Wireless Network Technologies and Standards (3)

Benefits of Wireless Networks

Companies can realize the following benefits by implementing wireless networks:
• Mobility
• Ease of installation in difficult-to-wire areas
• Reduced installation time
• Increased reliability
• Long-term cost savings
Mobility
User mobility indicates constant physical movement of the person and their network appliance. Many
jobs require workers to be mobile, such as inventory clerks, healthcare workers, policemen, emergency
care specialists, and so on. Wireline networks require a physical tether between the user’s workstation
and the network’s resources, which makes access to these resources impossible while roaming about the
building or elsewhere. As an analogy, consider talking on a wired phone having a cord connecting the handset to the telephone base station. You can utilize the phone only within the length of its cord. With a
wireless cellular phone, however, you can walk freely within your office, home, or even talk to someone
while driving a car. Wireless networking offers mobility to its users much like the wireless phone,
providing a constant connection to information on the network. This connection can be extremely useful
if you are at a customer’s site discussing a new product, delivering emergency care to a crash victim, or
in a hotel room sending and receiving e-mail. You cannot become mobile unless you eliminate the wire
through the use of wireless networking.
Installation in Difficult-to-Wire Areas
The implementation of wireless networks offers many tangible cost savings when performing
installations in difficult-to-wire areas. If rivers, freeways, or other obstacles separate buildings you want
to connect (see fig. 1.8), a wireless MAN solution may be much more economical than installing
physical cable or leasing communications circuits such as T1 service or 56 Kbps lines. Some
organizations spend hundreds, thousands, or even millions of dollars to install physical links with nearby
facilities. If you are facing this type of installation, consider wireless networking as an alternative. The
deployment of wireless networking in these situations costs thousands of dollars, but will result in a
definite cost savings in the long run.
Figure 1.8 A difficult-to-wire situation.
The asbestos found in older facilities is another problem that many organizations encounter. The
inhalation of asbestos particles is extremely hazardous to your health; therefore, you must take great care
when installing network cabling within these areas. When taking necessary precautions, the resulting cost
of cable installations in these facilities can be prohibitive. Some organizations, for example, remove the
asbestos, making it safe to install cabling. This process is very expensive because you must protect the
building’s occupants from breathing the asbestos particles agitated during removal. The cost of removing
asbestos covering just a few flights of stairs can be tens of thousands of dollars. Obviously, the advantage
of wireless networking in asbestos-contaminated buildings is that you can avoid the asbestos removal
process, resulting in tremendous cost savings.
In some cases, it might be impossible to install cabling. Some municipalities, for example, may restrict
you from permanently modifying older facilities with historical value. This could limit the drilling of
holes in walls during the installation of LAN cabling and network outlets. In this situation, a wireless
LAN might be the only solution. Right-of-way restrictions within cities and counties may also block the
digging of trenches in the ground to lay optical fiber for the interconnection of networked sites. Here, a wireless MAN or WAN might be the only alternative.
Reduced Installation Time
The installation of cabling is often a time-consuming activity. For LANs, installers must pull twisted-pair
wires above the ceiling and drop cables through walls to network outlets that they must affix to the wall.
These tasks can take days or weeks, depending on the size of the installation. The installation of optical
fiber between buildings within the same geographical area consists of digging trenches to lay the fiber or
pulling the fiber through an existing conduit. You might need weeks or possibly months to receive rightof-
way approvals and dig through ground and asphalt. The deployment of wireless LANs, MANs, or
WANs greatly reduces the need for cable installation, making the network available for use much sooner.
Thus, many countries lacking a network infrastructure have turned to wireless networking as a method of
providing connectivity among computers without the expense and time associated with installing
physical media.
Increased Reliability
A problem inherent to wired networks is the downtime due to cable faults. Moisture erodes metallic
conductors. These imperfect cable splices can cause signal reflections that result in unexplainable errors.
The accidental cutting of cables can also bring a network down quickly. Water intrusion can also damage
communications lines during storms. These problems interfere with the users’ ability to utilize network
resources, causing havoc for network managers. The advantage of wireless networking, then, is
experiencing fewer problems because less cable is used.
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Long-Term Cost Savings
Companies reorganize, resulting in the movement of people, new floor plans, office partitions, and other
renovations. These changes often require re-cabling the network, incurring both labor and material costs.
