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Wireless LAN
Presented By : Pooja Maheshwari
Guided By : Dr Jerry Gao
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LAN/WLAN World
LANs provide connectivity forinterconnecting computing resourcesat the local levels of an organization
Wired LANs
Limitations because of physical,hard-wired infrastructure
Wireless LANs provide
Flexibility
Portability
Mobility
Ease of Installation
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Medical ProfessionalsEducation
Temporary Situations
AirlinesSecurity Staff
Emergency Centers
Wireless LAN Applications
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In response to lacking standards, IEEEdeveloped the first internationallyrecognized wireless LAN standard
IEEE 802.11IEEE published 802.11 in 1997, after
seven years of work
Most prominent specification for WLANsScope of IEEE 802.11 is limited to
Physical and Data Link Layers.
IEEE 802.11 Wireless LANStandard
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Appliance Interoperability
Fast Product Development
Stable Future Migration
Price ReductionsThe 802.11 standard takes into
account the following significantdifferences between wireless andwired LANs:
Power Management
Security
Bandwidth
Benefits of 802.11 Standard
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IEEE 802 LAN Standards
Family
IEEE 802.3
CarrierSense
IEEE 802.4
Token
Bus
IEEE 802.5
TokenRing
IEEE 802.11
Wireless
IEEE 802.2Logical Link Control (LLC)
PHYOSI Layer 1
(Physical)
Mac
OSI Layer 2(Data Link)
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Access point (AP): A station that provides
access to the DS.Basic service set (BSS): A set of stations
controlled by a single AP.Distribution system (DS): A system used to
interconnect a set of BSSs to create anESS.
DS is implementation-independent. It can be awired 802.3 Ethernet LAN, 802.4 token bus,
802.5 token ring or another 802.11 medium.Extended service set (ESS):Two or more
BSS interconnected by DSPortal: Logical entity where 802.11 network
integrates with a non 802.11 network.
IEEE 802.11 Terminology
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WLAN TopologyAd-Hoc Network
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WLAN TopologyInfrastructure
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Distribution service (DS)Used to exchange MAC frames fromstation in one BSS to station in another
BSS
Integration serviceTransfer of data between station on
IEEE 802.11 LAN and station onintegrated IEEE 802.x LAN
IEEE 802.11 Services:Distribution of Messages
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AssociationEstablishes initial association betweenstation and AP
Re-associationEnables transfer of association from one
AP to another, allowing station to movefrom one BSS to another
DisassociationAssociation termination notice fromstation or AP
Association Related Services
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Re-Association
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AuthenticationEstablishes identity of stations to eachother
De-authenticationInvoked when existing authentication is
terminated
PrivacyPrevents message contents from beingread by unintended recipient
Access and Privacy Services
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IEEE 802.11 Medium
Access ControlMAC layer covers three functional
areas:
Reliable data deliveryAccess control
Security
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Reliable Data Delivery
Loss of frames due to noise, interference,and propagation effectsFrame exchange protocol
Source station transmits data
Destination responds with acknowledgment (ACK)If source doesnt receive ACK, it retransmitsframe
Four frame exchange for enhanced reliability
Source issues request to send (RTS)Destination responds with clear to send (CTS)Source transmits dataDestination responds with ACK
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Distributed Coordination Function (DCF)Distributed access protocol
Contention-Based
Makes use of CSMA/CA rather than CSMA/CD
Suited for ad hoc network and ordinaryasynchronous traffic
Point Coordination Function (PCF)Alternative access method on top of DCF
Centralized access protocolContention-Free
Works like polling
Suited for time bound services like voice ormultimedia
Access Control
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CSMA/CD vs. CSMA/CA
CSMA/CD CSMA/Collision detection For wire communication
No control BEFORE transmission
Generates collisions
Collision Detection-How? CSMA/CA CSMA/Collision Avoidance
For wireless communication
Collision avoidance BEFORE transmission
Why avoidance on wireless?
Difference in energy/power for transmit & receive
Difficult to distinguish between incoming weak
signals, noise, and effects of own transmission
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Interframe Space (IFS)
Defined length of time for control
SIFS - Short Inter Frame SpacingUsed for immediate response actions e.g ACK, CTS
PIFS - Point Inter Frame Spacing
Used by centralized controller in PCF schemeDIFS - Distributed Inter Frame Spacing
Used for all ordinary asynchronous traffic
DIFS (MAX) > PIFS > SIFS (MIN)
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RTS-CTS-DATA-ACK
DIFS: Distributed IFSRTS: Request To SendSIFS: Short IFSCTS: Clear To SendACK: Acknowledgement
NAV: Network Allocation VectorDCF: Distributed Coordination Function
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MAC Frame Format
Frame
Control
Duration
IDAddr 1 Addr 2 Addr 3 Addr 4Sequence
ControlCRC
Frame
Body
2 2 6 6 6 62 0-2312 4
802.11 MAC Header
Protocol
VersionType SubType
To
DSRetry
Pwr
Mgt
More
DataWEP Order
Frame Control Field
Bits: 2 2 4 1 1 1 1 1 1 1 1
DS
From More
Frag
M L F
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MAC Layer Frames
Data Frames
Control FramesRTS,CTS,ACK and PS-POLL
Management FramesAuthentication and De-Authentication
Association, Re-Association, andDisassociation
Beacon and Probe frames
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IEEE 802.11 Security
Authentication provided byopen system or shared keyauthentication(Authentication is used
instead of wired mediaphysical connection)
Privacy provided by WEP
(Privacy is used to provide theconfidential aspects of closedwired media)
An Integrity check isperformed using a 32-bit CRC
A h i i
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Authentication
WEP E i /D i
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WEP Encryption/Decryption
I WLAN S ?
