Wireless LAN

For the radio stations in Lancaster, Pennsylvania, seeWLAN (AM) and WLAN-FM.A wireless local area network (WLAN) is a wireless

This notebook computer is connected to a wireless access pointusing a PC card wireless card.

Computer connectedvia ethernet

Computer with longrange Wi-Fi dish

Wi-Fi router

Computer withinrange

Wi-Fi bridge

Computer within range

InternetServiceProvider

Ethernet

Ethernet

Ethernet

An example of a Wi-Fi network.

computer network that links two or more devices usinga wireless distribution method (often spread-spectrumor OFDM radio) within a limited area such as a home,school, computer laboratory, or oce building. Thisgives users the ability to move around within a local cov-erage area and still be connected to the network, and canprovide a connection to the wider Internet. Most modernWLANs are based on IEEE 802.11 standards, marketedunder the Wi-Fi brand name.Wireless LANs have become popular in the home due toease of installation and use, and in commercial complexesoering wireless access to their customers; often for free.

NewYork City, for instance, has begun a pilot program toprovide city workers in all ve boroughs of the city withwireless Internet access.[1]

An embedded RouterBoard 112 with U.FL-RSMA pigtail andR52 mini PCI Wi-Fi card widely used by wireless Internet ser-vice providers (WISPs)

1 HistoryNorman Abramson, a professor at the University ofHawaii, developed the worlds rst wireless computercommunication network, ALOHAnet (operational in1971), using low-cost ham-like radios. The system in-cluded seven computers deployed over four islands tocommunicate with the central computer on the Oahu Is-land without using phone lines.[2]

54 Mbit/s WLAN PCI Card (802.11g)

WLAN hardware initially cost so much that it was onlyused as an alternative to cabled LAN in places where ca-bling was dicult or impossible. Early development in-cluded industry-specic solutions and proprietary proto-cols, but at the end of the 1990s these were replaced by

1

2 3 TYPES OF WIRELESS LANS

standards, primarily the various versions of IEEE 802.11(in products using theWi-Fi brand name). An alternativeATM-like 5 GHz standardized technology, HiperLAN/2,has so far not succeeded in the market, and with therelease of the faster 54 Mbit/s 802.11a (5 GHz) and802.11g (2.4 GHz) standards, it is evenmore unlikely thatit will ever succeed.In 2009 802.11n was added to 802.11. It operates in boththe 2.4 GHz and 5 GHz bands at a maximum data trans-fer rate of 600 Mbit/s. Most newer routers are able toutilise both wireless bands, known as dualband. This al-lows data communications to avoid the crowded 2.4 GHzband, which is also shared with Bluetooth devices andmicrowave ovens. The 5 GHz band is also wider thanthe 2.4 GHz band, with more channels, which permitsa greater number of devices to share the space. Not allchannels are available in all regions.A HomeRF group formed in 1997 to promote a technol-ogy aimed for residential use, but it disbanded at the endof 2002.[3]

2 Architecture

2.1 Stations

All components that can connect into a wireless mediumin a network are referred to as stations. All stationsare equipped with wireless network interface controllers(WNICs). Wireless stations fall into one of two cate-gories: wireless access points, and clients. Access points(APs), normally wireless routers, are base stations forthe wireless network. They transmit and receive radiofrequencies for wireless enabled devices to communi-cate with. Wireless clients can be mobile devices suchas laptops, personal digital assistants, IP phones andother smartphones, or xed devices such as desktops andworkstations that are equipped with a wireless networkinterface.

2.2 Basic service set

The basic service set (BSS) is a set of all stations that cancommunicate with each other. Every BSS has an identi-cation (ID) called the BSSID, which is the MAC addressof the access point servicing the BSS.There are two types of BSS: Independent BSS (also re-ferred to as IBSS), and infrastructure BSS. An indepen-dent BSS (IBSS) is an ad hoc network that contains noaccess points, which means they can not connect to anyother basic service set.

2.3 Extended service set

An extended service set (ESS) is a set of connected BSSs.Access points in an ESS are connected by a distributionsystem. Each ESS has an ID called the SSID which is a32-byte (maximum) character string.

