IEEE 802.11 IEEE 802.11 WIRELESS LANWIRELESS LAN

V.Parthipan Assistant Professor ,Saveetha University

LANs provide connectivity for interconnecting computing resources at the local levels of an organization

Wired LANs Limitations because of physical, hard-wired infrastructure

Wireless LANs provide Flexibility PortabilityMobilityEase of Installation

In response to lacking standards, IEEE developed the first internationally recognized wireless LAN standard – IEEE 802.11

IEEE published 802.11 in 1997, after seven years of work

Most prominent specification for WLANs

Scope of IEEE 802.11 is limited to Physical and Data Link Layers.

Appliance Interoperability Fast Product Development Stable Future Migration Price Reductions The 802.11 standard takes into

account the following significant differences between wireless and wired LANs:

Power ManagementSecurityBandwidth

IEEE 802.3CarrierSense

IEEE 802.4TokenBus

IEEE 802.5TokenRing

IEEE 802.11Wireless

IEEE 802.2Logical Link Control (LLC)

PHYOSI Layer 1(Physical)

Mac

OSI Layer 2(Data Link)

Medical Professionals Education Temporary Situations Airlines Security Staff Emergency Centers

In historical building and small office where cabling is not economical.

Supports nomadic access by providing a wireless link between a LAN hub and mobile data terminal with an antenna.

Creation of an adhoc n/ws. i.e peer to peer network with no

centralized server that is set up temporarily to meet some immediate need.

CM10 Mbps Ethernet switch

UM

Bridge OrRouter

Server

100 Mbps Ethernet switch

Server

Mostly a wireless Lan will be linked into a wired LAN. This is called LAN Extension.

Control Module is wireless LAN acts as an interface to a wired LAN

If all wireless end systems are within the range of a single control module, then it is called single cell wireless LAN.

If multiple control Module are present ,then it is multiple cell wireless LAN.

CM- control module uses polling or token passing scheme to regulate access from end systems.

Hubs or user module(UM), that control number of stations directly without a wired LAN, can also be a part of wireless LAN

Wireless LAN requirement:- throughput – should provide high capacity. Number of nodes –should support many data. Connectivity of backbone LAN. Battery power consumption- use battery powered

workstations , so when not using n/w, can be set to sleep mode to reduce power consumption.

Transmission robustness and security: Highly interference prone should provide reliable transfer.

coallocated network operation –Wireless LAN operating in same area may face interference.

License free operation – should provide wireless products without license for frequency based used.

Hand off (or) Roaming – mobile station can move from cell to another.

Dynamic configuration: automated addition or relocation of end systems without disruption to others.

WLAN TOPOLOGYWLAN TOPOLOGY AD-HOC NETWORK AD-HOC NETWORK

WLAN TopologyWLAN TopologyInfrastructureInfrastructure

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 an ESS.

DS is implementation-independent. It can be a wired 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 DS

Portal: Logical entity where 802.11 network integrates with a non 802.11 network.

Distribution service (DS)Used to exchange MAC frames from station in one BSS to station in another BSS

Integration serviceTransfer of data between station on IEEE 802.11 LAN and station on integrated IEEE 802.x LAN

AssociationEstablishes initial association between station and AP. Each station must send its identify to all others through AP

Re-associationEnables transfer of association from one AP to another, allowing station to move from one BSS to another

DisassociationAssociation termination notice from station or AP

RE-ASSOCIATIONRE-ASSOCIATION

AuthenticationEstablishes identity of stations to each other

De-authenticationInvoked when existing authentication is terminated

PrivacyPrevents message contents from being read by unintended recipient.

