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Business Driven Data Communications (Gendron)Chapter 2 Building the Local Area Network Using Ethernet

2.1 Multiple Choice Questions

1) A ________ is an example of an ICT service component.A) switchB) NASC) routerD) desktop applicationAnswer: BDiff: 1 Page Ref: 41

2) The most widely used Ethernet Layer 2 standard is ________.A) Ethernet RawB) IEEE 802.2 LLCC) SnapD) Ethernet IIAnswer: DDiff: 1 Page Ref: 42

3) The difference between the four Ethernet data link standards is their ________.A) frame formatB) propagation methodC) Both A and BD) Neither A nor BAnswer: ADiff: 3 Page Ref: 42

4) Routing is done ________ LANs, and switching is done ________ a LAN. A) within, betweenB) between, withinC) within, withinD) between, betweenAnswer: BDiff: 1 Page Ref: 42

5) The router is capable of translating ________ and ________ standards.A) Layer 2, Layer 3B) Layer 3, Layer 4C) Layer 1, Layer 2D) Layer 4, Layer 5Answer: CDiff: 2 Page Ref: 42



6) When building a LAN, ________ is regularly used for vertical cabling runs, between switches. A) fiber opticB) UTPC) coaxD) Cat5eAnswer: ADiff: 1 Page Ref: 43

7) How many 4U devices can fit in a 72U rack if 12U are already used for other devices?A) 18B) 15C) 12D) 4Answer: BDiff: 3 Page Ref: 45

8) The first Ethernet was based on a ________ typology.A) ringB) starC) meshD) None of the aboveAnswer: DDiff: 2 Page Ref: 49

9) ________ is a switch method used to forward frames.A) Cut-throughB) Fragment-freeC) Adaptive switchingD) All of the aboveAnswer: DDiff: 2 Page Ref: 46

10) Managed switches allow for configuration changes ________.A) through a client computerB) remotelyC) automaticallyD) Both A and BAnswer: DDiff: 2 Page Ref: 46



11) ________ monitors the activity of a switch, checks switch health, and reports errors.A) SNMPB) STPC) VLAND) CSMAAnswer: ADiff: 1 Page Ref: 47

12) Ethernet is a(n) ________ protocol.A) synchronousB) asynchronousC) Layer 4D) Both A and CAnswer: BDiff: 3 Page Ref: 51

13) ________ came into use with a star typology.A) 10Base5B) 10BaseTC) 10Base2D) 100BaseFXAnswer: BDiff: 2 Page Ref: 51

14) CSMA is an attempt at collision ________.A) detectionB) avoidanceC) interruptionD) transmissionAnswer: BDiff: 2 Page Ref: 50

15) The Ethernet frame-________ contains the source and destination MAC address, and the ________.A) trailer, synch signalB) header, synch signalC) header, synch wordD) trailer, synch wordAnswer: CDiff: 3 Page Ref: 51



16) A Layer 2 frame has a(n) ________ encapsulated within it.A) segmentB) packetC) application messageD) All of the aboveAnswer: DDiff: 2 Page Ref: 52

17) The ________ in an Ethernet II frame is used to synchronize the sending and receiving devices.A) preambleB) SFDC) Both A and BD) None of the aboveAnswer: CDiff: 2 Page Ref: 53

18) The ________ is the field in an Ethernet II frame that is responsible for error detection.A) preambleB) payloadC) ethernet typeD) frame check sequenceAnswer: DDiff: 1 Page Ref: 53

19) The ________ standard governs Ethernet physical media and data link layer operations.A) IEEE 802.16B) IEEE 802.3C) IEEE 802.11D) None of the aboveAnswer: BDiff: 3 Page Ref: 53

20) The frequency spectrum covers frequencies between ________ Hz and infinity Hz.A) 1E(-3)B) 0C) 100D) 1000Answer: BDiff: 1 Page Ref: 54



21) Microwave communications are used in ________ applications.A) hard-wiredB) WAPC) LAND) point-to-pointAnswer: DDiff: 2 Page Ref: 55

22) ________ and ________ are used in point-to-point applications.A) Microwave, WiMAXB) Satellite, microwaveC) Satellite, WLAND) WLAN, WiMAXAnswer: BDiff: 2 Page Ref: 55

23) The technology that is based on IEEE standard 802.16 for broadband wireless access is ________. A) microwave communicationB) satellite communicationC) WiMAXD) WLANAnswer: CDiff: 1 Page Ref: 55

