Wireless Networking
1.0 About Wireless
2.0 Wireless Terms
3.0 Wireless Security
4.0 Wireless Products
5.0 Wireless Troubleshooting
6.0 Other Wireless Resources
1.0 About Wireless
1.1 What is Wireless Networking?
1.2 Why go Wireless?
1.3 Are there any disadvantages to Wireless?
1.4 How far can Wireless go?
1.5 Which is better. Cables or Wireless?
1.6 Will Wireless be fast enough for my Broadband
connection?
1.7 What do I need to buy to set up a Wireless network?
1.8 Do I have to buy the same brand of Wireless Network
cards and WAP?
1.9 Do I really need a Wireless Router or WAP to
set up a Wireless Network?
1.10 What are the minimum system requirements for
Wireless?
1.11 Are there any other Wireless Adapters besides
Airport for Macintosh?
1.12 What is Wireless Broadband?
1.13 What's the difference between 802.11A, B &
G?
1.14 What frequencies does Wireless use?
1.15 Will Wireless Networking conflict with my Cordless
Phone?
1.16 Are Wireless devices a health risk?
1.17 Can I use a Wireless Router just as a WAP?
1.1 What is Wireless Networking?
Traditionally Computers have been put together in Networks with cables
using hubs or switches to join them all together. Wireless Networking
is exactly the same in concept, except instead of the Ethernet cards &
cables we have Wireless Network cards, and instead of hubs and switches
we have a Wireless Access Point or Wireless Router.
The only difference is in the configuration to set up the extra security
precautions necessary to prevent your neighbours and people passing by
from accessing your Network and/or Internet connection.
1.2 Why go Wireless?
Convenience & Portability.
Wireless PCs are only dependant on having access to power, so furniture
rearranging or changing rooms no longer has to consider the position of
a data socket. Perfect for those in a temporary or leased premises where
drilling holes in walls and running cables all over the place would both
really annoy the landlord and also waste money if it all has to be ripped
out and/or reinstalled at a new premises when you move.
There's also something magical about surfing the Internet at the poolside
or back deck, or having full access to Network resources in the Boardroom
without having to drag cables all over the place.
Some buildings may be next to impossible to cable (or extremely expensive)
or have a Heritage listing that puts cabling out of the question, or maybe
just having Cables and/or ducting all over the place would not be aesthetically
pleasing.
Most Wireless networks I have set up have a combination of Wired &
Wireless segments anyway to take advantage of the benefits of both where
possible. Wireless Routers and Access points make integrating the Wired
& Wireless segments a no-brainer.
Whilst cables are generally faster for transferring data between computers
at this stage, wireless equipment has come down so much in price that
it is now a serious contender and often cheaper overall than running cables.
Apart from DIYs, average cost per PC to Cable, including sockets, cable
and Network card would generally run somewhere between $140-250.00 per
PC. In comparison, Wireless Network Cards start at around $50.00 and nothing
else is required apart from a Wireless Router or Access Point.
1.3 Are there any disadvantages to Wireless?
Where wireless has its limitations is in its range, penetration, comparative
speed and its security considerations.
Wireless works best with "line of sight" but it can penetrate
some obstacles with reasonable success. Steel framed homes and concrete
structures are generally not particularly wireless friendly but even with
these I've occasionally found some amazing performance (to my surprise).
This effect occurs because Wireless signals can bounce around and reflect
off obstacles to get into various nooks and crannies. I was in one home
where the wireless Router was two concrete floors down and we were still
getting a reliable connection, but then in other homes I've been losing
signal even through one concrete wall or floor.
Speed wise, wireless is a bit slower than cables so may not be suitable
for a large shared database or other bandwidth hungry applications.
With Security, nothing will remain 100% secure forever, so if you're in
an office with sensitive data on your PCs and a public carpark within
metres, it may be worthwhile reconsidering a decision to go wireless.
At the very least consider that this isn't a DIY job and a proper Network
consultant should be brought in to recommend the right product/s with
the right security features and to set up proper local security policies.
For most other home and small office users, security in this regard isn't
a major problem and I wouldn't lose any sleep worrying about it. The standard
WEP and WPA options are a lot better than many would have you believe
and it takes a very skilled cracker to get past them. Anything untoward
(like a clown parked outside your house pointing
a Pringles can at you) will become obvious pretty quickly and you'll
be able to change WEP keys and/or take action as necessary (eg garden
hose, large dog, half brick etc).
1.4 How far can Wireless go?
Range wise, outdoors, most WAPs and Wireless Routers with standard antennas
will usually go up to around 100 metres with clear line of sight,
but add a wall in the way and this drops considerably. A general rule
of thumb would be 2 to 3 timber framed plaster walls within around 30
metres for most standard products indoors.
Range can be improved with more powerful antennas*
or with the use of Wireless Repeaters or by running
cables to more WAP/s.
If you've struck a hitch with range or penetration there's quite a good
thread in the
Billion forums with lots of helpful tips and links for getting the
most out of your Wireless performance. See also FAQs 2.6
and 4.15 below dealing with gain and antenna selection.
* Be aware that upgrading antennas to improve range or building an
outdoor wireless link can be quite complex with unpredictable results
so it can easily become a very costly & disappointing exercise. For
this reason I cannot give product advice over the phone or by email and
strongly recommend hiring a technician who
specialises in wireless applications to come to your premises for an onsite
consultation to give you a recommendation on what you'll need to buy.
Shane emailed me with a quick and simple change he made to his MR814
Router utilising a saucepan lid to boost the signal (in effect creating
a DIY Parabolic
grid antenna). In his words -
"My wife uses a Centrino note book (older model with b/g WiFi card)
which is located on the upper level of the house at the other end of the
house. The signal strength was average when she was the only person using
the wireless network, however this would almost drop out completely once
the three children were online via each of their ‘b’ wireless card equipped
computers. I looked into an external antenna purchase however the router
did not seem to allow for that option. So based on a UHF antenna that
I made from a stainless steal salad bowl for my parents when I was a teenager
(which served as the household antenna for about 17yrs in country NSW),
I propped a stainless steel saucepan lid behind the router antenna. The
diameter of the lid is such that the tip of the antenna is level with
the centre of the lid. My theory was that the signal emanating from the
antenna was pulsing out in a 360 degree sphere, so maybe the lid would
focus the signal in the direction of my wife’s computer, like a radar
or satellite dish in reverse. Bottom line is that since the lid has been
in place my wife has full 11mb/s signal constantly." Pic - 
Outdoors (without obstructions) range can be quite remarkable with the
right equipment. For example Ips-Mesh
have been doing a lot of experimenting with seeing how far they can get
a wireless link without using amplifiers and so far they've managed a
remarkable 60km.
I had a bit of a hand in bridging two offices approximately
1.5 km apart wirelessly and it worked quite well. The equipment used
there would be pretty much what would be required for any sort of outdoor
wireless link once it goes beyond the range that the standard antennas
can do, but see also Freenet
for some interesting kits for Wireless outdoor bridging on a budget.