In some cases, the re-cabling costs of organizational changes are substantial, especially with large
enterprise networks. A reorganization rate of 15% each year can result in yearly reconfiguration expenses
as high as $250,000 for networks having 6,000 interconnected devices. The advantage of wireless
networking is again based on the lack of cable—you can move the network connection by simply
relocating an employee’s PC.
Wireless Network Concerns
The benefits of a wireless network are certainly welcomed by companies and organizations. Network
managers and engineers should be aware, however, of the following concerns that surround the
implementation and use of wireless networking:
• Radio signal interference
• Power management
• System interoperability
• Network security
• Installation issues
• Health risks
Radio Signal Interference
The purpose of radio-based networks is to transmit and receive signals efficiently over airwaves. This
process, though, makes these systems vulnerable to atmospheric noise and transmissions from other
systems. In addition, these wireless networks could interfere with other radio wave equipment. As shown
in figure 1.9, interference may be inward or outward.
Inward Interference
Most of us have experienced radio signal interference while talking on a wireless telephone, watching
television, or listening to a radio. Someone close by might be communicating with another person via a
short-wave radio system, causing harmonic frequencies that you can hear while listening to your favorite
radio station. Or, a remote control car can cause static on a wireless phone while you are attempting to
have a conversation. These types of interference might also disturb radio-based wireless networks in the form of inward interference.
Figure 1.9 Inward and outward interference.
A radio-based LAN, for example, can experience some inward interference either from the harmonics of
transmitting systems or other products using ISM-band frequencies in the local area. Microwave ovens
operate in the S band (2.4 GHz) that many wireless LANs transmit and receive. These signals result in
delays to the user by either blocking transmissions from stations on the LAN or causing bit errors to
occur in data being sent. These types of interference can limit the areas in which you can deploy a
wireless network. As an illustration, when deploying a wireless network at a site located in Washington,
D.C., along the Potomac River, a company occasionally experienced a great deal of delay from stations
located on the side of the building facing the river. The implementation team found, through radio
propagation tests, that a military base on the opposite side of the river was periodically transmitting a
radio signal. The interfering signal was strong enough for the LAN stations to misinterpret it as data
traffic, forcing the stations to wait an inefficient period of time.
NOTE:
To make matters worse, most radio-based products operate within the public, license free, ISM
bands. These products do not require users to obtain FCC licenses, which means the FCC does not
manage the use of the products. If you experience interference within the ISM band resulting from
another product operating within that band, you have no recourse. The FCC is not committed to
step in and resolve the matter, leaving you with the choice of dealing with delays the interference
causes or looking for a different technology to support your needs.
Interference with radio-based networks is not as bad as it might seem. The products using the ISM bands
incorporate spread spectrum modulation that limits the amount of damage an interfering signal causes.
The spread spectrum signal covers a wide amount of bandwidth, and a typical narrow bandwidth
interference only affects a small part of the information signal, resulting in few or no errors. Thus, spread
spectrum-type products are highly resistant to interference. Narrowband interference with signal-tointerference
ratios of less than 10 dB does not usually affect a spread spectrum transmission. Wideband
interference, however, can have damaging effects on any type of radio transmission. The primary source
of wideband interference is domestic microwave ovens that operate in the 2.4 GHz band. The typical
microwave oven operates at 50 pulses per second and sweeps through frequencies between 2400 and 2450 MHz, corrupting the wireless data signal if within 50 feet of the interfering source. Other
interference may result from elevator motors, duplicating machines, theft protection equipment, and
cordless phones.
Outward Interference
Inward interference is only half of the problem. The other half of the issue, outward interference, occurs
when a wireless network’s signal disrupts other systems, such as adjacent wireless LANs, navigation
equipment on aircraft, and so on. This disruption results in the loss of some or all of the system’s
functionality. Interference is uncommon with ISM band products because they operate on such little
power. The transmitting components must be very close and operating in the same bandwidth for either
one to experience inward or outward interference.
