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.