Of course there's dozens of places to buy antennas but I think Rob's done
a fantastic job there putting together his "Me and my Mates"
kits to suit various distances. Wayne also reports his cheap outdoor wireless
bridging experiences using DIY antennas - "I've got a couple of
Minitar APb's on a link 0.8km that are performing very well on quite small
BiQuad aerials. I have a moderate cable length at one end 10m CNT400
cable with pigtails. The other end has 5m of 9006 Cellfoil cable with
no pigtails or joins, terminated directly to a rev SMA connector."
If you want to connect your mates next door into your Wireless Network
with standard equipment, you might get away with it but it all
depends on the distance and any material the signal has to pass through.
In my home here I can get 70% signal strength in my Neighbour's house
next door and about 30-40% across the road (in the front rooms), but it's
worth pointing out that my area is extremely wireless friendly for some
reason and the results I get are exceptional compared to what most people
could generally expect.
1.5 Which is better. Cables or Wireless?
Cables are faster (at the time of writing) and more secure, but may involve
drilling and aesthetic changes to the premises to get the cables where
they need to go.
Wireless is portable and more convenient but may not have the range and
penetration necessary to extend through your whole premises.
Many homes and businesses will often find a combination of both to be
the go. My office at
OzTechnologies.com has the desktop PCs cabled
through a mini-rack and then a couple of laptops connect to the Network
wirelessly through a wireless Router.
1.6 Will Wireless be fast enough for my Broadband
connection?
The fastest ADSL connection at the time of writing is 1500kbs*
Cable Internet can go up to around 9000kbs (from some local sites).
802.11B wireless will max out at around 5-6000kbs.
802.11G wireless can go up to 18-22000kbs.
Super 802.11G can go up to 38-42000kbs.
A 100mbs Cabled network will average around 95000kbs (if set up properly
with the right equipment).
* Since the advent of ADSL2 & 2+ there
are now many ADSL plans that can go well in excess of 1500kbs, sometimes
even faster than cable internet!
So, you can see from this that except in the case of some sites on a
Cable Internet connection (or ADSL2/2+), even the slowest (802.11B) wireless
connection will be more than adequate. Where the faster wireless gear
comes into its own is in sending and receiving files across the local
network and/or accessing a shared database on a central server, particularly
if there are several Wireless PCs in operation at any given time.
However, 802.11G costs only marginally more than 802.11B so it's probably
worth spending that bit extra to get the faster Wireless speeds anyway.
I find at my online
shop that sales of 802.11G products outstrip the 802.11B products
by about 3 to 1.
1.7 What do I need to buy to set up a Wireless
network?
You will need a Wireless Router or Access
Point* and a Wireless PCI Card or USB
Adapter for each Desktop PC you want to be wireless, and a Wireless
PCMCIA card or USB Adapter for each Laptop PC you
want to be wireless. Bearing in mind that just because you're installing
a Wireless Router, all of the PCs don't necessarily have to be Wireless.
Wireless Routers also usually include a built-in 4 port switch so you
can run a combination of wired and wireless PCs on the network. It makes
no difference to Network browsing whether a PC is wireless or wired and
you'll probably find that you've got at least one PC that lives right
beside where the Router is, so there's not a lot of point making that
one Wireless if it never moves and a 2m patch lead and $20.00 non-wireless
Network card will do the trick.
* Wireless Routers share the Internet and have a built-in Access Point,
while a Wireless Access Point just provides the means to connect the PCs
wirelessly and does not share the Internet by itself. For more on this
see the Wireless Products section below.
1.8 Do I have to buy the same brand of Wireless
Network cards and WAP?
It's generally recommended that you stick with the same brands if possible
as there may be some features that a manufacturer has introduced for their
range that may not be usable if you mix the brands up (eg D-Link 256 bit
WEP encryption).
However, wireless standards and protocols are universal so conflicts are
fairly rare. I use the same Netgear, D-Link, Linksys and Minitar cards
to test out dozens of Wireless products and have never had an issue, and
I sell lots of various brands of Wireless Routers to Macintosh owners
using Airport cards, & people who've bought Laptops with Wireless
cards built into them, and they're all happy.
What you do have to watch though is mixing up brands and/or models with
specialised adaptations of wireless standards.
Some examples of this are -
No, but you're better off if you do. A Wireless Router or Access Point
will provide better range and reliability than an Ad-Hoc
Network, plus it's a lot less complicated to install.
If you're really keen on setting up Internet Sharing without a WAP or
Router, see timhiggins.com.
1.10 What are the minimum system requirements
for Wireless?
If your PC is more than 2 years old, carefully check the Wireless adapter
manufacturer's specifications for minimum system requirements before you
buy. Software wise, in most cases a minimum of Windows 98 Second Edition
(not 1st edition) is required to be able to install a wireless adapter
but there's also hardware issues with many products. Eg Many PCI cards
particularly with Prism 2 & Broadcom chipsets found in many Netgears,
D-Links, Minitars, SMCs and more, require V2.2 PCI compliant Motherboard
usually found in boards P3 and above, running in 3.3V mode. (5.0V PCI
mode won't work.)
Most PCMCIA cards (for Laptops) require a 32 bit cardbus. All Laptops
made in the last couple of years have this standard but really old ones
have a 16bit card bus so you'll have to hunt around a 16bit card. (16bit
cards are a dying breed and most that I know of are discontinued models
that just haven't sold out yet).
SiSoft Sandra
is a useful tool to find out the nitty gritty parts of your PC if you
have no idea what you've got.
1.11 Are there any other Wireless Adapters besides
Airport for Macintosh?
You should generally stick with whatever your Macintosh supplier recommends,
but if you're a DIY type and feeling adventurous, check out the
OrangeWare drivers. These offer driver support for other manufacturer's
wireless adapters so you will probably save a few dollars there, but there's
also support for 108mbs equipment which you can't get from Apple just
yet.
 Bear in mind that
these drivers are independent to Macintosh and the Wireless adapter manufacturers,
so there's no guarantees they they will work and any possible damage isn't
likely to be covered under either manufacturer's warranty.
1.12 What is Wireless Broadband?
Wireless Broadband is a term used to describe 3 quite different services.
The first is where a plain old Cable or ADSL service is broadcast
throughout a home or office using a Wireless Router
or Access Point. Any existing Cable or ADSL plan can
be made Wireless in this manner by adding a Wireless Router or Access
Point to an existing modem, or by replacing the existing modem with a
Wireless Router that includes a built-in modem.
Second is a service similar to Microwave Pay TV where Broadband
is received at your premises via an antenna. Price wise, ongoing costs
are a little more expensive than ADSL or Cable but installation costs
can be quite high due to the cost of the Antenna, the receiver and the
installation.
Third is a mobile Broadband service provided (so far) by unwired.com.au
and iBurst.com.au
and resold by several other ISPs. Coverage at the moment is limited to
areas around Sydney but will extend to other States in due course. Pricing
is similar to other broadband services but top download speed at this
stage is restricted to 1028kbs (Around 130 Kbytes/sec). The truly neat
part of this service is that the modem is portable, so you can take it
with you to a new address or even out in the field and still have service
(if in range). The unwired modem even has a rechargeable battery available.
See the Whirlpool
forums for discussion about Aussie wireless ISPs.
1.13 What's the difference between 802.11 A,
B & G?
