A+N+


Introduction to Computer Networks (Questions/Answers)

Questions and Problems
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Section 1-1

1. State whether the following network descriptions are describing a MAN, WAN, or LAN: 
        a. A network of users that share computer resources in a limited area. 
        b. A network of users that share computer resources across a metropolitan area. 
        c. A network that connects local area networks 

        a. LAN 
        b. MAN 
        c. WAN 

2. Expand the acronym NIC. 
        i. “Network Interface Card” 

3. Expand the acronym MAC. 
        i. “Media Access Control” 

4. Expand the acronym LAN. 
        i. “Local Area Network” 

5. Expand the acronym WAN. 
        i. “Wide Area Network” 

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Section 1-2

6. Define the term protocol. 
        i. Set of rules established for users to exchange information. 

7. Define the term topology. 
        i. Architecture of a network. 

8. Define the term deterministic. 
        i. Access to the network is provided at fixed time intervals 

9. A disadvantage of the token-ring system is that if an error changes the token pattern, it can cause the token to stop circulating. This can be eliminated by adding a  . . . 
       d. Token-ring hub (A hub that manages the passing of the token in a Token-Ring network.) 

10. State the network topology being used in the following figures (Bus, Star, Ring, or Mesh). 
       a. Mesh 
       b. Bus 
       c. Ring 
       d. Star 

11. What is the difference between a hub and a switch? 
       i. Hub – Broadcasts data it receives to all devices connected to its ports. 
      ii. Switch – Establishes a direct connection from the sender to the destination without passing the data traffic to other networking devices. 

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Section 1-3

12. Define the acronym CSMA/CD and the protocol that uses CSMA/CD. 
       i. “Carrier Sense Multiple Access with Collision Detection” 
      ii. The networking protocol “Ethernet”. 

13. What information is not included in an Ethernet frame? 
      a. Frame size 

14. What is the minimum size of the data payload in an Ethernet frame? 
       i. 46 bytes 
      ii. The data being transmitted, followed by the pad that is used to bring the total number of bytes up to the minimum of 46 if the data field is less than 46 bytes. 

15. What is the minimum and maximum size of an Ethernet frame? 
      i. Minimum – 64 bytes 
     ii. Maximum –  1518 bytes 

16. Define the acronym OUI. Where is the OUI used? 
      i. “Organizationally Unique Identifier” 
     ii. The first 3 bytes, 24 bits, or 6 digits of a MAC address. 

17. What does the OUI represent? 
      i. The vendor of the NIC “Network Interface Card” 

18. In Windows Vista or Windows XP, how would you find the Ethernet (MAC) address? 
      i. Selecting Start and then Run. In the Run window enter “cmd” and click OK. In the command prompt window that displays enter the command “ipconfig  /all” and hit Enter. The MAC address is listed under Ethernet adapter Local Area Network. The MAC address is labeled as the Physical Address. 

19. INTERNET SEARCH: Find the device manufacturer for the following Ethernet devices: 
     a. 00-C0-4F-49-68-AB – DELL 
     b. 00-0A-27-B7-3E-F8 – APPLE 
     c. 00-04-76-B6-9D-06 – 3Com 
     d. 00-00-36-69-42-27 – ATARI 

20. State the class of address (A, B, or C) for the following IP addresses: 
     a. 46.39.42.05 – Class A 
     b. 220.244.38.168 –  Class C 
     c. 198.1.0.4 –  Class C 
     d. 126.87.12.34 –  Class A 
     e. 99.150.200.251 – Class A 
     f. 128.64.32.16 – Class B 

21. Expand the acronym TCP/IP. 
     i. “Transmission Control Protocol/ Internet Protocol” 

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Section 1-4

22. Cite the three advantages of a wired network. 
     i. Faster network data transfer speeds (within the LAN) 
     ii. Relatively inexpensive to setup 
     iii. The network is not susceptible to outside interference. 

23. Cite three advantages of a wireless network. 
     i. User mobility 
     ii. Simple installations 
     iii. No cables 

24. What does it mean for a wireless networking device to be Wi-Fi compliant? 
     i. That the device has been tested by the Wi-Fi Alliance (Wireless Fidelity) and is certified for compliance with 802.11x wireless standards. 

