What is a Wireless LAN?(continue)
How WLANs Work
A wireless LAN (WLAN) is a flexible data communication system implemented as an
extension to, or as an alternative for, a wired LAN within a building or campus. Using
electromagnetic waves, WLANs transmit and receive data over the air, minimizing
the need for wired connections. Thus, WLANs combine data connectivity with user
mobility, and, through simplified configuration, enable movable LANs. Over the last
seven years, WLANs have gained strong popularity in a number of vertical markets,
including the health-care, retail, manufacturing, warehousing, and academic arenas.
These industries have profited from the productivity gains of using hand-held
terminals and notebook computers to transmit real-time information to centralized
hosts for processing. Today WLANs are becoming more widely recognized as a
general-purpose connectivity alternative for a broad range of business customers.
The U.S. wireless Lan market is rapidly approaching $1 billion in revenues
WLANs and other Wireless Technologies
Wireless LANs use electromagnetic airwaves (radio and infrared) to communicate
information from one point to another without relying on any physical connection.
Radio waves are often referred to as radio carriers because they simply perform the
function of delivering energy to a remote receiver. The data being transmitted is
superimposed on the radio carrier so that it can be accurately extracted at the
receiving end. This is generally referred to as modulation of the carrier by the
information being transmitted. Once data is superimposed (modulated) onto the
radio carrier, the radio signal occupies more than a single frequency, since the
frequency or bit rate of the modulating information adds to the carrier.
Multiple radio carriers can exist in the same space at the same time without
interfering with each other if the radio waves are transmitted on different radio
frequencies. To extract data, a radio receiver tunes in (or selects) one radio
frequency while rejecting all other radio signals on different frequencies.
In a typical WLAN configuration, a transmitter/receiver (transceiver) device, called
an access point, connects to the wired network from a fixed location using standard
Ethernet cable. At a minimum, the access point receives, buffers, and transmits data
between the WLAN and the wired network infrastructure. A single access point can
support a small group of users and can function within a range of less than one
hundred to several hundred feet. The access point (or the antenna attached to the
access point) is usually mounted high but may be mounted essentially anywhere that
is practical as long as the desired radio coverage is obtained.
End users access the WLAN through wireless LAN adapters, which are implemented
as PC cards in notebook computers, or use ISA or PCI adapters in desktop computers,
or fully integrated devices within hand-held computers. WLAN adapters provide an
interface between the client network operating system (NOS) and the airwaves (via
an antenna). The nature of the wireless connection is transparent to the NOS.
Bluetooth technology is a forthcoming wireless personal area networking (WPAN)
technology that has gained significant industry support and will coexist with most
wireless LAN solutions. The Bluetooth specification is for a 1 Mbps, small form-factor,
low-cost radio solution that can provide links between mobile phones, mobile
computers and other portable handheld devices and connectivity to the internet. This
technology, embedded in a wide range of devices to enable simple, spontaneous
wireless connectivity is a complement to wireless LANs — which are designed to
provide continuous connectivity via standard wired LAN features and functionality.
What frequency's does this all use?
The 802.11b standard uses frequency's in the 2.4Gig, called the ISM band.
This is a no-licence required free to use frequency range, setaside for this this of thing.
Australia's radio spectrum changes allow free unlicensed use by any person in the ISM
frequency bands.
Frequency band and EIRP (transmit power)
915 MHz - 928 MHz Not exceeding 1 W
2400 MHz - 2463 MHz Not exceeding 4 W
2463 MHz - 2483.5 MHz Not exceeding 200 mW
5725 MHz - 5875 MHz Not exceeding 1 W
The 2.4Gig channel's are as follows:
channel 1 = 2411Mhz centre freq.
channel 2 = 2416Mhz centre freq.
channel 3 = 2421Mhz centre freq.
channel 4 = 2426Mhz centre freq.
channel 5 = 2431Mhz centre freq.
channel 6 = 2436Mhz centre freq.
channel 7 = 2441Mhz centre freq.
channel 8 = 2446Mhz centre freq.
channel 9 = 2451Mhz centre freq.
channel 10 = 2456Mhz centre freq.
channel 11 = 2461Mhz centre freq.
channel 12 = 2466Mhz centre freq.
channel 13 = 2471Mhz centre freq.
channel 14 = 2484Mhz centre freq.
each channel needs 11Mhz either side of centre freq.
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How long of a distance can 802.11b wireless links go?
Withenough power the only limit is the curve of the earth. Unfortunately, there are laws
governing power output. Personally I've seen a guy doing 17km links, some perth guys
did 25km, and 33km are theoretically possible without any kind of power amplification.
Granted, all of these links had very good line of site to each other.
Wireless Networking
Wireless networking technologies take the concept of "no new wires" one step
further. In a wireless network, all of the computers in your home broadcast their
information to one another using radio signals. This can make networking
extremely easy, especially if you have computers all over your house. It also
makes it a whole lot simpler to move computers around. For example, a laptop
with a wireless network card is completely portable throughout the house!
In How Power-line Networking Works, we discussed peer-to-peer and client/server
networks. In wireless networking, a peer-to-peer (or point-to-point) wireless
network means that each computer can communicate directly with every other
computer on the network. But some wireless networks are client/server. They
have an access point, which is a wired controller that receives and transmits
data to the wireless adapters installed in each computer.
There are four types of wireless networks, ranging from slow and inexpensive to
fast and expensive:
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Bluetooth
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IrDA
HomeRF (SWAP)
WECA (Wi-Fi)
Bluetooth is not widely available yet and is not expected to replace the need for
high-speed data networks between computers. You can read more about this
cutting-edge technology in How Bluetooth Short Range Radio Systems Works.