802.11a runs in the 5gHz frequency range and will allow data speeds
of up to 108 mbs. The shorter wavelength of the 5gHz frequency greatly
reduces its range and penetration but it comes into it's own in areas
where it might be overcrowded or have other equipment (eg medical) operating
in the 2.4 gHz range. Its lower performance and comparitively hefty price
tag have made it fairly unpopular in Australia and it's now quite rare
to see products on the market ultilising the 802.11a standard.
802.11b operates in the 2.4gHz frequency range and was an advance
that led to wireless networking becoming popular and viable in Australia.
It promised throughput speeds of 11 mbs but as with all wireless technologies
you can at least halve the manufacturer's figures for true throughput
results using a network tool such as Qcheck.
Range can be anything up to 100 metres with clear line of sight with most
products out of the box but can be extended substantially with aftermarket
antennas and boosters.
802.11b+ operates in the 2.4gHz frequency range and was a variation
of 802.11b chipset used by D-Link in particular. It doubled the throughput
figures but would fall back to plain 802.11b speeds when used with other
wireless standards including the modern ones like 802.11g & n. See
also FAQ 2.15 below.
802.11g operates in the 2.4gHz frequency range and took wireless
speeds up to 54 mbs and with a bit more throughput to play with it effectively
extended the range a little bit too. It remains a popular and cost effective
choice.
802.11g+ operates in the 2.4gHz frequency range and was a variation
on the 802.11g chipsets that effectively doubled the data speeds. However,
when used in conjunction with 802.11g or n products it will fall back
to standard 802.11g speeds. See FAQs 2.16 & 2.17
below.
802.11n operates in the 2.4gHz & 5gHz frequency ranges and
at the time of writing allows speeds of up to 300 mbs (but that might
even double in the near future). Range is also greatly improved but the
corresponding wireless adapters must be used to get anything like the
promised performance. See also FAQ 2.20 below.
The table below shows data speeds you can expect when mixing and matching
products with different wireless standards.
| |
802.11a |
802.11b |
802.11b+ |
802.11g |
802.11g+ |
802.11n |
| 802.11a |
Up to 108mbs |
Not compatible |
Not compatible |
Not compatible |
Not compatible |
Not compatible |
| 802.11b |
Not compatible |
11mbs |
11mbs |
11mbs |
11mbs |
11mbs |
| 802.11b+ |
Not compatible |
11mbs |
22mbs |
11mbs |
11mbs |
11mbs |
| 802.11g |
Not compatible |
11mbs |
11mbs |
54mbs |
54mbs |
54mbs |
| 802.11g+ |
Not compatible |
11mbs |
11mbs |
54mbs |
108mbs |
54mbs |
| 802.11n |
Not compatible |
11mbs |
11mbs |
54mbs |
54mbs |
Up to 300mbs |
For more information see IEEE
802.11 in wikipedia.
1.14 What frequencies does Wireless use?
The table below shows some common uses of frequencies across the Radio
Frequency spectrum.
| 802.20 Wireless WAN |
|
|
|
|
|
|
<3.5gHz |
|
| 802.16 WiMAX (Metro Area LAN) |
|
|
|
|
|
2gHz-
|
11gHz, 10gHz |
-66gHz |
| 802.15 Bluetooth |
|
|
|
|
|
2.4-2.48gHz |
|
|
|
802.11B/B+
|
|
|
|
|
|
2.4gHz |
|
|
|
802.11G/G+
|
|
|
|
|
|
2.4gHz |
|
|
|
802.11A
|
|
|
|
|
|
|
5gHz |
|
|
Microwave Oven
|
|
|
|
|
|
|
|
|
|
Mobile Phones
|
|
|
|
|
|
|
|
|
|
Cordless Phones
|
|
|
|
|
|
|
|
|
|
Remote Control Toys
|
|
|
|
|
|
|
|
|
|
Baby Monitors
|
|
|
|
|
|
|
|
|
|
Short-wave Radio
|
|
|
|
|
|
|
|
|
|
Marine Radio
|
|
|
|
|
|
|
|
|
|
CB Radio
|
|
|
|
|
|
|
|
|
|
TV Stations
|
|
|
|
|
|
|
|
|
|
Radio Stations
|
|
|
|
|
|
|
|
|
|
Radio Navigation Beacon
|
|
|
|
|
|
|
|
|
| Omega Navigation |
|
|
|
|
|
|
|
|
|
240v Power (EMF)
|
|
|
|
|
|
|
|
|
| Human Brain Waves (EEG) |
|
|
|
|
|
|
|
|
| |
|
Band
|
VLF |
LF |
MF |
HF |
VHF |
UHF |
SHF |
EHF |
| Very Low Frequency |
Low Frequency |
Medium Frequency |
High Frequency |
Very High Frequency |
Ultra High Frequency |
Super High Frequency |
Extremely High Frequency |
|
Frequency Range
|
3kHz - 30kHz |
30kHz - 300kHz |
300kHz - 3mHz |
3mHz - 30mHz |
30mHz - 300mHz |
300mHz - 3gHz |
3gHz - 30gHz |
30gHz - 300gHz |
1.15 Will Wireless Networking conflict with
my Cordless Phone?
Not likely, although it has been known to happen occasionally*. I know
of one report where a Wireless network was known to drop out whenever
a certain cordless phone rang, but I've installed and sold hundreds (maybe
thousands) of wireless products and it has never come up for me personally.
I have a cordless phone less than a meter from where I test wireless Routers
and WAPs, and although frequencies vary between brands and models of cordless
phones, if it was going to be a common issue it would have come up frequently
by now. In any case, wireless products come with the ability to change
the Wireless channel so you can move it to a different frequency if you
do strike a problem.
However, I do have a baby monitor in my home that seems to upset a few
Wireless Routers on channel six for some reason. Other products are fine
with it so it's a bit of a mystery. Symptoms in this case are poor signal
strength, frequent dropouts, packet loss (from ping
test) and sometimes not even showing up in a scan for Wireless devices
using the Wireless Configuration Utility.
* Wayne reports "I have a Panasonic KX-TG2570ALS that
caused my wireless to drop out on a connection to a laptop. If the phone
is closer than 3m while in use it adversely effects the laptop's wireless
connection. This is a bit of a downer because I was using the laptop to
provide information while on the phone outside on the patio. It meant
moving in to a fixed line phone to regain the network connection."
1.16 Are Wireless devices a health risk?
In a nutshell - no.
Wireless devices and their emissions are strictly policed and tested by
the FCC in America and
ACA here for possible
health risks, and there's also many logical conclusions that can be drawn
from the chart above -
1. 802.11B/G devices use similar radio frequencies to common household
appliances like Baby Monitors and Microwave ovens, so if there
was a problem these would be banned by now or there'd at least be a media
storm about it.
2. We're constantly bombarded with TV & Radio station signals at similar
frequencies as well. If anything, these would be more dangerous as they're
considerably more powerful than these little home Networking devices.
However, you may notice that mobile phones also fall into a similar radio
frequency and these have come under suspicion for possible health risks,
but there are some major differences between mobile phones and Wireless
computer gear. For one, tumours that have been attributed to mobile phone
use are usually found around the ears and other areas where a mobile phone
is commonly held especially while ringing (eg on the hip). This indicates
that the danger is in having these devices close to the skin while they
are broadcasting, and you wouldn't normally walk around with a Wireless
Router stuck on the side of your head. Research
tends to blame the slight heating effects from Radio Frequency Radiation
when the device is held on the body, forcing the radiation to travel through
the body rather than reflecting off it as it would normally, plus mobile
phones have a considerably stronger output signal as well.