2.4 Distribution system

A distribution system (DS) connects access points in anextended service set. The concept of a DS can be usedto increase network coverage through roaming betweencells.DS can bewired or wireless. Current wireless distributionsystems are mostly based on WDS or MESH protocols,though other systems are in use.

3 Types of wireless LANsThe IEEE 802.11 has two basic modes of operation: adhoc mode and infrastructure mode. In ad hoc mode,mobile units transmit directly peer-to-peer. In infrastruc-ture mode, mobile units communicate through an accesspoint that serves as a bridge to other networks (such asInternet or LAN).Since wireless communication uses a more open mediumfor communication in comparison to wired LANs, the802.11 designers also included encryption mechanisms:Wired Equivalent Privacy (WEP, now insecure), Wi-Fi Protected Access (WPA, WPA2), to secure wirelesscomputer networks. Many access points will also of-fer Wi-Fi Protected Setup, a quick (but now insecure)method of joining a new device to an encrypted network.

3.1 Peer-to-peer

Peer-to-Peer or ad hoc wireless LAN

An ad hoc network (not the same as a WiFi Direct net-work[4]) is a network where stations communicate onlypeer to peer (P2P). There is no base and no one givespermission to talk. This is accomplished using the Inde-pendent Basic Service Set (IBSS).

3.2 Bridge 3

AWiFi Direct network is another type of network wherestations communicate peer to peer.In a Wi-Fi P2P group, the group owner operates as anaccess point and all other devices are clients. There aretwo main methods to establish a group owner in the Wi-Fi Direct group. In one approach, the user sets up aP2P group owner manually. This method is also knownas Autonomous Group Owner (autonomous GO). In thesecond method, also called negotiation-based group cre-ation, two devices compete based on the group owner in-tent value. The device with higher intent value becomesa group owner and the second device becomes a client.Group owner intent value can depend on whether thewireless device performs a cross-connection between aninfrastructure WLAN service and a P2P group, remain-ing power in the wireless device, whether the wireless de-vice is already a group owner in another group and/or areceived signal strength of the rst wireless device.A peer-to-peer network allows wireless devices to di-rectly communicate with each other. Wireless deviceswithin range of each other can discover and communi-cate directly without involving central access points. Thismethod is typically used by two computers so that theycan connect to each other to form a network. This canbasically occur in devices within a closed range.If a signal strength meter is used in this situation, it maynot read the strength accurately and can be misleading,because it registers the strength of the strongest signal,which may be the closest computer.

A B C

Hidden node problem: Devices A and C are both communicatingwith B, but are unaware of each other

IEEE 802.11 denes the physical layer (PHY) and MAC(Media Access Control) layers based on CSMA/CA(Carrier Sense Multiple Access with Collision Avoid-ance). The 802.11 specication includes provisions de-signed to minimize collisions, because two mobile unitsmay both be in range of a common access point, but outof range of each other.

3.2 Bridge

A bridge can be used to connect networks, typically ofdierent types. A wireless Ethernet bridge allows theconnection of devices on a wired Ethernet network to awireless network. The bridge acts as the connection pointto the Wireless LAN.

3.3 Wireless distribution system

Main article: Wireless Distribution System

A Wireless Distribution System enables the wireless in-terconnection of access points in an IEEE 802.11 net-work. It allows a wireless network to be expanded usingmultiple access points without the need for a wired back-bone to link them, as is traditionally required. The no-table advantage ofWDS over other solutions is that it pre-serves the MAC addresses of client packets across linksbetween access points.[5]

An access point can be either a main, relay or remotebase station. A main base station is typically connectedto the wired Ethernet. A relay base station relays data be-tween remote base stations, wireless clients or other re-lay stations to either a main or another relay base station.A remote base station accepts connections from wirelessclients and passes them to relay or main stations. Connec-tions between clients are made using MAC addressesrather than by specifying IP assignments.All base stations in a Wireless Distribution System mustbe congured to use the same radio channel, and shareWEP keys or WPA keys if they are used. They can becongured to dierent service set identiers. WDS alsorequires that every base station be congured to forwardto others in the system as mentioned above.WDS may also be referred to as repeater mode because itappears to bridge and accept wireless clients at the sametime (unlike traditional bridging). It should be noted,however, that throughput in this method is halved for allclients connected wirelessly.When it is dicult to connect all of the access points ina network by wires, it is also possible to put up accesspoints as repeaters.