(Infrared Data Association) is a standard for devices to communicate using
infrared light pulses. This is how remote controls operate, and the fact that all
remotes use this standard allows a remote from one manufacturer to control a
device from another manufacturer. Since IrDA devices use infrared light, they
depend on being in direct line of sight with each other. Although you can
purchase and install an IrDA-based network capable of transmitting data at
speeds up to 4 megabits per second (Mbps), the requirement for line of sight
means that you would need an access point in each room, limiting the usefulness
of an IrDA network in a typical home layout.
IrDA
Before we talk about SWAP and Wi-Fi, we need to understand the original
standard that both of these new specifications are based on. The original Institute
of Electrical and Electronics Engineers wireless-Ethernet specification, known as IEEE
802.11, designated two ways of communicating between devices and allowed for
speeds up to 2 Mbps. Both communication methods, direct-sequence spread
spectrum (DSSS) and frequency-hopping spread spectrum (FHSS), use the
frequency-shift keying (FSK) technology we discussed in power-line networking.
Also, both are based on spread-spectrum radio waves in the 2.4-gigahertz
(GHz) range.
simply means that data is sent in small pieces over a number of
the discrete frequencies available for use at any time in the specified range.
Devices using direct-sequence spread spectrum (DSSS) communicate by
splitting each byte of data into several parts and sending them concurrently on
different frequencies. DSSS uses a lot of the available bandwidth, about 22
megahertz (MHz). Devices using frequency-hopping spread spectrum (FHSS)
send a short burst of data, shift frequencies (hop) and then send another short
burst. Since the FHSS devices that are communicating agree on which
frequencies to hop to, and use each frequency for a brief period of time (less
than 400 milliseconds) before moving on, several independent FHSS networks
can exist in the same physical area without interfering with each other. Also, due
to FCC restrictions, as well as the fact that FHSS devices generally send data on
just two to four frequencies simultaneously, they only use 1 MHz or less of the
available bandwidth. Because they use any given frequency for such a short time,
FHSS devices are less prone to interference than DSSS devices. But DSSS is
capable of much greater speed than FHSS since these devices can send a lot
more data at the same time. Currently, FHSS-based devices are easier and
Spread spectrum
cheaper to produce, which has led the HomeRF group to adopt FHSS as the
method of communication for their products.
HomeRF and SWAP
(RF stands for radio frequency) is an alliance of businesses that have
developed a standard called Shared Wireless Access Protocol (SWAP). A sort
of hybrid standard, SWAP includes six voice channels based on the Digital
Enhanced Cordless Telecommunications (DECT) standard and the 802.11
wireless-Ethernet specification for data. SWAP devices make 50 hops per
second and transmit at 1 Mbps. Depending on the manufacturer, some of these
can step up to 2 Mbps if there is very little interference in their operational area.
HomeRF
Here are the advantages of SWAP:
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It's inexpensive ($70 to $200 per device).
It's easy to install.
It requires no additional wires.
It has no access point.
It uses six full-duplex voice channels and one data channel.
It allows up to 127 devices per network.
It allows multiple networks in the same location.
You can use encryption to make your data secure.
Here are the disadvantages of SWAP:
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It's not very fast (normally 1 Mbps).
It has a limited range (75 to 125 ft / 23 to 38 m).
It's not compatible with FHSS devices.
Physical obstructions (walls, large metal objects) can interfere with
communication.
It's difficult to integrate into existing wired networks.
This wireless PCI card is inserted inside your computer to
build a wireless network.
The actual wireless transceiver, with a small, integrated antenna, is built into an
ISA, PCI or PCMCIA card. If you have a laptop computer, the PCMCIA card
plugs directly into one of the PCMCIA slots. For desktop computers, you will
either need a dedicated ISA or PCI HomeRF card, or a PCMCIA card with a
special adapter. ISA and PCI adapters are inserted inside the computer and have
a slot that is accessible from the back of your computer so you can plug in the
PCMCIA card. USB adapters are external devices that you plug the PCMCIA card
into and then connect to a USB port on the computer. Some of the HomeRF
manufacturers sell kits that include the appropriate adapter along with the
PCMCIA cards and installation software. Currently, because of the need to use
dedicated cards, only computers can participate in a SWAP network. Printers
and other peripheral devices need to be physically connected to a computer and
shared as a resource by that computer.
In most cases, SWAP-based networks are point-to-point. Some manufacturers
do offer access points as an option to increase the effective range of the wireless
network, but they are not required equipment. Mainly because of this lack of an
access point, HomeRF networks are significantly cheaper than the other viable
wireless network, WECA's Wi-Fi. But the tradeoffs for cost are speed and
distance. If you can set up a wired network using HomePNA or traditional
Ethernet, you will get 10 to 100 times the speed for the same amount of money
or less. However, unless you plan to send large amounts of data (like video) back
and forth, SWAP speed is probably adequate for most home use, and the
freedom of no wires can be quite appealing. Just remember that this is still a
developing technology.
WECA and Wi-Fi
The Wireless Ethernet Compatibility Alliance (WECA) has gone in a completely different
direction from HomeRF. Targeted more at office use than home networks, Wi-Fi
(for "wireless fidelity", like Hi-Fi for "high fidelity" in audio equipment) is
essentially a seal of approval that says the manufacturer's product is compliant
with a variation of the IEEE 802.11 specification known as IEEE 802.11b. This
specification drops FHSS and focuses on DSSS because of the higher data rate
it can attain. Under 802.11b, devices communicate at a speed of 11 Mbps
whenever possible. If signal strength or interference is disrupting data, the
devices will drop back to 5.5 Mbps, then 2 Mbps and finally down to 1 Mbps.
Though it may occasionally slow down, this keeps the network stable and very
reliable.