However, I would not be so quick to give a thumbs up for "zero risk"
once people start to modify products to increase their output signals
with super high gain antennas or adding amplifiers to the wireless output.
Andrew
Clapp has a bit to say on this topic with his home built antenna design.
1.17 Can I use a Wireless Router just as a WAP?
Yes, all that's needed is to disable the router features. This involves
3 things:
1. Don't plug anything into the Internet (WAN) port
2. Disable its DHCP server
3. Set its IP address in the same range as your existing network. As an
example, your other router which is connected to the Internet (hereafter
called the Gateway) has an IP address of 192.168.1.1 and your PCs have
IP addresses of 192.168.1.2 onwards. (In this example the Gateway's DHCP
server has been set to issue IP address of 192.168.1.2 to 192.168.1.100.)
After you've disabled the Wireless Router's DHCP server, give it an IP
address using the same first three octets (192.168.1.) but a different
last number below 255 but outside the Gateway's DHCP range. ie Anything
from 192.168.1.101 to 192.168.1.254. (To access the Router's menu now
you'll need to go to its new IP address. eg http://192.168.1.101).
With these 3 things in place, any wireless PC will connect and bridge
through the wireless router to the Gateway for its Internet access.
This is what a Netgear WPN824 looks like configured as a WAP under the
LAN IP Setup section -
Note new LAN IP address and "Use Router as DHCP Server" is unchecked.
Note: For the difference between a Wireless Router and a WAP
see the Wireless Products section below.
2.0 Wireless Terms
2.1 What is Ad-Hoc mode?
2.2 What is Infrastructure mode?
2.3 What is DBi?
2.4 What is DBm?
2.5 What is EIRP?
2.6 What is antenna gain?
2.7 What is the Fresnel Zone?
2.8 What is Mw?
2.9 What is SSID?
2.10 What is a wireless configuration utility?
2.11 What is XP's WZC?
2.12 What is WDS?
2.13 What is WLAN?
2.14 What is a Wireless Hotspot?
2.15 What is D-Link's 802.11B Enhanced Equipment?
2.16 What is D-Link's XtremeG?
2.17 What is Netgear's "Super G"?
2.18 What is SpeedBooster?
2.19 What is Netgear's XR Technology?
2.20 What is MIMO/Pre-N?
2.1 What is Ad-Hoc mode?
Ad-Hoc is peer to peer networking. ie The Wireless PCs connect to each
other rather than to a central access point. eg PC1 connects to PC2, PC2
connects to PC3 etc. Great for setting up a quick wireless LAN to share
some files with others, but on the downside it gets very difficult to
manage and throughput becomes worse and worse as the number of wireless
devices increases. It's also very difficult to bridge to the wired LAN
this way and/or setup Internet Sharing with more than one other wireless
PC.
Where Ad Hoc Wireless is most interesting is in the large scale peer to
peer "Mesh" Wireless Community projects where a bunch of homes
function as "nodes" to extend the range of the mesh far and
wide. See links to Wireless Community Groups below.
2.2 What is Infrastructure mode?
Infrastructure is the most common form of Wireless Networking where all
of the PCs connect to a central Access Point.
2.3 What is dBi?
dB is decibel. dBi is a comparative ratio and refers to "Decibels
compared to an isotropic* antenna".
Basically it's an industry term used to describe the "gain"
of an antenna.
* An Isotropic Antenna is a theoretical "standard" antenna
which has an equal broadcast of 360° in all directions.
2.4 What is dBm?
dBm is another ratio and is decibels compared to 1 milliwatt which is
an industry term used to describe the transmit or receive power of a wireless
device.
2.5 What is EIRP?
Effective Isotropic Radiated Power.
EIRP = dBm + Antenna Gain - line Loss
Yet another ratio. This one expresses the overall result of the transmission
power of a Wireless product combined with its antenna's gain. It comes
in handy for working out if your combination of products and/or modifications
are going to be legal or not (Ignorance is no excuse and you'll get fined
anyway if you blow the EIRP, and they do drive around scanning for infringements
too).
For a practical example of how to use EIRP check out Benelec's
EIRP calculator.
If we go to the
Bi-directional Amplifier section we can start by adding in the Transmission
power of our Wireless Access point, add in the length of all our leads,
add in the transmission power of the Amplifier and lastly the proposed
antenna gain and it comes up with our EIRP in dBm. Up the top of the page
it shows the Australian legal maximums on the various radio channels,
and the idea is to get as close to these as possible without going over.
Notice that on channels 1-9 we can go up to 4 watts. I think in the USA
they're allowed 2 watts and around half that again in the UK. (Wireless
congestion isn't as much of an issue here which is why we're allowed so
much more power.)
TV and radio stations broadcast at anything from a couple of hundred to
several thousand Watts. To broadcast at these levels you need a license
and an allocated frequency.
2.6 What is antenna gain?
Many people conclude that antenna gain is the power of the antenna, but
they'd be wrong. The only way to make an antenna "more powerful"
as such, is to increase the amount of power feeding into it. Gain is more
correctly thought of as the characteristics of the antenna as a relationship
(expressed in dBi) to a theoretical "standard" antenna which
has an equal broadcast of 360° in all directions.
To explain further, in the figures below the circles represent the broadcast
pattern of the two antennas in a vertical cross section. For the sake
of argument we'll say that the Low Gain antenna is our "isotropic"
0 dBi gain antenna (with the theoretical perfect 360° broadcast in
all directions) and the Higher Gain antenna has a 5 dBi gain. What we've
done by increasing the gain is to focus the broadcast pattern in a more
concentrated area so that there's less vertical coverage but it extends
further out horizontally. Useful for example in a large low set house
where you don't really need to service a 2nd or 3rd floor above but might
be having trouble getting good signal at the other end of the house. (Note:
My testing of 2.5 dBi vs 5 dBi antennas shows a general
increase in range of between 10-20% with the 5 dBi so we're not talking
about a huge change here, but it may be enough to get around a problem
area if the signal is there but a little choppy to be usable.)
Note: My diagrams are nothing like reality due to my limited drawing
skills. The broadcast patterns are more of a donut shape if shown in a
3d view. Benelec
have quite a good little article with better diagrams here if you'd
like to do some more reading on this subject.
Note 2: What most people want to know is "How does this
equate to distance?". Hopefully this description of gain will go
some way to explaining why I tend to run away screaming from that one.
The answer is the proverbial "How long is a piece of string?".
There's the transmission power of the WAP, environmental variables and
the receive power/EIRP at the other end, the Fresnel Zone etc etc, so
it's just impossible or at least extremely difficult (at least for me)
to answer accurately. The best answer you'll probably get from anywhere
is "the closer you can get to the maximum legal EIRP you can get,
the more likely it is to work" but as to how far the signal can go
in terms of metres or kilometres is anyone's guess. However, most technicians
who specialise in Wireless will have a selection of products they commonly
deal with and they'll have a good idea of what to expect from these in
a given situation, but quite often it's a trial and error process (erring
heavily on the side of overkill if the gear has to be purchased up front).
