Wireless LANs 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 802.11b 2.4-GHz band Separated into 22-MHz channels Throughput 11-Mbps theoretical 5-Mbps actual 100 meters node limit Oldest, least expensive Replaced by 802.11g 802.11a Released after 802.11b 5-GHz band Not congested like 2.4-GHz band Lower interference, requires more transmit power (wireless telephones, microwaves) Throughput 54 Mbps theoretical 11 and 18 Mbps effective Attributable to higher frequencies, unique modulating data method, more available bandwidth 20-meter node limit More expensive, least popular (Compared to 802.11b) 802.11g Affordable as 802.11b Throughput 54 Mbps theoretical 20 to 25 Mbps effective 100-meter node range 2.4-GHz frequency band Compatible with 802.11b networks 802.11n Primary goal Wireless standard providing much higher effective throughput Maximum throughput: 600 Mbps Multiple-Input and Multiple-Output (MIMO) technology – utilization of multiple wireless signals and antennas 400-meter node range* 802.11n (cont.) 2.4-GHz or 5-GHz frequency range Backward compatible Not all 802.11n features work 802.11ac 2.4 & 5-GHz bands Dual band wireless technology Capability to transmit on the 5 GHz band of 802.11a and also the 2.4 GHz band used by 802.11b, 802.11g, and 802.11n. Throughput 1300-Mbps (5-GHz) theoretical 450-Mbps (2.4-GHz) theoretical 802.11ax Between 1 GHz and 6 GHz 3.5 Gbps per data stream (MIMO capable) Capacity for 4x more devices Reduce power consumption Target Wake Time (TWT) allows devices to negotiate when and how often they will wake up to send or receive data BSS Color, marks frames from neighboring networks so that your router can ignore them. Wireless Summary Standard Frequency Theoretical Range Maximum Throughput 802.11b 2.4 GHz 11-Mbps 46m 802.11a 5 GHz 54-Mbps 20m 802.11g 2.4 GHz 54-Mbps 46m 802.11n 2.4 GHz or 5 GHz 65-Mbps 600-Mbps (MIMO) 46m 802.11ac 5 GHz 1.3-Gbps 70m 802.11ax 2.4 GHz or 5 GHz 3.5 Gbps TBD 14 Gbps (MIMO) Avoiding Pitfalls Access point versus client configurations SSID mismatch Incorrect encryption Incorrect channel, frequency Standard mismatch (802.11 a/b/g/n/ac) Incorrect antenna placement Verify client within 330 feet* Interference Check for EMI sources Avoiding Pitfalls