Photo courtesy Nexland
The ISB Wavebase by Nexland allows you to connect wireless
devices to your fast Internet connection.
Here are the advantages of Wi-Fi:
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It's fast (11 Mbps).
It's reliable.
It has a long range (1,000 ft / 305 m in open areas, 250 to 400 ft / 76 to
122 m in closed areas)
It's easily integrated into existing wired-Ethernet networks.
It's compatible with original 802.11 DSSS devices.
Here are the disadvantages:
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It's expensive.
It can be difficult to set up.
Speed can fluctuate significantly.
Wi-Fi offers Ethernet speeds without the wires, but you pay for it. There are Wi-Fi
compatible PC cards that operate in peer-to-peer mode, but Wi-Fi usually
requires access points, which range in cost from about $300 to $1,400. Most
access points have an integrated Ethernet controller to connect to an existing
wired-Ethernet network. It also has an omni-directional antenna to receive the
data transmitted by the wireless transceivers. Apple sells an inexpensive ($299 list)
and easy-to-configure access point called Airport. Airport has to be connected to
an Apple computer (iMac, PowerMac, iBook), but it will accept signals from any
802.11b-compatible wireless-network card, whether it's PC or Mac-based.
Like HomeRF systems, the majority of Wi-Fi wireless transceivers available are
in PCMCIA card form. But some manufacturers do offer PCI or ISA format cards,
not just adapters. The cost per card ranges from $99 to more than $300.
Because these products are not targeted at the home market, they are not
typically sold in "do-it-yourself" kits. Instead, everything is a la carte, allowing
customers to build a system that exactly meets their needs.
This is the base unit of a wireless system used to connect
workers with laptops.
At the HowStuffWorks offices, we have installed the 3Com Airconnect wireless
system with great results. Several of our staff members now freely roam about
the workplace with their laptops constantly connected to the network. We
invested about $1,400 for the access point and three PCMCIA cards. That's not a
bad investment to foster a dynamic work environment, but is certainly on the
expensive side for most home networks.
If you are a Mac owner, setting up a Wi-Fi-compatible network is easy, and
reasonable in terms of cost. Otherwise, this is an expensive undertaking that
requires careful consideration of your needs. In fact, you can buy an inexpensive
Apple computer and an Airport access point for close to the amount of money
you would invest in most other access points currently available.
There are two other networking technologies that we will discuss: phone-line and
power-line networks. Click on the title to go to one of these articles for more
information, or proceed to A Word About Macs or The Future of Home Networking.
Benefits of WLAN
The widespread strategic reliance on networking among competitive businesses and
the meteoric growth of the Internet and online services are strong testimonies to the
benefits of shared data and shared resources. With wireless LANs, users can access
shared information without looking for a place to plug in, and network managers can
set up or augment networks without installing or moving wires. Wireless LANs offer
the following productivity, service, convenience, and cost advantages over traditional
wired networks:
Range/Coverage
The distance over which RF waves can communicate is a function of product design
(including transmitted power and receiver design) and the propagation path,
especially in indoor environments. Interactions with typical building objects, including
walls, metal, and even people, can affect how energy propagates, and thus what
range and coverage a particular system achieves. Most wireless LAN systems use RF
because radio waves can penetrate many indoor walls and surfaces. The range (or
radius of coverage) for typical WLAN systems varies from under 100 feet to more
than 500 feet. Coverage can be extended, and true freedom of mobility via roaming,
provided through microcells.
Throughput
As with wired LAN systems, actual throughput in wireless LANs is dependent upon
the product and how it is configured. Factors that affect throughput include airwave
congestion (number of users), propagation factors such as range and multipath, the
type of WLAN system used, as well as the latency and bottlenecks on the wired
portions of the WLAN. Typical data rates range from 1 to 11 Mbps.
Mulitpath Effects
As Figure 9 shows, a radio signal can take multiple paths from a transmitter to a
receiver, an attribute called multipath. Reflections of the signals can cause them to
become stronger or weaker, which can affect data throughput. Affects of multipath
depend on the number of reflective surfaces in the environment, the distance from
the transmitter to the receiver, the product design and the radio technology.
Figure 9. Radio Signals Traveling over Multiple Paths
Integrity
Wireless data technologies have been proven through more than fifty years of
wireless application in both commercial and military systems. While radio
interference can cause degradation in throughput, such interference is rare in the
workplace. Robust designs of proven WLAN technology and the limited distance over
which signals travel result in connections that are far more robust than cellular
phone connections and provide data integrity performance equal to or better than
wired networking.
Interoperability with Wired Infrastructure
Most wireless LAN systems provide industry standard interconnection with wired
systems including Ethernet (802.3) and Token Ring (802.5). Standards based
interoperability makes the wireless portion of the network completely transparent to
the rest of the network. Wireless LAN nodes are supported by network operating
systems(NOS) in the same way any other LAN node via network device drivers. Once
installed, the NOS treats the wireless nodes like any other component of the network.
Interoperability with Wireless Infrastructure
There are several types of interoperability that are possible between wireless LANs.
This will depend both on technology choice and on the specific vendor's
implementation. Products from different vendors employing the same technology and
the same implementation typically allow for the interchange of adapters and access
points. An eventual goal of the IEEE 802.11 specification, currently being drafted by
a committee of WLAN vendors and users, is to allow compliant products to
interoperate without explicit collaboration between vendors.
Interference and Coexistence
The unlicensed nature of radio-based wireless LANs means that other products that
transmit energy in the same frequency spectrum can potentially provide some
measure of interference to a WLAN system. Micro-wave ovens are a potential
concern, but most WLAN manufacturers design their products to account for
microwave interference. Another concern is the co-location of multiple WLAN
systems. While co-located WLANs from different vendors may interfere with each
other, others coexist without interference. This issue is best addressed directly with
the appropriate vendors.