Techniques for Reducing Interference
When dealing with interference, you will want to coordinate the operation of radio-based wireless
network products with your company’s frequency management organization, if one exists. This will
avoid potential interference problems. In fact, the coordination with frequency management officials is
mandatory before operating radio-based wireless devices of any kind on a U.S. military base. The
military does not follow the same frequency allocations issued by the FCC. The FCC deals with
commercial sectors of the U.S., and the military has their own frequency management process. You must
obtain special approvals from the government to operate ISM-based products on military bases because
they may interfere with some of their systems. The approval process can take several months to
complete.
Another tip, especially if no frequency management organization exists within your company, is to run
some tests to determine the propagation patterns within your building. These tests let you know if
existing systems may interfere with, and thus block and cause delay to, your network. You will also
discover whether your signal will disturb other systems. See Chapter 8, “Designing a Wireless Network,”
for details on ways to perform propagation tests (site survey).
Power Management
If you are using a portable computer in an automobile, performing an inventory in a warehouse, or caring
for patients in a hospital, it might be cumbersome or impossible to plug your computer into an electrical
outlet. Thus, you will be dependent on the computer’s battery. The extra load of the wireless NIC in this
situation can significantly decrease the amount of time you have available to operate the computer before
needing to recharge the batteries. Your operating time, therefore, might decrease to less than an hour if
you access the network often.
To counter this problem, vendors implement power management techniques in their PCMCIA format
wireless NICs. Proxim’s wireless LAN product, RangeLAN2/PCMCIA, for example, maximizes power
conservation. RangeLAN2 accommodates advanced power management features found in most portable
computers. Without power management, radio-based wireless components normally remain in a
receptive state waiting for any information. Proxim incorporates two modes to help conserve power: the
Doze Mode and the Sleep Mode. The Doze Mode, which is the default state of the product, keeps the
radio off most of the time and wakes up periodically to determine if any messages await in a special
mailbox. This mode alone utilizes approximately 50 percent less battery power. The Sleep Mode causes
the radio to remain in a transmit-only standby mode. In other words, the radio wakes up and sends
information if necessary, but is not capable of receiving any information. Other products offer similar
power management features.
System Interoperability
When implementing an ethernet network, network managers and engineers can deploy NICs from a
variety of vendors on the same network. Because of the stable IEEE 802.3 standard that specifies the
protocols and electrical characteristics that manufacturers must follow for ethernet, these products all
speak exactly the same language. This uniformity allows you to select products meeting your
requirements at the lowest cost from a variety of manufacturers. Today, this is not possible with most
wireless network products, especially wireless LANs and MANs. The selection of these wireless
products is predominantly single vendor, sole-source acquisitions. Products from one vendor will not
interoperate with those from a different company. This raises a problem when deploying the network.
Once you decide to buy a particular brand of wireless network component, you must continue to purchase that brand to ensure that the components can talk the same language as the existing ones.
Putting yourself in this situation is risky. What happens if your wireless vendor decides to discontinue
the product you chose?
As mentioned earlier, the solution to this problem, at least for wireless LANs, is very near. The IEEE
802.11 Working Group plans to issue final standards for wireless LANs by 1997. Wireless LAN vendors
should embrace the standard because they are active in the standard development process. Shifting their
products to the standard will be easy for them.
Network Security
Network security refers to the protection of information and resources from loss, corruption, and
improper use. Are wireless networks secure? Among businesses considering the implementation of a
wireless system, this is a common and very important question. To answer this question, you must
consider the functionality a wireless network performs. As described earlier, a wireless network provides
a bit pipe, consisting of a medium, synchronization, and error control that supports the flow of data bits
from one point to another. This setup corresponds to the lowest levels of the network architecture and
does not include other functions such as end-to-end connection establishment or login services.
Therefore, the only security issues relevant to wireless networks include those dealing with these lower
architectural layers, such as data privacy.
Security Threats
The main security issue with wireless networks, especially radio networks, is that they intentionally
propagate data over an area that may exceed the limits of the area the organization physically controls.
For instance, radio waves easily penetrate building walls and are receivable from the facility’s parking lot
and possibly a few blocks away. Someone can passively retrieve your company’s sensitive information
by using the same wireless NIC from this distance without being noticed by network security personnel
(see fig. 1.10). This problem also exists with wired ethernet networks, but to a lesser degree. Current
flow through the wires emits electromagnetic waves that someone could receive by using sensitive
listening equipment. They must be very close to the cable, however, meaning they must first break
through physical security.
