Presented by Hampton Smith

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

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

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

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

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

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

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

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

802.11a  Comes after b. 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 b)  Incompatible with b and legacy.  Most held out for g, which was already in the works.

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

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

Problems with  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)

Further Reading  1.html 1.html 1.html  (Google search “IEEE get wireless ”)  summer97/ieee802.htm summer97/ieee802.htm summer97/ieee802.htm  (Google search “IEEE short tutorial”)