25. What are the most common types of equipment that are used to establish a broadband connection to the ISP? 
     i. Cable Modem 
     ii. DSL Modem 

26. Name six issues that should be considered when planning a home network? 
     i. Data Speed – “Wired of Wireless?” 
     ii. Cost – “Cost of equipment?” 
     iii. Ease of Implementation– “Cables already ran? Wireless setup is usual minimal.” 
     iv. Appearance– “Wireless networks are neater with no cables.” 
     v. Home Access– “Wireless for mobility, but wired for faster transfer rates.” 
     vi. Public Access– “ISP is the limiting factor for the data transfer rate for the public access.” 

27. Why is checking the lights of a networking device that connects to the ISP important? 
     i. Link Verification will typically appear as a Lit Link Light. 
     ii. The presence of a link light indicates that the transmit and receive pairs are properly aligned and the connected devices are communicating. 
     iii. Absence of the light indicates a possible cabling or hardware problem. 

28. What is the purpose of a Range expander? 
     i. The wireless signal might not be reaching all the areas that need coverage. 
     ii. The device relays the wireless signals from an access point or wireless router into areas with a weak signal or no signal at all. 
     iii. Range Extender – Device that relays the wireless signals from an access point or wireless router into areas with a weak signal or no signal at all 

29.  What is a hotspot? 
     i. A limited geographic area that provides wireless access for the public. 

30. List five steps that can be used to protect the home network. 
     i. Change the default factory passwords. 
     ii. Change the default SSID. “Service Set Identifier” 
     iii. Turn on encryption. 
     iv. Turn off the SSID broadcast. 
     v. Enable MAC address filtering. 

31. You have the choice of selecting a networking device with WEP and another with WPA. Which offers better security and why? 
     a. WPA - Basically put it’s an upgrade overlay for WEP. 
     b. WPA uses Temporal Key Integrity Protocol (TKIP). TKIP is designed to allow WEP to be upgraded. This means that all the main building blocks of WEP are present, but corrective measures have been added to address security problems. 

32. What are the potential problems of using the default factory passwords? 
     i. They are known to the public. 
     ii. Security hole for public access to your network. 

33. What is the purpose of the SSID, and what can the network administrator do to protect the network from hackers who might have learned the SSID? 
     i. The purpose of the SSID is to identify your wireless network and is used by your access point or wireless router to establish an association. 
     ii. The network administrator can change it periodically and turn off broadcasting it in the device’s menu. 

34. What is the purpose of MAC filtering on a wireless network? 
     i. Only wireless devices that have specific MAC addresses will be allowed access to the network. 

35. How does NAT (Network Address Translation) help protect outsider access to computer in the home network? 
     i. NAT translates the private IP address to a public address for routing over the Internet. 
     ii. Private IP address being  10.0.0.0 – 10.255.255.255, 172.16.0.0-172.31.255.255, 192.168.0.0-192.168.255.255) 
     iii. Public IP address being the ISP issuing an IP address to the router from an available pool of IP addresses manage by the ISP. 

36. What is Stateful Packet Inspection “SPI”? 
     i. A type of firewall protection that inspects incoming data packets to make sure they correspond to an outgoing request. 

37. What is a VPN, and how does it protect the data transferred over a wireless network? 
     i. A VPN is a Virtual Private Network and it establishes a secure network connection and is a way to protect your LAN’s data from being observed by outsiders. 
     ii. A VPN enables a remote or mobile user to access the network as if they were actually physically at the network. 
     iii. The VPN connection is encrypted, providing privacy for the data packets being transmitted. 

38. How is IP addressing typically handled in a home network? 
     i. Is managed by the router or wireless router that connects to the ISP. 
     ii. The ISP will issue an IP address to the router from an available pool of IP addresses manage by the ISP. 
            i. The computers on the network should then be issued private IP addresses using NAT “Network Address Translation”. 

39. What is Port Address Translation “PAT”? 
     i. A port number is tracked with the client computer’s private address when translating to a public address. 
     ii. When you are assigned a private address with NAT “Network Address Translation” there is no way for the router to pinpoint the specific computer because it uses the same address for all computers. With PAT “Port Address Translation” the router uses the port number to identify the computer that accessed the internet and delivers the data packet to the right computer. 

40. A router on a home network is assigned an IP address of 128.123.45.67. A computer in the home network is assigned a private IP address of 192.168.10.62. The computer is assigned the public IP address 128.123.45.67:1922. Which IP address is used for routing data packets on the internet? Is overloading being used? 
     i. 128.123.45.67 is being used for routing data packets on the internet. 
     ii. Overloading is being used when the computer was assigned a private address and started sending data packets, which after the packets reach the router and are then sent using the public address assigned to the router by the ISP. 