IEEE 802.11 MEDIUM ACCESS IEEE 802.11 MEDIUM ACCESS CONTROLCONTROL

MAC layer covers three functional areas:

Reliable data deliveryAccess controlSecurity

MAC FRAME FORMATMAC FRAME FORMAT

Frame

Control

Duration

IDAddr 1 Addr 2 Addr 3 Addr 4Sequence

ControlCRC

FrameBody

2 2 6 6 6 62 0-2312 4

802.11 MAC Header

Protocol

VersionType SubType

ToDS

RetryPwrMgt

MoreData

WEP Order

Frame Control Field

Bits: 2 2 4 1 1 1 1 1 1 1 1

DSFrom More

Frag

MAC LAYER FRAMESMAC LAYER FRAMES

Data Frames Control Frames

RTS,CTS,ACK and PS-POLL Management Frames

Authentication and De-AuthenticationAssociation, Re-Association, and DisassociationBeacon and Probe frames

IS WLAN SECURE ?IS WLAN SECURE ?

The Parking Lot attack

Man in the middle attack

Freely available tools like Air Snort, WEP crack to snoop into a WLAN

PHYSICAL MEDIA DEFINED BY PHYSICAL MEDIA DEFINED BY ORIGINAL 802.11 STANDARDORIGINAL 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 spectrum Doesn’t penetrate walls, so no eavesdropping

FREQUENCY HOPPING FREQUENCY HOPPING SPREAD SPECTRUMSPREAD SPECTRUM

Signal is broadcast over seemingly random series of radio frequencies

Signal hops from frequency to frequency at fixed intervals

Receiver, hopping between frequencies in synchronization with transmitter, picks up message

AdvantagesEfficient utilization of available bandwidthEavesdropper hear only unintelligible blipsAttempts to jam signal on one frequency succeed only at knocking out a few bits

DIRECT SEQUENCE SPREAD DIRECT SEQUENCE SPREAD SPECTRUMSPECTRUM

Each bit in original signal is represented by multiple bits in the transmitted signal

Spreading code spreads signal across a wider frequency band

DSSS is the only physical layer specified for the 802.11b specification

802.11a and 802.11b differ in use of chipping method 802.11a uses 11-bit barker chip802.11b uses 8-bit complimentary code keying (CCK) algorithm

IEEE 802.11A AND IEEE IEEE 802.11A AND IEEE 802.11B802.11B

IEEE 802.11a – limited data rateMakes use of 5-GHz bandProvides rates of 6, 9 , 12, 18, 24, 36, 48, 54 MbpsUses orthogonal frequency division multiplexing (OFDM)

IEEE 802.11b 802.11b operates in 2.4 GHz band Provides data rates of 5.5 and 11 MbpsComplementary code keying (CCK) modulation scheme.Multiple carrier signals at different frequency sending some of the bits on each channel.

IEEE 802.11 standards :

IEEE 802.11 a

Multipath Effect(Multipath Fading)

is simply a term used to describe the multiple

Paths the radio wave may follow between

transmitter and receiver

IEEE 802.11 standards :

IEEE 802.11 a

Orthogonal Frequency Division Multiplexing(OFDM)

OFDM a digital multi-carrier modulation method. A large number of closely-spaced orthogonal sub-carriers are used to carry data.

Although the principles and some of the benefits have been known since the 1960s, OFDM is popular for wideband communications today by way of low-cost digital signal processing components that can efficiently calculate the FFT.

IEEE 802.11 standards :

IEEE 802.11 a

Frequency = 5 GHzMaximum Speed = 54 MbpsRange = about 35 meters(Varies)Encoding Scheme = OFDM

IEEE 802.11 standards :

IEEE 802.11 b

Frequency = 2.4 GHz (ISM band)Maximum Speed =11 MbpsRange = about 38meters(Varies)Encoding Scheme = DSSSModulation Technique= BPSK(1 Mbps), DQPSK(2 Mbps), CCK(5.5 Mbps,11Mbps)

FUTURE OF WLANFUTURE OF WLAN

WLANs move to maturityHigher Speeds Improved SecuritySeamless end-to-end protocolsBetter Error controlLong distancesNew vendorsBetter interoperabilityGlobal networking