Presentation on theme: "Maulana Azad National Institute of Technology,Bhopal Department of Computer Science & Engineering IEEE 802.11 WLAN Guided By: Mrs. NAMITA TIWARI Presented."— Presentation transcript:
Maulana Azad National Institute of Technology,Bhopal Department of Computer Science & Engineering IEEE 802.11 WLAN Guided By: Mrs. NAMITA TIWARI Presented By: Manisha Bhadoria Manisha Bhadoria 082112111 082112111
Technology Tree for Wireless LAN HomeRFBluetooth
What is unique about wireless? Difficult media Difficult media interference and noise quality varies over space and time shared with Unwanted 802.11 devices microwave ovens, bluetooth, etc., shared with non-802 devices (unlicensed spectrum: microwave ovens, bluetooth, etc.,) Full connectivity cannot be assumed Hidden node problem Multiple international regulatory requirements
Uniqueness of Wireless (continued) Mobility variation in link reliability power management battery usage: requires power management want seamless connections Security no physical boundaries overlapping LANs
Wireless LANs: Characteristics Types Infrastructure based Ad-hoc Advantages Flexible deployment Minimal wiring difficulties More robust against disasters (earthquake etc) Historic buildings, conferences, trade shows,… Disadvantages Low bandwidth compared to wired networks (1-10 Mbit/s) Proprietary solutions Need to follow wireless spectrum regulations
IEEE 802 Protocol Layers
Protocol Architecture Functions of media access control (MAC) layer: On transmission, assemble data into a frame with address and error detection fields On reception, disassemble frame and perform address recognition and error detection Govern access to the LAN transmission medium Functions of logical link control (LLC) Layer: Provide an interface to higher layers and perform flow and error control
Components/Architecture Station (STA) - Mobile node Access 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.
infrastructure network ad-hoc network AP wired network AP: Access Point Source: Schiller
IEEE 802.11 Architecture (model) Distribution system (DS) – the network backbone Access point (AP) – a bridge or relay Basic service set (BSS) Stations competing for access to shared wireless medium Isolated or connected to backbone DS through AP The entity in which the stations are within range of each other although BSSs can easily overlap Extended service set (ESS) Two or more basic service sets interconnected by DS usually a wired LAN
802.11 Architecture Model DS ESS
Wireless LAN: Motivation Can we apply media access methods from fixed networks? Example CSMA/CD Carrier Sense Multiple Access with Collision Detection send as soon as the medium is free, listen into the medium if a collision occurs (original method in IEEE 802.3)
Medium access problems in wireless networks signal strength decreases proportional to the square of the distance sender would apply CS and CD, but the collisions happen at the receiver sender may not “hear” the collision, i.e., CD does not work CS might not work, e.g. if a terminal is “hidden”
Difference Between Wired and Wireless If 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. A B C A B C Ethernet LAN Wireless LAN
Fragmentation Wireless LANs have high bit error rates. The probability of erroneous frame is much higher for wireless links 802.11 uses fragmentation to reduce the frame error rate.
MAC management Synchronization - finding and staying with a WLAN - synchronization functions Power Management - sleeping without missing any messages - power management functions Roaming - functions for joining a network - changing access points - scanning for access points Management information base
Scanning Scanning is required for many functions - finding and joining a network - finding a new access point during roaming Passive scanning - find networks simply by listening for beacons Active scanning - on each channel send a probe and wait for probe response
802.11 Protocol Architecture MAC Entity basic access mechanism fragmentation/defragmentation encryption/decryption MAC Layer Management Entity synchronization power management roaming MAC MIB (management information base) Physical Layer Convergence Protocol (PLCP) PHY-specific, supports common PHY SAP provides Clear Channel Assessment signal (carrier sense)
802.11 Protocol Architecture (cont.) Physical Medium Dependent Sublayer (PMD) modulation and encoding PHY Layer Management 224us channel tuning (channel switching delay : 224us in 802.11b) PHY MIB Station Management interacts with both MAC Management and PHY Management
Commercial Products : WLAN Cards One piece Two pieces
Commercial Products : AP
Outdoor Application - Antenna
Wi-Fi Protected Access (WPA) - Authentication Open system authentication Exchange of identities, no security benefits Shared Key authentication Shared (secret) Key assures authentication WEP (wired equivalent privacy) is easily broken since key is used to encrypt every transmission Immediate solution for WEP was to increase key length from 40, to 128, to 156 bits where 128 bits is the minimum used today.
IEEE 802.11a, 802.11b and 802.11g IEEE 802.11a 5-GHz band with data rates of 6, 9, 12, 18, 24, 36, 48, 54 Mbps Uses orthogonal frequency division multiplexing (OFDM) Subcarrier modulated using BPSK, QPSK, 16-QAM or 64-QAM IEEE 802.11b Provides data rates of 5.5 and 11 Mbps at 2.4 GHz Complementary code keying (CCK) modulation scheme IEEE 802.11g 2.4 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.
802.11a : 802.11a The 802.11a 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 802.11a a significant advantage. However, this high carrier frequency also brings a disadvantage: The effective overall range of 802.11a is less than that of 802.11b/g; 802.11a signals cannot penetrate as far as those for 802.11b because they are absorbed more readily by walls and other solid objects in their path due to their smaller wavelength.
802.11b : 802.11b 802.11b has a maximum raw data rate of 11 Mbit/s and uses the same media access method defined in the original standard. 802.11b products appeared on the market in early 2000, since 802.11b is a direct extension of the modulation technique defined in the original standard. The dramatic increase in throughput of 802.11b (compared to the original standard) along with simultaneous substantial price reductions led to the rapid acceptance of 802.11b as the definitive wireless LAN technology. 802.11b 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.
802.11-2007 : 802.11-2007 In 2003, task group TGma was authorized to "roll up" many of the amendments to the 1999 version of the 802.11 standard. REVma or 802.11ma, 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, 802.11REVma was renamed to the current standard IEEE 802.11-2007. This is the single most modern 802.11 document available that contains cumulative changes from multiple sub-letter task groups.
Useful Web Sites from Stallings IEEE 802.11 Wireless LAN Standard IEEE 802.11 Wireless LAN Working Group: Contains working group documents plus discussion archives. IEEE 802.11 Wireless LAN Working Group Wi-Fi Alliance: An industry group promoting the interoperabiltiy of 802.11 wireless products with each other. Wi-Fi Alliance
References Brian P Crow, Indra Widjaja, J G Kim, Prescott T Sakai. IEEE 802.11 Wireless Local Area Networks. IEEE Communications Magazine www.breezecom.com Jochen H. Schiller, Mobile Communications