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Wireless Networks
Frequently Asked Questions |
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"I wonder if it will do what I need it to...?"
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General wireless LAN questions
- What is a wireless LAN?
- What are the benefits of
a wireless LAN?
- How does it work?
- What does it cost?
- Will it work with
existing networks?
- What are some typical
wireless LAN configurations?
- How many computers can I
connect to an access point?
- Is it secure?
- What is the range of the
signal and will walls affect the wireless LAN?
- What is "line of
sight"?
Technical wireless LAN questions
- What is "Bluetooth"?
- What is "Wi-Fi"?
- Can I operate Bluetooth
and Wi-Fi together?
- What is CSMA/CA?
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| 1.
What Is A Wireless LAN? |
A wireless LAN is the same as a
normal wired LAN without the cabling. These are replaced with radio
or infrared links that perform the same functions as a traditional
cabled LAN - file and printer sharing, internet access via a hub and
so on.
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| 2.
What Are The Benefits Of A Wireless LAN? |
A wireless LAN is implemented as an
extension to, or as an alternative for, a cabled LAN. Often the use
of cables is impractical and sometimes impossible, in which case
wireless LANs have proven their effectiveness: very portable, no
need to wire every workstation and every room, entire networks can
be easily moved without the requirement for additional wiring, cable
drops or re-configuration of the network. Different LANs at distant
locations can also be connected (called "bridging"), which means
that remote offices can be joined easily through the wireless LAN
infrastructure.
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| 3.
How Does It Work? |
Wireless LANs use radio airwaves to
communicate information from one point to another without relying on
any physical connection. The data being transmitted is superimposed
(modulated) on the radio carrier so that it can be accurately
extracted at the receiving end. An access point converts the wired
Ethernet signals to radio waves and are typically installed in
ceilings or mounted high on a wall. To set up the access point,
simply plug in a phone line from an existing internet connection to
the access point. If an existing Ethernet network exists, you simply
plug the access point into a spare slot in the hub. End users access
the wireless LAN through wireless 802.11 LAN adapters (Network
Interface Cards). These are mostly implemented as PC cards in laptop
computers, PCI cards in desktop computers or as USB devices.
Configure the network with the Wireless Encryption Protocol. Users
then can access the network with speeds of up to 11 Mbps.
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| 4.
How Much Does It Cost? |
As with many projects of this
nature, the cost of implementing a wireless network varies according
to the size of the network and the location(s) to be connected to
it. In general, wireless LANs are roughly the same the price as a
traditional cabled network, but it should be remembered that
wireless LANs are considerably easier to install, minimising
disruption to your organisation. e-Motion IT Solutions can arrange
for a no obligation site survey to ascertain your requirements and
produce a specified report for your organisation including full
pricing details.
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| 5.
Will it work with existing networks? |
Wireless LAN uses a tried and tested
method for networking, Ethernet. Wireless LANs will work on any
existing Ethernet network, the only difference is the lack of cables
from a computer/printer etc. to a hub/router. It operates in the
same manner as a wired Ethernet network in every other aspect.
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| 6.
What are some typical wireless LAN configurations? |
Peer-to-Peer Network :- Ad-Hoc
Mode:
| This is the most
basic wireless LAN configuration, also known as an ad-hoc
network. The wireless LAN consists of two or more PCs equipped
with wireless adapter cards. This forms an independent network
when the clients are within range of each other. In this
configuration, each client would only have access to the
resources of the other client and not to any central server. |
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Clients and Access Point :-
Infrastructure Mode:
| This wireless LAN
configuration is common in SOHO (Small Office Home Office)
situations, and is referred to as Infrastructure Mode. The
access point allows each client to have access to shared
resources as well as to other clients. The access point connects
to the wired network from a fixed location using standard
cabling. |
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Multiple Access Points :-
Roaming:
| Due to transmission range
limitations, in a very large facility such as a college campus, it
will probably be necessary to install more than one access point.
Access point positioning is accomplished by means of a site survey.
The goal is to blanket the coverage area with overlapping coverage
cells so that clients might roam throughout the area without ever
losing network contact. The ability of clients to move seamlessly
among a cluster of access points is called roaming. Access points
hand the client off from one to another in a way that is invisible
to the client, ensuring unbroken connectivity. |
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| 7.
How many computers can I connect to an access point? |
Theoretically you can connect 254
computers to an access point. IP addresses 0 to 255 are assigned for
private use, but as 0 and 255 are assigned as special numbers, that
leaves 254 addresses remaining for use. But realistically, for
communication efficiency, 20 to 30 computers can be connected to the
one access point. Ideally, e-Motion IT Solutions recommend about 10
- 15 computers per access point.