Simplicity/Ease of Use
Users need very little new information to take advantage of wireless LANs. Because
the wireless nature of a WLAN is transparent to a user&#acirc;s NOS, applications
work the same as they do on tethered LANs. WLAN products incorporate a variety of
diagnostic tools to address issues associated with the wireless elements of the
system; however, products are designed so that most users rarely need these tools.
WLANs simplify many of the installation and configuration issues that plague network
managers. Since only the access points of WLANs require cabling, network managers
are freed from pulling cables for WLAN end users. Lack of cabling also makes moves,
adds, and changes trivial operations on WLANs. Finally, the portable nature of
WLANs lets network managers pre-configure and troubleshoot entire networks before
installing them at remote locations. Once configured, WLANs can be moved from
place to place with little or no modification.
Security
Because wireless technology has roots in military applications, security has long been
a design criterion for wireless devices. Security provisions are typically built into
wireless LANs, making them more secure than most wired LANs. It is extremely
difficult for unintended receivers (eavesdroppers) to listen in on wireless LAN traffic.
Complex encryption techniques make it impossible for all but the most sophisticated
to gain unauthorized access to network traffic. In general, individual nodes must be
security-enabled before they are allowed to participate in network traffic.
Cost
A wireless LAN implementation includes both infrastructure costs for the wireless
access points and user costs for the wireless LAN adapters. Infrastructure costs
depend primarily on the number of access points deployed; access points range in
price from $800.00 to $2,000.00. The number of access points typically depends on
the required coverage region and/or the number and types of users to be serviced.
The coverage area is proportional to the square of the product range. Wireless LAN
adapters are required for standard computer platforms, and range in price from
$200.00 to $700.00. The cost of installing and maintaining a wireless LAN is
generally lower than the cost of installing and maintaining a wired LAN for two
reasons. First, a WLAN eliminates the direct costs of cabling and the labor associated
with installing and repairing it. Second, because WLANs simplify moves, adds, and
changes, they reduce the indirect costs of user downtime and administrative
overhead.
Scalability
Wireless networks can be designed to be extremely simple or quite complex.
Wireless networks can support large numbers of nodes and/or large physical areas
by adding access points to boost or extend coverage.
Battery Life for Mobile Platforms
End-user wireless products are capable of being completely untethered, and run off
the battery power from their host notebook or hand-held computer. WLAN vendors
typically employ special design techniques to maximize the host computer&#acirc;s
energy usage and battery life.
Safety
The output power of wireless LAN systems is very low, much less than that of a
hand-held cellular phone. Since radio waves fade rapidly over distance, very little
exposure to RF energy is provided to those in the area of a wireless LAN system.
Wireless LANs must meet stringent government and industry regulations for safety.
No adverse health affects have ever been attributed to wireless LANs.
Benefits of WLANs
The widespread strategic reliance on networking among competitive businesses and
the meteoric growth of the Internet and online services are strong testimonies to the
benefits of shared data and shared resources. With wireless LANs, users can access
shared information without looking for a place to plug in, and network managers can
set up or augment networks without installing or moving wires. Wireless LANs offer
the following productivity, service, convenience, and cost advantages over traditional
wired networks:
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Mobility-Wireless LAN systems can provide LAN users with access to real-time
information anywhere in their organization. This mobility supports
productivity and service opportunities not possible with wired networks.
Installation Speed and Simplicity-Installing a wireless LAN system can be fast
and easy and can eliminate the need to pull cable through walls and ceilings.
Installation Flexibility-Wireless technology allows the network to go where
wire cannot go.
Reduced Cost-of-Ownership-While the initial investment required for wireless
LAN hardware can be higher than the cost of wired LAN hardware, overall
installation expenses and life-cycle costs can be significantly lower. Long-term
cost benefits are greatest in dynamic environments requiring frequent moves,
adds, and changes.
Scalability-Wireless LAN systems can be configured in a variety of topologies
to meet the needs of specific applications and installations. Configurations are
easily changed and range from peer-to-peer networks suitable for a small
number of users to full infrastructure networks of thousands of users that
allows roaming over a broad area.
Wireless LAN Technology Options
Manufacturers of wireless LANs have a range of technologies to choose from when
designing a wireless LAN solution. Each technology comes with its own set of
advantages and limitations.
Spread Spectrum
Most wireless LAN systems use spread-spectrum technology, a wideband radio
frequency technique developed by the military for use in reliable, secure, missioncritical communications systems. Spread-spectrum is designed to trade off
bandwidth efficiency for reliability, integrity, and security. In other words, more
bandwidth is consumed than in the case of narrowband transmission, but the
tradeoff produces a signal that is, in effect, louder and thus easier to detect,
provided that the receiver knows the parameters of the spread-spectrum signal
being broadcast. If a receiver is not tuned to the right frequency, a spread-spectrum
signal looks like background noise. There are two types of spread spectrum radio:
frequency hopping and direct sequence.
Narrowband Technology
A narrowband radio system transmits and receives user information on a specific
radio frequency. Narrowband radio keeps the radio signal frequency as narrow as
possible just to pass the information. Undesirable crosstalk between communications
channels is avoided by carefully coordinating different users on different channel
frequencies.
A private telephone line is much like a radio frequency. When each home in a
neighborhood has its own private telephone line, people in one home cannot listen to
calls made to other homes. In a radio system, privacy and noninterference are
accomplished by the use of separate radio frequencies. The radio receiver filters out
all radio signals except the ones on its designated frequency.
Frequency-Hopping Spread Spectrum Technology
Frequency-hopping spread-spectrum (FHSS) uses a narrowband carrier that changes
frequency in a pattern known to both transmitter and receiver. Properly synchronized,
the net effect is to maintain a single logical channel. To an unintended receiver,
FHSS appears to be short-duration impulse noise.