Another security problem is the potential for electronic sabotage, in which someone maliciously jams the
radio-based network and keeps you from using the network. Remember, wireless networks utilize a
carrier sense protocol to share the use of the common medium. If one station is transmitting, all others
must wait. Someone can easily jam your network by using a wireless product of the same manufacture
that you have within your network and setting up a station to continually resend packets. These
transmissions block all stations in that area from transmitting, which is most serious if your company
stands to experience a great loss if the network becomes inoperable.

Wireless Network Technologies and Standards (2)

Wireless Network Architecture
In general, networks perform many functions to transfer information from source to destination.
1. The medium provides a bit pipe (path for data to flow) for the transmission of data.
2. Medium access techniques facilitate the sharing of a common medium.
3. Synchronization and error control mechanisms ensure that each link transfers the data intact.
4. Routing mechanisms move the data from the originating source to the intended destination.
A good way to depict these functions is to specify the network’s architecture. This architecture describes
the protocols, major hardware, and software elements that constitute the network. A network
architecture, whether wireless or wired, may be viewed in two ways, logically and physically.
Logical Architecture of a Wireless Network
A logical architecture defines the network’s protocols—rules by which two entities communicate.
People observe protocols every day. Individuals participating in a business meeting, for example,
interchange their ideas and concerns while they avoid talking at the same time. They also rephrase a
message if no one understands it. Doing so ensures a well-managed and effective means of
communication. Likewise, PCs, servers, routers, and other active devices must conform to very strict
rules to facilitate the proper coordination and transfer of information.
One popular standard logical architecture is the 7-layer Open System Interconnection (OSI) Reference
Model, developed by the International Standards Organization (ISO). OSI specifies a complete set of
network functions, grouped into layers. Figure 1.2 illustrates the OSI Reference Model.
The OSI layers provide the following network functionality:
• Layer 7—Application layer. Establishes communications with other users and provides
services such as file transfer and e-mail to the end users of the network.
• Layer 6—Presentation layer. Negotiates data transfer syntax for the application layer and
performs translations between different data types, if necessary.
• Layer 5—Session layer. Establishes, manages, and terminates sessions between applications.
• Layer 4—Transport layer. Provides mechanisms for the establishment, maintenance, and
orderly termination of virtual circuits, while shielding the higher layers from the network
implementation details.
• Layer 3—Network layer. Provides the routing of packets from source to destination.
• Layer 2—Data Link layer. Ensures synchronization and error control between two entities.
• Layer 1—Physical layer. Provides the transmission of bits through a communication channel
by defining electrical, mechanical, and procedural specifications.
NOTE:
Each layer of OSI supports the layers above it.
Does a wireless network offer all OSI functions? No. As shown in figure 1.3, wireless LANs and MANs
function only within the Physical and Data Link layers, which provide the medium, link synchronization,
and error control mechanisms. Wireless WANs provide these first two layers, as well as Network Layer
routing. In addition to the wireless network functions, a complete network architecture needs to include
functions such as end-to-end connection establishment and application services.
Physical Architecture of a Wireless Network
The physical components of a wireless network implement the Physical, Data Link, and Network Layer
functions (see fig. 1.4). The network operating system (NOS) of a network, such as Novell Netware,
supports the shared use of applications, printers, and disk space. The NOS, located on client and server
machines, communicates with the wireless Network Interface Card (NIC) via driver software, enabling
applications to utilize the wireless network for data transport. The NIC prepares data signals for
propagation from the antenna through the air to the destination comprised of the same set of components.
End-User Appliances
As with any system, there must be a way for users to interface with applications and services. Whether
the network is wireless or wired, an end-user appliance is a visual interface between the user and the
network. Following are the classes of user appliances:
• Desktop workstations
• Laptops
• Palmtops
• Pen-based computers
• Personal Digital Assistants (PDA)
• Pagers
The desktop workstation is currently the most common type of network user appliance. The personal
computer (PC), developed initially by IBM and based on Intel’s microprocessor and Microsoft’s
Windows, is found in many organizations and appears to be the industry standard for the office. Some
companies employ Apple’s Macintosh (Mac) computers as well. The Mac seems to suit artisans because
of its excellent graphics support.
