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802.11

802.11. Presented by Hampton Smith. 802.11. An IEEE (Institute for Electrical and Electronics Engineers) protocol ratified in 1997 which defines a standard for wireless connectivity. Now known as 802.11 Legacy. Applies to the Physical and Media Access Control layers. 802.11 Legacy.

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802.11

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  1. 802.11 Presented by Hampton Smith

  2. 802.11 • An IEEE (Institute for Electrical and Electronics Engineers) protocol ratified in 1997 which defines a standard for wireless connectivity. • Now known as 802.11 Legacy. • Applies to the Physical and Media Access Control layers.

  3. 802.11 Legacy • Allowed for a 1-2 Mb/s data rate • 3 channels, 2.4 GHz (ISM) • CSMA/CA, with a random backoff • Security • RC4 Encryption • Authentication through a list or a shared private key

  4. 802.11 Legacy • Topologies • Ad hoc (on the fly) • Infrastructure • Data Transmission Types: • Direct Sequence Spread Spectrum (DSSS) • Frequency Hopping Spread Spectrum (FHSS) • Infrared Spectrum

  5. DSSS vs FRSS • Both use Spread Spectrum • Spread Spectrum means all devices transmit within the same bandwidth, devices don’t have assigned frequencies.

  6. DSSS Reduces peak amplitude Maintains total power Data encoded using “clipping bit” and transferred at an increased data rate over multiple frequencies Resistant to feedback and temporary noise generators FHSS Maintains peak amplitude “Hops” from frequency to frequency many times per second. Avoids feedback by not transmitting on any one frequency for long DSSS vs FHSS

  7. Data Transmission • Sender sends RTS (ready to send) • Contains information about size of data and the sender • Receiver sends CTS (clear to send) • Sender sends packet • Packet verified through CRC • Receiver sends ACK (acknowledgement) • This avoids the “hidden node problem.” A X B

  8. Topologies • Ad hoc • Uses Spokesman Election Algorithm (SEA) to determine Master and Slaves • Nodes communicate directly • Infrastructure • Nodes communicate through an Access Point • Access Point relays messages between nodes and between the nodes and the outside

  9. 802.11b • Eliminates FHSS option • Boosts data rate to a nominal 11 Mb/s (practically about 5 Mb/s) • Does this through voodoo

  10. 802.11a • Comes after 802.11b. Go figure. • Increases theoretical data rate to 54 Mb/s (practical: 27 Mb/s) • Operates on 5 GHz license free band • Limited range (about half of 802.11b) • Incompatible with 802.11b and 802.11 legacy. • Most held out for 802.11g, which was already in the works.

  11. 802.11g • Same transfer as 802.11a (nominal 54 Mb/s, practical 27 Mb/s). • Operated on original 2.4 GHz spectrum • Same range as 802.11b • Compatible with 802.11b and 802.11 legacy technologies. • Best of both worlds option.

  12. Security • RC4 older code, still checked out. • Several studies determined that wireless was woefully less secure than wired counterpart. • Drafts of 802.11i, but not ratified until 2004. • WPA (Wi-Fi (Wireless Fidelity) Protected Access) Organization.

  13. Problems with 802.11 • Limited range, commercial and industrial implementations need repeaters and access points in many places. • Industrial applications use lots of metal and electric equipment which can reflect, nullify, distort, and broadcast its own signals. • Security • 2.4 GHz band not unlicensed everywhere (Italy, for example)

  14. Further Reading • http://standards.ieee.org/getieee802/802.11.html • (Google search “IEEE get wireless 802.11”) • http://www.computer.org/students/looking/summer97/ieee802.htm • (Google search “IEEE 802.11 short tutorial”)

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