24) The order of satellites from lowest orbit to highest orbit is ________.A) LEO, GEO, MEOB) GEO, LEO, MEOC) LEO, MEO, GEOD) MEO, LEO, GEOAnswer: CDiff: 3 Page Ref: 56

25) "WiFi" and "hotspot" are terms used to describe ________ devices.A) WLANB) WiMAXC) 802.16D) microwaveAnswer: ADiff: 2 Page Ref: 56



26) A host computer would use a wireless device to connect to a ________.A) WLANB) WAPC) Both A and BD) None of the aboveAnswer: CDiff: 3 Page Ref: 57

27) WAPs can operate in ________ or ________ mode.A) over the air, adhocB) infrastructure, point-to-pointC) over the air, infrastructureD) None of the aboveAnswer: BDiff: 2 Page Ref: 57

28) WLAN devices generally use IEEE ________ standard.A) 802.16B) 802.3C) 802.11D) None of the aboveAnswer: CDiff: 1 Page Ref: 58

29) IEEE 802.11 devices use radio frequency ________ to propagate signals.A) modulationB) multiplexingC) Both A and BD) Neither A nor BAnswer: ADiff: 1 Page Ref: 58

30) The difference between IEEE standards 802.11a, b, g, and n is ________.A) speedB) frequencyC) Both A and BD) Neither A nor BAnswer: CDiff: 2 Page Ref: 58



31) In order for wireless access devices and WAPs to communicate, they must share the same ________.A) IP addressB) clientC) SSIDD) hostAnswer: CDiff: 2 Page Ref: 59

32) The weakest form of wireless security is ________.A) WEPB) a non-broadcasted SSIDC) WPA2D) WPAAnswer: BDiff: 2 Page Ref: 59

33) ________ uses the security algorithm RC4 for encryption.A) WEPB) WPAC) Both A and BD) Neither A nor BAnswer: CDiff: 3 Page Ref: 59

34) ________ is the current standard for wireless security.A) WEPB) WPAC) WPA2D) None of the aboveAnswer: CDiff: 1 Page Ref: 60

35) A ________ provides wireless authentication services.A) RADIUS serverB) NASC) LAND) WPAAnswer: ADiff: 1 Page Ref: 60



36) When a wireless device travels too far from a WAP, ________ occurs with a closer WAP having the same SSID.A) feedbackB) handoffC) mobilityD) None of the aboveAnswer: BDiff: 1 Page Ref: 61

37) WAPs allow ________ transmission(s) at a time.A) oneB) fewC) manyD) None of the aboveAnswer: ADiff: 2 Page Ref: 61

38) Wireless devices use ________ to control traffic between WAPs and clients.A) CSMA/CDB) CSMA/CA + ACKC) Both A and BD) Neither A nor BAnswer: BDiff: 2 Page Ref: 61

39) An 802.3 frame is converted into an 802.11 frame by a ________.A) WANB) hostC) WAPD) clientAnswer: CDiff: 3 Page Ref: 61

40) RTS/CTS is generally a(n) ________ process.A) fastB) slowC) expensiveD) inexpensiveAnswer: BDiff: 2 Page Ref: 62



41) When radio signals are poorly received because they are blocked by objects, this is known as ________.A) rapid attenuationB) multipath interferenceC) electromagnetic interferenceD) shadow zonesAnswer: DDiff: 2 Page Ref: 63

42) Radio signals tend to attenuate ________ wired media propagated signals.A) slower thanB) about the same asC) faster thanD) much slower thanAnswer: CDiff: 2 Page Ref: 63

43) When several radio signals are received out of phase, this is most likely caused by ________.A) rapid attenuationB) shadow zonesC) the frequency effectD) multipath interferenceAnswer: DDiff: 2 Page Ref: 63

44) 802.11b and 802.11g signals tend to attenuate ________ 802.11a signals.A) slower thanB) about the same asC) faster thanD) much, much faster thanAnswer: ADiff: 3 Page Ref: 63

45) Compared to 802.11 technologies, PAN technologies are ________ and ________.A) long range, slowerB) long range, fasterC) short range, slowerD) short range, fasterAnswer: CDiff: 2 Page Ref: 63



46) Standard-driven techniques for building and campus telecommunication cabling infrastructure is known as ________.A) structured cablingB) engineered cablingC) horizontal cablingD) vertical cablingAnswer: ADiff: 1 Page Ref: 64