Smaller computers have been effective in satisfying portable computing needs of business executives and
other professionals. Laptops, which measure roughly 8×10×3 inches, can run the same type of software
as the desktop computers, but fit in a briefcase and include rechargeable batteries to sustain operations
where electricity is not present. Palmtops fit in the palm of your hand, but they generally do not perform
as well as the leading laptop and desktop computers. For some applications, such as electronic patient
record keeping, pen-based computers are handy because they enable you to enter data into a portable device via a pen. More and more mobile professionals also are turning to PDAs that enable them to keep
track of contacts, schedules, and tasks. Apple’s Newton PDA, for instance, combines contact
management software and electronic book creation software for salespeople. Pagers are also available as
user appliances. Pagers get your attention when someone calls a special telephone number. These
devices, however, are more than just beepers. Some pagers are now capable of receiving and sending
limited alphanumeric text due to narrowband PCS.
Because wireless network appliances are often put into the hands of mobile people who work outside, the
appliance must be tough enough to resist damage resulting from dropping, bumping, moisture, and heat.
Some companies now offer more durable versions of the portable computer. Itronix, for example, sells
the X-C 6000 Cross Country 486 portable computer. The X-C 6000’s case is built from strong,
lightweight magnesium and includes an elastomer covering that protects the unit from weather and
shock. The unit is impervious to rain, beverage spills, and other work environment hazards.
Some of these vendors also produce pen-based and handheld computers well-suited for wireless
applications. Telxon has a PTC-1184 full-screen 486 pen-based computer that combines pen-based
technology with bar code scanning and AIRONET’s MicroCellular radio-based wireless network
interface card. This system makes it possible to use the unit in environments such as hospitals, factory
floors, and warehouses.
Network Software
A wireless network supports the NOS and its applications, such as word processing, databases, and email,
enabling the flow of data between all components. NOSs provide file and print services, acting as a
platform for user applications. Many NOSs are server-oriented, as shown in figure 1.5, where the core
software resides on a high-performance PC. A client, located on the end user’s appliance, includes server
software that directs the user’s command to the local computer resources, or puts it out onto the network
to another computer. Some wireless networks may also contain middleware that interfaces mobile
applications to the wireless network hardware.
Wireless Network Interface
Computers process information in digital form, with low direct current (DC) voltages representing data
ones and zeros. These signals are optimum for transmission within the computer, not for transporting
data through wired or wireless media. A wireless network interface couples the digital signal from the
end-user appliance to the wireless medium, which is air, to enable an efficient transfer of data between
sender and receiver. This process includes the modulation and amplification of the digital signal to a
form acceptable for propagation to the receiving location. Modulation is the process of translating the
baseband digital signal to a suitable analog form. This process is very similar to the common telephone
modem, which converts a computer’s digital data into an analog form within the 4 KHz limitation of the
telephone circuit. The wireless modulator translates the digital signal to a frequency that propagates well
through the atmosphere. Wireless networks employ modulation by using radio waves and infrared light.
Amplification raises the amplitude of the signal so it will propagate a greater distance. Without
amplification, you would have a difficult time talking to a crowd of 1,500 people outside in an open area.
But, add amplification, such as a PA system, and everyone can hear you.
Figure 1.5 The server-based network operating system.
NOTE:
Chapter 2, “Wireless Local Area Networks (LANs),” covers modulation techniques in more detail.
The wireless network interface also manages the use of the air through the operation of a
communications protocol. For synchronization, wireless networks employ a carrier sense protocol similar
to the common ethernet standard. This protocol enables a group of wireless computers to share the same
frequency and space. As an analogy, consider a room of people engaged in a single conversation in
which each person can hear if someone speaks. This represents a fully connected bus topology (where
everyone communicates using the same frequency and space) that ethernet and wireless networks, especially wireless LANs, utilize. To avoid having two people speak at the same time, you should wait
until the other person has finish-ed talking. Also, no one should speak unless the room is silent. This
simple protocol ensures only one person speaks at a time, offering a shared use of the communications
medium. Wireless networks use carrier sense protocols and operate in a similar fashion, except the
communications are by way of radio signals or infrared light. Figure 1.6 illustrates the generic carrier
sense protocol.