Figure 7. Frequency Hopping Spread Spectrum
Direct-Sequence Spread Spectrum Technology
Direct-sequence spread-spectrum (DSSS) generates a redundant bit pattern for each
bit to be transmitted. This bit pattern is called a chip (or chipping code). The longer
the chip, the greater the probability that the original data can be recovered (and, of
course, the more bandwidth required). Even if one or more bits in the chip are
damaged during transmission, statistical techniques embedded in the radio can
recover the original data without the need for retransmission. To an unintended
receiver, DSSS appears as low-power wideband noise and is rejected (ignored) by
most narrowband receivers.
Infrared Technology
Infrared (IR) systems use very high frequencies, just below visible light in the
electromagnetic spectrum, to carry data. Like light, IR cannot penetrate opaque
objects; it is either directed (line-of-sight) or diffuse technology. Inexpensive
directed systems provide very limited range (3 ft) and typically are used for PANs
but occasionally are used in specific WLAN applications. High performance directed
IR is impractical for mobile users and is therefore used only to implement fixed
subnetworks. Diffuse (or reflective) IR WLAN systems do not require line-of-sight,
but cells are limited to individual rooms.
WLAN Configurations
Independent WLANs
The simplest WLAN configuration is an independent (or peer-to-peer) WLAN that
connects a set of PCs with wireless adapters. Any time two or more wireless adapters
are within range of each other, they can set up an independent network (Figure 3).
These on-demand networks typically require no administration or preconfiguration.
Figure 3.
Independent WLAN
Access points can extend the range of independent WLANs by acting as a repeater
(see Figure 4), effectively doubling the distance between wireless PCs.
Figure 4. Extended-Range Independent WLAN Using Access Point as Repeater
Infrastructure WLANs
In infrastructure WLANs, multiple access points link the WLAN to the wired network
and allow users to efficiently share network resources. The access points not only
provide communication with the wired network but also mediate wireless network
traffic in the immediate neighborhood. Multiple access points can provide wireless
coverage for an entire building or campus.
Figure 5. Infrastructure WLAN
Microcells and Roaming
Wireless communication is limited by how far signals carry for given power output.
WLANs use cells, called microcells, similar to the cellular telephone system to extend
the range of wireless connectivity. At any point in time, a mobile PC equipped with a
WLAN adapter is associated with a single access point and its microcell, or area of
coverage. Individual microcells overlap to allow continuous communication within
wired network. They handle low-power signals and &#atilde;hand off&#atilde; users
as they roam through a given geographic area.
Figure 6. Handing off the WLAN Connection Between Access Points
Do Wireless LANs Pose a Health Risk to
the Consumer?
Introduction
Influence on the health is one of most discussed topics of radio LANs, since radio
devices emit radio frequency electromagnetic energy. This document wants to clarify
that radio devices are not bad for the health of people using Wireless LANs (WLANs).
Also a list of frequently asked questions will be presented.
Safe, Low-Power Radi
Wireless LAN (WLAN) devices emit radio frequency electromagnetic energy. Because
WLANs are designed to operate within the guidelines found in radio frequency safety
standards and recommendations, WLANs are safe for use by consumers. These
standards and recommendations reflect the consensus of the scientific community
and result from deliberations of panels and committees of scientists who continually
review and interpret the extensive research literature.
Radio Frequency Safety Standards
The following organizations have independently issued similar recommendations for
exposure to radio frequency electromagnetic energy. &#aacute; Standards
Coordinating Committee 28 of the Institute of Electrical and Electronics Engineers
(IEEE) &#aacute; National Council on Radiation Protection and Measurements (NCRP)
&#aacute; National Radiological Protection Boards (NRPB) in the United Kingdom.
&#aacute; International Radiation Protection Association's International Non-Ionizing
Radiation Committee (IRPA/INIRC) (under World Health Organization sponsorship)
IEEE/ANSI Standard (ANSI/IEEE C95.1-1992)
In September of 1992, the IEEE Standard Board approved the IEEE Standards for
Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic
Fields, 3 kHz to 300 GHz, IEEE C95.1-1991. This standard is a revision of the
American National Standard Safety Levels with Respect to Human Exposure to Radio
Frequency Electromagnetic Fields, 3kHz to 100GHz, ANSI C95.1-1982. The IEEE
standard resulted from the deliberations of over 120 leading biologists, biophysicists,
physiologists, physicists, physicians, engineers and members of other scientific
disciplines representing academia, federal agencies with public responsibilities,
industry and other interested groups and organizations. In November of 1992, the
American National Standards Institute (ANSI) approved the IEEE C95.1-1991
standard. The following is stated in the IEEE standard: " No verified reports exist of
injury to human beings who have been exposed to electromagnetic fields within the
limits of frequency and [specific absorption rate] specified by previous ANSI
standards, including ANSI C95.1-1982."IEEE USAB Entity Position Statement
"Measurements have shown that routine exposure of users and other persons to low
power portable and mobile transceivers and cellular telephones do not induce rates
of [radio frequency] absorption that exceed any of the maximum permissible rates of
energy absorption defined by these guidelines" [IEEE, ANSI]. Therefore, based on
present knowledge, the exposures from low-power transceiver are considered to be
without risk for the users and the public. (Quoted from the IEEE USAB Entity Position
Statement Human Exposure to Radio frequency Fields from Portable and Mobile
Telephones and other Communication Devices, December 2, 1992.)
