IEEE 802.11 / Wi-Fi

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IEEE 802.11 / Wi-Fi
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- Jacob, Jebin- Kim, Jong Jin - Mwangi,
Lydiah
Wi-Fi Group
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Presentation Overview

• IEEE 802.11
• Layer Distribution
• Basic access method
• Modes of Operation
• Comparison between 802.11a, b, g
• Wi-fi Products in Market
• Competing Technologies
• Hype Cycle

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What is 802.11???

• Set of protocols which attempts to define the low
  layers of OSI model for a connection without
  using wire
• The physical layer
• The data link layer,
• Logical Link control (LLC)
• Media Access Control (MAC)

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Physical Layer Description

• Frequency Hopping Spread Spectrum
• Direct Hopping Spread Spectrum
• Infrared

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Physical Layer

• Original 802.11
• Direct-sequence spread spectrum
• Operating in 2.4 GHz
• Data rates of 1 and 2 Mbps
• Frequency-hopping spread spectrum
• Operating in 2.4 GHz
• Data rates of 1 and 2 Mbps
• Infrared
• 1 and 2 Mbps
• Wavelength between 850 and 950 nm

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IEEE 802.11 LAN

• Distribution system (DS)
• Access point (AP)
• Basic service set (BSS)
• Extended service set (ESS)

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How Does a Station Join an Access Point

• Discovery
• Passive Scanning
• Station waits to receive a Beacon Frame from
  access point
• Active Scanning
• Station tries to find an Access point by
  transmitting Probe request frames and wait
  for Probe Response from AP

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How Does a Station Join an Access Point (contd)

• Authentication Process
• Interchange of information between the AP and
  the
• station, where each side proves the knowledge of
  a given password
• Association Process
• Exchange of information about the stations and
  Access
• point capabilities

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Basic Access Method

• (CSMA / CSA)

• Station desiring to transmit senses the medium
• If the medium is busy, station will defer its
  transmission
• If medium is sensed free then the station
  transmit
• MAC Level Acknowledgements
• MAC layer performs the Collision Detection
  by reception of an acknowledgement to any
  transmitted fragment

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Fragmentation

• LAN protocols use small packets (typically 1518
  bytes)
• Higher Bit Error Rate of a radio link
• Less overhead to retransmit it (In case of
  error)
• Frequency Hopping system (hopping every 20 ms)

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Inter Frame Spaces

• Short Inter Frame Space (SIFS)
• separate transmissions in a single dialog
• Point Coordinate IFS (PIFS)
• Access point to gain access to a medium
• Distributed IFS (DIFS)
• Indicate a station is willing to transmit
• Extended IFS (EIFS)
• used by a station to indicate an error in packet

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Infrastructure Mode
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Peer to Peer / Ad-hoc mode
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802.11a,b,g  Compared
Source www.netgear.com
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Wi-Fi Products

• Wireless Broad band gateway- 150.00
• 802.11g 4- Port Route/Print Server
• It includes a wireless access point, broadband
  modem, router, and firewall
• Wireless G Notebook Network card-49.99
• Gives a notebook computer Wi-Fi capability by
  simply sliding into the pc card slot on the side
  of the computer
• Wireless G to USB 2.0 flex Adapter-64.88
• Adds Wi-Fi connectivity via the USB port.

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Products (contd)

• PCI adapter - 49.99
• Adds Wi-Fi connectivity to a desk top computer
• Access Points-559.00
• Connects all wireless devices to each other
• CompactFlash adapter -
  8.99
• Adds Wi-Fi connectivity to a PDA

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Wi-Fi Users

• Home
• Office
• College
• Airports and Hotels
• Hospitals
• factories

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Competing Technologies

• Bluetooth
• 802.15 WPAN
• 802.16 Wimax
• 802.20
• 3G

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Hype Cycle
Source Gartner Research www.gartner.com      
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Website
http//members.lycos.co.uk/wifigroup/
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Questions ???
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Thank You