Figure 1.6 The operation of the carrier sense protocol.
Wireless networks handle error control by having each station check incoming data for altered bits. If the
destination station does not detect errors, it sends an acknowledgment back to the source station. If the
station detects errors, the data link protocol ensures that the source station resends the packet. To
continue the analogy, consider two people talking to each other outside. If one person is speaking and a
disruption occurs, such as a plane flying overhead, the dialog might become distorted. As a result, the
listener asks the speaker to repeat a phrase or two. The wireless network interface generally takes the
shape of a wireless NIC or an external modem that facilitates the modulator and communications
protocols. These components interface with the user appliance via a computer bus, such as ISA (Industry
Standard Architecture) or PCMCIA (Personal Computer Memory Card International Association). The
ISA bus comes standard in most desktop PCs. Many portable computers have PCMCIA slots that accept
credit card-sized NICs. PCMCIA specifies three interface sizes, Type I (3.3 millimeters), Type II (5.0
millimeters), and Type III (10.5 millimeters). Some companies also produce wireless components that
connect to the computer via the RS-232 serial port.
The interface between the user’s appliance and NIC also includes a software driver that couples the client’s application or NOS software to the card. Several de facto driver standards exist, including ODI
(Open Data-Link Interface) and NDIS.
Antenna
The antenna radiates the modulated signal through the air so that the destination can receive it. Antennas
come in many shapes and sizes and have the following specific electrical characteristics:
• Propagation pattern
• Radiation power
• Gain
• Bandwidth
The propagation pattern of an antenna defines its coverage. A truly omnidirectional antenna transmits its
power in all directions, whereas a directional antenna concentrates most of its power in one direction.
Figure 1.7 illustrates the differences. Radiation power is the output of the radio transmitter. Most wireless
network devices operate at less than 5 watts of power.
Figure 1.7 The omnidirectional versus directional antennas.
A directional antenna has more gain (degree of amplification) than the omnidirectional type and is
capable of propagating the modulated signal farther because it focuses the power in a single direction.
The amount of gain depends on the directivity of the antenna. An omnidirectional antenna has a gain
equal to one; that is, it doesn’t focus the power in any particular direction. A directional antenna,
however, is considered to add gain (amplification) to the signal in certain directions. Consider the
example of watering your lawn with a garden hose. Attach a circular sprayer to the end of the hose and
turn the water on. The water pressure is divided among many directions, and the resulting water spray
will reach seven or eight feet. If a more directive nozzle is attached to the hose, the spray might reach
twenty feet because the device concentrates the water pressure in one direction. Similarly, the
combination of transmit power and gain of an antenna defines the distance the signal will propagate.
Long-distance transmissions require higher power and directive radiation patterns. With wireless
networks, these signals are relatively low power, typically one watt or less. Most wireless LANs and
WANs utilize omnidirectional antennas, and wireless MANs use antennas that are more directive. Bandwidth is the effective part of the frequency spectrum that the signal propagates. For example, the
telephone system operates over a bandwidth roughly from 0–4 KHz. This is enough bandwidth to
accommodate most of the frequency components within our voices. Radio wave systems have greater
amounts of bandwidth located at much higher frequencies. Data rates and bandwidth are directly
proportional—the higher the data rates, the more bandwidth you will need.
The Communications Channel
All information systems employ a communications channel along which information flows from source
to destination. Ethernet networks may utilize twisted-pair or coaxial cable. Wireless networks use air as
the medium. At the earth’s surface, where most wireless networks operate, pure air contains gases such
as nitrogen and oxygen. This atmosphere provides an effective medium for the propagation of radio
waves and infrared light. Rain, fog, and snow, however, can increase the amount of water molecules in
the air and can cause significant attenuation to the propagation of modulated wireless signals. Smog
clutters the air, adding attenuation to the communications channel as well. Attenuation is the decrease in
the amplitude of the signal, and it limits the operating range of the system. The ways to combat
attenuation are to either increase the transmit power of the wireless devices, which in most cases is
limited by the FCC, or to incorporate special amplifiers called repeaters that receive attenuated signals,
revamp them, and transmit downline to the end station or next repeater.