4 RoamingThere are two denitions for wireless LAN roaming:

Internal Roaming (1): The Mobile Station (MS)moves from one access point (AP) to another APwithin a home network because the signal strength istoo weak. An authentication server (RADIUS) per-forms the re-authentication of MS via 802.1x (e.g.

4 6 PERFORMANCE AND THROUGHPUT

AccessPoint

AccessPoint

AccessPoint

MobileStation

MobileStation

AuthenticationServer

AuthenticationServer

File-Server File-Server

(2)

(1)

(1)

Foreign-NetworkHome-Network

Roaming among Wireless Local Area Networks

with PEAP). The billing of QoS is in the home net-work. A Mobile Station roaming from one accesspoint to another often interrupts the ow of dataamong the Mobile Station and an application con-nected to the network. The Mobile Station, for in-stance, periodically monitors the presence of alter-native access points (ones that will provide a bet-ter connection). At some point, based on propri-etary mechanisms, the Mobile Station decides tore-associate with an access point having a strongerwireless signal. The Mobile Station, however, maylose a connection with an access point before asso-ciating with another access point. In order to pro-vide reliable connections with applications, the Mo-bile Stationmust generally include software that pro-vides session persistence.[6]

External Roaming (2): The MS (client) movesinto a WLAN of another Wireless Internet ServiceProvider (WISP) and takes their services (Hotspot).The user can independently of his home network useanother foreign network, if this is open for visitors.There must be special authentication and billing sys-tems for mobile services in a foreign network.

5 ApplicationsWireless LANs have a great deal of applications. Modernimplementations of WLANs range from small in-homenetworks to large, campus-sized ones to completely mo-bile networks on airplanes and trains. Users can accessthe Internet from WLAN hotspots in restaurants, hotels,and now with portable devices that connect to 3G or 4Gnetworks. Oftentimes these types of public access pointsrequire no registration or password to join the network.Others can be accessed once registration has occurredand/or a fee is paid.

6 Performance and ThroughputWLAN, organised in various layer 2 variants (IEEE802.11) has dierent characteristics. Across all avoursof 802.11 maximum achievable throughputs are either

given based on measurements under ideal conditions orin the layer 2 data rates. This however does not applyto typical deployments in which data is being transferredbetween two endpoints of which at least one is typicallyconnected to a wired infrastructure and the other end-point is connected to an infrastructure via a wireless link.

Graphical representation of Wi-Fi application specic (UDP)performance envelope 2.4 GHz band, with 802.11g

Graphical representation of Wi-Fi application specic (UDP)performance envelope 2.4 GHz band, with 802.11n with 40MHz

This means that typically data frames pass an 802.11(WLAN) medium and are being converted to 802.3 (Eth-ernet) or vice versa. Due to the dierence in the frame(header) lengths of these two media the e.g. applica-tions packet size determines the speed of the data trans-fer. This means that e.g. applications which use smallpackets (e.g. VoIP) create dataows with a high overheadtrac (e.g. a low goodput). Other factors which con-tribute to the overall application data rate are the speedwith which the application transmits the packets (i.e. thedata rate) and of course the energy with which the wire-less signal is received. The latter is determined by dis-tance and by the congured output power of the commu-nicating devices.[7][8]

Same references apply to the attached throughput graphswhich show measurements of UDP throughput measure-ments. Each represents an average (UDP) throughput(please note that the error bars are there, but barely visibledue to the small variation) of 25 measurements. Each iswith a specic packet size (small or large) and with a spe-cic data rate (10 kbit/s 100 Mbit/s). Markers for traf-

5c proles of common applications are included as well.Please note, this text and measurements do not coverpacket errors but information about this can be foundat above references. The table below shows the maxi-mum achievable (application specic) UDP throughput inthe same scenarios (same references again) with variousdierence WLAN (802.11) avours. The measurementhosts have been 25 meters apart from each other, pleasenote that loss is again ignored.

7 References[1] NY Muni Wireless Network Launch in Sight. Internet

News. Retrieved 2010-11-03.