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Is WLAN Secure ?The Parking
Lot attackMan in the
middle attack
Freelyavailable toolslike Air Snort,
WEP crack tosnoop into aWLAN
Ph i l M di D fi d b
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Physical Media Defined byOriginal 802.11 Standard
Frequency-hopping spread spectrumOperating in 2.4 GHz ISM bandLower cost, power consumptionMost tolerant to signal interference
Direct-sequence spread spectrumOperating in 2.4 GHz ISM bandSupports higher data ratesMore range than FH or IR physical layers
InfraredLowest costLowest range compared to spread spectrumDoesnt penetrate walls, so no eavesdropping
F H i S d
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Frequency Hopping SpreadSpectrum
Signal is broadcast over seemingly randomseries of radio frequencies
Signal hops from frequency to frequency atfixed intervals
Receiver, hopping between frequencies insynchronization with transmitter, picks upmessage
AdvantagesEfficient utilization of available bandwidthEavesdropper hear only unintelligible blipsAttempts to jam signal on one frequency succeedonly at knocking out a few bits
Di t S S d
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Direct Sequence SpreadSpectrum
Each bit in original signal is representedby multiple bits in the transmitted signalSpreading code spreads signal across a
wider frequency bandDSSS is the only physical layer
specified for the 802.11b specification802.11a and 802.11b differ in use ofchipping method802.11a uses 11-bit barker chip802.11b uses 8-bit complimentary code
keying (CCK) algorithm
IEEE 802 11 d IEEE
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IEEE 802.11a and IEEE802.11b
IEEE 802.11aMakes use of 5-GHz band
Provides rates of 6, 9 , 12, 18, 24, 36, 48, 54 Mbps
Uses orthogonal frequency division multiplexing(OFDM)
IEEE 802.11b802.11b operates in 2.4 GHz band
Provides data rates of 5.5 and 11 MbpsComplementary code keying (CCK) modulationscheme
For more information:http://home.no.net/coverage/rapport/80211.htm
Oth St d d
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Other Standards
Japan has introduced Millimeter WaveWireless LAN (MWWL).Europe has introduced HIPERLAN (High
Performance Radio Local Area Network)
Features,capabilities, and technology similarto those of IEEE 802.11 used in USDeveloped by ETSI (EuropeanTelecommunications standards institute)
Provides high speed communications(20Mbps)Has technical advantages such as inclusionof Quality of Service
HIPERLAN r f r nc m d l
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HIPERLAN-reference model
Medium Access Control
(MAC) Sublayer
Channel Access Control
(CAC) Sublayer
Physical (PHY) Layer
Application Layer
Presentation Layer
Session Layer
Transport Layer
etwork Layer
Data Link Layer
Physical Layer
higher layer protocols
OSI
Reference Model
HIPERLAN
Reference Model
For more information: http://www.hiperlan.uk.com/
http://www.netplan.dk/hip.htm
F t f WLAN
http://www.netplan.dk/hip.htmhttp://www.hiperlan.uk.com/http://www.netplan.dk/hip.htmhttp://www.netplan.dk/hip.htmhttp://www.hiperlan.uk.com/ -
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Future of WLANWLANs move to maturity
Higher SpeedsImproved Security
Seamless end-to-end protocols
Better Error controlLong distances
New vendors
Better interoperabilityGlobal networking
Anywhere, anytime,any-form connectivity
R f
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References
Geier, Jim (1999). Wireless LANs.Macmillan Technical Publishing.
Held, Gil (2001). Data over WirelessNetworks. McGraw Hill.
Stallings, William (2001). WirelessCommunications and Networks.Prentice Hall.
http://www.wlana.org/
http://www.intel.com/network/connectivity/resources/doc_library/documents/pdf/np1692-01.pdf
http://www.wlana.org/http://www.intel.com/network/connectivity/resources/doc_library/documents/pdf/np1692-01.pdfhttp://www.intel.com/network/connectivity/resources/doc_library/documents/pdf/np1692-01.pdfhttp://www.intel.com/network/connectivity/resources/doc_library/documents/pdf/np1692-01.pdfhttp://www.intel.com/network/connectivity/resources/doc_library/documents/pdf/np1692-01.pdfhttp://www.intel.com/network/connectivity/resources/doc_library/documents/pdf/np1692-01.pdfhttp://www.intel.com/network/connectivity/resources/doc_library/documents/pdf/np1692-01.pdfhttp://www.intel.com/network/connectivity/resources/doc_library/documents/pdf/np1692-01.pdfhttp://www.intel.com/network/connectivity/resources/doc_library/documents/pdf/np1692-01.pdfhttp://www.wlana.org/