Wireless Roaming

Roaming means that wireless clients can remain connected to the same network ESSID while moving around within an extended service area (ESA).

clients can roam within an extended service area (ESA)
- ESA is created by installing APs with the same ESSID and security configuration connected by a wired network (distribution system)
- APs are configured with different channels so where BSAs overlap, there is no interference
- when client detects bad signal,
  - it checks for another signal with the same ESSID on other channels or frequency bands
  - it signal is stronger, then it switches to new AP
    - may need to reauthenticate
    - 802.11r fast roaming enables use of existing authentication
when roaming, reestablishing a connection can cause time-out problems for apps
- needs to be a balance between staying and switching signals
- some APs can configure roaming aggressiveness
  - to stop client from switching too easily
  - or to stop client from staying connected for too long

SSID Broadcast and Beacon Frame

SSID broadcast enables a WLAN to advertise its presence
- WLAN is discoverable in a list reported by client
- if disabled
  - user must configure network connection manually
a beacon is a special management frame broadcast by the AP to advertise the WLAN
- contains
  - SSID/ESSID
    - unless broadcast is disabled
  - BSSID
  - supported data rates and signaling
  - encryption/authentication requirements
- broadcast interval can be modified
  - measured in ms
  - default is 100 ms
  - increasing interval
    - reduces overhead of broadcasting the frame
    - but delays joining the network
    - can hamper roaming between APs

Info

even with SSID broadcast suppressed,

can still easily detect a network with a sniffer

clients use it when connecting to the AP

Info

WDS support and implementation varies between vendors

so best to use APs from same vendor