[2] History of Wireless. Johns Hopkins Bloomberg Schoolof Public Health. Archived from the original on 2007-02-10. Retrieved 2007-02-17.

[3] Wayne Caswell (November 17, 2010). HomeRFArchives. Retrieved July 16, 2011.

[4] http://www.wi-fi.org/knowledge-center/faq/same-ad-hoc-mode

[5] Wireless Distribution System Linked Router NetworkDD-WRT Wiki. Retrieved December 31, 2006.

[6] How Wi-Fi Roaming Really Works. Retrieved 2008-10-09.

[7] Towards Energy-Awareness in Managing Wireless LANApplications. IEEE/IFIP NOMS 2012: IEEE/IFIP Net-work Operations and Management Symposium. Re-trieved 2014-08-11.

[8] Application Level Energy and Performance Measure-ments in a Wireless LAN. The 2011 IEEE/ACM Inter-national Conference on Green Computing and Communi-cations. Retrieved 2014-08-11.

6 8 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

8 Text and image sources, contributors, and licenses8.1 Text

Wireless LAN Source: http://en.wikipedia.org/wiki/Wireless%20LAN?oldid=636001599 Contributors: Bryan Derksen, HelgeStenstrom,Rjstott, Ed Poor, LA2, Aldie, Kurt Jansson, Heron, Patrick, D, Norm, Nixdorf, Ixfd64, Alo, Haakon, Ronz, Nanshu, Poor Yorick, Rl,Mulad, Crissov, Pladask, Tero, Tempshill, Joy, JorgeGG, Jeq, Bearcat, Robbot, Fredrik, Ashley Y, Lupo, JoelWhitehouse, Lzur, TobiasBergemann, Dave6, Manifest, Giftlite, Curps, Kravietz, Ferdinand Pienaar, AlistairMcMillan, VampWillow, Bobblewik, Edcolins, Neilc,Comatose51, Utcursch, Mendel, Fast, OverlordQ, Cy0x, Monkeyman, Jda, RossPatterson, Discospinster, Rich Farmbrough, Rhobite, Dr-Mac, FiP, Clawed, Rupertslander, Fittysix, Ratatosk, MarkS, S.K., Robotje, R. S. Shaw, Cwolfsheep, Kjkolb, MelSkunk, Towel401, Pearle,Cenora, Nsaa, QuantumEleven, Sysiphe, Klafubra, Guy Harris, Eric Kvaalen, Arthena, Jeltz, Andrewpmk, M7, Wtshymanski, StephanLeeds, Antti Kurittu, RainbowOfLight, Woodstone, Larytet, Mahanga, Brookie, Woohookitty, Mindmatrix, Asteiner, Riumplus, Fred J,Colin Watson, SCEhardt, Wisq, Weevil, ObsidianOrder, G.hartig, XP1, Seraphimblade, Bruce1ee, Thangalin, SNIyer12, Cjpun, Mike-cron, Alejo2083, FlaBot, Moreati, Ausinha, Nivix, Fragglet, RexNL, Ewlyahoocom, Kolbasz, Mrschimpf, Coolhawks88, CStyle, Chobot,Sathakselva, Gwernol, Roboto de Ajvol, Logixoul, Sarranduin, Hede2000, Bhny, Hydrargyrum, Stephenb, Manop, Archelon, Gaius Cor-nelius, Ksyrie, Big Brother 1984, Msikma, Msoos, PhilipO, 21655, Zzuuzz, ADFX-03, Adamdavid85, KGasso, Petri Krohn, Tobixen,Nelson50, JLaTondre, Allens, Porttikivi, Elbperle, Twilight Realm, Qoqnous, SmackBot, Tarun2701, Mmernex, Bobet, Reedy, McGed-don, KelleyCook, Canthusus, Zephyris, Mcld, Gilliam, Ohnoitsjamie, ERcheck, Matt0401, Briandjohnson, Thumperward, Snori, Oli Filth,SchftyThree, Nbarth, Colonies Chris, Konstable, Firetrap9254, Jnavas, Appaloosa2k, Ramas