Conclusion
The interpretation of over four decades of research in this area has led to a scientific
consensus on the safety of exposure to radio frequency electromagnetic fields. This
consensus is reflected in the recommendations and standards developed by expert
committees such as NCRP Scientific Committee 53, IEEE Standards Coordinating
Committee 28, IRPA/INIRC and NRPB. Manufacturers of Wireless Networking
products design their products to operate within the guidelines of these standards
and recommendations and, therefore, are considered safe.
Questions and Answers
Can you absolutely assure customers that Wireless LAN products are safe?
Extensive research on the safety of exposure to radio frequency electromagnetic
energy has been carried out for more than four decades. This research is continually
reviewed and interpreted by committees of scientists who develop safe limits for
exposure. Manufacturers of wireless LANs monitor this research and participate in
the consensus standards process and ensure that WLAN products operate within the
guidelines of these standards. Consequently, manufacturers of WLAN products
believe their products are safe.
What if the network has 100 nodes?
Only one transmitter is active at any point in time, so the radiated power of a total
network even when it has 100 nodes is actually equivalent to the radiated power of a
single transmitter. WLAN transmitters operate at a power of 0.035 Watts (35 mW) in
the 2.4 GHz band depending on the specific product in use and the local regulations.
How does WLAN technology differ from cellular technology?
WLAN products use a "bursty" type of transmit/receive protocol, while Cellular
transmits and receives constantly (connection oriented). As an example: If a user
would transfer data on an average of 100 MB per day, the WLAN transmitter would
be on the air for approximately 10 minutes. Moreover, a typical hand held-cell phone
has a RF power output of 0.600 Watts (600 mW) or almost 20X more output power!
The number of supported computers per access point varies with the business
applications and other system factors.
To ensure optimal wireless performance, consider these questions:
WLAN Benefits
You're in business. You know that it takes more than
luck to keep pace in today's market. And, you know
the decisions you make every day show up right on
your bottom line. You require flexibility, agility,
responsiveness-in short, the ability to move more
quickly than your competitors and meet the needs of
your customers. We think wireless networking could
be a natural fit. Here's why.
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It's flexible. With a wireless network you and
your staff can work anywhere, anytime within
your network.
It's fast. Intel wireless technologies offer high
performance and bandwidth to keep all your
essential applications and transactions
running.
It's responsive. As you change your business
operations, your wireless network can change
with you.
It's customized. Your wireless network can be
configured the way you want it-even
combined with your current wired network.
And it's cost effective. Wireless networks can
be implemented gradually. Just install what
you need, when you need it.
Whether your company is thinking of a wireless
solution to network an entire campus or a select
group of high-productivity workers within a wired
organization, WLAN installations offers companies a
way to improve their business operations and
increase revenues. You can connect 802.11a and
802.11b products to the same wired network
backbone. Since the two standards use different
frequencies, you can put their access points near
each other without interference.
When it's Time to Consider WLAN for Your
Business
The information and resources available here can
help you learn more about WLAN solutions for your
company, if you are:
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Retrofitting an existing network
Adding or expanding a secondary network
Adding, moving, or changing employees to
new locations
Increasing mobility of part or all of your
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workforce
Enhancing network performance
Expanding business operations
Upgrading or expanding current wireless
hardware and/or software
Investing in a cost-effective network
When it's Time to Consider 802.11a WLAN
You should consider an 802.11a WLAN with Intel®
PRO/Wireless 5000 LAN products when:
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The savings you gain through higher system
performance is more important than initial
system cost
You need the bandwidth and speed to handle
large graphics, audio, data, and video files
You need greater network capacity than an
802.11b WLAN can give you
You want your WLAN to match the speed of
wired networks
You will have many users per access point
You want to replace your wired network with
a wireless one
When it's Time to Consider 802.11b WLAN
You should consider an 802.11b WLAN with Intel®
PRO/Wireless 2011b LAN products when:
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Initial system cost is your main concern
Data rates up to 11 Mbps are sufficient
Your goal is global implementation
You want to expand an existing 802.11b
WLAN
You need WLAN access for handheld PCs
You will have a small number of users per
access point
You want to add limited pockets of WLAN to
your existing wired LAN
A traditional, wired local area network (LAN) sends
packages of data from one piece of equipment to
another across cables or wires. A wireless local area
network (WLAN) relies instead upon radio waves to
transfer data. These radio signals are transferred
between access points installed at key locations in
the physical environment (such as on walls or
ceilings) and wireless adapters attached to
computing systems. A WLAN eliminates cables and
wires and takes advantage of the fact that radio
waves can pass through environmental obstacles,
such as ceilings and walls. Wireless networks offer
unprecedented flexibility for computer users, along
with remote management capabilities for business
owners or system administrators.
There are two primary components of a wireless
network design: infrastructure and client adapters.
Intel wireless infrastructure products consist of
gateways and access points, which serve as data
conduits and, where needed, provide a bridge
between wireless and existing wired networks.
Gateways are typically used for smaller businesses,
while access points serve medium and enterprise
businesses. Client adapters provide the links
between computers and the network, as well as
converting data into a format that the network can
use. The adapter selected depends on the type of
device being used. Adapters include WLAN PC
cards, PCI cards, USB devices, and modules.
Another important consideration in a WLAN is the
antenna. Antennas serve to direct the radio waves
into the desired area in a specific coverage pattern.
For each key component of a WLAN, the particular
equipment chosen depends on a particular site-with
its unique usage patterns and environmental factors.
Accessories
Full breadth of products: 802.11a and 802.11b
solutions for your home office, small and medium
business, or large organization.
High performance: Up to 54 Mbps throughput
and advanced roaming capabilities provide reliable
access to e-mail, the Internet, file sharing and other
network resources away from the desk.
Manageable: Intel® PROSet software allows for
simple configuration of your wireless network.
Easy setup: Expand your network quickly and
easily by adding wireless access points and
adapters. Installs in minutes. Ideal when wiring is
difficult or cumbersome.