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Section 1-5

41. Which of the following is not a step in building an office LAN? 
     a. Obtaining proper government permits 
    

42. What does RJ-45 represent? 
     c. An 8-pin modular connector for twisted pair Ethernet 


43. What is an uplink port? 
     i. Allows the connection of a hub or switch to another hub or switch without having to use a crossover cable. 

44. What is the maximum speed and length for Category 6 cabling? 
     i. Maximum Speed – 1000 Mbps 
     ii. Maximum Length -  100 Meters 

45. What do the link lights on a hub represent? 
     i. The presence of a link light indicates the transmit and receive pairs are properly aligned and the connected devices are communicating. 
     ii. Absence of the light indicates a possible cabling or hardware problem. 

46. What does cross-connected mean? 
     i. Transmit and receive signal pairs are crossed to properly align the transmit signal on one device with the receive signal on the other device. 

47. Documentation: Draw a network diagram similar to Figure I-26 consisting of 3 computers, a switch, and a printer. Use the MAC addresses given in Table I-6. Assign each network device an IP address from the private address space 192.168.5.x network. You are the network administrator and may choose the host address for each device. 



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Section 1-6

48.What command would you use to ping 10.3.9.42 indefinitely? 
     i. ping  192.168.0.1 –t 

49.What command would you use to ping 192.168.5.36 20 times with 1024 bytes of data? 
     i. ping  192.168.0.1 –n 20 -l 1024 

50. Expand the acronym TTL. 
     i. “Time To Live” 

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Section 1-7

51. Expand the acronym ARP. 
     i. Address Resolution Protocol 
52. What is the purpose of an ARP request? 
     i. They are used to map an IP address to its MAC address 
53. Expand the acronym ICMP. 
     i. Internet Control Message Protocol 
54. What is an echo request? 
     i. Part of the ICMP protocol that requests a reply from a computer. 
55. What is the purpose of a protocol analyzer? 
     i. A protocol analyzer is used to inspect captured data packets. 

Chapter 2 - Physical Layer Cabling: Twisted Pair (Questions/Answers)

QUESTIONS AND PROBLEMS
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Section 2-2

1. When was the first major standard describing a structured cabling system released? 
     c. 1995 

2. What doe EIA and TIA stand for? 
     i. EIA – Electronics Industries Alliance 
     ii. TIA – Telecommunications Industry Association 
  
3. What are the three parts of the EIA/TIA 568-B standard? 
     i. EIA/TIA-568-B.1: Commercial Cabling Standard, Master Document 
     ii. EIA/TIA-568-B.2: Twisted-pair Media 
     iii. EIA/TIA-568-B.3: Optical Fiber Cabling Standard 

4. Identify the six subsystems of a structured cabling system. 
     i. Building Entrance (Also called (EF) Entrance Facilities) 
     ii. Equipment Room (ER) 
     iii. Telecommunications Closet (Also called (TR) Telecommunications Room or (TE) Telecommunications Enclosure) 
     iv. Backbone Cabling 
     v. Horizontal Cabling 
     vi. Work Area 

5. Which subsystem does permanent networking cabling within a building belong to? 
     i. Backbone Cabling 

6. What is a cross-connect? 
     i. Cross-connect – A space where you are going to take one or multiple cables and connect them to one or more cables or equipment. 

7. What is the main cross-connect? 
     i. Main Cross-Connect (MC) – Usually connects two or more buildings and is typically the central telecommunications connection point for a campus or building. It is also called the Main Distribution Frame (MDF) or Main Equipment Room. The MC connects to telco, an ISP, and so on. Another term for the MC is the campus distributor. (CD) 

8. The Telco and the ISP usually connect to what room in the campus network hierarchy? 
     i. Equipment Room 

9. What is the WO, and what is its purpose? 
     i. (WO) Workstation or Work Area Outlet – Also called the TO (Telecommunications Outlet), it’s used to connect devices to the cable plant. The cable type typically used is CAT3, CAT5, CAT5e, CAT6, CAT6A, and various coaxial cables. Devices typically connected to these outlets are PCs, printers, servers, phones, televisions, and wireless access points. 

