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 vs FHSS  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

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 B X

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/getieee802/802.1 1.html http://standards.ieee.org/getieee802/802.1 1.html http://standards.ieee.org/getieee802/802.1 1.html  (Google search “IEEE get wireless 802.11”)  http://www.computer.org/students/looking/ summer97/ieee802.htm http://www.computer.org/students/looking/ summer97/ieee802.htm http://www.computer.org/students/looking/ summer97/ieee802.htm  (Google search “IEEE 802.11 short tutorial”)