47) The internal network of a campus interfaces with the outside world at the ________.A) equipment roomsB) main cross-connectsC) entrance facilityD) network coreAnswer: CDiff: 2 Page Ref: 64

48) The ________ provides interconnections for equipment rooms in a structured cabling plan.A) backbone (vertical) cablingB) horizontal cablingC) Both A and BD) Neither A nor BAnswer: ADiff: 3 Page Ref: 64

49) ________ runs from each telecommunication closet to the work area components.A) Vertical cablingB) Horizontal cablingC) Main cross-connectsD) None of the aboveAnswer: BDiff: 1 Page Ref: 64

50) Vertical and horizontal cabling interconnect in the ________.A) equipment roomB) telecommunication closetC) main cross-connectsD) All of the aboveAnswer: DDiff: 3 Page Ref: 64, 65



51) ________ include(s) the communication outlets and wiring needed to connect user components to the network in a wired LAN.A) Backbone cablingB) Vertical cablingC) Main cross-connectsD) Work area componentsAnswer: DDiff: 1 Page Ref: 65

52) ________ should be considered when designing an equipment room.A) Environmental conditioningB) Power conditioning and availabilityC) Uninterruptible Power Supply needsD) All of the aboveAnswer: DDiff: 1 Page Ref: 68, 69

53) A centralized location where IT staff can monitor, control, and maintain the equipment necessary for a wired LAN is known as the ________.A) network coreB) entrance facilityC) data centerD) None of the aboveAnswer: CDiff: 2 Page Ref: 69

54) A single UTP connection is commonly referred to as a ________.A) dropB) lineC) trunkD) boxAnswer: ADiff: 1 Page Ref: 70

55) ________ facilitate(s) network operations and allow(s) direct user interface.A) Print servicesB) Service componentsC) Network attached storageD) All of the aboveAnswer: DDiff: 2 Page Ref: 72, 73



56) A ________ stores and organizes information about a network's users and resources.A) NASB) directory serverC) RADIUS serverD) database serverAnswer: BDiff: 2 Page Ref: 73, 74

57) ________ is most often used to connect UTP connections to user componentsA) RJ45B) Cat5eC) Both A and BD) Neither A nor BAnswer: CDiff: 2 Page Ref: 70, 75

58) The security algorithm used by WPA2 is ________.A) RC4B) AESC) Neither A nor BD) Both A and BAnswer: BDiff: 1 Page Ref: 60

59) The IEEE standards 802.11b and 802.11g operate at a frequency of ________ and the speed of 802.11b is ________ 802.11g.A) 2.4 GHz, faster thanB) 2.4 GHz, slower thanC) 5 GHz, faster thanD) 5 GHz, slower thanAnswer: BDiff: 3 Page Ref: 58

60) MAC addresses are ________ addresses.A) within-network hardwareB) out-of-networkC) between-networkD) None of the aboveAnswer: ADiff: 2 Page Ref: 51



2.2 True/False Questions

1) In an Ethernet LAN, all ports on a switch with an active switching table see all traffic.Answer: FALSEDiff: 1 Page Ref: 44

2) Switches are Layer 2 devices that operate within a LAN and use shared bandwidth across the bus.Answer: FALSEDiff: 3 Page Ref: 44

3) The LLC sublayer in the data link layer of Ethernet always provides flow control, acknowledgement, and error recovery.Answer: FALSEDiff: 2 Page Ref: 53

4) In order to use a microwave channel in the United States, the user must obtain government permission.Answer: TRUEDiff: 1 Page Ref: 55

5) WiMAX cannot support cellular data and voice services.Answer: FALSEDiff: 2 Page Ref: 56

6) Devices used to support WLAN applications operate under an FCC license in the United States.Answer: FALSEDiff: 3 Page Ref: 56

7) WLAN technologies use wired media to propagate signals.Answer: FALSEDiff: 1 Page Ref: 57

8) Wireless Ethernet is the same as an 802.11 LAN.Answer: FALSEDiff: 2 Page Ref: 57

9) Wireless signal suffers from different degradation problems than wired signal propagation.Answer: TRUEDiff: 1 Page Ref: 62

10) The correct format for a UNC is \\HostName\ShareFolder\Resource.Answer: TRUEDiff: 1 Page Ref: 72



2.3 Essay Questions

1) Describe how WAPs provide wireless traffic control for several users in a wireless LAN.Answer: WAPs can provide connectivity to a number of clients simultaneously; however, only one client can transmit at a time, otherwise their signals will overlap and be unintelligible. Therefore, it is necessary that WAPs implement flow control. The way 802.11 devices work means that they cannot hear each other, and so collision detection schemes like CSMA/CD will not work. Instead of CSMA/CD, 802.11 devices implement carrier sense multiple access with collision avoidance + acknowledgment (CSMA/CA+ACK) to control traffic between WAPs and clients.

