1. The IEEE 802.11 Specification By Matthew Ruston November 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

5. 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

6. Specification History  IEEE 802.11b also published in 1999 Maximum data rate: 11Mbps 2.4Ghz band Indoor Range: 38 meters Outdoor Range: 140 meters

7. 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

8. 802.11 Architecture  A 802.11 compliant network design can be partitioned into a set of various objects.

9. 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 Ethernet802.11 Wireless Physical

10. 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.

12. 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 it’s 2.4Ghz band. Uses phase shifts of the carrier wave to encode a binary message. Design again, best illustrated… SymbolPhase Shift 000 01Π/2 radians 11Π radians 103 Π/2 or – Π/2 radians

14. 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.

15. 802.11 Data Link Architecture  Much like 802.2, the Ethernet specification, 802.11 relies on Frames to encompass a single datagram.  Ethernet Frame: PreambleDest. Address Source Address TypeDataCRC 8 bytes6 bytes 2 bytes 46-1500 bytes 4 bytes

16. 802.11 Data Link Architecture  802.11 Frame  802.11 Frame Control Breakdown Frame Control DurationAddress 1 Address 2 Address 3 Seq. Control Address 4 PayloadCRC 2 bytes 6 bytes 2 bytes6 byes0-2312 bytes 2 bytes Protoco l Version TypeSubtyp e To DSFrom DS More Frag. RetryPower Mgt. More Data WEPOrder 2 bits 4 bits1 bit

17. 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.

20. 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.

21. 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.

23. [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 systems—Local and metropolitan area networks—Specific requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications—Amendment 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/download/802.11b-1999.pdf]. Accessed Nov. 18, 2007. [4] IEEE Computer Society, IEEE-SA Standards Board, “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—Amendment 4: Further Higher-Speed Physical Layer Extension in the 2.4 GHz Band”. 2003. [http://standards.ieee.org/getieee802/download/802.11g-2003.pdf]. Accessed Nov. 18, 2007.