If you are a network administrator, you may wonder how wireless might fit
into your existing network infrastructure. Wireless can serve in many capacities,
from a simple extension (like a several kilometer Ethernet cable) to a
distribution point (like a large hub). Here just a few examples of how your
network can benefit from wireless technology.
Wireless networking protocols
The primary technology used for building low-cost wireless networks is currently
the 802.11 family of protocols, also known in many circles as Wi-Fi.
The 802.11 family of radio protocols (802.11a, 802.11b, and 802.11g) have
enjoyed an incredible popularity in the United States and Europe. By implementing
a common set of protocols, manufacturers world wide have built
highly interoperable equipment. This decision has proven to be a significant
boon to the industry and the consumer. Consumers are able to use equipment
that implements 802.11 without fear of “vendor lock-in”. As a result,
consumers are able to purchase low-cost equipment at a volume which has
benefitted manufacturers. If manufacturers had chosen to implement their
own proprietary protocols, it is unlikely that wireless networking would be as
inexpensive and ubiquitous as it is today.
While new protocols such as 802.16 (also known as WiMax) will likely solve
some difficult problems currently observed with 802.11, they have a long way
to go to match the popularity and price point of 802.11 equipment. As
equipment that supports WiMax is just becoming available at the time of this
writing, we will focus primarily on the 802.11 family.
There are many protocols in the 802.11 family, and not all are directly related
to the radio protocol itself. The three wireless standards currently implemented
in most readily available gear are:
• 802.11b. Ratified by the IEEE on September 16, 1999, 802.11b is probably
the most popular wireless networking protocol in use today. Millions of
devices supporting it have shipped since 1999. It uses a modulation called
Direct Sequence Spread Spectrum (DSSS) in a portion of the ISM band
from 2.400 to 2.495GHz. It has a maximum rate of 11 Mbps, with actual
usable data speeds up to about 5 Mbps.
• 802.11g. As it wasnt finalized until June 2003, 802.11g is a relative latecomer
to the wireless marketplace. Despite the late start, 802.11g is now
the de facto standard wireless networking protocol as it now ships as a
standard feature on virtually all laptops and most handheld devices.
802.11g uses the same ISM range as 802.11b, but uses a modulation
scheme called Orthogonal Frequency Division Multiplexing (OFDM). It
has a maximum data rate of 54 Mbps (with usable throughput of about
22 Mbps), and can fall back to 11 Mbps DSSS or slower for backwards
compatibility with the hugely popular 802.11b.
• 802.11a. Also ratified by the IEEE on September 16, 1999, 802.11a uses
OFDM. It has a maximum data rate of 54Mbps, with actual throughput of
up to 27 Mbps. 802.11a operates in the ISM band between 5.745 and
5.805 GHz, and in a portion of the UNII band between 5.150 and
5.320GHz. This makes it incompatible with 802.11b or 802.11g, and the
higher frequency means shorter range compared to 802.11b/g at the same
power. While this portion of the spectrum is relatively unused compared to
2.4GHz, it is unfortunately only legal for use in a few parts of the world.
Check with your local authorities before using 802.11a equipment, particularly
in outdoor applications. 802.11a equipment is still quite inexpensive,
but is not nearly as popular as 802.11b/g.
In addition to the above standards, there are a number of vendor-specific extensions
to equipment, touting higher speeds, stronger encryption, and increased
range. Unfortunately these extensions will not operate between equipment from
different manufacturers, and purchasing them will effectively lock you into that
vendor for every part of your network. New equipment and standards (such as
802.11y, 802.11n, 802.16, MIMO and WiMAX) promise significant increases
in speed and reliability, but this equipment is just starting to ship at the time
of this writing, and availability and vendor interoperability is still uncertain.
Due to the ubiquity of equipment and unlicensed nature of the 2.4GHz ISM band,
this book will concentrate on building networks using 802.11b and 802.11g.
