Appendix A
Answers to Review Questions
Chapter 1: Introduction to Computer Networking
1. C, E. Wireless LAN technology operates at Layers 1 (Physical) and 2 (Data Link) of the OSI model. The Session layer opens, closes, and manages sessions between end-user application processes. The Network layer is responsible for addressing and routing functions of data and the Application layer is the interface to the user.
2. C. The bus topology is also known as a high-speed linear bus and was commonly used with early IEEE 802.3 networks. The ring topology is rarely used with LANs today but is still widely used by Internet service providers (ISPs) for high-speed, resilient backhaul connections over fiber-optic links. In a mesh topology, each device in the mesh network has one or more connections to other devices. The star topology consists of multiple devices connected by a central connection device and is the most commonly used method of connecting devices on a LAN today.
3. B. The Physical layer is the lowest layer in the OSI model and consists of bit-level data streams and computer network hardware connecting the devices together. The Data Link layer is responsible for organizing bit-level data for communication between devices on a network, and the Network layer is responsible for addressing and routing functions of data.
4. B. The logical address is an IP address. The Layer 2 address is the hardware address or physical address on the network adapter.
5. D. The Data Link layer is responsible for organizing bit-level data for communication between devices on a network and detecting and correcting Physical layer errors. The Physical layer consists of bit-level data streams and computer network hardware connecting the devices together. The Application layer provides an interface to the user and the Transport layer is for connection-oriented and connectionless communications.
6. B. The Network layer is responsible for addressing and routing of information. The Physical layer consists of bit-level data streams and computer network hardware connecting the devices together. The Transport layer is for connection-oriented and connectionless communications. The Application layer provides an interface to the user, and the Transport layer is for connection-oriented and connectionless communications.
7. C. Encapsulation allows for Application layer data communication between two stations using lower layers as a support system. Logical addressing is the Layer 3 or IP address, and physical addressing is the hardware or media access control address. Data encryption scrambles the data, and point-to-point communications may be used to connect LANs together.
8. A. The ring topology may use a token passing access method. The bus topology is also known as a high-speed linear bus and was commonly used with early IEEE 802.3 networks. A mesh topology is where each device in the mesh network has one or more connections to other devices. The star topology consists of multiple devices connected by a central connection device and is the most commonly used method of connecting devices on a LAN today.
9. D. The Application layer provides an interface to the user. The Physical layer consists of bit-level data streams and computer network hardware connecting the devices together. The Data Link layer is responsible for organizing bit-level data for communication between devices on a network. The Presentation layer provides delivery and formatting of information for processing and display, and the Transport layer is for connection-oriented and connectionless communications.
10. A. The media access control (MAC) address is a unique address of the network adapter. The logical address is an IP address as well as the Layer 3 address.
11. D. Encapsulation is adding header and trailer information to a frame. The MAC address is a physical address assigned by the device manufacturer. The IP address is the logical address assigned to a device and the topology is the physical arrangement of devices in a network.
12. A, C. Peer communication is a logical or “horizontal” link between devices. The vertical link would be equivalent to the encapsulation between layers. The physical link is related to addressing.
13. B. The physical address of a network device determines the actual hardware address and is used to identify the source and destination of a frame. The routing information is part of the logical addressing process as well as the logical location.
14. B. The Data Link layer of the OSI model is responsible for compiling or packaging bits into frames. The Physical layer allows frames to be sent and received across a medium. The Transport layer is responsible for connection-oriented or connectionless protocols. The Network layer is responsible for addressing and routing of frames, and the Application layer is the interface to the user.
15. D. TCP is a connection-oriented protocol that uses acknowledgments. UDP is a connectionless protocol and does not guarantee delivery. IP is used for addressing and routing. ARP is used to resolve physical addresses to logical addresses, and HTTP is an Application layer protocol.
16. A. Internet Protocol (IP) is used for addressing and routing functions and operates at Layer 3 of the OSI model. TCP is a connection-oriented delivery protocol. UDP is a connectionless protocol and ARP is used to resolve addresses.
17. D. The Network layer is responsible for translating physical (MAC) addresses into logical (IP) addresses. The Application layer is where the user sends data to the OSI model. The Session layer opens, closes, and manages sessions, and the Transport layer is for session delivery.
18. B. The Data Link layer consists of two sublayers the LLC and the MAC. The PLCP and PMD are at the Physical layer. TCP and UDP are Transport layer protocols, and HTTP and FTP are Application layer protocols.
19. A. The Physical layer of the OSI model is used to deliver data to a destination. The Data Link layer is responsible for organizing bit-level data for communication between devices on a network. The Network layer is responsible for addressing and routing functions of data, and the Transport layer is responsible for connections.
20. B. 192.168.200.1 is a valid logical IP address. 255.255.0.0 is an example of a subnet mask. Both AB.CD.EF12.34.56 and 12.34.56.AB.CD.EF would represent physical (MAC) addresses.
Chapter 2: Introduction to Wireless Local Area Networking
1. A, C. Semidirectional and highly directional antennas are used for point-to-point links. Omnidirectional antennas are for point-to-multipoint links. Long-range omnidirectional antennas do not exist.
2. B. Point-to-multipoint links typically have three or more connections.
3. A. MIMO can use reflections due to the multiple radio chain technology. Reflections will hurt throughput in a single-input single-output (SISO) technology. Antenna diversity is used with SISO to lessen the effects of reflections.
4. D. The FCC is the local regulatory authority responsible for frequency regulation in the United States. ETSI is a European standards organization responsible for producing standards for information and communications technologies. The Wi-Fi Alliance is an interoperability testing organization. The IEEE creates standards, and WPA is a pre-802.11 certification by the Wi-Fi Alliance.
5. D. 802.11g LANs operate in the 2.4–2.5 GHz ISM band. 900 MHz is not used with 802.11 wireless LANs, and 5 GHz is for 802.11a.
6. E. The Wi-Fi Alliance performs interoperability testing and verifies standards compliance. The FCC is the local regulatory authority responsible for frequency regulation in the United States. ETSI is a European standards organization responsible for producing standards for information and communications technologies. The IEEE creates standards and WPA2 is a post-802.11 certification by the Wi-Fi Alliance.
