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Wireless networking
LOOK MUM,
NO CABLES
By GREG SWAIN
Fig.1: a simple Adhoc
network.
Here’s a wireless computer network that’s a cinch to
install and get going. It works just like a regular
network but without messy cables.
W
IRELESS NETWORKS have
two big advantages: convenience and ease of set up.
They’re convenient because there are
no cables to install and they’re easy
to set up for exactly the same reason.
Usually, a wired network (LAN) is
the most cost-effective method but it
does tie the PCs to set locations. By
contrast, a wireless LAN means that
PCs can be moved from one location to
another and still have network access
– something that can be very useful for
mobile users with laptops.
A wireless LAN also has advantages in situations where it’s difficult to
install cables or if you don’t want to
drill holes through walls. And it can
save you from digging up concrete
paths if you want to “connect” two
buildings together.
In short, if you can’t go through it,
over it or around it, a wireless network
is the answer.
Wireless network cards
Although still relatively expensive,
the cost of wireless networking is now
on the way down. Diamond Multimedia’s HomeFree system has been
32 Silicon Chip
popular at the bottom end of the market, although hampered by its rather
leisurely 1Mb/s transmission speed.
By contrast, this new system from
Eumitcom Technology (and sold by
MicroGram Computers) runs at a brisk
11Mb/s, which is far more useful for
business applications. It’s based on
PCMCIA wireless networking cards
which plug straight into the PCMCIA slots fitted to laptop computers.
However, by using a “PCMCIA-to-PCI
Adapter”, they can be fitted to conventional PCs as well.
Each PCMCIA card is actually a network card and radio transceiver rolled
into one. The omnidirectional antenna
circuitry for the card is located at one
end and protrudes from the laptop
(or PC) by about 4cm when the card
is pushed into place.
The transceiver operates in the
2.4GHz band using spread spectrum
wireless technology, to ensure security and reliability. What’s more, the
cards don’t really need a separate base
station (or access point) to operate.
All you have to do is set up several
computers with these cards and you
have a working network (this is known
as an “Adhoc” network).
Of course, you still have to install
the relevant networking protocols, set
up workgroups and computer names,
and share resources, just as you would
for a conventional wired network.
The setting up procedure for the
PCMCIA card is straightforward – just
insert the card into its slot, reboot the
computer and install the driver when
prompted. You then install the con
figuration utility software, which is
supplied on a separate disk.
Transmission mode
Among other things, the configuration utility lets you set the channel
number and the mode – see Fig.3.
The mode is set to “Adhoc” for a
small stand-alone wireless network
or to “Infrastructure” if you intend
using an Access Point. There are also
options that allow you to encrypt the
transmissions.
The configuration utility also
shows the current transmission rate
(or throughput), as well as the link
quality and signal strength from an
Access Point.
The effective range for an Adhoc
Fig.2: two or more Access Points can be using to create
overlapping “cells” and to link networks together (eg,
between buildings). An Access Point is also needed to
interface a wireless network to a conventional wired
LAN.
This view shows the Access Point (centre)
and two Wireless LAN PCMCIA cards.
The PCMCIA cards function as a network
card and radio transceiver rolled into
one and can be used without the Access
Point to create a simple “Adhoc” network
– see Fig.1.
January 2001 33
The PCMCIA cards can either be plugged directly into a notebook
computer or used with a PC by installing a PCMCIA-to-PCI adapter
or a PC Card Drive.
network running at 11Mb/s is about 30
metres (line of sight), although greater distances are possible at reduced
transmission rates. In operation, the
system can automatically switch down
to either 5.5Mb/s, 2Mb/s or 1Mb/s for
line-of-sight ranges of 50m, 100m and
120m respectively.
PCMCIA-to-PCI adapter
Here’s a device that you probably
haven’t seen before – it’s called a
“Wireless LAN PCMCIA-to-PCI Adapt
er” and it functions as a PCMCIA card
to PCI bridge. In a nutshell, this card
plugs into a spare PCI slot on your PC’s
motherboard and accepts the wireless
PCMCIA network card.
The card slot is accessed through
a cutout in the backplane connector
– you just slide the card in until it
“clicks” home, just as you would with
a laptop computer.