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| 8.
Is it secure? |
The Wired Equivalent Privacy (WEP)
algorithm is used to protect wireless communication from
eavesdropping. WEP also prevents unauthorized access to a wireless
network. WEP relies on a secret key that is shared between a mobile
station (e.g. a laptop with a wireless Ethernet card) and an access
point. The secret key is used to encrypt packets before they are
transmitted, and an integrity check is used to ensure that packets
are not modified in transit.
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| 9.
What is the range of the signal and will walls affect the wireless
LAN? |
802.11b wireless networking has a
range of about 300 meters in a large open space, and about 100
meters in a typical indoor office environment. Transmission speeds
decrease as the distance between the portable workstation and the
access point increases. The range greatly depends on line of sight
between the workstation and access point.
As for walls, wireless LANs use
radio frequencies for communication. So unlike infrared signals,
which require an unobstructed line of sight between the remote unit
and the base station, radio frequencies can pass through solid
objects such as walls.
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10. What is "line of sight"? |
Just as it sounds - line of sight.
Basically, if you can see point A from point B, you have line of
site between these two points.
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| 1. What
is "Bluetooth"? |
Bluetooth is a 'shortwire' replacement
for the mass of cables we use to connect 'personal' devices so they can
share information. When talking about 'personal' devices we are
referring to portable PCs, mobile telephones & headsets, PDAs, digital
cameras, MP3 players and so on. As Bluetooth develops, we will see more
enabled devices, particularly around the home.
Bluetooth is designed primarily to work
in the background, and, because the speeds are much lower than Wi-Fi, it
should be considered as a low-key automated way of exchanging and
synchronising localised information. However, Bluetooth does have
networking capabilities to a maximum of seven users, with one machine as
the master. The maximum working reach for Bluetooth is 100 m (in the
Toshiba version) but will initially be around 10m. With the addition of
software, it becomes ideal for ad-hoc work (i.e. project teams) or for
presentations where a PowerPoint (or similar software) presentation in
view-only (save disabled) or view and save versions to be shared. It can
also pass real time text messages using the 'Chat' feature.
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| 2. What
is "Wi-Fi"? |
Wi-Fi is the 'longwire' (network cable
from desk to hub/server) wireless replacement technology. It is designed
to allow users to log onto an office/business network without the need
to physically attach via a network card (for portables, a LAN adapter
may be built into either the PC, or a docking station. Alternatively, a
PC Card may be used.) As long as the user has network access rights,
they should be able to log on to the network from anywhere within the
network area (building or site). It simplifies the network
infrastructure as physical cabling is only needed to connect the
wireless access point to a hub or server. By removing physical cabling,
costs can be saved, and there is less physical structure to fail /
troubleshoot. It also increases the flexibility of the workforce in
being able to go anywhere within the network but remain connected.
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| 3. Can
I operate Bluetooth and Wi-Fi together? |
In a shared environment where both Wi-Fi
and Bluetooth are operating concurrently, Bluetooth will loose some of
its available bandwidth to the Wi-Fi system. It is not 'chopped' but
declines between 17 - 22 % (max) (according to test data from Ericsson).
WECA (Wi-Fi) Statement :
"Bluetooth" is made for different applications and uses short-range
radio frequencies to interconnect electronic devices such as mobile
phones, digital cameras and PCs. It is also slower and works within your
personal area network (PAN). WECA supports the efforts of the Bluetooth
Special Interest Group, and Wi-Fi™ products are expected to coexist with
Bluetooth designs.
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| 4. What
is CSMA/CA? |
Ethernet technologies normally use CSMA/CD
- Carrier Sense Multiple Access / Collision Detection, however this is
not possible within the wireless LAN structure. The reason being that
when a node is transmitting it cannot hear any other node in the system
which may be transmitting since it's own signal will drown out any
others arriving at the node. With this protocol CSMA/CA Carrier Sense
Multiple Access/Collision Avoidance a node that receives a packet to be
transmitted, it first listens to the network to ensure that no other
node is transmitting. If the channel is clear it transmits the
packet(s). If the channel is busy, it chooses a random "back-off
factor", which determines the amount of time the node must wait before
it is allowed to transmit again. For periods when the channel is clear
the transmitting node decrements it's back off counter. When the channel
is busy, the transmitting node does not decrement it's back off counter.
When the back off counter reaches 0 the node transmits the packet. The
probability that two node will choose the same back off factor is small,
meaning that collisions between packets are minimised.
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