Safe and reliable: Security features encrypt data
to help ensure privacy, while restricting network
access to authorized users.
Wireless Ethernet Adapters
Intel® PRO/Wireless 5000 LAN CardBus
Adapter and Starter Kit
Intel® PRO/Wireless 5000 LAN PCI
Adapter
Wireless Ethernet Dual Access Points
Intel® PRO/Wireless 5000 LAN Dual
Access Point
Wireless Ethernet Access Points and
Starter Kits
Intel® PRO/Wireless 5000 LAN Access
Point and Starter Kit
Wireless Ethernet Adapters
Xircom® CreditCard™ Wireless Ethernet
Adapter
Intel® PRO/Wireless 2011B LAN PC
Card
Intel® PRO/Wireless 2011B LAN USB
Device
Intel® PRO/Wireless 2011B LAN PCI
Adapter
Wireless Ethernet Dual Access Points
Intel® PRO/Wireless 5000 LAN Dual
Access Point
Wireless Ethernet Access Points
Intel® PRO/Wireless 2011B LAN Access
Point
Xircom® Wireless Ethernet Access Point
Intel® Wireless Gateway
Intel® Wireless Gateway (WiFi*/802.11b)
Wireless Ethernet Starter Kits
Xircom® Wireless Ethernet Starter Kit
Wireless Modules for Handhelds
Xircom® Springport™ Wireless Ethernet
Module
Xircom® Wireless LAN Module for
Palm* Handhelds
Wireless LAN Antennas
Intel® 2.4 GHz Directional Yagi Antenna
Intel® 2.4 GHz Omni-Directional
Indoor/Outdoor Antenna
Intel® 2.4 GHz Low Profile Directional
Antenna
Intel® 2.4 GHz Omni-Directional Ceiling
Mount Antenna
Wireless LAN Power Injectors
Intel® PRO/Wireless 2000 LAN Power
Injector
Tropicana Hotel & Casino, Atlantic City,
New Jersey
Intel® PRO/Wireless LAN Products
Optimize Network Traffic Within the Casino
Back to WLAN Testimonials
Tropicana Atlantic spans about four city blocks in
Atlantic City. Greg Dyer, the PC network manager
for Tropicana, oversees the IT staff and network
system of approximately 1,200 users.
"We have currently a combo of about 13 fiber optic
closets throughout the property and 12 NT* servers,
POS (point of sales) systems, and slot rating
systems. These slot rating systems show how long a
customer has been playing the slot machines and
also profiles the customers. We have IBM* AS400
servers that run the hotel purchasing, marketing,
financials and sales systems. On the client side, we
have over 800 networked PCs and appliances."
"My job is to evaluate new technologies that will help
the hotel and casino streamline efficiency. I chose
the Intel® Wireless networking solution because it is
a solid performing product."
Wireless Convenience in the Casino
Tropicana decided to go wireless in the casino
because it offers an alternative to traditional wiring.
There are six Intel® PRO/Wireless LAN Access
Points in different strategic locations throughout the
building: in the atrium, casino, reception and theatre
areas. These areas represent the six special event
locations. The casino marketing staff uses Intel®
PRO/Wireless LAN PC cards in their laptops and
utilizes the wireless LAN for marketing activities,
special events and promos.
Just prior to implementing the wireless LAN, the
marketing department was having an event in a
room that they had spent time and money wiring a
computer network. The Fire Department came in
and shut down the event because the wires violated
building code. Now, with wireless network, the hotel
and casino promoters can set up an event, and even
"...the experience
working on the Intel®
Wireless network has
given us excellent
results: flexibility, no
more cabling issues,
and it's opened up a
whole new creative
solution for our special
events group."
Greg Dyer
PC Network Manager,
Tropicana Hotels & Casinos
move it from one area of the hotel/casino to another
if a greater number of people arrive.
"We move around so much with special events and
promotional giveaways. Although Tropicana is the
biggest hotel in New Jersey, it's difficult to find areas
to hold special events. If you are a customer who
meets a certain profile, you'll receive certain prizes.
We give away anything from t-shirts to fine china."
"Every time we've had an event within the hotel,
we've had to cable or network that area of the
hotel—whether it's on the casino floor, in the lounge,
in the pool deck area. We don't want to pull people
into a back hallway to give them their prize. Some of
the large convention areas are sometimes the only
areas available, but it's not necessarily the best area
to hold these events. We want our customers to feel
at ease, so now that we have the Intel®
PRO/Wireless LAN network, we are not limited to a
particular room. The staff uses their wireless
networking laptops and they can easily monitor the
prize giveaways and marketing event from their
networked laptop."
"Sometimes we use the wireless network like a
registration desk. At bingo, for example, the hotel
staff uses their wireless networked laptops to
register the clients."
Intel or Bust!
Tropicana chose Intel® Wireless networking
products to deploy throughout its hotel and casino.
Mr. Dyer states "there is a reliable name (Intel)
behind the architecture. We had looked at a couple
other brands that we felt weren't as strong, but we
felt comfortable with the Intel® brand name. So far,
the experience working on the Intel Wireless
network has given us excellent results: flexibility, no
more cabling issues, and it's opened up a whole
new creative solution for our special events group.
And, we can move wherever the fire department
wants us to hold the event!"
Gambling on Wirele$$
"We are considering opening up our conventions
department to host computer/tech events where we
can lease out wireless Internet access for our clients
if they want to hold seminars or tradeshows,"
explains Mr. Dyer. "We are also exploring point-topoint bridging opportunities to link multiple hotel
towers, thus keeping T-1 leased line costs down."
"We are also considering running Intel®
PRO/Wireless LAN products on handhelds or PDAs
on the casino floor. We'd like to be able to rate
players right at the tables instead of running back
and forth to the casino pits."