Wireless Network Technologies and Standards (1)

Part I
Wireless Network Technologies and Standards

CHAPTER 1
Introduction to Wireless Networking

Many organizations utilize traditional wire-based networking technologies to establish connections
among computers. These technologies fall into the following three categories:
• Local area networks (LANs)
• Metropolitan area networks (MANs)
• Wide area networks (WANs)
LANs support the sharing of applications and printers, transfer of files, and sending e-mail within a room
or building. Today, the industry standard for LANs is ethernet technology with 10baseT Category 5
twisted-pair wiring. MANs, which can cover the size of a college campus or large city, interconnect
LANs by using protocols such as FDDI (Fiber Distributed Data Interface) and depend on leased circuits
and optical fiber for transmission of the data. WANs, on the other hand, utilize telephone circuits, leased
lines, and private circuits to support worldwide networking by using circuit and packet switching
protocols.
Traditional networking technologies offer tremendous capabilities from an office, hotel room, or home.
Activities such as communicating via e-mail with someone located in a faraway town or conveniently
accessing product information from the World Wide Web are the result of widespread networking. But,
limitations to networking through the use of wire-based systems exist because you cannot utilize these
network services unless you are physically connected to a LAN or a telephone connection.
Over the last thirty years, researchers and companies have been busy developing protocols and systems
that provide wireless connectivity for LANs, MANs, and WANs. This work has not been easy and has
met much resistance from end users. Today, though, products are available that fit into all categories of
networks and satisfy the need for mobility. This chapter introduces wireless networking by describing the
following:
• The history of wireless networks
• Wireless network architecture
• The benefits of wireless networking
• Concerns surrounding the implementation and use of wireless networks
• The wireless network market
• The future of wireless networks

The History of Wireless Networks

The first indication of wireless networking dates back to the 1800s and earlier. Indians, for example, sent
information to each other via smoke signals from a burning fire. The sender would simply wave a deer
skin over the fire—in sequences similar to Morse code—to send messages warning others that a war was
imminent, or just to say, “I’ll be late for dinner.” This smoke signal system was a true network. People
manning intermediate fires would relay messages if a great distance separated the source of the message
and the destination. The world has seen much progress since those days. Messengers on horseback
eventually became a more effective means of transferring information, while later the telephone made
communications much easier and faster.
Prior to the nineteenth century, scientists thought light was the only wavelength component of the
electromagnetic spectrum. During the nineteenth and twentieth centuries, researchers learned that the
spectrum actually consists of longer wavelengths (lower frequencies) as well. Experiments showed that
lower frequencies, such as radio waves and infrared light, could be sent through the air with moderate
amounts of transmit power and easy-to-manufacture antennas. As a result, companies began building
radio transmitters and receivers, making public and private radio communications, television, and
wireless networking possible.
Network technologies and radio communications were brought together for the first time in 1971 at the
University of Hawaii as a research project called ALOHANET. The ALOHANET system enabled
computer sites at seven campuses spread out over four islands to communicate with the central computer
on Oahu without using existing, unreliable, expensive phone lines. ALOHANET offered bi-directional
communications, in a star topology, between the central computer and each of the remote stations. The
remote stations had to communicate with each other via the centralized computer. ALOHANET became
popular among network researchers because of the unique combination of packet switching and
broadcast radio. The U.S. military embraced the technology, and DARPA (Defense Advanced Research
Projects Agency) began testing wireless networking to support tactical communications in the battlefield.
Because of limited spectrum allocations, radio-based networks could only deliver very low data rates.
Research done at the University of Hawaii and DARPA, however, helped pave the way for the
development of the initial ethernet technology, as well as fueled the development of radio-based
networks available today.
The advent of the wired ethernet technology steered many commercial companies away from radio-based
networking components toward the production of ethernet-related products. Companies did not mind
running cable throughout and between their facilities to take advantage of ethernet’s whopping 10 Mbps
data rates. In the eighties, amateur radio hobbyists, “hams,” kept radio networking alive within the U.S. and Canada by designing and building Terminal Node Controllers (TNCs) to interface their computers
through ham radio equipment (see fig. 1.1). These TNCs act much like a telephone modem, converting
the computer’s digital signal into one that a ham radio can modulate and send over the airwaves by using
a packet switching technique. In fact, the American Radio Relay League (ARRL) and the Canadian
Radio Relay League (CRRL) have been sponsoring the Computer Networking Conference since the early
eighties in order to provide a forum for the development of wireless WANs. Thus, hams have been
utilizing wireless networking for years, much longer than the commercial market.