For a WAP connected to a wired LAN, the 802.3 (Ethernet) frame format is used within the LAN, and that 802.11 frame is sent by the WAP. The WAP converts that 802.3 frame into an 802.11 frame for wireless transmission via CSMA/CA+ACK.

The CMSA/CA process then proceeds as follows:1) The sender (WAP or client wireless access device) listens for traffic.2) If it hears traffic it sets a random timer and waits.3) If there is no traffic, it then checks the last time it heard traffic.4) If the elapsed time since the last time the sender heard traffic is less than the elapsed-time-since-last-transmit value, the sender waits a random amount of time. It then sends traffic if no sender is transmitting.5) If the elapsed time since the last time the sender heard traffic is greater than the elapsed-time-since-last-transmit value, the sender transmits.

The ACK process proceeds as follows:1) The receiver immediately sends back an acknowledgment.2) If the sender does not receive an acknowledgment, it retransmits using CSMA/CA.Diff: 3 Page Ref: 61, 62



2) Describe the CSMA/CD procedure to control traffic in an Ethernet LAN.Answer: Because Ethernet originally used a shared coax cable in a bus typology, a way was needed to determine whether the bus was busy or whether a computer could use it and send a message. A scheme was developed called carrier sense multiple access with collision detection (CSMA/CD) as part of the original Ethernet standard. CSMA/CD was simpler than the other major competing network technology (Token Ring) which used a ring typology and a token-passing scheme to control collisions.

CSMA/CD can be broken into two parts: (1) carrier sense multiple access (CSMA) and (2) collision detection (CD). These two procedures create the CSMA/CD scheme. CSMA is an attempt at collision avoidance and is implemented in the host computer Ethernet adapter card.

CSMA/CD follows these steps:1) The host computer prepares a frame at Layer 2. 2) The host computer determines whether the transmission medium is busy. It needs to know if another computer is using the media. If another computer is communicating, then the host computer waits a predetermined amount of time, called the interframe gap.3) The host computer then propagates the frame over the media at Layer 1—it starts to communicate.4) If a collision occurs, then the host goes to the collision detection procedure.5) Transmission counters reset, and frame transmission ends.

The collision detection procedure includes the following steps:1) The host continues transmission for a predetermined length of time to be sure all receivers on the bus detect the collision.2) The host computer then increments the retransmissions counter.3) If the maximum number of retransmission attempts has occurred, the host aborts transmission.4) If the maximum number of transmission attempts has not occurred, then the host waits a random amount of time based on the number of collisions.5) The host then restarts the CSMA procedure at the beginning.Diff: 3 Page Ref: 50



3) Explain wireless propagation effects and how they differ from propagation over wired media.Answer: Wireless signal propagation suffers from propagation problems, although they are different problems from those experienced by wired propagation. Wireless propagation problems are tricky to diagnose because different clients accessing the same WAP can experience different problems. The main wireless signal propagation problems are outlined below:

Dead spots or shadow zones are areas where radio signals are poorly received because they are blocked by objects. Radio waves can go through or around some objects, but not all. It could be a building, elevator, very thick wall, or other dense object that prevents or slows radio wave transmission.

The strength of radio signals attenuates (reduces) much faster than signals propagated over wire or fiber optic cable. This phenomenon is referred to as the Inverse Square Law Attenuation. Basically, it means that signal strength rapidly declines the farther you get from the antenna, and that the receiver must be close to the antenna or that signal strength must be high. This factor greatly influences how far WLAN transmission can propagate.

Electromagnetic interference (EMI) is caused by motors and other electrical equipment, such as florescent lights or microwave ovens, that radiate electrical energy. Sometimes the radio frequency energy that is radiated is at the same frequency as the WLAN transmission, and if the EMI is close enough or powerful enough, it can interfere with WLAN performance.

