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Tutorial
Wireless LAN Technology and
Network Implementation
Bandwidth
Bandwidth
alone should not be the deciding factor in equipment purchase
and installation.
In a wired environment, many devices share the same
wires.
In a wireless environment, many devices share the same
radio spectrum. However, with the use of spread-spectrum
technology, the resources are reused many times over.
It
is said that bigger is better, so more bandwidth is better,
right?
It may not be. In wired networks, sometimes the rating
of the wire's clock speed is confused with traffic throughput.
Because Ethernet uses CSMA/CD with statistical multiplexing,
the general rule is to design networks in which the throughput
does not exceed 30% of the rating, so an Ethernet-based 10Mbps
link would have an average throughput of 3Mbps.
But
what if I need more bandwidth for killer applications?
We have been waiting for that killer application for
some time now.
VoIP, Videoconferencing, and even on-line interactive
training courses use much less BW than one would think.
An interactive videoconference uses around 2MHz of
stream bandwidth.
What
does that mean in real life?
It all depends on your applications.
In my 802.11b home network, I used several test
procedures1 to
examine network performance and found no difference between
the wired PC and the wireless PC.
802.11
Standards
Now
that we have discussed some of the basic concepts of wireless
communications, let’s take a look at the difference between
802.11 a, b, and g.
The
wireless 802.11 standard is a top-level standard that has been
divided into several subsections, including 802.11a, 802.11b,
and 802.11g.
The 802.11 umbrella covers the sub-committee standards
802.11a, b, and g, along with any other 802.11 standards.
There has been more than just the IEEE committee work on
wireless standards. Thinking that it could improve both
marketing and product quality, a consortium called "Bluetooth”
was formed. Bluetooth’s promoters include 3Com, Agere,
Ericsson, IBM, Intel, Microsoft, Motorola, Nokia, and Toshiba,
as well as hundreds of associate and adapter member companies.
In Figure 8, we see a comparison between the different 802.11
and Bluetooth standards. Standards
a and b were approved at the same time, but products
supporting 802.11b, being less expensive to make, have flooded
the market. It
should be noted that 802.11b operates in the 2.4 GHz range,
with an operational bandwidth of 11Mbps. Notice that the
802.11a standards operates at 5Ghz with an operational l
bandwidth of 54Mbps. These two standards are not compatible.
| Wireless
LAN Standards |
| |
802.11a |
802.11b |
802.11g |
Bluetooth |
| Data
Rate |
54-72 |
11 |
54 |
721
Kbps
56 Kbs |
| Frequency |
5Ghz |
2.4Ghz |
2.4Ghz |
2.4Ghz |
| Modulation |
OFDM |
DSSS/CCK |
DSSS/PBCC |
FHSS |
| Channels |
12/8 |
11/3 |
11/3 |
79
( 1Mhz wide) |
| Bandwidth
Available |
300 |
83.5 |
83.5
(22MHz per channel) |
83.5 |
| Power |
40-800mW |
100mW |
100mW |
100mW
|
Figure
8: Wireless LAN Standards
So what do you do with all the 802.11b equipment you have
already invested in when 802.11a products hit the market? The
solution is relatively easy and cost-effective – secure a
dual band. This will give you dual-standard access points,
which operate both at the 802.11a and 802.11b standard.
Three performance tests: Toast.Net,
FTP transfer, and Net Meeting.
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