wireless network IEEE 802.11
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Transcript of wireless network IEEE 802.11
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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