7. C. 802.11a uses OFDM; ERP-OFDM is used in 802.11g. HR/DSSS is used with 802.11b and 802.11g. FHSS is specified in the original IEEE 802.11 standard and is obsolete with respect to modern Wi-Fi technology.
8. A, C, D. 802.11b can use 1, 2, 5.5, and 11 Mbps. 6 and 12 Mbps are OFDM data rates and used in 802.11a and 802.11g networks.
9. A, D. 802.11g is backward compatible with DSSS and HR/DSSS. 802.11a OFDM operates in the 5 GHz band. ERP-OFDM is not used in 802.11a technology and 802.3af is for Power over Ethernet (PoE).
10. A. The UNII-3 band can be used indoors or outdoors, but was at one time mainly used outdoors only.
11. C. 802.11i addresses security. 802.11e addresses quality of service. DSSS is a PHY technology defined in the IEEE 802.11 standard, and MIMO (multiple-input multiple-output) is used with IEEE 802.11n technology.
12. B. Wi-Fi Alliance performs interoperability testing for IEEE 802.11 wireless LAN standards-based equipment. The IEEE creates standards. The FCC is the local regulatory authority responsible for frequency regulation in the United States and ETSI is a European standards organization responsible for producing standards for information and communications technologies.
13. D. WMM is a proactive Wi-Fi Alliance certification for quality of service. WPA and WPA are certifications that address wireless security. IEEE 802.11w is for protection of management frames and IEEE 802.11r is for Fast Transition (FT); neither currently has an associated Wi-Fi Alliance certification.
14. A. Wi-Fi Protected Setup was designed with SOHO users in mind. Enterprise organizations use IEEE 802.11i, WPA, and WPA2 certifications. The FCC is the local regulatory authority responsible for frequency regulation in the United States.
15. C, D. 802.11g can use ERP-OFDM and DSSS. The 802.11 standard specifies FHSS for 1 and 2 Mbps. OFDM is used with 802.11a devices, and MIMO (multiple-input multiple-output) is used with 802.11n technology.
16. D. WPA was designed as a pre-802.11i solution for wireless security and intended as an interim certification. 802.11a, 802.11n, and 802.11g are communication amendments, and the 802.11e amendment specifies quality of service.
17. D. 802.11e is a specific function amendment addressing quality of service. 802.11e can operate in either the 5 GHz frequency range or the 2.4 GHz frequency range. 802.11i addresses wireless security, and 802.11e can work with all data rates, not only 1, 2, 5.5, and 11 Mbps.
18. D. The IEEE requires 6, 12, and 24 Mbps for 802.11a. The data rates of 1, 2, 5.5, and 11 Mbps are for the 2.4 GHz band and 802.11b/g.
19. B, C. WPA 2.0 Personal and WPS are both designed with the small business in mind. Wired Equivalent Privacy (WEP) is legacy and not secure. Wi-Fi Multimedia (WMM) addresses QoS, and WPA 2.0 enterprise is designed for larger organizations.
20. A, D. WPA 2.0 consists of personal mode using passphrase and enterprise mode using 802.1X/EAP.
Chapter 3: Wireless LAN Infrastructure Devices
1. D. In computer terminology, half duplex is two-way communication but only one way at a time. Full duplex is two-way communication in both directions simultaneously.
2. C. An autonomous access point is an intelligent, self-contained network infrastructure device. Controller-based access points (also called thin access points) work with a wireless LAN controller.
3. A, C, D. SOHO access points typically are managed from a web browser and do not have a command-line interface feature.
4. B, C. Bridges must be on the same RF channel and have the same SSID in order to communicate.
5. B, E. Wireless repeaters do extend the cell size and will potentially allow more users to connect. However, using a wireless repeater will decrease throughput.
6. B. A wireless LAN controller uses centralized administration, not distributed administration.
7. B. Many SOHO access points use 15 dBm or 32 mW for transmit output power.
8. C. The PoE standard specifies 48 VDC as nominal. The range is 32–57 VDC.
9. A. A midspan device will inject power into an Ethernet cable. Endpoint power is delivered directly from a switch or controller.
10. B. Layer 2 is the Data Link layer. A MAC address is a unique identifier of the network card.
11. A, C. SOHO uses HTTP or HTTPS for configuration. Enterprise can also use CLI. SMTP is Simple Mail Transfer Protocol.
12. B. An administrator should avoid configuring an access point from the wireless side of the network unless absolutely necessary.
13. A, B. Depending on the specific function, APs operate at Layers 1 and 2. Repeaters function only at Layer 1.
14. A, B, D. Enterprise access points have adjustable output power. Power sourcing equipment is used in PoE to deliver power and data.
15. B. VLANs involve logical separation of ports.
16. A. A controller-based access point connected to a port on the switch is considered to have direct connectivity.
17. B. PSE delivers DC power, not RF power. The DC power is delivered to an end device such as an access point.
18. C. Root access point is the default mode in most cases. An access point in root access point mode allows users to connect to the network.
19. A, B. Single-port and multiport injectors combine power and data in the same cable. Endpoint power is out of the switch port. There is no such thing as an endspan injector.
20. A, B, D. Wireless LAN controllers may contain many advanced features, including centralized administration, captive portal, and built-in RADIUS services. Network Address Translation (NAT) and IP routing are common in wireless residential gateway devices.
Chapter 4: Wireless LAN Client Devices
1. D. Wireless USB adapters connect through a USB port in the notebook computer. Virtually all notebook computers have USB ports. PCI adapters are for desktop computers and are installed in an available PCI slot on the motherboard. Wireless Full Mini-PCIe is internal to the device and would require an available interface.
2. C. PCMCIA cards are available in three types. The only difference in the three types is the thickness. PCI adapters are for desktop computers and are installed in an available PCI slot on the motherboard. A wireless Half Mini-PCIe adapter is internal to the device and would require an available interface. An ISA (Industry Standard Architecture) adapter is a legacy interface within a desktop computer.
3. D. SDIO cards were originally designed for flash memory storage used in digital cameras and evolved to be used in IEEE 802.11 wireless devices. PCMCIA cards are available in three types. The only difference in the three types is the thickness. Because of advancements in technology, both PCMCIA and SD cards are not as popular as they once were but are still available and used. PCI adapters are for desktop computers and are installed in an available PCI slot on the motherboard. An ISA (Industry Standard Architecture) adapter is a legacy interface within a desktop computer. It would be rare to find a wireless adapter that uses an ISA slot.
