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📘 06-04: Wireless Design & Roaming

Network Systems

Module 06: Wireless Networking

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📌 Service Sets

Term Meaning
BSS (Basic Service Set) One AP + its associated clients
BSSID The AP's MAC address (identifies the BSS)
SSID The network name clients connect to
ESS (Extended Service Set) Multiple APs sharing one SSID over a common backbone

An ESS lets clients roam seamlessly between APs without dropping the connection.

📌 Site Survey

A site survey measures RF conditions to plan coverage:

  • Passive — listen to existing signals
  • Active — associate and measure throughput
  • Predictive — model coverage from a floor plan

Output: a heat map of signal strength, revealing coverage gaps and interference.

📌 Design Principles

  • Use channels 1/6/11 (2.4 GHz) to avoid overlap; spread channels in 5 GHz.
  • In high-density areas, lower AP power and add more APs to shrink cells, reduce co-channel interference, and increase capacity.
  • Band steering pushes dual-band clients to 5 GHz.

📶 Wireless LAN Controller (WLC)

A WLC centrally manages many "thin" APs: - Pushes configuration - Coordinates channels/power (RRM) - Enables fast roaming and unified monitoring

📌 Guest Access

A captive portal intercepts new clients and redirects to a login/terms page before granting Internet access — common for guest Wi-Fi (often on a separate VLAN).

Tip

Key idea — BSS = one AP; ESS = many APs, one SSID (enables roaming). Plan with a site survey/heat map, avoid channel overlap, and use a WLC to manage APs at scale.

See also: Frequencies, Channels & Antennas, Virtual LAN (VLAN)