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ZyXEL – SBG Support Notes
DSSS modulation.
What is 802.11b?
802.11b is the first revision of 802.11 standard allowing data rates up to
11 Mbps in the 2.4GHz ISM band. It is also known as 802.11 High-Rate and
Wi-Fi. 802.11b only uses DSSS modulation, and the maximum speed of 11
Mbps has fallbacks to 5.5, 2 and 1 Mbps.
How fast is 802.11b?
The IEEE 802.11b standard has a nominal speed of 11 megabits per
second (Mbps). However, depending on signal quality and how many other
people are using the wireless Ethernet through a particular Access Point,
usable speed will be much lower (on the order of 4 or 5 Mbps, which is still
substantially faster than most dialup, cable and DSL modems).
What is 802.11a?
802.11a is the second revision of 802.11 that operates in the unlicensed 5
GHz band and allows transmission rates of up to 54 Mbps. 802.11a uses
OFDM (orthogonal frequency division multiplexing) modulation as opposed
to FHSS or DSSS. Higher data rates are possible by combining channels.
Due to higher frequency, range is less than lower frequency systems (i.e.,
802.11b and 802.11g) and can increase the cost of the overall solution
because a greater number of access points may be required. 802.11a is
not directly compatible with 802.11b or 802.11g networks. In other words,
a user equipped with an 802.11b or 802.11g radio card will not be able to
interface directly with an 802.11a access point. Multi-mode NICs can solve
this problem.
What is 802.11g?
802.11g is an extension of 802.11b. 802.11g increases 802.11b's data
rates to 54 Mbps and still utilizes the 2.4 GHz ISM band. Modulation is
based upon OFDM (orthogonal frequency division multiplexing) technology.
An 802.11b radio card will interface directly with an 802.11g access point
(and vice versa) at 11 Mbps or lower depending on range. The range at 54
Mbps is less than for 802.11b operating at 11 Mbps.
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