2.7 What is the Fresnel Zone?
Named after the scientist who first documented it, Dr Clarence Zone.
(Sorry, couldn't resist that one.) It's actually named after 19th century
French physicist Augustin-Jean Fresnel and defines the line of sight area,
taking into account any obstacles. Basically it's a scientific way of
working out what antenna gain and mast height will be required to get
optimum signal from one wireless point to another.
Zytrax have a useful Fresnel
Zone calculator. Basically you tell it the distance you need to cover
all up and then the distance to the first obstacle, and it works out what
mast height you need for optimum wireless signal. It also takes into account
curvature of the earth and so on, so it's not the kind of thing that will
be useful for a simple home Network, but I think it's worth mentioning
here for the sake of explaining Wireless signal characteristics a bit
better. eg In my dodgy diagram above we can see that simple line of sight
could have been achieved with a much shorter mast but then the house in
the middle would have been extending into the Fresnel Zone and adversely
effecting wireless performance. The same principle can be applied if,
for example, there was a bank of metal filing cabinets in between the
Wireless Router and the PC the signal had to travel to, or if there are
too many walls in between. Higher is better in this case, so maybe moving
the Router to the second floor or up in the roof will service the area
you need to cover much better. I have a high set home with the living
areas upstairs so I find I get better overall coverage by having the wireless
router on the bottom floor.
2.8 What is Mw?
Milliwatts. The unit of measure used to express the transmission power
of amplifiers.
2.9 What is SSID?
Service Set Identifier. Also sometimes called BSSID and ESSID depending
on what particular Network subset it is identifying, but for us laymen
we'll just ignore all that and assume they all mean the same thing.
Basically Wireless Access Points and Routers have a name that they broadcast
out by default so that wireless devices can identify them in order to
know what or who they're connecting to. eg Let's say a product's SSID
is "Netgear WAP". The Access point will Broadcast it's name
every few seconds saying something in computer-speak like "Hi, my
name is Netgear WAP. To connect to me, please ask for Netgear WAP.".
All Wireless Routers and WAPs have a default SSID (and it isn't hard to
find out what they are, even with a quick Google) so it's generally recommended
that you at least change the SSID to something else. Even better is to
disable the SSID broadcast if you can. Of course, this means creating
a profile in your PC's Wireless configuration utility specifying the SSID,
but the advantage in doing this is that it makes it that much harder for
an unauthorised person to connect to your Wireless network. The theory
being, if they don't know what the name is, they can't configure their
Wireless configuration utilities to connect to it. However, it's not regarded
as a proper security precaution as a hardened cracker may be able to capture
this information (eventually) from the signals your Wireless PC sends
out while looking for the WAP or Router, or use the
rogue Access Point method to get one of your PCs to connect to it
and give away the information.
2.10 What is a wireless configuration utility?
A wireless configuration utility is an application that runs on your
Wireless PC that is used to scan for WAPs to connect to and to configure
the wireless security settings. Most utilities have the ability to create
"Wireless Profiles" so you don't have to go through configuring
all of the Security and Network information each time you reboot the PC.
2.11 What is XP's WZC?
With the popularity of Wireless, Microsoft decided to include a Wireless
Configuration Utility into Windows XP which they named the Wireless
Zero Configuration utility. Great stuff, however it can be a bit of
a pain because the Wireless Adapter manufacturers usually include their
own Wireless Utility with the drivers, and running both at the same time
will usually cause some bad behaviour like being unable to locate or connect
to a WAP or Router, or suffer from frequent dropouts.
Some people recommend disabling the WZC service completely (Right-click
My Computer > Manage > Services and Applications > Services)
but I've found that this can also play havoc with some manufacturer's
utilities as well, so the best option is just to untick the option for
Windows to control the Wireless device.
To do this, go to Control Panel > Network Connections. Right Click
on the icon for the Wireless Card and select properties. Select the Wireless
Networks Tab and untick the box entitled "Use Windows to configure
my wireless network settings".
Note: If the Wireless Network tab isn't visible, see the
troubleshooting section below.
2.12 What is WDS?
Wireless Distribution System.
An option available in some wireless devices to allow a wireless device
to act as both a Wireless Client and an Wireless Access Point at the same
time. In other words, it can receive a signal from another WAP and re-transmit
it. A useful feature for extending the range of a Wireless Network but
it does have a drawback in that throughput (speed) is pretty much halved.
Be aware also that I get a lot of reports of WDS having compatibility
problems between differing manufacturers, and even different models from
the same manufacturer. WDS is a great feature to have and it's well worth
spending a little more on a product that does have WDS just in case you
do strike a problem with range, but read the specifications carefully
before you buy so you get the right products and don't accidently strike
a compatibility problem.
See also Wireless Repeaters below.
2.13 What is WLAN?
Wireless Local Area Network. (Your Wireless Network.)
2.14 What is a Wireless Hotspot?
A Wireless Hotspot is a place where you can BYO wireless PC or PDA and
get Internet Access. Many Cafes now provide a Wireless Hotspot and the
service can be either free or paid or reserved for customer use.
There's also subscription based services at multiple locations such as
those provided by Telstra
and Optus.
And then there's the unofficial Wireless Hotspots known to WarDrivers
which are the poor saps that haven't secured their Wireless Networks properly...
2.15 What is D-Link's 802.11B Enhanced equipment?
802.11B Enhanced is a variation of plain old 802.11B 11mbs wireless which
allows double (22mbs) Wireless data speeds. ( True throughput is closer
to 8-10mbs which is still faster than most Broadband Internet connections.)
Several other manufacturers like Alloy and SMC also adopted this chipset
in a few products. The main advantage is it's about the same price as
an equivalent 802.11B product (usually cheap as chips) and is backwards
compatible with standard 802.11B products, however, if used with standard
802.11B products the speed will fall back to 11mbs (around 5mbs in true
throughput).
2.16 What is D-Link's XtremeG?
XtremeG is D-Link's version of 108mbs Wireless which is marketed under
various other names with other manufacturers. It is fully backwards compatible
with normal 802.11B and 802.11G products but will fall back to these slower
speeds if used with these slower products. To get the 108Mpbs wireless
you must use all XtremeG products on your Wireless Network. One 54mbs
product on the Network will cause the whole Network to operate at 54mbs.
It's also not very friendly with 802.11B Enhanced (22mbs) products. These
will usually fall back to 11mbs but sometimes won't work very well at
all with poor range, really slow speeds and poor reliability sometimes
reported.
True throughput is around 40mbs which is fantastic compared to 802.11B
and quite noticeable when browsing the Network or using shared resources.
One disadvantage due to the "channel bonding" technology that
allows 108mbs speeds is that it only works on Radio Channel 6 which can
be a bit of a pain if you have other Wireless Networks nearby (neighbours
etc) already using that channel. Most of the time it's not much of a problem
but occasionally the interference can cause poor range and frequent dropouts.
2.17 What is Netgear's "Super G"?
Same as D-Link's XtremeG above.
2.18 What is SpeedBooster?
Speedbooster is Linksys's version of enhanced 802.11G. While it only
promises an increase in speed of up to 35% which is a bit slower than
the Netgear & D-Link versions, it doesn't use channel bonding so isn't
restricted to any particular Wireless channel. It is also copes with mixed
modes (combinations of standard 802.11G and even 802.11B products) better.
