Wireless Networking 169
Signals and Noise on a WLAN
On a wired Ethernet network, it is usually a fairly simple process to diagnose the cause
of interference. When using RF technology, you must take into account many kinds of
interference:
■ Narrowband—This is the opposite of spread spectrum technology. As the name
implies, narrowband does not affect the entire frequency spectrum of the wireless
signal. One solution to a narrowband interference problem is simply changing
the channel that the AP is using. Actually, diagnosing the cause of narrowband
interference can be a costly and time-consuming experience. To identify the source
requires a spectrum analyzer and even a low cost model can cost $3000 to $4000
in the U.S. Examples of narrowband interference include CB radios and ham
radios.
■ All band—All band interference affects the entire spectrum range. Bluetooth
technologies hop across the entire 2.4 GHz many times per second and can cause
significant interference on an 802.11b network. It is not uncommon to see signs
in facilities that use wireless networks requesting that all Bluetooth devices be
shut down before entering. In homes and offices, a device that is often overlooked
as causing interference is the standard microwave oven. Leakage from a micro-
wave of as little as 1 watt into the RF spectrum can cause major network disrup-
tion. Wireless phones operating in the 2.4-GHz spectrum can also cause network
degradation.
■ Weather—Generally, the RF signal is not affected by even the most extreme
weather conditions. However, fog or very high moisture conditions can and do
affect wireless networks. Lightning can also charge the atmosphere and alter the
path of a transmitted signal.
Signal Range Concerns
The first and most obvious source of a signal problem is the transmitting station and
antenna type. A higher output station transmits the signal further, and a parabolic dish
antenna that concentrates the signal increases the transmission range.
In a small office, home office (SOHO) environment, most access points utilize twin

omnidirectional antennae that transmit the signal in all directions, thereby reducing
the range of communication. Figure 3-50 illustrates an omnidirectional antenna.
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170 Chapter 3: Networking Media
Figure 3-50 Omnidirectional Antenna
Wireless Security
The exponential growth of networking, including wireless technologies, has led to
increased security risks. Increasing the security means increasing the time spent manag-
ing the system.
The first level of security in a wireless LAN consists of protecting the radio frequency
waveform itself. Wireless access points radiate radio waves over a large area that is
not contained in a physical building, which makes the radio waves accessible to eaves-
droppers and thus increases vulnerability. The radio waves of wireless bridges are con-
centrated in a beam. An eavesdropper must get into the beam path to intercept the
communication. Therefore, wireless access points usually require better security than
wireless bridges.
WEP
Wired equivalent privacy (WEP) is a security mechanism, defined within the 802.11
standard, that is designed to protect the over-the-air transmission between wireless
LAN access points and NICs. The IEEE 802.11b requires 40-bit encryption keys.
However, many vendors, such as Cisco, support the optional 128-bit standard.
The main goals with WEP follow:
■ Deny access to the network by unauthorized users who do not possess the appro-
priate WEP key
■ Prevent the decoding of captured WLAN traffic that is WEP-encrypted without
the possession of the WEP key
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Wireless Networking 171
WEP uses the RC4 stream cipher that was invented by Ron Rivest of RSA Data Secu-
rity, Inc., (RSADSI) for encryption. The RC4 encryption algorithm is a symmetric-stream

