When discussing wireless LAN speeds, it is important to understand that data rates do not
equate to actual network throughput. The data rate for the IEEE 802.11a standard, for example,
is 54 Mbps. Actual throughput, however, is closer to 20 Mbps to 30 Mbps.
Why the difference?
There could be several reasons for this discrepancy, but the primary cause is due to the wireless
LAN protocol and its associated overhead. As with Ethernet, wireless LANs are based on a
Carrier Sense Multiple Access network protocol.
But unlike Ethernet which implements a Collision Detection scheme (where data is retransmitted if a collision is detected), wireless LANs implement a Collision Avoidance scheme (where data is only sent when the air is free).
This CSMA/CA protocol, as defined, does not allow for simultaneous, two-way traffic. Thus, while Optical Wireless solutions are ?full-duplex,? RF solutions are, by their very nature, ?half-duplex.?
Thus, an 11 Mbps IEEE 802.11b network will, on average, have an effective throughput of only 4
Mbps to 6 Mbps, while a 54 Mbps IEEE 802.11a network has a resulting throughput of 20 Mbps
to 30 Mbps.