g., TCP/IP, etc)
802.2 Logical Link Control (LLC)
802.11 MAC Header (a,b,g identical)
IEEE 802.11a,b,g
802.11 PLCP Header (a,b,g distinct)
Physical Medium Specs (RF, DSSS, OFDM, etc.)
Figure 2.4: 802.11 and the OSI Model.
2.2.7.1 Radio frequencies and channels
Where Ethernet sends electrical signals through wires, WLANs send radio frequency (RF)
energy through space. Wireless devices are equipped with a special network interface card
(NIC) with one or more antennae, a radio transceiver set, and circuitry to convert between
RF signals and the digital pulses used by computers.
Guide to Wireless LAN Analysis
25
Depending on the design of the antenna, radio waves may emanate more or less
equally in all directions (the most common design), or be stronger in one direction than in
others. Radio waves broadcast on a given frequency can be picked up by any receiver
within range tuned to that same frequency.
Effective or usable range depends on a number of factors. In general, higher power
and lower frequency increase the range at which a signal can be detected. Distance from
the signal source and interference from intervening objects or other signals all tend to
degrade reception.
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