1IEEE 802.11 WLAN Guided By: Presented By: 082112111 Maulana Azad National Institute of Technology,Bhopal Department of Computer Science & EngineeringIEEE WLANGuided By:Mrs. NAMITA TIWARIPresented By:Manisha Bhadoria
3What is unique about wireless? Difficult mediainterference and noisequality varies over space and timeshared with Unwanted devicesshared with non-802 devices (unlicensed spectrum: microwave ovens, bluetooth, etc.,)Full connectivity cannot be assumedHidden node problemMultiple international regulatory requirements2
4Uniqueness of Wireless (continued) Mobilityvariation in link reliabilitybattery usage: requires power managementwant seamless connectionsSecurityno physical boundariesoverlapping LANs4
5Wireless LANs: Characteristics TypesInfrastructure basedAd-hocAdvantagesFlexible deploymentMinimal wiring difficultiesMore robust against disasters (earthquake etc)Historic buildings, conferences, trade shows,…DisadvantagesLow bandwidth compared to wired networks (1-10 Mbit/s)Proprietary solutionsNeed to follow wireless spectrum regulations
7Protocol Architecture Functions of media access control (MAC) layer:On transmission, assemble data into a frame with address and error detection fieldsOn reception, disassemble frame and perform address recognition and error detectionGovern access to the LAN transmission mediumFunctions of logical link control (LLC) Layer:Provide an interface to higher layers and perform flow and error control
8Components/Architecture Station (STA) - Mobile nodeAccess Point (AP) - Stations are connected to access points.Basic Service Set (BSS) - Stations and the AP with in the same radio coverage form a BSS.Extended Service Set (ESS) - Several BSSs connected through APs form an ESS.
10IEEE 802.11 Architecture (model) Distribution system (DS) – the network backboneAccess point (AP) – a bridge or relayBasic service set (BSS)Stations competing for access to shared wireless mediumIsolated or connected to backbone DS through APThe entity in which the stations are within range of each other although BSSs can easily overlapExtended service set (ESS)Two or more basic service sets interconnected by DS usually a wired LAN
12Wireless LAN: Motivation Can we apply media access methods from fixed networks?Example CSMA/CDCarrier Sense Multiple Access with Collision Detectionsend as soon as the medium is free, listen into the medium if a collision occurs (original method in IEEE 802.3)
13Medium access problems in wireless networks signal strength decreases proportional to the square of the distancesender would apply CS and CD, but the collisions happen at the receiversender may not “hear” the collision, i.e., CD does not workCS might not work, e.g. if a terminal is “hidden”
14Difference Between Wired and Wireless Ethernet LANWireless LANBABCACIf both A and C sense the channel to be idle at the same time, they send at the same time.Collision can be detected at sender in Ethernet.Half-duplex radios in wireless cannot detect collision at sender.
15Fragmentation Wireless LANs have high bit error rates. The probability of erroneous frame is much higher for wireless linksuses fragmentation to reduce the frame error rate.
16MAC managementSynchronization finding and staying with a WLAN - synchronization functionsPower Management sleeping without missing any messages - power management functionsRoaming functions for joining a network - changing access points scanning for access pointsManagement information base
17ScanningScanning is required for many functions - finding and joining a network - finding a new access point during roamingPassive scanning find networks simply by listening for beaconsActive scanning on each channel send a probe and wait for probe response
18802.11 Protocol Architecture MAC Entitybasic access mechanismfragmentation/defragmentationencryption/decryptionMAC Layer Management Entitysynchronizationpower managementroamingMAC MIB (management information base)Physical Layer Convergence Protocol (PLCP)PHY-specific, supports common PHY SAPprovides Clear Channel Assessment signal (carrier sense)8
19802.11 Protocol Architecture (cont.) Physical Medium Dependent Sublayer (PMD)modulation and encodingPHY Layer Managementchannel tuning (channel switching delay : 224us in b)PHY MIBStation Managementinteracts with both MAC Management and PHY Management9
20Commercial Products : WLAN Cards One pieceTwo pieces10
24Wi-Fi Protected Access (WPA) - Authentication Open system authenticationExchange of identities, no security benefitsShared Key authenticationShared (secret) Key assures authenticationWEP (wired equivalent privacy) is easily broken since key is used to encrypt every transmissionImmediate solution for WEP was to increase key length from 40, to 128, to 156 bits where 128 bits is the minimum used today.
25IEEE 802.11a, 802.11b and 802.11g IEEE 802.11a IEEE 802.11b 5-GHz band with data rates of 6, 9 , 12, 18, 24, 36, 48, 54 MbpsUses orthogonal frequency division multiplexing (OFDM)Subcarrier modulated using BPSK, QPSK, 16-QAM or 64-QAMIEEE bProvides data rates of 5.5 and 11 Mbps at 2.4 GHzComplementary code keying (CCK) modulation schemeIEEE g2.4 GHz, up to 54 Mbps, OFDM.11g and .11b can operate simultaneously but with an .11b user in the cell the wireless network will degrade the .11g performance (AP must do translation for .11b) but still much faster than .11b alone.
26802.11a : a The a standard uses the same data link layer protocol and frame format as the original standard, but an OFDM based air interface (physical layer). It operates in the 5 GHz band with a maximum net data rate of 54 Mbit/s, plus error correction code, which yields realistic net achievable throughput in the mid-20 Mbit/s. Since the 2.4 GHz band is heavily used to the point of being crowded, using the relatively un-used 5 GHz band gives a a significant advantage. However, this high carrier frequency also brings a disadvantage: The effective overall range of a is less than that of b/g; a signals cannot penetrate as far as those for b because they are absorbed more readily by walls and other solid objects in their path due to their smaller wavelength.
27802.11b : b b has a maximum raw data rate of 11 Mbit/s and uses the same media access method defined in the original standard b products appeared on the market in early 2000, since b is a direct extension of the modulation technique defined in the original standard. The dramatic increase in throughput of b (compared to the original standard) along with simultaneous substantial price reductions led to the rapid acceptance of b as the definitive wireless LAN technology b devices suffer interference from other products operating in the 2.4 GHz band. Devices operating in the 2.4 GHz range include: microwave ovens, Bluetooth devices, baby monitors and cordless telephones.
28: In 2003, task group TGma was authorized to "roll up" many of the amendments to the 1999 version of the standard. REVma or ma, as it was called, created a single document that merged 8 amendments (802.11a,b,d,e,g,h,i,j) with the base standard. Upon approval on March 08, 2007, REVma was renamed to the current standard IEEE  This is the single most modern document available that contains cumulative changes from multiple sub-letter task groups.
29Useful Web Sites from Stallings IEEE Wireless LAN StandardIEEE Wireless LAN Working Group: Contains working group documents plus discussion archives.Wi-Fi Alliance: An industry group promoting the interoperabiltiy of wireless products with each other.
30ReferencesBrian P Crow, Indra Widjaja, J G Kim, Prescott T Sakai. IEEE Wireless Local Area Networks. IEEE Communications MagazineJochen H. Schiller, Mobile Communications