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1 IEEE 802.11 WLAN Guided By: Presented By: 082112111
Maulana Azad National Institute of Technology,Bhopal Department of Computer Science & Engineering IEEE WLAN Guided By: Mrs. NAMITA TIWARI Presented By: Manisha Bhadoria

2 Technology Tree for Wireless LAN
HomeRF Bluetooth

3 What is unique about wireless?
Difficult media interference and noise quality varies over space and time shared with Unwanted devices shared with non-802 devices (unlicensed spectrum: microwave ovens, bluetooth, etc.,) Full connectivity cannot be assumed Hidden node problem Multiple international regulatory requirements 2

4 Uniqueness of Wireless (continued)
Mobility variation in link reliability battery usage: requires power management want seamless connections Security no physical boundaries overlapping LANs 4

5 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

6 IEEE 802 Protocol Layers

7 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

8 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.

9 infrastructure network
AP: Access Point AP AP wired network AP ad-hoc network Source: Schiller

10 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

11 Architecture Model ESS DS

12 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)

13 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”

14 Difference Between Wired and Wireless
Ethernet LAN Wireless LAN B A B C A C 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.

15 Fragmentation Wireless LANs have high bit error rates.
The probability of erroneous frame is much higher for wireless links uses fragmentation to reduce the frame error rate.

16 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

17 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

18 802.11 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) 8

19 802.11 Protocol Architecture (cont.)
Physical Medium Dependent Sublayer (PMD) modulation and encoding PHY Layer Management channel tuning (channel switching delay : 224us in b) PHY MIB Station Management interacts with both MAC Management and PHY Management 9

20 Commercial Products : WLAN Cards
One piece Two pieces 10

21 Commercial Products : AP

22 Outdoor Application - Antenna

23 Outdoor Application

24 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.

25 IEEE 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 Mbps Uses orthogonal frequency division multiplexing (OFDM) Subcarrier modulated using BPSK, QPSK, 16-QAM or 64-QAM IEEE b Provides data rates of 5.5 and 11 Mbps at 2.4 GHz Complementary code keying (CCK) modulation scheme IEEE g 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.

26 802.11a : 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[citation needed]. 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.

27 802.11b : 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 [4] This is the single most modern document available that contains cumulative changes from multiple sub-letter task groups.

29 Useful Web Sites from Stallings
IEEE Wireless LAN Standard IEEE 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.

30 References Brian P Crow, Indra Widjaja, J G Kim, Prescott T Sakai. IEEE Wireless Local Area Networks. IEEE Communications Magazine Jochen H. Schiller, Mobile Communications



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