Installing this card is straightforward enough, although your PC will
need to have a couple of spare interrupt request lines (IRQs) – one for the
adapter card itself and another for the
PCMCIA card. The supplied setup diskette includes drivers for Windows 95
OSR2, Windows 98, Windows NT and
Windows 2000. The setup program
automatically identifies the operating
system and installs the correct driver.
You then slide the PCMCIA wireless
LAN card into place and install the
driver for this device.
In case you’re wondering, the PCM-
Fig.3: the Wireless LAN Configuration Utility, lets you set the channel number
and mode. It also shows the transmission rate and indicates the link quality and
signal strength from an Access Point.
34 Silicon Chip
CIA-to-PCI Adapter works only with
the wireless PCMCIA LAN cards. If
you want to use other PCMCIA cards
in a PC, take a look at MicroGram’s
“PC Card Drive”. This device looks
very similar to the other unit but has
two slots and works with Type 1, 2 &
3 PCMCIA cards.
In fact, it’s the PC Card Drive that’s
pictured in this article. Naturally, it’s
more expensive than the other adapter
card (see below).
Access Point
An “Access Point” is required if you
want to connect your wireless LAN to
a conventional LAN. In addition, an
Access Point effectively doubles the
range between wireless PCs on the
network, since it acts as a base station.
You can also set up multiple Access
Points with overlapping coverage areas so that mobile users can freely roam
from one “cell” to the next.
Similarly, two Access Points can
be used to link two building together,
Fig.4: the Wireless LAN Configuration
Utility is automatically launched at
start-up and is minimised to the PC’s
System Tray.
Fig.5: the Access Point also comes with a configuration utility.
Clicking the Scan button displays any detected Access Points, as
shown here.
Fig.6: double clicking
an Access Point in Fig.5
brings up the dialog box
shown above, so that you
can assign it a temporary
IP address.
using Point-to-Point mode.
Disarmingly simple in appearance,
the Access Point is housed in a grey
plastic box and is fitted with an
omnidirectional antenna at the back.
Also on the back panel are an RJ-45
socket for connection to a standard
network hub, plus an RS-232 socket
which provides alternative connectivity direct to a PC.
The Access Point also comes with
a configuration utility which can be
installed on any machine on the network – either wireless or wired.
Clicking the Scan button in this
utility detects the Access Point and
displays it as shown in Fig.5. You then
assign a temporary IP address to the
Access Point (see Fig.6), after which
you use the Access Point’s built in
web server to assign a permanent address and to make other configuration
changes (Fig.7).
Alternatively, you can configure the
Access Point to obtain its IP address
from a DHCP server on the network.
The bottom line
We tested the system by fitting
wireless PCMCIA cards to two computers – one a laptop, the other a conventional PC (via the PC Card Drive).
To complete the setup, we plugged
an Access Point into the hub on our
wired network.
Initially, we set the mode to Adhoc
so that we could test the wireless network between the two computers fitted
with the PCMCIA cards. The network
came straight up – no problems.
We then set the mode to Infrastructure” and scanned for the Access
Point. It too came straight up and after
running the configuration software,
we had access between the wireless
machines and the wired segment of
the LAN.
In short, it all worked – what more
can we say?
Cost and availability
Fig.7: the Access Point comes with an inbuilt web server. This lets you change
the configuration settings, including assigning a permanent IP address, subnet
mask and default gateway. The IP can also be obtained from a DHCP server.
Unfortunately, you’re still paying
for the R&D for this type of gear, so
it’s not exactly as “cheap as chips”. At
the time of writing, the Access Point
(Cat. 11339) was priced at $1155;
the Wireless LAN PCMCIA card
(Cat.11340) at $490; and the Wireless
LAN PCMCIA-to-PCI Station Adapter
(Cat.11344) at $79 (prices include
GST).
The PC Card Drive (Cat.6523) retails for $259 but note that you don’t
need this card unless you want to
fit other types of PCMCIA cards to
a PC. Normally, you would use the
much cheaper PCMCIA-to-PCI Station
Adapter instead.
Further information is available
from MicroGram Computers, Unit
1, 14 Bon Mace Close, Berkeley Vale
2261. Phone (02) 4389 8444. Their
website is at www.mgram.com.au or
you can email info<at>mgram.com.au
SC
for up-to-date pricing.
January 2001 35
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