WLAN Architecture (COTN1220_05) PDF

WLAN (WIRELESS LAN) ARCHITECTURE Ad hoc WLAN Wireless nodes transmit directly to each other Use wireless NICs No intervening connectivity device Poor performance Many spread out users, obstacles block signals WLAN ARCHITECTURE (CONT.) An ad hoc WLA...

WLAN (WIRELESS LAN) ARCHITECTURE Ad hoc WLAN Wireless nodes transmit directly to each other Use wireless NICs No intervening connectivity device Poor performance Many spread out users, obstacles block signals WLAN ARCHITECTURE (CONT.) An ad hoc WLAN 4 WLAN ARCHITECTURE (CONT.) Infrastructure WLAN Stations communicate with access point Not directly with each other Access point requires sufficient power, strategic placement Access point (AP) Accepts wireless signals from multiple nodes Retransmits signals to network Base stations, wireless routers, wireless gateways WLAN ARCHITECTURE (CONT.) WLAN may include several access points Dependent upon number of stations Maximum number varies: 10-100 WLAN ARCHITECTURE (CONT.) An infrastructure WLAN 8 WLAN ARCHITECTURE (CONT.) 9 ASSOCIATION Packet exchanged between computer, access point Gain Internet access Scanning Surveying surroundings for access point Active scanning transmits special frame Probe – A station sends a probe request frame when it needs to obtain information from another station. ASSOCIATION Passive scanning listens for special signal Beacon fame – contains the service set identifier (SSID), timestamp, and other information about the access point. ASSOCIATION (CONT’D.) SSID (service set identifier) Unique character string identifying access point In beacon fame information Configured in access point Better security, easier network management BSS (basic service set) Station groups sharing access point BSSID (basic service set identifier) Station group identifier ASSOCIATION (CONT’D.) ESS (extended service set) Access point group connecting same LAN Share ESSID (extended service set identifier) Allows roaming Station moving from one BSS to another without losing connectivity Several access points detected Select strongest signal, lowest error rate Poses security risk Powerful, rogue access point ASSOCIATION (CONT’D.) A network with a single A network with multiple BSSs BSS forming an ESS ASSOCIATION (CONT’D.) HotSpot The HotSpot will normally only allow you to use the Internet. Not interact with other computers or gadgets using the same HotSpot. Ad-Hoc The Ad-Hoc is a wireless network without the need of a big server, or a router. Ad-Hoc rely on each computers Wi-Fi Card to set up and Connect to other computers through one of the other WIRELESS LANS Multipath signal propagation 802.11 WLANS Wireless technology standard Describes unique functions Physical and Data Link layers Differences Specified signaling methods, geographic ranges, frequency usages Developed by IEEE’s 802.11 committee Wi-Fi (wireless fidelity) standards 802.11b, 802.11a, 802.11g, 802.11n, 802.11ac, 802.11ax Share characteristics Half-duplexing*, access method, frame format 802.11 WLANS