cipher that supports a variable-length key. A symmetric cipher uses the same key for
both encryption and decryption. The key is the one piece of information that must be
shared by both the encrypting and decrypting endpoints.
Recently, encryption analysts have reported weaknesses in the authentication and WEP
encryption schemes in the IEEE 802.11 WLAN standard. Improvements on WEP have
been developed to address the weaknesses found by encryption analysts. However, it is
not recommended to use WEP as a sole security mechanism for a WLAN. WEP should
be supplemented with additional higher-level security mechanisms, such as a VPN or
firewalls.
VPN, EAP, and LEAP
A number of new security solutions and protocols, such as Virtual Private Network
(VPN) and Extensible Authentication Protocol (EAP) are evolving. Using EAP, the
access point does not provide authentication to the client but passes the duties to a
more sophisticated server designed for that purpose. Using an integrated VPN server,
VPN technology creates a tunnel on top of an existing protocol such as IP. This tunnel
is a Layer 3 connection as opposed to the Layer 2 connection between the AP and the
sending node.
The following list briefly describes EAP and LEAP:
■ EAP-MD5 Challenge—EAP is the earliest authentication type, which is very similar
to Challenge Handshake Authentication Protocol (CHAP) password protection
on a wired network. EAP allows wireless client adapters that can support differ-
ent authentication types to communicate with different back end servers, such as
Remote Authentication Dial-In User Service (RADIUS).
■ Lightweight Extensible Authentication Protocol (LEAP)—Cisco has developed
a derivation of EAP based on mutual authentication called LEAP. Mutual authenti-
cation means that both the user and the access point to which the user is attempt-
ing to connect must be authenticated before access onto the corporate network is
allowed. Mutual authentication protects enterprises from unauthorized APs serving
as a potential entrance into the network. LEAP is the type of authentication pri-
marily used on Cisco WLAN access points. LEAP provides security during credential

exchange, encrypts using dynamic WEP keys, and supports mutual authentication.
VPN security levels include the following:
■ User authentication—Allows only authorized users to connect, send, and receive
data over the wireless network.
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172 Chapter 3: Networking Media
■ Encryption—Provides encryption services, further protecting the data from
intruders.
■ Data authentication—Ensures the integrity of the data, authenticating source,
and destination devices.
VPN technology effectively closes the wireless network because an unrestricted WLAN
automatically forwards traffic between nodes that appear to be on the same wireless
network. WLANS often extend outside the perimeter of the home or office in which
they are installed, and without security, intruders can infiltrate the network with little
effort. Conversely, it takes minimal effort on the part of the network administrator to
provide low-level security to the WLAN.
Summary
In this chapter, you learned the following key points:
■ Electricity is based on the ability of electrons of certain types of atoms to separate,
or flow, from the confines of their atoms.
■ Opposite charges attract and like charges repel. Electricity flows from negative to
positive within electrical circuits.
■ Materials can be classified as insulators, conductors, or semiconductors, depending
on their ability to allow electrons to flow.
■ The concepts of voltage, current, resistance, and impedance provide a means of
measuring electricity, which is required to be able to design and manufacture
electronic devices.
■ Alternating current and direct current are the two types of current. AC provides
power to our homes, schools, and work places. DC is used with electrical devices
that depend on a battery to function.

■ STP cable combines the techniques of shielding, cancellation, and twisting of
wires. ScTP cable is essentially a twisted pair wrapped in a metallic foil shield.
■ UTP cable is a four-pair wire medium used in a variety of networks.
■ Coaxial cable consists of four main parts: copper conductor, plastic insulation,
braided copper shielding, and outer jacket.
■ Specifications or standards are sets of rules or procedures that are widely used
and serve as the accepted method of performing a task.
■ Optical fiber is a good transmission medium when it is properly installed, tested,
and maintained.
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Summary 173
■ Light energy, a type of electromagnetic energy wave, is used to transmit large
amounts of data securely over relatively long distances.
■ Light rays obey the laws of reflection and refraction as they travel through a glass
fiber, which allows fibers with the property of total internal reflection to be man-
ufactured. Total internal reflection makes light signals stay inside the fiber, even if
the fiber is not straight.
■ Attenuation of a light signal becomes a problem over long cables, especially if
sections of cable are connected at patch panels or spliced. Therefore, cable and
connectors must be properly installed and thoroughly tested with high-quality
optical test equipment before their use.
■ In wireless data communication, the radio spectrum is the part of the electromag-
netic spectrum used to transmit voice, video, and data.
■ Modulation is the process by which the amplitude, frequency, or phase of a radio
frequency or lightwave is changed to transmit data.
■ To take advantage of unlicensed radio bands, you have to use spread-spectrum
techniques. Two important modulation technologies are frequency-hopping
spread spectrum (FHSS) and direct-sequence spread spectrum (DSSS). DSSS
offers greater reliability and more throughput than FHSS.
■ The wireless signal deteriorates with distance. A wireless device connects at a