4. B. A PCI adapter is a 32-bit card that requires a PCI slot inside a desktop computer. Notebook computers, tablets, and barcode scanners with either have built-in wireless capabilities or a port for an external adapter interface.
5. A. A device driver is a required component for the USB adapter to function with the operating system. Installation of client utility software may not be required when using a device that has the wireless client software built into the operating system, such as Windows Wireless Zero Configuration. Profiles are typically a function of the client utility software.
6. B. A USB 2.0 adapter can be connected to a port on the outside of the computer. Mini-PCI and Half Mini-PCIe are typically used in notebook computers and other portable devices and require some level of disassembly. PCMCIA cards can be used in desktop computers only if an internal PCI adapter is used, which will require disassembly of the computer case.
7. C. A wireless workgroup bridge will connect an Ethernet segment to a wireless network, allowing all devices connected to a common physical layer boundary to communicate wirelessly. A PCMCIA adapter is used to connect a single device such as a notebook computer to a wireless network. An Ethernet bridge is not a wireless device and is used to connect Ethernet segments together.
8. B. The original USB standard was intended to replace serial and parallel ports. A PCI slot is found on the motherboard in a desktop computer. ISA (Industry Standard Architecture) and EISA (Extended ISA Industry Standard Architecture) are also slots that would be found on some motherboards in a desktop computer.
9. A. Serial communication transmits one bit at a time. Parallel transmits several bits at a time.
10. D. A Mini-PCI card may be mounted in a notebook computer motherboard by removing a panel within the computer case. PCI adapters are for desktop computers and are installed in an available PCI slot on the motherboard, and PCMCIA, another name for PC Card, will use an external interface on a notebook computer.
11. B. Most manufacturers recommend installing a wireless USB adapter at a specific point. This is usually after the device driver has been copied to the computer during the setup process. In order for the device drivers to load, the device must be powered on. USB and other adapters are capable of being inserted or removed while a device is powered on. Technical support should be called when the user has exhausted other troubleshooting steps.
12. D. Enterprise client utilities have more advanced features such as a site survey utility. PCI configuration includes physical settings prior to installation. A spectrum analyzer is a separate product used to analyze radio frequency. A setup wizard can be a part of a SOHO-grade adapter as well as an enterprise-grade adapter.
13. B. Device drivers are required in order for the network adapter to communicate with the operating system. A Mini-PCI card is used to allow a device to connect to a network. Third-party and enterprise client utilities are used to configure the settings for a wireless network.
14. B. A wireless workgroup bridge acting as a client device will connect an Ethernet segment to an access point, eliminating the need to install wireless adapters in all of the Ethernet computers. Two wireless NICs connected together are said to be in ad hoc mode. Connecting two client bridges together is not common practice.
15. C. CF cards are identical in length and width. Type I is 3.3mm thick and Type II is 5.0mm thick. The other characteristics are the same.
16. B, C. PCMCIA and USB devices connect to an interface external to the computer and no disassembly is required. PCI, PCIe, and Mini-PCI adapters all require some type of disassembly of the computer device.
17. D. Pocket PCs have SD slots and can use SDIO cards. Access points may use a Mini-PCI adapter or have a surface mount radio adapter. Not all desktop computers or notebook computers have interfaces for SDIO cards.
18. A. Wireless network cards require device drivers in order for the card to work with the computer operating system. The OS (operating system) uses the device driver to control the wireless network adapter or other device that is installed.
19. A. Wireless workgroup bridges can connect wired devices to a wireless LAN. Mini-PCI adapter and PCI adapters are standalone adapters used to connect a device to a wireless network.
20. B. Device drivers are required. A third-party client utility is optional because manufacturers usually include a utility with the device.
Chapter 5: Physical Layer Access Methods and Spread-Spectrum Technology
1. C. IEEE wireless LAN devices use half-duplex communication. Half duplex is defined as two-way communication only one way at a time. Wired LANs can use full-duplex communication, which is two-way communication transmitting in both directions simultaneously. An example of duplex is to combine signals from two different frequencies into a single transmitter/receiver.
2. A. DSSS devices operate in the 2.4 to 2.5 GHz ISM band. OFDM devices operate in the 5 GHz UNII bands.
3. B. 802.11g operates in the 2.4 GHz ISM band. A total of three access points can be co-located before interference becomes an issue.
4. D. The IEEE 802.11n amendment devices use MIMO, multiple radio chains, and antennas to operate. 802.11a/b/g devices use one radio and may use multiple antennas for diversity.
5. C. Spread-spectrum technology sends data over many subcarrier frequencies. Narrowband technology is not used in IEEE-based WLANs but is used in other technology such as radio and TV. Wireless broadband provides high-speed wireless data communications and wireless Internet over a wide area network. Wideband uses a wide range of frequencies, and spectral mask refers to the signal levels of the radio frequency.
6. B, C, D. 802.11b channels need to be separated by at least five channels or 25 MHz to be considered non-overlapping. Channels 3 and 9 are separated by six channels, channels 6 and 11 are separated by five channels, and channels 2 and 8 are separated by six channels. All of these scenarios are nonoverlapping channels.
7. A. CSMA/CA uses collision avoidance. CSMA/CD uses collision detection. CSMA/CR and CSMA/DSSS do not exist.
8. A. DSSS uses Barker code at 1 Mbps. CCK is for 5.5 Mbps. DBPSK and DQPSK are modulation technologies, not spreading codes.
9. A. FM radio stations use narrowband communication, which is high power and narrow frequency. WLANs use spread-spectrum technology, which is low power and wide frequency.
10. C. HR/DSSS channels are 22 MHz wide. FHSS uses 1 MHz subcarrier frequencies. OFDM, ERP-OFDM, and HT-OFDM use 20 MHz–wide channels, and HT-OFDM can also use 40 MHz–wide channels.
11. D. Bluetooth operates in the 2.4 GHz band and can cause interference with WLAN devices that operate in the 2.4 GHz band, including FHSS, DSSS, and OFDM.