To get the extra 35% speeds you must use Speedbooster Wireless Network
cards as well as the Router/WAP. Otherwise the data speed will fall back
to the fastest speed the card is capable of. Also, being a proprietary
Wireless adaptation means that if you use other brand 802.11G enhanced
products with a Speedbooster Router or WAP, the speed will fall back to
54mbs max.
2.19 What is Netgear's XR Technology?
Netgear's XR (Extended Range) technology doesn't actually boost the signal
as the name might indicate. What it does is allow reliable connections
at weaker signals by trading distance for throughput. In other words,
as the distance increases (or signal strength decreases) it steps the
speed back rather than just dropping out. It works very well and is available
on most Netgear 108mbs products including WGT624,
WGT634U, WGU624,
WG111T, WG311T, WG511T, WG511U, WAG311 & WAG511.
Click
here for a press release from Atheros announcing the new XR and "Double
108mbs" technology.
Note: To allow XR to work, you must choose an auto Wireless mode and not
"108mb only" or "11mb only".
2.20 What is MIMO/Pre-N?
MIMO stands for Multiple Input Multiple Output and is a new Wireless
technology characterised by 3 or more antennas.
Pre-N is Belkin's name for their product (1st MIMO product to hit the
market) and stands for "precedes 802.11n".
MIMO is a smarter and more powerful Wireless chipset which can provide
greater range than ever before, negating the need for multiple WAPs needed
in many current Wireless installations. Tom's
Networking has a quick reference table of the 3 new chipsets from
Airgo, Video54 and Atheros.
See the Router Review section for reviews
of MIMO products.
3.0 Wireless Security
3.1 What is Wardriving?
3.2 What is Mac Address Authentication?
3.3 How do I use Mac Address Authentication?
3.4 Is Mac Address Authentication effective?
3.5 What is WEP?
3.6 How do I use WEP?
3.7 Is WEP effective?
3.8 What is WPA?
3.9 How do I use WPA?
3.10 Is WPA effective?
3.11 Is hiding SSID good for security?
3.12 Can VPN be used to secure a Wireless Network?
3.1 What is Wardriving?
Wardriving is
an enthusiast hobby that involves driving around in a car (or Taxi, Bicycle,
on foot etc) with a wireless Laptop or PDA and recording the Wireless
Access points discovered. There is obviously a less than honourable element
that will try to utilise any Wireless connection they find to gain
"free" Internet access (at the owner's expense) or steal
software/registration codes or just poke their noses where they don't
belong.
Legally it's a grey area as technically they're in a public area scanning
public radio frequencies and it's very difficult to prove they've accessed
your PCs at all (and usually they wouldn't anyway. It's the Internet connection
that's more interesting).
Many of these characters have the attitude that if people don't secure
their Wireless Networks then they must be deliberately providing a free
Internet (Wireless Hotspot) community service and in many ways they wouldn't
be wrong...
3.2 What is Mac Address Authentication?
Every device that connects to a Network (or the Internet) has a unique
identifying tag called a Mac (Machine) address. Mac address authentication
can be set up on a Router or WAP to either allow only certain specified
Mac addresses (and no others) to connect, or to deny access to certain
Mac addresses.
3.3 How do I use Mac Address Authentication?
To find the Mac address of your PC's Network Card:-
Windows 95 - ME: Click Start > Run > winipcfg <enter>
> More info
Windows 2000/XP: Click Start > Run > CMD <enter> >
ipconfig/all
Tip: If you get all your Wireless PCs connected to the WAP
or Router prior to setting up any security, you'll generally find a very
handy section in the Router or WAP's configuration menus called something
like "Attached Devices" which will display all of the PC's by
name along with their respective Mac addresses.
Then it's simply a matter of turning Mac address authentication on in
the Router's configuration menus (sometime called Access Control and other
similar terms) and specifying which Mac addresses you want to allow or
deny.
3.4 Is Mac Address Authentication effective?
It's actually not bad at all and will cover most situations quite well,
plus it has a minimal overhead so is least likely to impact on the Wireless
network performance. Where it has a weak point is that it is possible
for a hacker to eventually capture enough data floating around the airwaves,
or use the
rogue Access Point method to be able to copy the Mac Address of an
authorised PC to gain access to the Wireless Network. In most cases the
give-away that this has happened will be a PC suddenly and mysteriously
being knocked off the Network.
3.5 What is WEP?
Wireless Equivalent Privacy. The most common method of securing a wireless
network where connection to a Wireless Access point is achieved by specifying
a special key which is a string of random letters and numbers. Similar
in concept to a username and password, WEP keys vary in complexity from
64 bit up to 128 bit and even 256 with some products.
Drawbacks? It does have a bit of an overhead and can take as much as 20%
of the overall throughput (data speed per second). However, most people
would be hard pressed to notice this relatively small drop in performance.
3.6 How do I use WEP?
The Access Point or Router will have a section where you can switch on
WEP and specify a key by use of a passphrase.
However, many products don't have a feature to generate a key from a pass
phrase which can be a bit disconcerting for people at first glance.
Not to worry. There are many WEP key generators online like this one at
andrewscompanies.com.
But it isn't actually that hard to DIY anyway - For 64 bit WEP specify
any 10 digits (choose hexadecimal and not ASCII if given an option) using
any combination 0-9, A-F. 128 bit WEP is 26 digits using any combination
of 0-9, A-F.
On the Wireless PC, open its Wireless Configuration Utility (they're all
much the same in principle but with different layouts).
Specify the same (either 64 or 128 bit) WEP key (or passphrase if you
have that option), save settings and you're away.
Note: If you only have a Wireless PC to work with while setting
up security, remember you need to do the settings on the Router/Access
point first and then your PC second, otherwise it's much the same effect
as painting yourself into a corner...
Here is a quick step by step example using the
basic Billion 5100W and the WEP key generator at http://www.andrewscompanies.com/tools/wep.asp.
1. Go into the Wireless section in the Billion and select 128-bit WEP
from the from the WEP encryption pull down menu.
2. Then at the web link above, click the "generate 128bit key"
button and copy the Hex key it generates at the bottom of the screen.
3. Paste the key into the Billion menu where it says Key1
4. Click Apply to save it. If you're using a wireless PC to do this you'll
drop out at this point but not to worry.
5. Open the Wireless Configuration Utility on your PC. (In this case I'm
using the utility provided by Minitar for their wireless cards but the
principles are similar for all)
6. In the Site Survey, locate the 5100W (SSID is "wlan-ap" by
default) and click on it to highlight it.
7. Click the "Add Profile" button and then select the Authentication
and Security tab.
8. Tick the box beside "Encryption" and change WEP Key type
to "Hexadecimal".
9. Select "128" Bits beside "WEP Key Length" and copy
the key as above beside Key#1
10. Click "OK" and then click the "Activate" button.
If all went well you should get a yellow tick in a green square beside
the profile.
If something went wrong you may have to start over if you're connecting
from a Wireless PC. If you've got a PC plugged into it with a cable you
should be able to retrace your steps, but if you only have a Wireless
PC you'll need to reset the Router using the reset hole at the back (hold
the button down inside the hole with a paper-clip or something for a good
ten seconds) and start from scratch. (Nearly everyone has to have a few
goes the first time they try it before they get it right).
