PRESENTATION ON

IEEE 802.11

Prepared By:

Shreejan Acharya

BEX 68114

Slides Includes

IntroductionPhysical Layer ArchitectureFrame formatDifferent ProtocolsMedia Access Control (MAC)

Introduction

Created and maintained by IEEE Set of media control(MAC) and physical layer Used to implement wireless local area

network(WLAN) In the frequency band 2.4,3.6,5 and 60 GHz Wi-fi refers to the IEEE 802.11 communication for

WLAN

The Linksys WRT54G contains a router with an 802.11b/g radio and two antennas

Introduction cntd.

Adopted in 1997Family of 802Origins in a 1985 ruling by the U.S. Federal

Communications commissionConsist of series of half duplex over the air

modulationUses same basic protocols It uses two spread spectrum technology

Frequency Hopping Spread Spectrum (FHSS) Direct Sequence Spread Spectrum (DSSS)

802.11 Physical Layer (PHY)

The 802.11 physical layer (PHY) is the interface between the MAC and the wireless media where frames are transmitted and received.

The PHY provides three functions. First, the PHY provides an interface to exchange frames

with the upper MAC layer for transmission and reception of data.

Secondly, the PHY uses signal carrier and spread spectrum modulation to transmit data frames over the media.

Thirdly, the PHY provides a carrier sense indication back to the MAC to verify activity on the media.

Architectures

Station (STA) Architecture: It contains IEEE 802.11

conformant MAC and PHY interface to the wireless medium, but does not provide access to a distribution system

Access-Point Architecture: Device that contains

IEEE802.11 conformant MAC and PHY interface to the wireless medium, and provide access to a distribution system for associated stations

Implemented in infra-structure products that connect to wired backbones

General terminologies

BSS (basic service set):Group of stations that communicate each other

IBSS(independent basic service set):It is a BSS without access point

Extended Service Set (ESS):A set of one or more Basic Service Sets inter

connected by a distribution System (DS)

BSS IBSS

General terminologies cntd

Service Set Identifier (SSID):It is network name similar to domain idOne network (ESS or IBSS) has one SSID

Basic Service Set Identifier (BSSID)It is cell identifier and is 6 octets longSimilar to NW ID in pre-IEEE Wave LAN systems

Frame format

Bytes 2 22 6 66

66 2 6 0-2312

4

Frame control Duration ID

A1 A2 A3 seq.ctrl

A4 Frame body

CRC

802.11 MAC header

Bits :2 2

2

4 1 1 1 1 1 1 1

Protocol version

type Sub type

To DS From DS

More flag

Retry PwrMgt

More data

wep rsvd

Frame control Field

protocols

802.11 legacyRelease in Jun 1997Original version of 802.11Specifies two net bit rate 1or 2 mbits per secIt has forward error correction codeThree alternatives physical layer

Diffuse infraredFrequency hopping spread spectrumDirect sequence spread spectrum

802.11a(ofdm waveform)

Release in sep 1999Data rates 1.5 to 54 mbit/sFirst widely accepted 802 familyOperates at 5GHz frequency bandLess range

802.11b

Release on the market in 2000Maximum raw data rate of 11mbit/sHigh throughputLow costInterference problem

802.11g

Release on june 2003Operates in the 2.4 GHz bandUses OFDM based transmission schemeOperates at the average bit rate of 22 Mbit/s or

maximum 54 Mbit/sIts hardware are full back compatible with

802.11b hardware

802.11n

Release on October 2009It is the improvement over previous 802.11

standardIt has MIMO antennasOperates at the 2.4 GHz or less than 5GHz

bandsData rates from 54 Mbit/s to 600 Mbit/s

802.11ac

Release in December 2013It is an amendment to IEEE 802.11It has wider channels(80 or 160 MHz)Operates at 5GHz bandIt supports multi-user MIMOData rates up to 1300 Mbit/s

802.11ad

Release in Dec 2012It defines new physical layer for 802.11 n/wOperates in the 60GHz millimeter wave

spectrumProduct implementing this standard are being

brought under the name of wigig brandPeak transmission rate 7 Gbit/s

Other Protocols

802.11 AHEstimated to release 2016Bandwidth 900MHz

802.11 AJ Estimated to release 2016Bandwidth 24/60

802.11 AXEstimated to release 2019Bandwidth 2.4/5

802.11 Media Access Control The 802.11 MAC layer provides functionality to allow reliable data delivery

for the upper layers over the wireless PHY media.

The data delivery itself is based on an asynchronous, best-effort,

connectionless delivery of MAC layer data.

There is no guarantee that the frames will be delivered successfully.

The 802.11 MAC provides a controlled access method to the shared wireless

media called Carrier-Sense Multiple Access with Collision Avoidance

(CSMA/CA).

CSMA/CA is similar to the collision detection access method deployed by

802.3 Ethernet LANs.

802.11 Media Access Control cntd

Another function of the 802.11 MAC is to protect the data being delivered by providing security and privacy services.

Security is provided by the authentication services and by Wireless Equivalent Privacy (WEP), which is an encryption service for data delivered on the WLAN.

Security

For security 802.11 specifies two Authentication modes:OSA(Opens Systems Authentication)• Device that request to access the network is granted

without any security check

Shared Key Authentication• Device that request to access the network is granted

with security check• WEP: wired equivalent privacy

ESSID offers casual separation of traffic

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