12. D. OFDM can be used in 802.11a or ERP-OFDM used in 802.11g and supports a maximum data rate of 54 Mbps. 802.11b supports a maximum data rate of 11 Mbps. OFDM is also used with 802.11n devices, but the maximum data rate is 600 Mbps.
13. C. HT-OFDM used in IEEE 802.11n can support data rates as high as 600 Mbps, OFDM used in 802.11a supports a maximum of 54 Mbps, and DSSS supports a maximum of 11 Mbps. Ethernet is not a wireless LAN technology.
14. C, D. IEEE 802.11a wireless LANs operate in the 5 GHz UNII bands. 802.11b/g wireless LANs operate in the 2.4 GHz ISM band.
15. D. IEEE 802.11b and 802.11g amendments are interoperable. 802.11a networks operate in the 5 GHz UNII bands and therefore are incompatible with 802.11b/g.
16. D. 802.11b operates in the 2.4 GHz ISM band and will allow for 14 channels. The channels that can be used will depend on where the wireless LAN is located.
17. A. FHSS uses 1 MHz subcarrier frequencies to transfer data. 20 MHz–wide, 22 MHz–wide, and 40 MHz–wide channels are used with other technologies.
18. B. The IEEE 802.11b amendment specifies data rates of 5.5 and 11 Mbps. OFDM allows for data rates up to 54 Mbps and is used in IEEE 802.11a and IEEE 802.11g amendments.
19. C. FHSS constantly changes frequencies while transmitting data in a WLAN. DSSS, OFDM, and MIMO use set channels and frequencies to transmit data.
20. D. Current MIMO technology allows for up to 600 Mbps. One way this is accomplished is by using multipath as a benefit rather than a hindrance.
Chapter 6: Radio Frequency Fundamentals for Wireless LAN Technology
1. B. Frequency is the number of times in one second a signal will oscillate. Phase is a shift, amplitude is height, and wavelength is a distance of one cycle.
2. B. There are three nonoverlapping channels in the 2.4 GHz ISM band. Fourteen channels are available in this band. The locale will determine which channels can be used.
3. A, D. The capacity of an access point is dependent upon the number of users and software applications in use. Too many users or too many bandwidth-intensive applications will affect the performance of an access point.
4. A. Refraction occurs when a signal changes speed and bends when passing between mediums of different densities. Reflection bounces off a smooth surface, diffraction will pass around, and scattering bounces off an uneven surface.
5. A, E. RF communications require a transmitter and receiver. A transistor is an electronic component; a reactor does not exist in RF.
6. B, D. dB and dBi are relative measures of RF power. mW, dBm, and watt are absolute measures of RF power.
7. C. 25 MHz is required for channels to be considered nonoverlapping. 22 MHz is the width of a DSSS channel in the 2.4 GHz band.
8. A, C. Amplitude and phase are two characteristics of RF signals. Reflection, refraction, and diffraction are behaviors of RF.
9. B. UNII-1 band has four channels available for wireless LAN use. Eleven channels are available in UNII-2e.
10. A, C. Watt and mW are absolute measures of RF power. dB, dBi, and dBd are relative measures.
11. A. Channels 1 and 6 are nonoverlapping. There must be a separation of five channels (with the exception of channel 14) to be considered nonoverlapping in the 2.4 GHz band.
12. D. There are 14 channels available in the unlicensed 2.4 GHz ISM band. The channels used are determined by the locale.
13. B. The wavelength is the measurement of one complete cycle of an RF signal. The higher the frequency, the shorter the wavelength; therefore the shorter the range. Frequency is the number of times an RF signal cycles in one second, amplitude is the height from a 2D perspective, and phase is a shift.
14. B. Obstacles affect the RF line of sight. Phase and amplitude are characteristics of radio frequency, and interference affects the throughput.
15. C. There are 11 channels available for wireless LAN use in the unlicensed UNII-2e band. The other three 5 GHz bands have only 4 channels each.
16. A. The amplitude is the height of an RF signal. The length of one cycle is the wavelength, the shift is phase, and width is not a valid factor.
17. B. A 2.4 GHz 802.11b signal is 22 MHz wide. 25 MHz is the distance required to be considered nonoverlapping.
18. B. An RF signal that bounces off a smooth surface is reflection. Refraction passes through, diffraction bends around, and scattering bounces off a non-smooth surface.
19. C. The gain of an antenna is measured in dBi. This is a relative measure of power.
20. D. Diffraction passes or bends around an obstacle. Reflection bounces off a smooth surface, refraction passes through, and scattering bounces off an uneven surface.
Chapter 7: Wireless LAN Antennas and Accessories
1. D. Omnidirectional antennas have a horizontal beamwidth of 360°. The vertical beamwidth will vary depending on the design and the gain of the antenna.
2. B. Antennas provide an increase in RF coverage by means of passive gain. Passive gain occurs when isotropic RF energy is focused into a specific radiation pattern. Active gain requires the use of an external power source.
3. A. Horizontal beamwidth is parallel to the earth's surface. This is based on how the E-field propagates away from the antenna element. Vertical beamwidth is perpendicular to the earth's surface.
4. B. An access point will require two antennas for diversity. Although there are two antennas, a single input/single output access point will have only one radio. The access point provides additional intelligence to determine which antenna to use. Other wireless LAN technologies such as MIMO may use up to three antennas.
5. B. A lightning arrestor is used to protect a wireless LAN system from an indirect lightning strike. A lightning arrestor will direct transient or induced electrical current to earth ground as a result of a lightning strike.
6. A. Active gain requires an external power source to provide an increase in signal strength. An amplifier is an example of a device that uses active gain. Antennas provide an increase in strength by using passive gain.
7. C. Highly directional antennas are typically used for long-range point-to-point connectivity such as bridge links. Omnidirectional antennas are used as part of an access point system or to provide point-to-multipoint links.
8. A. Changing the orientation of a device or antenna will change the polarization and affect the received signal strength. The signal strength may either increase or decrease depending on how the polarization is changed from the original position. Wavelength, frequency, and phase are characteristics of radio frequency.
9. A, C. Point-to-point and point-to-multipoint both require RF line of sight to be able to effectively communicate. Scattering, reflection, and refraction are all behaviors of radio frequency.