Arrow, Stefon, Dethme0w, E946, Cv-parikh, JonHarder, Szarka, Radagast83, FlyHigh, Ricky@36, Terrak, Jidanni, GCW50, Teancum, Bjankuloski06en, Wskish, IronGargoyle,Jadams76, Arathalion, ShakingSpirit, Andnewman, Igoldste, Beno1000, FakeTango, Astral9, Esposimi, Mzub, JasonWoof, Xcentaur,JForget, CmdrObot, CaspianM, Requestion, Erencexor, Themightyquill, Slackerhobo, Christian75, Johnbouma, Chiefcoolbreeze, Kozuch,Zalgo, Thijs!bot, Epbr123, Fabian.a, Abevacqua, Hai Dang Quang, John254, Electron9, Cooljuno411, Dawnseeker2000, Natalie Erin,Mmortal03, Dzubint, AntiVandalBot, Widefox, CodeWeasel, Seaphoto, Marokwitz, Alphachimpbot, Ctrow, Caroline margaret, JAnD-bot, Drizzd, Kirrages, Suede, Acroterion, Edoxin, Jhansonxi, Bongwarrior, VoABot II, Jareth86, JamesBWatson, Mhwhiteman, Dbackes,JPG-GR, Nposs, LookingGlass, Ciaccona, DerHexer, JaGa, Techmonk, MartinBot, Jim.henderson, Zack Holly Venturi, Leyo, Haner,Sddoc, Felipe1982, Mange01, Whaatt, Laurusnobilis, Edwardw818, Nana.collins59, Burzmali, LordCo Centre, DorganBot, Wikieditor06,VolkovBot, Dbeilfuss, TobyDZ, ElinorD, Kmax769, Saligron, AllGloryToTheHypnotoad, BotKung, Zoef1234, Tinytom21, Rcassidy, Al-termike, Falcon8765, Enviroboy, Lauriwriter, Le Fou, PRH969, Ljay2two, Copenhagis, Kbrose, Svex, Bing11, Foakgul, Markun, Flyer22,Djjosh81, Editore99, Lightmouse, Blake324, Sunrise, ClueBot, PipepBot, Chomperhead, The Thing That Should Not Be, Ottawahitech,G2h2, Excirial, Alexbot, Lunchscale, Jotterbot, Jaizovic, Frau K, Mlas, Alla tedesca, SoxBot III, Vanished user uih38riiw4hjlsd, Fastily,Pgallert, Afrikaner, NellieBly, Willox303, Asksatan42, Addbot, Mannact, Captain-tucker, Umerqureshi, AkhtaBot, Cst17, Joycloete,AndersBot, CUSENZA Mario, Favonian, Arubanetworks, Whotspot02, Tide rolls, Teles, Robo56, Zbaloca, Luckas-bot, Legobot II,Wavyriver, Melvalevis, AnomieBOT, Arjun G. Menon, Garga2, Jim1138, ClerkShow8, Aneah, R.srinivaas, Xqbot, Mmmeg, IL vitto,GliderMaven, FrescoBot, W Nowicki, RicHard-59, Okaven, EagleEye96, BurGay, I dream of horses, 10metreh, Phearson, Jandalhandler,Lissajous, Markus tauber, Vrenator, Suusion of Yellow, Sean Reynolds, EmausBot, WikitanvirBot, Playmobilonhishorse, KingPingo,Tommy2010, Seikku Kaita, ZroBot, H3llBot, Messi rules, Lastfasch, DASHBotAV, AbbasSarfraz, Assassin15, ClueBot NG, Spike-TorontoRCP, Wilde Jagd, Ajay.bhagti, Dfarrell07, Qzxpqbp, HMSSolent, Calabe1992, Northamerica1000, Mifter Public, Erin100280,Ranjit89, ChrisGualtieri, Casper Lundgreen, MadGuy7023, Charming43, Mogism, Frosty, Dave Braunschweig, Ludatbooick, Nshunter,Lesser Cartographies, Soa Lucifairy, Rachitgupta1792, Thebookman2 and Anonymous: 544

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HistoryArchitectureStationsBasic service setExtended service setDistribution system

Types of wireless LANsPeer-to-peerBridgeWireless distribution system

RoamingApplications Performance and Throughput References Text and image sources, contributors, and licensesTextImagesContent license