Final Wlan

8/21/2019 Final Wlan

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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
http://home.no.net/coverage/rapport/80211.htmhttp://home.no.net/coverage/rapport/80211.htm


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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/

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