Figure 1.1 The ham radio terminal node controllers.
In 1985, the Federal Communications Commission (FCC) made the commercial development of radiobased
LAN components possible by authorizing the public use of the Industrial, Scientific, and Medical
(ISM) bands. This band of frequencies resides between 902 MHz and 5.85 GHz, just above the cellular
phone operating frequencies. The ISM band is very attractive to wireless network vendors because it
provides a part of the spectrum upon which to base their products, and end users do not have to obtain
FCC licenses to operate the products. The ISM band allocation has had a dramatic effect on the wireless
industry, prompting the development of wireless LAN components.
During the late eighties, the decreasing size of computers from desktop machines to laptops allowed
employees to take their computers with them around the office and on business trips. Computer
companies then scrambled to develop products that would support wireless connectivity methods. In
1990, NCR began shipping WaveLAN, one of the first wireless LAN adapters for PCs. Motorola was
also one of the initial wireless LAN vendors with a product called Altair. These early wireless network
adapters had limited network drivers, but soon worked with almost any network operating system.
Rapidly, companies such as Proxim, Xircom, Windata, and others began shipping their products as well.
These initial companies were pioneers in the wireless networking arena. They felt their wireless products
would feed a market desperately wanting to meet mobility needs. Network managers and system
administrators, however, did not trust the technology enough to purchase the pricy wireless adapters. The
WaveLAN network adapters, for example, initially listed for $1,400 each. Vendors quickly found that
they had to reduce prices. Businesses were afraid these new wireless products lacked security, were too
slow (at least slower than ethernet), and were not standardized. Over time, though, vendors began
incorporating encryption to protect data transmissions, and operation at higher frequencies increased the
bandwidth to near-ethernet speeds. The market also saw a substantial drop in price to $300–$500 per
card. The lack of standards, however, limited widespread use of wireless LAN products.
The current depressed state of the wireless LAN market should change as standards mature. The Institute
for Electrical and Electronic Engineers (IEEE) 802 Working Group, responsible for the development of
LAN standards such as ethernet and token ring, initiated the 802.11 Working Group to develop a
standard for wireless LANs. This group began operations in the late eighties under the chairmanship of
Vic Hayes, an engineer from NCR. At the present time, 802.11 is still working on the standard. A final
standard should pass in 1997.
End users and network managers have had a difficult time showing a positive business case for
purchasing wireless LAN components in the office unless there is a requirement for mobility. Most sales
of wireless LAN adapters to date have been in healthcare and financial environments. Sensing a bleak
market for wireless LAN products, wireless LAN vendors began equipping their wireless LAN
components in 1995 with directional antennas to facilitate point-to-point connections between buildings
located within the same metropolitan area. These wireless MAN products satisfy a widespread need—the
capability to connect facilities where traditional cable installation and leased circuits are costly. The sales
of these wireless MAN products have been favorable.
The most widely accepted wireless network connection, though, has been wireless WAN services, which
began surfacing in the early nineties. Companies such as ARDIS and RAM Mobile Data were first in
selling wireless connections between portable computers, corporate networks, and the Internet. This
service enables employees to access e-mail and other information services from their personal appliance
without using the telephone system when meeting with customers, traveling in the car, or staying in a hotel room.
Narrowband Personal Communications Services (PCS), a spectrum allocation located at 1.9 GHz, is a
new wireless communications technology offering wireless access to the World Wide Web, e-mail, voice
mail, and cellular phone service. Vice President Al Gore kicked off the FCC PCS auction in 1995 by
selling 30-MHz licenses to television and telephone companies. The total take for 1995 was $7.7 billion.
The U.S. government expects to raise $15 billion from the auctioning during 1996.
Because of PCS, the wireless industry is quickly gaining momentum. As a result, a vast number of
wireless networking products should appear on the market in 1997. SkyTel began shipping the first PCS
product in 1996, a pocket-sized two-way pager, which can receive pages as well as respond.