10. C, D. Cables and connectors can both result in a loss of signal strength. Antennas and amplifiers will add gain or increase signal strength. A transmitter outputs an absolute amount of power.
11. A. 802.11g access points require only one antenna to function. Systems that support antenna diversity will require two antennas to correctly operate.
12. B. 802.11a access points can use antenna diversity. Gain and polarization are considered RF concepts.
13. A. The image is an example of an omnidirectional antenna. This type of antenna provides a horizontal radiation pattern of 360°.
14. C. Of the answers listed, wind would have the biggest impact on a wireless LAN system. Rain, snow, and hail do not affect wireless transmission unless the weather is severe. In this case, the collection of the elements may have an impact on the wireless LAN signal transmitted or received.
15. C. Wireless LAN cables and devices are rated at 50 ohms impedance. Cable and satellite television is rated at 75 ohms.
16. B. The curvature of the earth or earth bulge will have an impact on a wireless LAN signal after seven miles. If the signal needs to travel farther than seven miles, the antenna will have to be installed in a higher location.
17. A. A patch antenna provides semidirectional coverage. The amount of coverage depends on the design and gain of the antenna. Parabolic dishes are highly directional.
18. B. The horizontal RF radiation pattern of an antenna is displayed using an azimuth chart. The vertical radiation pattern is displayed using an elevation chart.
19. D. It is recommended that at least 60 percent of the Fresnel zone be free of obstruction in order to have acceptable RF line of sight. Up to 40 percent of the zone can be blocked by obstructions without affecting the signal.
20. D. The image shows a patch antenna. This is an example of a semidirectional antenna.
Chapter 8: Wireless LAN Terminology and Technology
1. B. When a wireless client device listens for beacons, it is performing passive scanning. Active scanning is sending a probe request. Authentication occurs after the probe phase. Power save puts the device into a low power state.
2. C. Dynamic rate switching (also called dynamic rate selection) allows a wireless LAN device to adjust data rates based on received signal. Dynamic frequency selection allows an access point to pick the best frequency to operate on based on the environment. Transmit power control automatically adjusts output power. Transmit save mode does not exist.
3. A. An IBSS uses no access points and is also known as peer-to-peer or ad hoc networking. A BSS uses one access point.
4. C. If a device is part of a peer-to-peer network, it will connect to other like devices. An access point and a wireless switch are both infrastructure networking devices and will be part of either a BSS or ESS.
5. A. The data rate decreases as a wireless LAN device moves away from an access point. The data rates increase as a wireless LAN device moves closer to one access point. The output power does not change based on the location of the wireless device in the radio range of the access point.
6. C. An SSID can be a maximum of 32 characters or octets and is also case-sensitive.
7. B. If access points on the same distribution system are set with different SSIDs, the client will lose the connection while roaming unless all SSIDs are set in the client utility. The channel is set by the access point, and the BSSID is the MAC address of the AP radio.
8. C. Beacons are management frames and are used in the passive scanning process. Data frames carry data payload. Control frames reserve the medium and acknowledgment frames. Detail frames do not exist.
9. B. The client must authenticate to an access point before it can associate. After both authentication and association have been completed, the client is considered to be part of the BSS.
10. B. Moving throughout a location will cause a wireless client to roam from one access point to another. As part of the roaming process a client sometimes, but not always, needs to reauthenticate.
11. A, C. To successfully set up an ad hoc network, a user must know two parameters, the SSID and the RF channel it will be operating on. The BSSID is automatically generated in an ad hoc network. The BSSID is the MAC address of an AP radio; APs are not used in ad hoc networks. Protection mode does not apply to the situation.
12. B. Open system authentication uses two frames. The first frame is from the client to the access point and the second frame is from the access point back to the client. Shared-key authentication uses four frames.
13. C. In 802.11b/g and mixed mode environments, throughput will be affected because of ERP protection mechanisms. Association and authentication are normal frames exchanged and do not affect throughput. HT protection mode is for 802.11n.
14. A, C. An SSID has a maximum of 32 characters or octets. SSIDs are case-sensitive.
15. A. The BSSID is the unique identifying MAC address of the access point's radio network adapter. This abbreviation is sometimes confused with SSID, which is a network name. The other MAC addresses are used in networking but are not representative of the BSSID.
16. B. A network consisting only of wireless client stations is an independent basic service set (IBSS). Other terms for this type of network are ad hoc and peer-to-peer. Infrastructure mode is a term used with a basic service set that consists of a single access point. Active and passive are scanning modes in which wireless devices connect to a wireless network.
17. C. Because the computer is almost always plugged into an AC power source, it is unnecessary to have the device perform power save functions. Therefore, active mode (sometimes referred to as continuous aware mode) is the best solution. Power save mode would work well for a device that is on battery power and will help extend the battery life. Association and passive mode do not pertain to power save.
18. A. An ESS as stated in the IEEE 802.11 standard is one or more interconnected basic service sets.
19. A. In order for a wireless client to become part of a basic service set, it must first authenticate and then associate. The distribution system is the network in which the access point is physically connected. Deauthentication and reauthentication occur when a client either logs off the wireless network or roams from one access point to another.
20. B. A BSS consists of only one access point. An IBSS has zero access points. A network with more than one access point would be considered an ESS.
Chapter 9: Wireless LAN Security Basics
1. A, B, E. WPA Enterprise, WEP, and MAC filtering can all be used to secure 802.11g access points. PPTP is a Layer 3 security solution that consists of both tunneling and encryption. IPSec is a Layer 3 VPN encryption mechanism. RBAC stands for role-based access control and is a way of restricting access to only authorized users.
2. A, D. Both WPA2 Personal and WEP support shared key security. The WPA2 Personal algorithm creates a 256-bit preshared key. WEP can be used with either a 64-bit or 128-bit key. WPA Enterprise, 802.1X/EAP, and WPA2 Enterprise all use the 802.1X process to create a key.
3. B. Passphrases are available for use with WPA Personal or WPA2 Personal and are capable of providing strong security for the home user or small office. SSID hiding should not be used for security because the SSID can be found in frames other than beacons. MAC filters are considered legacy solutions and can be easily spoofed using software downloadable from the Internet. 128-bit WEP can be cracked very quickly using software tools and is therefore not a secure solution.