3.7 Is WEP effective?
WEP is ok for stopping neighbours and other general sticky beaks close
enough to pick up your wireless signal from getting into your network
and/or taking advantage of your Internet connection. However, it can be
cracked
in less than 3 minutes by those with the knowledge and tools so I
wouldn't call WEP an effective security method by itself any more.
3.8 What is WPA?
WPA is the latest form of wireless encrytion and has two basic types
of implementation. The first is fairly complex and is more of a corporate
method utilising a "Radius Server" which is only available on
Server operating systems, but WPA-PSK (Pre-shared key) is designed just
for home & small office users who usually DIY, and it's a piece of
cake. Much the same as WEP in that it uses a key to authenticate, WPA-PSK
will automatically change its key every so often which makes it much harder
for an eavesdropper to sniff enough info to attempt to put together the
key.
3.9 How do I use WPA?
WPA is almost identical to set up as WEP and involves specifying either
a keyword (to generate a key) or the key itself using the methods above
for WEP.
The same principle applies for the Wireless PC. Using its Wireless Configuration
Utility, specify the same key, and don't forget if you've only got a Wireless
PC to work from that you'll need to do the Router/ Access Point first
and then your PC.
Note: WPA-PSK is a fairly recent upgrade to many products and
you may need to download the latest firmware and Wireless Configuration
Utilities from the manufacturer if you can't see the option. Windows XP's
WZC utility has a WPA upgrade available through Windows
Update.
3.10 Is WPA effective?
WPA is one of the toughest forms of Wireless Security using encryption,
but it does have a fairly high overhead. Not so much affecting the throughput
(I usually get similar wireless speeds with WPA-PSK as I do with no security)
but more with how much processing power it takes to deal with. Cheaper
WAPs and Routers in theory may start to stall and stutter with as few
as 5-10 active Wireless PCs running WPA, but I'm yet to test this or hear
from anyone who has stressed a Router or WAP out with too many WPA protected
client PCs.
At this stage I have only heard rumours of it being crackable and most
of those centre around using "dictionary
attacks" where people use easy to guess words for their pass-phrases.
3.11 Is hiding SSID good for security?
Hiding SSID is fairly limited as far as security goes. It will make your
WAP "invisible" to a degree to your neighbours and other people
who might innocently discover your wireless network and connect out of
curiosity but it is quite easy to work around for someone with a moderate
amount of knowledge using readily available tools such as Netstumbler
or by using the rogue
Access Point method. There's also evidence to suggest that hiding
SSID might degrade network performance so all in all there's probably
very little to be gained in hiding it.
3.12 Can VPN be used to secure a Wireless Network?
VPN (Virtual Private Network) is usually used to network PCs together
across the Internet where a variety of authentication measures are employed
including encryption and username/passwords in order to secure the connection
so that not just anyone can connect to a VPN server. These same authentication
processes can be utilised to secure a Wireless Network, but you need a
product to support this feature and they're usually fairly expensive (and
complicated to set up).
4.0 Wireless Products
4.1 What is a WAP?
4.2 What is a Wireless Router?
4.3 What is a Wireless Bridge?
4.4 What is a Wireless Client?
4.5 What is a Wireless Media Player?
4.6 What is a Wireless PCI Card?
4.7 What is a Wireless PCMCIA Card?
4.8 What is a Wireless USB Adapter?
4.9 What is a Wireless Compact Flash Card?
4.10 What is a Wireless Repeater?
4.11 What is Power over Ethernet?
4.12 Why would I want a removable antenna?
4.13 Antenna types
4.14 What is a Yagi antenna?
4.15 How do I choose a different Antenna?
4.1 What is a WAP?
Wireless Access Point.
A WAP is to wireless PCs what a switch is to cabled PCs. All it does
is provide a central point for the Wireless PCs to connect to, and allow
for Wireless Security methods like WEP or WPA to be controlled from.
They do NOT connect to an ISP, share an Internet connection or provide
any form of Internet security (Firewall). For that, you'll need a Router
or a software method set up on a PC.
4.2 What is a Wireless Router?
A Wireless Router is a Router with a
WAP built into it, and I'm yet to see one that doesn't also have a built-in
4 port switch so they more or less combine the three devices in the image
above into one. Some also have built-in modems to provide even more cost
and space savings.
Where someone might prefer to keep these devices separate is for larger
Networks or where there are certain desired features only available in
one product that doesn't come with the other options.
4.3 What is a Wireless Bridge?
A Wireless bridge connects two points together wirelessly instead of
using a cable. The bridge can be plugged either directly into a Network
Card in a PC or into a hub or switch and it will function just the same.
The Bridge is generally configured via your Web Browser (the same as
a Router) or using a software tool that the manufacturer provides. Usually
they require specifying the Mac Address of the bridge
that they'll be connecting to and have security options like WEP
available.
Many WAPs and devices sold as bridges can function in several modes -
Bridge to Bridge (As shown in the image above)
Bridge to multi-point (Same as above just with several bridges connecting
together)
Repeater (the 2nd bridge can function as a bridge [receiver] and Access
Point at the same time).
Note: Many bridges, particularly the cheaper ones, only have the
one mode and cannot function as Wireless clients to connect to receive
from another Wireless device other than another bridge of the same brand
and model.
4.4 What is a Wireless Client?
A Wireless Client is a variation of a Wireless Bridge except its job
is to receive a wireless signal rather than broadcasting one like
a WAP or straight bridge does. Many Wireless Bridges can also function
in Wireless Client mode, but not all do so read the spec sheets carefully
before you buy.
A Wireless Client receives from another source, and unlike straight
bridges, they're usually (but not always) compatible with other brands
and models of Wireless Products that can send a Wireless Broadcast.
They're most commonly used to link a remote hub/switch to an existing
network without having to run a cable, and to connect devices like Game
Consoles to the Internet wirelessly.
4.5 What is a Wireless Media Player?
A Wireless Media Player is a device that can find digital media from
networked PCs and then play them on a Home Entertainment System.
See my review of the D-Link DSM-320.
4.6 What is a Wireless PCI Card?
A Wireless PCI Card is fitted to the Motherboard of a Desktop
PC (so that the antenna sticks out of the back) and allows the PC to connect
to a Wireless Access Point or Wireless Router.
Beware of minimum
system requirements when buying PCI adapters.
4.7 What is a Wireless PCMCIA Card?
A Wireless PCMCIA Card goes into the PCMCIA (aka Card Bus) slot of a
Laptop PC and allows it to connect to a Wireless Access Point or
Wireless Router.
Beware of minimum
system requirements when buying PCMCIA adapters.
4.8 What is a Wireless USB Adapter?
A Wireless USB Adapter goes into the USB port of a Laptop or Desktop
PC and allows it to connect to a Wireless Access Point or Wireless Router.
The two shown here do exactly the same job except one can be plugged directly
into a USB port without a cable and the other needs a cable. (Both come
with cables). USB adapters have advantages in that they can be installed
without opening the PC case or using any tools, and if need be they can
be mounted higher off the ground and/or away from the PC to improve the
wireless range by using an extension cable.
Speed wise, if plugged into a USB 2.0 capable Motherboard any throughput
difference will be negligible. However, if you only have a USB1.1 capable
motherboard then a PCI or PCMCIA card will be the better way to go. For
many though, the ease of installation will outweigh any loss of performance
in this situation.