slower speed if it is moved out of optimal range.
■ Noise can be caused through structures (walls with metal) or by electrical equip-
ment. Both adversely affect the range of wireless communications.
■ Wireless standards include IEEE 802.11, IEEE 802.11a, IEEE 802.11b, and
IEEE 802.11g.
■ Wired equivalent privacy (WEP) is a security mechanism, defined within the
802.11 standard, that is designed to protect the over-the-air transmission
between wireless LAN APs and NICs.
■ A number of new security solutions and protocols, such as VPN, EAP, and LEAP,
are emerging.
To supplement all that you’ve learned in this chapter, refer to the chapter-specific Videos,
PhotoZooms, and e-Lab Activities on the CD-ROM accompanying this book.
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174 Chapter 3: Networking Media
Key Terms
AM (amplitude modulation) Modulates the height of the carrier wave.
angle of incidence The angle at which the ray hits the glass surface.
angle of reflection The angle between the reflected ray and the normal.
attenuation Loss of communication signal energy.
backbone The part of a network that acts as the primary path for traffic that is
most often sourced from, and destined for, other networks.
coaxial cable A cable consisting of a hollow outer cylindrical conductor that
surrounds a single inner wire conductor.
crosstalk The unwanted reception of electromagnetic signals on a wire from a
nearby wire.
dispersion The broadening of light signals along the length of the fiber.
DSSS (direct-sequence spread spectrum) A technology in which transmissions are
more reliable because each bit (1 or 0) is represented by a string of 1s and 0s, called
a chipping sequence.
EIA (Electronic Industries Association) A group that specifies electrical transmission

standards. The EIA and TIA have developed numerous well-know communication
standards.
EMI (electromagnetic interference) An electromagnetic field that has the potential to
disrupt the operation of electronic components, devices, and systems in its vicinity.
FHSS (frequency-hopping spread spectrum) A technology in which transmissions
hop from one frequency to another in random patterns. This feature enables the
transmissions to hop around narrowband interference, resulting in a clearer signal
and higher reliability of the transmission.
fiber-optic cable A physical medium capable of conducting modulated light trans-
mission. Compared with other transmission media, fiber-optic cable is more expensive
but is not susceptible to electromagnetic interference. Sometimes called optical fiber.
FM (frequency modulation) Modulates the frequency of the wave.
IEEE (Institute of Electrical and Electronic Engineers) A professional organization
whose activities include the development of communications and network standards.
IEEE LAN standards are the predominant LAN standards.
impedance The resistance to the movement of electrons in an AC circuit.
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Key Terms 175
media The plural of medium. Media refers to various physical environments through
which transmission signals pass. Common network media include twisted-pair, coaxial,
fiber-optic cable, and the atmosphere (through which microwave, laser, and infrared
transmission occurs).
modal dispersion When multiple modes of light propagating through fiber travel
different distances, depending on their entry angles, which causes them to arrive at the
destination (receiving end of the cable) at slightly different times.
multimode A type of fiber-optic cable that transmits more than one light path.
noise An unwanted electrical signal on a wire that interferes with the quality of the
signal by altering its shape.
patch panel An assembly of pin locations and ports that can be mounted on a rack
or wall bracket in the wiring closet. Patch panels act like switchboards that connect

