The%20IEEE%20802.11%20Specification%20%20%20%20%20By%20Matthew%20Ruston%20November%2025,%202007

1
The IEEE 802.11 Specification By Matthew
RustonNovember 25, 2007
2
Overview

• Introduction to 802.11 Wireless Networking
• Specification History
• High-level Architecture
• Physical Architecture
• Data Link Architecture

3
802.11 Wireless Networking

• Revolutionized wireless communication
• Allows compliant devices to communicate using
  radio transmissions are specific frequencies.
• Found in
• Automobiles
• Digital Cameras
• Printers
• Cell Phones

4
Specification History

• First IEEE 802.11 standard released in 1997
• Maximum data rate 2Mbps
• 2.4Ghz band
• Indoor Range 20 meters
• Outdoor Range 100 meters

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Specification History

• IEEE 802.11a released in 1999
• Maximum data rate 54Mbps
• 5.1 - 5.8Ghz band
• Indoor range 35 meters
• Outdoor range 120 meters
• Limited indoor effectiveness due to high
  frequency use

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Specification History

• IEEE 802.11b also published in 1999
• Maximum data rate 11Mbps
• 2.4Ghz band
• Indoor Range 38 meters
• Outdoor Range 140 meters

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Specification History

• IEEE 802.11g released in 2003
• The current industry adopted specification
• Maximum data rate 54Mbps
• 2.4Ghz band (backwards compatible with 802.11b)
• Indoor range 38 meters
• Outdoor range 140 meters

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802.11 Architecture

• A 802.11 compliant network design can be
  partitioned into a set of various objects.

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802.11 Architecture

• The 802.11 specification fits perfectly within
  the OSI networking model. Thus common place
  protocols such as TCP or UDP are not effected by
  the use of a 802.11 network.

Application
Presentation
Session
Transport
Network
Data Link 802.3 Ethernet 802.11 Wireless  
Physical 802.3 Ethernet 802.11 Wireless  
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802.11 Physical Layer Architecture

• Relies on encoding radio waves with binary
  information to send datagrams.
• Multiple methods implemented by the various
  802.11 specifications.

11
802.11 Physical Architecture

• Uses the Frequency Hopping Spread-Spectrum (FHSS)
  specification to transmit encoded information.
• A device will hop between a predetermined and
  configured set of frequency channels during the
  transmission.
• If one of the channels has interference or noise
  this communication protocol will ensure that the
  majority of the information can still transmit
  successfully.

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802.11 Physical Architecture

• To encode information into the transmission a
  system called Gaussian Frequency Shift Keying
  (GFSK) is used.
• Best explained if illustrated

13
802.11b Physical Architecture

• Uses a method called Differential Phase Shift
  Keying (DPSK) to encode information into its
  2.4Ghz band.
• Uses phase shifts of the carrier wave to encode a
  binary message. Design again, best illustrated

Symbol Phase Shift
00 0
01 ?/2 radians
11 ? radians
10 3 ?/2 or ?/2 radians
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802.11a/g Physical Architecture

• Although they are not backwards compatible they
  use Orthogonal Frequency Division Multiplexing
  for a transmission protocol.
• Has been omitted due to complexity.

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802.11 Data Link Architecture

• Much like 802.2, the Ethernet specification,
  802.11 relies on Frames to encompass a single
  datagram.
• Ethernet Frame

Preamble Dest. Address Source Address Type Data CRC
8 bytes 6 bytes 6 bytes 2 bytes 46-1500 bytes 4 bytes
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802.11 Data Link Architecture

• 802.11 Frame
• 802.11 Frame Control Breakdown

Frame Control Duration Address 1 Address 2 Address 3 Seq. Control Address 4 Payload CRC
2 bytes 2 bytes 6 bytes 6 bytes 6 bytes 2 bytes 6 byes 0-2312 bytes 2 bytes
Protocol Version Type Subtype To DS From DS More Frag. Retry Power Mgt. More Data WEP Order
2 bits 2 bits 4 bits 1 bit 1 bit 1 bit 1 bit 1 bit 1 bit 1 bit 1 bit
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802.11 Data Link Architecture

• To help illustrate the data link architecture,
  Wireshark was used to capture and analyze
  information from a 802.11 datagram.

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802.11 Data Link Transport

• 802.11 uses CSMA/CA for datagram transmission
  management.
• Carrier Sense Multiple Access With Collision
  Avoidance
• Each wireless device with sense the radio
  channel before transmission. If it appears busy
  it will wait a short random amount of time before
  retesting the channel.

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802.11 Data Link Transport

• Collision Avoidance is implemented by using two
  special frames between a wireless device and its
  associated access point (AP).
• Device wishing to transmit will send a Request To
  Send frame to the AP.
• If the AP deems the channel available it will
  respond with a Clear To Send frame to the device.

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• 1 IEEE Computer Society, IEEE-SA Standards
  Board, Information technology
  Telecommunications and information exchange
  between systems Local and metropolitan area
  networks Specific requirements Part 11
  Wireless LAN Medium Access Control (MAC) and
  Physical Layer (PHY) Specifications. 1999,
  Reaffirmed June 2003. IEEE-SA Standards Board.
  http//standards.ieee.org/getieee802/download/802
  .11-1999.pdf. Accessed Nov. 18, 2007.
• 2 IEEE Computer Society, IEEE-SA Standards
  Board, Telecommunications and information
  exchange between systemsLocal and metropolitan
  area networksSpecific requirementsPart 11
  Wireless LAN Medium Access Control (MAC) and
  Physical Layer (PHY) specificationsAmendment 1
  High-speed Physical Layer in the 5 GHz band.
  1999, Reaffirmed June 2003. http//standards.ieee
  .org/getieee802/download/802.11a-1999.pdf.
  Accessed Nov. 18, 2007.
• 3 IEEE Computer Society, IEEE-SA Standards
  Board, Supplement to IEEE Standard for
  Information technology - Telecommunications and
  information exchange between systems - Local and
  metropolitan area networks - Specific
  requirements Part 11 Wireless LAN Medium
  Access Control (MAC) and Physical Layer (PHY)
  specifications Higher-Speed Physical Layer
  Extension in the 2.4 GHz Band. 1999, Reaffirmed
  June 2003. http//standards.ieee.org/getieee802/d
  ownload/802.11b-1999.pdf. Accessed Nov. 18,
  2007.
• 4 IEEE Computer Society, IEEE-SA Standards
  Board, IEEE Standard for Information
  technologyTelecommunications and information
  exchange between systemsLocal and metropolitan
  area networksSpecific requirementsPart 11
  Wireless LAN Medium Access Control (MAC) and
  Physical Layer (PHY) specificationsAmendment 4
  Further Higher-Speed Physical Layer Extension in
  the 2.4 GHz Band. 2003. http//standards.ieee.or
  g/getieee802/download/802.11g-2003.pdf. Accessed
  Nov. 18, 2007.