4. C. In order to provide a secure connection between your laptop and the office network, a Layer 3 VPN solution would be the best choice. Passphrase security and WEP require the access point to be configured, and this typically is not the case in public hotspots. 802.1X/EAP is enterprise security and usually does not apply to public hotspots.
5. E. A MAC filter is used to allow or deny wireless LAN devices access to a wireless access point. WEP is a shared key security mechanism. IPSec encryption is used in Layer 3 VPNs. SSIDs are used as a network name and for segmentation. RF is radio frequency and cannot be filtered.
6. B. The IEEE 802.11i amendment to the standard requires CCMP. WEP is an optional authentication/encryption method defined in the original 802.11 standard. TKIP is an enhancement to WEP that usually was accomplished as a firmware upgrade for older equipment. PPTP and VPN are both Layer 3 solutions and not defined in any IEEE wireless amendment.
7. A. A virtual private network (VPN) is a Layer 3 security solution that provides secure data transmissions over a public network infrastructure such as the Internet. WEP, WPA, 802.1X/EAP, and WPA 2.0 are examples of Layer 2 security solutions.
8. A. Role-based access control (RBAC) is a method used to restrict access only to authorized users. RBAC assigns permissions or access to roles to which users can be added.
9. D. If the SSID of the wireless network is hidden, the user will need knowledge of the SSID in order to connect to the wireless network. The SSID broadcast is only enabled on an access point or wireless LAN controller/switch. Getting a new password from the help desk will not provide the SSID of the wireless network. Entering a username and password is user-based authentication.
10. C. RADIUS is a centralized authentication method that is used to authenticate users on a wireless network. Accessing a corporate network using a modem is a function of remote access services. Making a call to the help desk and requesting a username and password is not a function of RADIUS; however, the help desk may be able to assist with username and password issues. Requesting remote assistance to help solve a software problem is more related to troubleshooting and not a function of RADIUS.
11. B. In 802.1X networking, the access point is also known as the authenticator. The supplicant is another term for the client device, and the authentication server can be a RADIUS or AAA authentication source.
12. D. The original IEEE 802.11 standard identifies WEP as an optional authentication/encryption method. AES and CCMP are addressed in the 802.11i amendment to the standard. TKIP is an enhancement to WEP and not identified in the original standard. EAP provides an authentication process and is used with 802.1X networks.
13. A, C. Higher levels of RF activity reported by an intrusion prevention system could mean an RF denial-of-service attack is underway or could be misrepresented as interference from a neighboring access point. A deauthentication storm or encryption attack would be identified differently in a wireless intrusion prevention system. A misconfigured client workstation would not cause this type of alert.
14. C. WEP is typically 64-bit or 128-bit encryption. The numbers 5, 10, 13, and 26 are related to the number of characters the WEP key can be in either ASCII or hexadecimal.
15. B. PIN-based security is mandatory for both access points and client devices in order to be considered Wi-Fi Protected Setup certified. PBC or push-button configuration is optional for client devices in this certification. WPA is a pre-802.11i certification that addresses TKIP and is used in either SOHO or enterprise-based wireless networks. Wi-Fi Protected Setup is not intended for enterprise WLAN deployments.
16. B. A wireless intrusion prevention system will automatically monitor the network for signatures that match potential intrusion techniques. An intrusion prevention system has the capability to automatically shut down a rogue access point. An intrusion detection system requires a manual shutdown. A WIPS will not notify a network administrator of a recent firmware upgrade.
17. B. If WEP must be used on a wireless network, the devices that use WEP should be separated using VLANs. This will protect the rest of the network from being compromised. Voice transmissions can be seen with the correct tools. CCMP/AES is available in newer devices that support the latest wireless security methods but is not available in older devices.
18. B. An intruder can spoof a MAC address in order to circumvent the MAC filter and gain access to the wireless network. Encryption cracking is a different form of intrusion that also could possibly allow an intruder to steal a user's authentication credentials. An RF denial-of-service attack is caused by transmitting high-energy RF to prevent access to the wireless network.
19. C. PIN-based security is usually used with SOHO brand wireless devices that support Wi-Fi Protected Setup certification (WPS). The devices are typically used in small office/home office installations or by home-based users. WPA 2.0 solutions can use either passphrase or 802.1X/EAP.
20. A. Layer 2 Tunneling Protocol (L2TP) commonly uses IPSec for encryption. PPTP is another VPN method that uses MPPE 128-bit encryption. AES and WEP are used with Layer 2 802.11-based wireless networks.
Chapter 10: Wireless LAN Site Survey Basics
1. A, C. The purpose of a wireless site survey is to find areas of RF coverage and interference and to determine placement of equipment such as access points and bridges. The cost of equipment and selection of manufacturer also play a role but are not part of the site survey objective.
2. A. The number of required access points is a good gauge whether a site survey is required. The geographic location of the business, number of wiring closets, and the number of servers do not determine if a site survey is required.
3. C. Typically the first step of a wireless LAN site survey is to gather the necessary business requirements. Interviewing managers and users is the next step, followed by determining RF coverage and documenting existing networks. Installing access points is one of the final steps.
4. A. Enterprise wireless LAN deployments typically use omnidirectional antennas connected directly to an access point. Other antenna types may be used but are not as common in this type of deployment.
5. D. Manufacturing environments typically use equipment that interferes with devices in the 2.4 GHz ISM band. Wireless 3G and cellular telephones work in other frequency ranges and do not affect wireless LANs. 900 MHz is not used by IEEE 802.11 wireless networks. CB radios work at a different frequency range.
6. C. Healthcare locations typically have equipment that works in the 2.4 GHz ISM band. These devices could potentially cause interference with a wireless network that operates in this band. Office, government, and education installations will not have as much ISM equipment.
7. C. The type of applications—either hardware or software—that will be used on the wireless network will have a large impact on the final deployment. This is an important question to ask end users. The other questions also need to be answered, but they should be asked of managers and IT staff.
8. A, C. Physical and data security requirements are part of a wireless LAN site survey. These requirements may have an impact on the number of access points or other devices required for the network. Access point, device, and infrastructure security also plays a role but is typically not considered part of an initial site survey.