workstations’ cables to each other and to the outside.
PM (phase modulation) Modulates the polarity (phase) of the wave.
reflection The photons of light striking a surface and leaving that surface in an equal
but opposite direction.
refraction The change in direction of a beam of light when it enters another medium.
resistance The property of a material that resists electron movement.
RFI (radio frequency interference) The noise on wires caused by radio signals.
single-mode An optical fiber that has only one mode of light transmission. Contrast
with multimode.
SS (spread spectrum) A modulation technique developed in the 1940s that spreads a
transmission signal over a broad band of radio frequencies. The term spread spectrum
describes a modulation technique that sacrifices bandwidth to gain signal-to-noise
performance.
standard A set of rules or procedures that are either widely used or officially specified.
STP (shielded twisted-pair) A two-pair wiring medium used in a variety of network
implementations. STP cabling has a layer of shielded insulation to reduce EMI.
thicknet An early form of coaxial cable using 10BASE5 for networking. Thicknet
was once desirable because it could carry signals up to 500 meters.
thinnet A simple, thin, coaxial network cable for the 10BASE2 system. Thinnet can
carry a signal only 185 meters, but was much easier to work with than thicknet.
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176 Chapter 3: Networking Media
TIA (Telecommunications Industry Association) A standards association that pub-
lishes standards for telecommunications.
UTP (unshielded twisted-pair) A four-pair wire medium used in a variety of networks.
wavelength The length of a wave measured from any point on one wave to the corre-
sponding point on the next wave. The wavelength of light is usually measured in
nanometers (nm).
WEP (wired equivalent privacy) A security mechanism, defined within the 802.11
standard, that is designed to protect the over-the-air transmission between wireless

LAN APs and NICs.
Check Your Understanding
Complete all the review questions to test your understanding of the topics and con-
cepts in this chapter. Answers are listed in Appendix C, “Check Your Understanding
Answer Key.”
1. Match the columns:
1) Neutrons A) Particles that have a negative charge
2) Protons B) Particles that have no charge (neutral)
3) Electrons C) Particles that have a positive charge
A. 1-C, 2-B, 3-A
B. 1-A, 2-C, 3-B
C. 1-B, 2-C, 3-A
D. 1-B, 2-A, 3-C
2. Which of the following regarding electricity is untrue?
A. Opposite charges react to each other with a force that causes them to be
attracted to each other.
B. Like charges react to each other with a force that causes them to repel
each other.
C. In the case of opposite and like charges, the force increases as the charges
move closer to each other.
D. None of the above.
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Check Your Understanding 177
3. Match the following to their respective units of measurement:
1) Voltage A) Ohm
2) Current B) Ampere
3) Resistance C) Volt
A. 1-C, 2-B, 3-A
B. 1-B, 2-C, 3-A
C. 1-A, 2-C, 3-B

D. 1-C, 2-B, 3-A
4. Electrons flow in loops called .
A. Open; voltage
B. Closed; voltage
C. Open; circuits
D. Closed, circuits
5. What is the maximum cable length for STP?
A. 100 feet
B. 150 feet
C. 100 meters
D. 1000 meters
6. How many pairs of wires make up a UTP cable?
A. 2
B. 4
C. 6
D. 8
7. Which connector does UTP use?
A. STP
B. BNC
C. RJ-45
D. RJ-69
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178 Chapter 3: Networking Media
8. What is an advantage that coaxial cable has over STP or UTP?
A. It is capable of achieving 10 Mbps to 100 Mbps.
B. It is inexpensive.
C. It can run for a longer distance unboosted.
D. None of the above.
9. What does the twisting of the wires do in a twisted-pair cable?
A. It makes it thinner.

B. It makes it less expensive.
C. It reduces noise problems.
D. It allows six pairs to fit in the space of four pairs.
10. What is the importance of the EIA/TIA standards? Select all that apply.
A. They provide a framework for the implementation of the OSI reference
model.
B. They provide guidelines for manufacturers to follow to ensure compatibility.
C. They provide the minimum media requirements for multiproduct and multi-
vendor environment.
D. None of the above.
11. A fiber-optic cable transmits multiple streams of LED-generated
light.
A. Multimode
B. Multichannel
C. Multiphase
D. None of the above
12. What is one advantage of using fiber-optic cable in networks?
A. It is inexpensive.
B. It is easy to install.
C. It is an industry standard and is available at any electronics store.
D. It is capable of higher data rates than either coaxial or twisted-pair cable.
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