Betting on the Future with Intel PRO/Wireless
Tropicana chose to implement a wireless solution
because it offers them more flexibility. "We wanted
to get our feet wet, and test wireless LANs. The next
step is wireless point of sale systems and remote
cashier stations in the parking lots or beach areas,"
says Mr. Dyer.
Intel® PRO/Wireless LAN products allow Tropicana
to creatively manage their special events, stay in
line with fire code, and offer new ways to monitor
their casino floor.
High Tech High School, San Diego, California
Magnet Technology High School uses Intel® Wireless Products to Educate
Students
Back to WLAN Testimonials
is a public high school, founded in 2000. The school currently has
approximately 200 students. The core curriculum focuses on science, math and
technology.
High Tech High
Peter Estacio is Director of Information Technology at HTH, where approximately
half of the teaching staff are using Intel® PRO/Wireless LAN products. "Our
courses and classrooms are mobile."
High Tech Goes Wireless:
Old Building Meets New Technology
The HTH building is very old. Mr. Estacio explains, "HTH is on the naval training
center, which was built about 50 or 60 years ago. The building wasn't set up for a
wired network. There were a lot of structural impediments that kept us from
wiring every classroom. We did some great work to retrofit the building, but it's
not ideal. Some areas, such as the labs, still need a network—that's why we
installed a wireless LAN."
Intel helped HTH perform a site survey, a method to help determine where to
install Access Points. Three Intel® PRO/Wireless LAN Access Points were
deployed throughout the building to ensure full coverage. Teachers utilize the
wireless network as they roam from the teacher lounge to the classroom. Some
students use the wireless network to access the Internet or transfer files.
Working Around Bunsen Burners
The biotech lab at HTH has square tables where students perform lab
experiments. The set-up of the lab makes it difficult to install computers: there
are butane tanks, Bunsen burners and other flammable equipment that interferes
with large, desktop computers.
Laptop computers, configured with Intel® PRO/Wireless LAN PC cards, allow the
students to be more mobile as they move from one area of the lab to another.
And, it allows the teacher to visit each table with his/her laptop to record
the experiment.
Using Wireless networks to Build Yo-Yos
"We have a few hands-on labs such as a biotech lab and the engineering
manufacturing lab," explains Mr. Estacio. "Due to large equipment in the
manufacturing lab (i.e. woodworking equipment), space is wasted by desktop
computers. We are now switching to laptop computers so students can use
server-based CAD/CAM (computer aided design/computer aided manufacturing)
design techniques in this lab."
"For example, in the past, if a student designed a yo-yo, they would design it on
the computer in a classroom and then go to the manufacturing lab with a printout
of their design. Now, with their wireless-enabled laptops, they can take their
laptops directly to the manufacturing area."
"They access the data over the network and use the Internet to tweak their
design. We are teaching them to be proficient and efficient mechanical
engineers."
Looking Through the Crystal Ball: The Future of Wireless at HTH
HTH hopes to keep its students ahead of the technology curve. Mr. Estacio will
soon begin teaching students the benefits of wireless networking. He will use
Intel® PRO/Wireless LAN equipment and material from Intel's course Designing
Flexible Wireless LAN Solutions to give the high school students exposure to
wireless networking. The students will learn how to perform site surveys, and
they will receive extensive hands-on experience in wireless LAN design,
implementation, and management. Students who complete his course will have a
solid understanding of the latest wireless networking technology, and will be well
on their way towards a career in high tech, thanks to High Tech High.
View full article (67.5 KB PDF)
Summary:
Sitting at their desks in an isolated and geographically dispersed community in central Oklahoma,
students in the Wanette Public School District can go everywhere. Using an Intel® PRO/Wireless
LAN to turn every classroom into a virtual, combined library-laboratory, the district enables
teachers and students to experience a world-class education not otherwise possible in this rural
farming community. Access to the Internet, for example, adds millions of virtual books and
periodicals to the school’s small library. The district’s 802.11b Intel® PRO/Wireless LAN allowed
school administrators to make quick and easy modifications to the learning environment without
the need for costly building improvements or new classrooms. Examining the network in the
Wanette Public School District in closer detail, this case study shows how wireless technology
equalizes educational opportunities for students in a rural environment.
Profiled Organization:
Wanette School District, Wanette Oklahoma, USA
The Challenge:
Provide students and teachers in a small, rural school district with increased access to advanced,
up-to-date resources, information and curriculum materials, without the need for costly building
improvements or new construction.
The Solution:
Add wireless networking technology to the existing wired network to optimize information access
for the entire student population. The Wanette Public School District installed an Intel®
PRO/Wireless LAN featuring 12 Intel® PRO/Wireless 2011 LAN Access Points and laptop PCs
equipped with 32 Intel® PRO/Wireless 2011 Adapters. The district also has 250 networked PCs
running Intel® Pentium® II, Pentium® III and Pentium® 4 processors located throughout the
classrooms and the schools’ two dedicated computer labs.
Benefits:
The addition of the wireless LAN has cost-effectively extended the availability of the district’s
network to all teachers and students throughout the district’s two school buildings. Enhanced
student and teacher productivity has been realized through increased access to educational
material, integrated curriculum opportunities and anytime-anywhere networking experiences.
Indian Scenario:
Govt has deregularised the use of WLAN for indoor use recently (November 2002). ie.
Licence for wlan use within indoors is not required.
Present market of WLAN is 200 crores.Expected to go to 600 crores.
One access point costes about 50,000/- Rs. Each client costs aprox. 10,000/- ie for 10
users the cost of Wlan setup can be 1.5 laks now.But rates may fall in near future.
Expected speeds of WLAN to go up to 54mbps in next few months.