9. C. Of all the devices listed, the voice handset would be the best candidate that would use roaming features of a wireless network, mostly because of mobility and features. Notebook computers and tablet devices may have roaming capabilities, but these devices are not as sensitive to latency. Wireless cameras are usually stationary devices.
10. B. The number of devices is an important determining factor in the number of access points required for a wireless LAN deployment. The type and manufacturer of devices are not concerns. The antenna in a client device will help with providing and maintaining device connectivity.
11. A. Interviewing managers and users will help determine the performance expectations of the wireless LAN because they are the ones who will be using it and they have the best understanding of the needs of an organization. Locations of RF interference and access points are part of the network design stage, which takes place after the gathering of information stage. In most cases, creating floor plans is not a primary responsibility of a site survey; however, obtaining floor plans is significant.
12. D. Floor plans of facilities can sometimes be imported into site survey software programs. This helps in determining the RF propagation by placing access points in a simulated environment. Access point models as well as cost estimates are required at a later time in a site survey.
13. D. Storage of paint and other liquids in large quantities can cause RF to be absorbed.
14. A, F. The business requirements and purpose of the wireless LAN are two areas that would be discussed at an initial meeting regarding a site survey. The other topics will be discussed at a later time.
15. C. An RF jamming attack would fall under physical security. Access point security, infrastructure security, and wiring closet security do not involve RF jamming. Data security is a separate issue.
16. B. The aesthetic requirements are usually discussed with hotel management since they are the ones responsible for the appearance of the hotel. PoE requirements and RF coverage and interference would be questions for a different group, which in some cases may be an outside provider.
17. A. The applications used will determine the number of access points in a wireless LAN deployment. Bandwidth-intensive applications may require more access points. Security requirements are important but typically do not strongly affect the number of access points required. Ceiling height is a factor when determining the RF coverage, not necessarily the number of infrastructure devices.
18. B. Access point output power is a determining factor in what type of coverage the AP will provide. Wiring closet locations and electrical power requirements are more related to wired infrastructure connectivity. Floor plans and blueprints will be used to note access point locations.
19. D. The initial gathering of information includes number of users, applications and their use, and other wireless networks in the area. The cost of the proposed equipment is not usually addressed at this point.
20. C. Office building deployments commonly use omnidirectional antennas that are mounted directly to an access point. Manufacturing, warehousing, and sports arena deployments more often use a combination of omnidirectional, semidirectional, and sometimes highly directional antennas.
Chapter 11: Performing an RF Wireless LAN Site Survey
1. A, C. The main objectives of a wireless site survey are to determine areas of RF interference and RF coverage as well as locations of access points and other infrastructure devices. The applications used have more to do with capacity planning. Wiring closet locations and security implantations are factors that need to be taken into account but are not the main objectives.
2. D. Because of RF propagation, site surveys are really three-dimensional. Therefore in a three-story building all floors need to be taken into consideration. Omnidirectional antennas may be polarized either vertically or horizontally. Single-channel architectures use the same channel for multiple floors.
3. A, B. A spectrum analyzer and a tool that passively scans for wireless networks such as NetStumbler can be used for a manual site survey. The other options' association and authentication can be viewed using a protocol analyzer and are not “standalone” tools.
4. A, C. Manual site surveys can be either passive or active. Scanning is a method of locating wireless LANs. A spectrum analyzer will allow you to see the RF. A packet is information that carries computer data from one device to another.
5. B, D. Non-Wi-Fi interference is interference by anything other than wireless LANs that operates in the same frequency range. AM radios and digital TV systems do not operate in the license-free bands. 802.11b interference is wireless LAN interference. Radar systems operate in the 5 GHz UNII band.
6. C. Recommended received signal strength for voice applications in the 2.4 GHz ISM band at a data rate of 54 mbps is about –67 dBm. A recommended signal-to-noise ratio is more than 20 to 25 dB.
7. C. A predictive modeling site survey is software-based and takes the attenuation values of the building and other materials into consideration. Active and passive are forms of manual site surveys and record actual information about the site.
8. B. OFDM networks operate in the 5 GHz UNII band and would not affect an 802.11g network that operates in the 2.4 GHz ISM band. FHSS, DSSS, and ERP-OFDM all operate in the 2.4 GHz ISM band and could cause interference with an 802.11g network.
9. A, B. The signal strength and SNR are two important values to record during the manual site survey process. Signal loss and propagation loss have different effects, and packet retries are more of an issue with dynamic rate selection.
10. C. Manual site surveys can be very accurate because actual readings are taken at the site using test access points and a wireless client. This can take quite some time to complete depending on the size of the location. Wireless hardware is required to perform the site survey, and access to the whole facility is required.
11. A. A spectrum analyzer can be used to view radio frequency. Wireless packets, data rates, and association frames can be viewed with a protocol analyzer.
12. B. Since new hardware will be purchased and backward compatibility is not required, you could recommend using wireless network hardware that works in the 5 GHz band. This will eliminate interference from the other tenants that are using the 2.4 GHz ISM band. Automatic channel selection, spectrum analysis, and predictive modeling site survey will not help because surrounding access points already use the entire band.
13. B. A predictive modeling site survey will take less time than a passive survey because a passive survey requires a manual analysis. On-site protocol analysis or scanning utility will determine areas of RF interference from wireless LANs. The predictive modeling survey does not help you choose manufacturers' equipment to be used in a deployment.
14. D. A verification of the predictive survey should be performed to verify that the survey meets the customer's requirements. Although not required, it should be considered.
15. D. Dead spots (areas that lack RF coverage) should be identified on floor plans or blueprints. This is part of standard documentation practices. Marking them with tape, taking a photograph, and showing the site manager in person are not the best ways to document dead spots.
16. B. An active site survey requires the survey device to associate to an access point. A passive site survey monitors all access points in the area. A predictive modeling site survey does not involve associating to an access point. Associating to an access point is not a required part of manual testing.
17. D. A semidirectional antenna such as a Yagi is a good choice for an application requiring coverage down a long hallway or corridor. Low- or high-gain omnidirectional antennas will provide 360-degree horizontal coverage. Parabolic dish antennas are typically used for outdoor long-range bridging.
18. D. In this situation, correct antenna selection is important to provide optimal coverage as well as proper aesthetics. In this example, a spectrum analysis or protocol analysis could be performed but is not required. Environmental conditions are typically not an issue in a small office deployment.