Radio signals can bounce off walls, floors, and other objects that are between the sender and the receiver (remember radio signals are propagated in a sphere), which can cause the receiver to receive two or more signals that are out of phase with each other. Out of phase means that the signals arrive at the receiver at slightly different times, making it difficult, if not impossible for the receiver to understand the garbled signal.

Different wireless standards operate at different frequencies. This is an important point because the frequency of the signal can affect the signal's ability to propagate. Slower frequency signals have a greater ability to flow around objects than faster ones. That means that 802.11b (2.4 GHz) and 802.11g (2.4 GHz) have a greater ability to travel around objects than 802.11a (5 GHz). Slower signals also have better attenuation properties; slower signals experience less rapid attenuation than faster signals.Diff: 1 Page Ref: 62, 63



4) Summarize the most widely used wireless security protocols.Answer: Because wireless connection to a WAP does not require a physical media (e.g., UTP),wireless access presents particular security issues. The first and most obvious security measure is to not broadcast the SSID; however, because the SSID is transmitted in clear text in each frame it would be easy for a hacker to detect. Over time, from the original introduction of 802.11 to now, several security protocols have emerged. Initially, the Wired Equivalent Privacy (WEP) used RC4 (a security algorithm) for encryption. WEP was easy to hack into so the IEEE 802.11 working group began to devise new security specifications, 802.11i. As a stopgap measure the Wi-Fi Alliance (an industry trade group) announced an interim specification based on an IEEE 802.11i wireless security draft called Wi-Fi Protected Access (WPA), while waiting for IEEE to announce the new security specification. Vendors began to implement WPA in products around mid-2003, prior to the actual ratification of the 802.11i standard. When the final 802.11i specification was ratified in 2004, devices already existed with WPA security standard. The ratified new 802.11i became known as WPA2 and used Advanced Encryption Standard (AES) rather than RC4. Many clients and WAPs support all three security standards, WEP, WPA, and WPA2. WPA2 is the current standard.

WPA2 operates in two modes: Enterprise and Personal. Enterprise WPA2 uses a RADIUS server, and Personal WPA2 uses a pre-shared key. Personal WPA2 requires that a key (i.e., a string of alphanumeric characters) be entered into the WAP, and the same key be entered in the hosts. That key is used by the WAP and the host to authenticate to each other and to encrypt data as it is transmitted wirelessly.

Enterprise WPA2 uses a RADIUS server that provides authentication services. RADIUS servers are officially known as Remote Authentication Dial In User Service (RADIUS) from this protocol's early roots as a dial-up authentication server; however today the RADIUS server's function has expanded to include authentication to a number of network-based services, including 802.11 WAPS. Clients must be configured to use a RADIUS server for WAP authentication. The RADIUS server allows the client to authenticate to it, and then the RADIUS server provides the security credentials necessary for the client to authenticate to the WAP.Diff: 2 Page Ref: 59, 60



5) Explain the role of the data link layer in an Ethernet LAN, including a discussion of how two hosts would communicate and utilize the LLC and MAC sublayers.Answer: The data link layer is the interface between the physical layer (Layer 1) and the Internet layer (Layer 3). The data link layer is responsible for transmission within the LAN or physical link. In Ethernet, the data link layer is actually broken up into two sublayers: the MAC sublayer and the Logical Link Control (LLC) sublayer. The MAC sublayer implements CSMA/CD for traffic control while the LLC provides traffic control for the various standards and the media. Although not often implemented, the LLC sublayer optionally provides flow control, acknowledgment, and error recovery. The LLC sublayer provides the interface between the Internet layer, and the MAC sublayer. For example, if a host was configured to work with both the IP and IPX (legacy Novell) standards at Layer 3 (i.e., Internet layer), then the LLC would be responsible for taking an incoming frame from the MAC layer and routing it to the correct Layer 3 process.

For communication between Host A and Host B, the following process occurs: The appropriate Layer 3 process prepares a packet with the between-network addressing (e.g., IP address), then passes it off to the LLC sublayer of the data link. The LLC can be thought of as traffic control, keeping track of which Layer 3 process sends/gets the packet. The LLC passes the packet off to the MAC sublayer, which adds MAC addresses (i.e., hardware addresses) and prepares the frame for propagation. The MAC sublayer passes the frame off to the physical layer for propagation. The receiving host reverses the process.Diff: 2 Page Ref: 53, 54 figure


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