, baby monitors)
  • Better wall penetration and longer range than 5 GHz

5 GHz Band

  • 25+ non-overlapping 20 MHz channels (varies by country)
  • Less congested, more available spectrum
  • Higher frequencies = more attenuation through obstacles
  • Supports wider channels (40, 80, 160 MHz) for higher throughput

Wireless Security Evolution

Security Type Encryption Key Management Status
Open None None Avoid - no security
WEP RC4 (64/128-bit) Static keys Deprecated - easily cracked
WPA TKIP PSK or 802.1X Legacy - better than WEP
WPA2 AES-CCMP PSK or 802.1X Current standard
WPA3 AES-GCMP SAE or 802.1X Latest - mandatory PMF

Authentication Methods

  • Personal (PSK): Pre-shared key - used for small networks
  • Enterprise (802.1X): RADIUS authentication - used for corporate deployments
  • WPA3 includes Simultaneous Authentication of Equals (SAE) to prevent offline dictionary attacks

CSMA/CA Operation

  • Listen before transmit - check if medium is clear
  • If busy, wait random backoff time (exponential backoff)
  • Send RTS (Request to Send) for large frames
  • Receive CTS (Clear to Send) from AP
  • Transmit data and wait for ACK
  • No ACK received = assume collision, retransmit

Power Management

  • Clients can enter Power Save Mode to conserve battery
  • AP buffers frames for sleeping clients
  • Beacon frames sent every 100ms by default contain buffered data notifications
  • Clients wake up periodically to check for buffered traffic

Vocabulary

  • SSID: Service Set Identifier - network name broadcast by AP
  • BSSID: Basic Service Set Identifier - MAC address of the AP radio
  • ESSID: Extended Service Set ID - multiple APs with same SSID for roaming
  • MIMO: Multiple Input Multiple Output - multiple antennas for increased throughput
  • MU-MIMO: Multi-User MIMO - serves multiple clients simultaneously
  • OFDMA: Orthogonal Frequency Division Multiple Access - divides channels into smaller resource units
  • PMF: Protected Management Frames - encrypts management traffic (mandatory in WPA3)

Notes

  • Channel planning is critical - overlapping channels cause interference, not collision domains
  • 2.4 GHz travels further but 5 GHz provides more bandwidth and less congestion
  • Wireless is a shared medium - all clients in coverage area share total bandwidth
  • Half-duplex operation means effective throughput is roughly 50% of advertised speeds
  • Enterprise deployments should use 802.1X with RADIUS for scalable authentication
  • Site surveys are essential for proper AP placement - don’t just guess coverage patterns
  • Modern networks should disable legacy rates (1, 2, 5.5, 11 Mbps) to improve efficiency
  • WPA2 minimum for any production network - WEP can be cracked in minutes
  • Consider band steering and load balancing features to optimize client distribution