19. A. Co-channel interference is caused by two access points operating on the same radio frequency channel. Access points operating on channels 1 and 2 may cause adjacent channel interference. Channels 1, 6, and 11 are nonoverlapping channels and will not interfere with one another.
20. A, E. A walkthrough of the location and spectrum analysis are both recommended guidelines when performing a manual site survey. Equipment purchase and client device configuration are additional factors to consider but are not part of the manual site survey. A predictive analysis is a software-based site survey solution that does not require manual testing.
Chapter 12: Troubleshooting and Maintaining IEEE 802.11 Wireless Local Area Networks
1. D. Multipath is caused by reflected signals arriving at the receiver at slightly different times (delay spread). Refraction is an RF behavior caused by passing through an object of different density, resulting in a change of the signal strength. Absorption is the result of a signal not reflecting or bending or passing around an obstacle.
2. B. A wireless client device showing a low received signal strength value could be too far away from an access point. Of the answers listed, an additional access point would be the best solution. Upgrading the client device or the firmware would not help the situation. Multipath is caused by reflections and cannot be eliminated.
3. B. A user experiencing a slow connection could be too far away from an access point to get a strong enough signal to move data at the highest rate. A 5.8 GHz phone is operating at a different frequency and would not cause interference with an 802.11g wireless LAN. A MAC filter is set on an access point and will either allow or disallow a client connection. If a firmware upgrade was causing a problem for an access point, it would affect all users.
4. A. Increasing the output power of the access point will result in a higher received signal at the wireless client device. Enabling load balancing will not improve signal strength but will limit the number of devices that associate with an access point and may improve throughput. Upgrading the ISP service to faster data rates will not improve signal strength for the wireless client. Enabling security such as WPA 2.0 will not increase the signal strength seen by the client but is recommended to secure the transmission.
5. C. Incorrect security parameters such as a WPA passphrase will prevent a wireless client device from completing a Layer 2 connection and obtaining an IP address from a DHCP service. If the client device is different technology like 802.11a, the device would not have been able to connect. If a static IP address is used, it will not display all zeros. Although a computer virus can create problems for the client device, it would not prevent the device from obtaining an IP address after connecting to the wireless network.
6. B. A sudden change in performance might occur if an access point for a new tenant is set to the same RF channel as your client's access point. This could cause interference, which would degrade performance. A firmware upgrade on the access point usually fixes problems or provides enhancements. Received signal strength is typically an issue based on distance from an access point. Diversity antennas would help minimize the problems associated with multipath and in most cases would improve performance rather than degrade it.
7. A. A hidden node problem caused by obstacles or obstructions could be resolved by adding another access point so wireless client devices would not be subject to clear channel assessment issues. Setting an access point to Mixed Mode will allow both 802.11b and 802.11g clients to connect to the network. Increasing the distance between the access point and the clients will not improve the situation but will actually make it worse. Adjusting the received signal strength on the client would improve performance for that client but would not necessarily solve the hidden node problem.
8. B. The wireless LAN client device would be mostly affected by weak signal strength. An infrastructure device such as an access point generates the signal received by the client. Multipath is a phenomenon that is a result of several wavefronts of the same signal reaching a receiver at different times. A transmitter device is responsible for sending an RF signal.
9. A. A passphrase or preshared key will be validated after an 802.11 authentication and association. In order for the client device to get a valid IP address, a successful authentication, association, and passphrase would have to occur. A deauthentication will end the authentication state, and a disassociation will no longer allow a device to pass traffic across the access point.
10. C. Two factors that may have an impact on throughput in a wireless LAN are distance from the access point or the output power level of an access point. The IP address and MAC address identify the device on the network and would not affect throughput. The output power of the client device has more to do with its transmitting capabilities than the receiver's capabilities.
11. A. The device driver is a required component that allows the wireless network adapter card to interface with the operating system. A device driver does not provide security nor does it identify the network.
12. A. Hidden node caused by different technology types is the result of the access point not being able to differentiate between spread-spectrum technologies. An access point set to Mixed Mode will understand both HR/DSSS and ERP-OFDM, which will solve the problem. Adding another access point or increasing output power would not solve the problem, although that would be a solution for other hidden node scenarios. Removing an obstacle is a valid solution for a different hidden node problem.
13. D. A corrupt device driver may cause the network adapter card in a wireless client device to operate incorrectly or to malfunction. A terminated Internet connection would be a global problem and would affect all users. An upgrade or incorrect firmware would not cause the problem only for a single user.
14. A. Layer 1 provides the physical connectivity between devices, which use the air as the medium to carry the radio frequency. Layers 3 and 4 are responsible for TCP/IP. Layer 7 is the interface to the user, also known as the Application layer.
15. C. Windows 98 and later are designed to use the Automatic Private IP Address service. This service will provide an IP address to client devices in the range of 169.254.x.x. This will allow local connectivity for any devices that are connected to a common LAN.
16. A. The distance from an access point could affect the received signal strength for a wireless client device. The distance from other clients has no impact on devices that are connected to an access point. The distance from an Ethernet switch or from the wiring closet has no impact on a wireless client.
17. B. The signal-to-noise ratio represents the difference between the received signal strength and the level of the noise floor. A good signal-to-noise ratio will give a client the ability to distinguish between signal and noise and allow it to recover data that was transmitted.
18. D. 802.11n takes advantage of multipath, which is typically a problem for other wireless LAN technologies. By using multipath, 802.11n devices will have better throughput than 802.11g devices. Received signal strength means the same thing across technologies. DHCP is a service that provides IP addresses automatically. Hidden node is a problem that may degrade throughput for connected devices.
19. A. Adding access points can help increase the throughput for a wireless LAN client device. This is possible because additional access points would allow for load-balancing features and therefore provide less contention at that access point. Upgrading the client software to full-duplex mode is not an option, and if the RF noise was increased, throughput would be less. Hiding the SSID has no impact on throughput.
20. C. Increasing the gain of an antenna will provide a larger RF coverage cell, thereby providing more received signal at the same distance for a wireless client device. Upgrading the wireless client will not improve the received signal strength. Load balancing will help with throughput, and Microsoft WZC is an example of a built-in client utility.
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