4.9 What is a Wireless Compact Flash Card?
A Wireless Compact Flash Card Card goes into a Palm or PDA
and allows it to connect to a Wireless Access Point or Wireless Router.
4.10 What is a Wireless Repeater?
A Wireless Repeater can receive a wireless signal (like a Wireless Client)
and then rebroadcast it (like a WAP). This is handy for situations where
you might want to extend the range of your Wireless LAN and running a
cable to fit a second WAP is impossible or too expensive.
Note: Some of the more expensive WAPs and/or Bridges have Repeater
modes but bear in mind they usually only work with the same brand and
model WAP as the sending unit.
D-Link have a repeater compatability chart available for their products
here.
I have it on good
authority that the Linksys
WRT54GL running the DD-WRT
open source firmware will work in repeater mode with just about anything.
I haven't tried this one myself and I'm told that configuration isn't
always straight forward and may take a bit of trial and error but you
should be able to get assistance in the forums at DD-WRT
and maybe Whirlpool
if you get stuck.
4.11 What is Power over Ethernet?
Power over Ethernet is basically just sending extra
low voltage power (such as from a power pack) through an ethernet
data cable instead of a conventional power cable. Great for situations
where a power point may not be readily available or perhaps just look
messy. eg wall & ceiling mounted IP cameras or Wireless Access Points
mounted in roof cavities.
Early versions of the technology used two modules, a power inserter and
a receiver, such as the Netgear POE101
(no longer available) or Linksys WAPPOE12. These days the technology is
becoming smarter and many supported devices such as PoE
Switches and many IP
Cameras & Wireless
Access Points now have the applicable input and receive modules already
built into them.
Something to keep an eye out for when purchasing equipment is IEEE
802.3af support. This indicates it adheres to a standard (ie correct
voltage/amps etc) and isn't likely to suffer a compatibility problem.
We'll see more and more products declaring 802.3af support as time goes
by but in the meantime it'll be important to do your homework to ensure
equipment will work together.
4.12 Why would I want a removable antenna?
Having a removable antenna allows for it to be easily upgraded to an
antenna with different broadcast properties. eg To allow an outdoor antenna
to be fitted or even just a higher gain antenna to extend the wireless
range.
4.13 Antenna types
There are two basic types of antennas, Omnidirectional and Directional
(aka unidirectional):
   
Omnidirectional antennas (above) broadcast and receive in all directions
at once and are the standard antennas fitted to WAPs and Routers. They're
available for indoor and outdoor applications and come in all sorts of
designs and levels of "gain". (Note the panel design second
from the left. Similar designs are available as directional antennas,
so read the spec sheets carefully before you buy)
   
Directional antennas (above) broadcast and receive in a single
direction and the broadcast/receive pattern tends to fan out in a cone
shape. The dimensions of this "cone shape" vary according to
the gain and the distance it has to go, and at a certain distance (depending
on the amplification) the outer extremities of the cone shape will die
off leaving the centre as the strongest point. (Picture an oval shape
being stretched out.)
When purchasing an
antenna pay particular attention to the fittings. Most will require an
additional cable. eg Netgear
ANT2405 shows a short cable already on it but it has a male end (the
same as on Routers and WAPs) so will require a female to female cable
in order to be fitted.
4.14 What is a Yagi antenna?
 A "Yagi"
antenna is a directional antenna in a metal grid pattern that looks like
a UHF TV antenna. Sometimes they're housed inside bazooka style casings
to improve the directional abilities.
The name comes from Japanese inventors Hidetsugu
Yagi and his assistant Shintaro Uda who came up with the basic design
in the 1930s.
4.15 How do I choose a different Antenna?
A very tough one to answer (and one I'm loathe to) as the variables are
enormous.
For indoor equipment, upgrading a WAP from a 2.5dbi to a 5 dBi antenna
(cost around $30 - 80.00) will generally yield a 10 - 20% increase in
range, so it's not a huge step up. This increase may be enough to stabilise
a choppy connection with a tendency to drop out, but it's usually not
going to be sufficient to get a PC connected that previously had no signal
at all. eg I found that the position of my DSM-320
required the signal to have to get around (or through) two concrete pillars
to get to the Wireless Router and it would occasionally drop the wireless
link. After upgrading it to a 5dbi antenna (that I nicked from a Billion
7500G demo unit I had here) it stayed totally stable. The chart below
shows measurements in dBm using Netstumbler
comparing a couple of different antennas fitted to a Billion 743GE.
Green is the standard 2.5dBi antenna
Pink is a 5dBi omnidirectional of unknown origins.
Purple is a 5dBi Netgear
ANT2405 panel antenna.
Measurements were taken walking down the street with the laptop with the
743GE inside on the lower floor with signal travelling through one single
brick wall. Line of sight is everything with wireless. The drop at around
20m in the chart above is caused by my driveway going downhill into a
dip so that I started to drop below the radio wave at around that point
and then it came up a bit as I moved further away.
For outdoor wireless, tools like Benelec's
EIRP calculator are invaluable but it's still an area for the experts
as far as I'm concerned. The equipment at this level isn't exactly cheap
and the price varies considerably from one antenna to another, so a few
dollars in the pocket of an experienced technician to consult on the job
will generally save a lot of dollars and wasted time down the track.
5.0 Wireless Troubleshooting
5.1 Can't detect Router or Access Point
5.2 The drivers won't install.
5.3 PC connects to WAP but no data flow
5.4 PC connects but drops out
5.5 "Wireless LAN Card lost" message
5.6 Wireless not working after upgrading XP to SP2.
5.7 Wireless Network Tab not visible under Wireless Card
properties.
5.1 Can't detect Router or Access Point
1. If using XP, check WZC utility is not interfering.
See also 5.7 below.
2. Check under Device Manager for yellow dots indicating the card hasn't
installed properly.
3. Check WLAN is switched on in the WAP and no security is enabled or
SSID has been turned off. (Routers like the D-Link DSL-G604T have Wireless
turned off by default and you need to log in with a patch cable to switch
it on first.)
4. Move the PC and WAP as close as possible together to see if range is
a problem (See this
Billion forum post for a wonderful run through of things to do to
improve range.)
5. The WAP or Wireless Card/PC may be faulty. (The best way to determine
which part might be faulty is to see if another Wireless PC can connect
to the WAP, or if the PC can connect to another WAP.)
6. If you have recently upgraded the Firmware on the Router or WAP, reset
it to factory default settings and reconfigure from scratch.
7. Try different Radio channels on the WAP just in case there's another
Wireless device nearby already using that channel and jamming your signal.
5.2 The drivers won't install.
1. Check the manufacturer's minimum system requirements
to see if your PC and Operating System are compatible with the card.
2. Check the manufacturer's website for driver updates and google
for other people who may have experienced the same problem with that card.
5.3 PC connects to WAP but no data flow
This behaviour is common if WEP or WPA-PSK is enabled on the WAP but
an incorrect pass key is being used to try to connect to it.
If all else fails, uninstall the drivers, reboot and reinstall and/or
reset the Router back to factory default settings.
This is also commonly experienced if XP's WZC utility is enabled while
you have a 3rd | 