10. The patch cable from a computer typically terminates into which of the following? 
     a. Jack in a wall plate 

11. What is the overall length limitation of an individual cable run from the telecommunications closet to a networking device in the work area? 
     i. 100 Meters 

12. A general rule of thumb is to allow how many meters for the cable run from the telecommunications closet to the work area? 
     i. 90 Meters 

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Section 2-3

13. How many pins does an RJ-45 modular plug have? 
     i. 8 

14. What is the difference in CAT 5 and CAT 5e? 
     i. CAT 5 – Up to 100MHz/100Mbps, 100-m length 
     ii. CAT 5e – 100MHz/1000Mbps (Applications with improved noise performance in a full duplex mode. 
15. What is the data rate for Ethernet? 
          i. 10 Mbps 

16. What is the data rate for FastEthernet? 
     i. 100Mbps 

17. What improvements will CAT6 and CAT7 cable provide? 
     i. CAT6- Can support 10-Gbps data rates but over a distance less than 55 meters. 
     ii. CAT6a Supports 10-Gbps data rates up to 100 meters 
     iii. CAT7-support 10-Gbps up to 100 meters with improved bandwidth. 

18. What is the data rate for gigabit Ethernet? 
     i. 1000Mbps (802.3z) 

19. What is a benefit of using shielded twisted-pair cabling? 
     i. Cable with the addition of a shield is called shielded twisted-pair (STP) cable. The addition of this shield reduces the potential for electromagnetic interference (EMI) as long as the shield is grounded. 
          a. EMI originates from devices such as motors and power lines, and from some lighting devices such as fluorescent lights.20. 

20. Which cable, UTP or STP, is preferred by the industry? 
     i. Industry testing on STP cable has shown that the addition of a shield does increase the usable bandwidth of the cable by increasing the noise rejection between each of the wire pairs. However, the tests have shown that there is not a significant advantage of placing a shield over a properly installed 4pair 100-ohm UTP cable. 
     ii. Most manufacturers are recommending the use of UTP cable for cabling computer networks except for very noisy environments. 

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Section 2-4

21. What are the color maps and pin # assignments for T568A and T568B? 
     i. T568A – White-Green/Green/White-Orange/Blue/White-Blue/Orange/White-Brown/Brown 
          a.          1 2     3           4      5    6  7        8 
ii. T568B – White-Orange/Orange/Blue/White-Blue/Green/White-Green/White-Brown/Brown 
          a.          1   2    3       4   5        6    7        8 

22. What is the difference between T568A and T568B? 
     i. They are just two different manufacturer standards used to wire the modular connector hardware. 
          a. There is no performance improvement with either, just a color order choice. 
          b. Industry tends to favor T568A wiring order; however, either order can be used as long as the order is maintained throughout the network. 

23. How many wires are in a CAT6 twisted-pair cable? 
     i. 8 

24. How many wire pairs are in a CAT6 twisted-pair cable? 
     i. 4 

25. In regards to a CAT6 cable, what pin numbers in an RJ-45 connecter are used to carry data in a FastEthernet network? 
      


26. What does an “X” on the input to a hub represent? 
     i. This means that transmit and receive pairs are internally swapped to maintain proper signal alignment of the TX and RX pairs. Even if the “X” is missing, the switch or hub still properly aligns the TX and RX wire pairs. 

27. Define the term cross-connected input. 
     i. Transmit and receive pairs are swapped to maintain proper signal alignment of the TX and RX pairs. 

28. Draw a picture of properly aligned transmit and receive signal of a computer’s data link that is running Ethernet data rates. 



29. What is the difference between “straight” and “cross-connected” input ports? 
     i. Straight – The four wire pairs connect to the same pins number on each end of the cable. 
     ii. Cross-Connected – The transmit pair of device A connects to the receive pair on device B, and the transmit pair of B connects to the receive pair of A. 

30. Draw the wire-map for a “cross over” CAT6 UTP cable running FastEthernet. 



31. Define a UTP link test. 
     i. Defines the point from one cable termination to another 

32. Define a UTP full channel test. 
     i. Consists of all the link elements from the hub or switch to the wall plate 

33. Define the term NEXT and what it measures. 
     i. NEXT (Near-end Crosstalk- A measure of the level of crosstalk or signal coupling within the cable, with a high NEXT (dB) value being desirable. 

34. A NEXT measurement of 59.5 dB is made on wire pairs 1–2/3–6. A next measurement of 51.8db is made on wire pairs 3–6/7–8. Which cable pairs have the best measure NEXT performance? 
     i. Wire pairs 1-2/3-6 (A high NEXT (dB) value is desirable.) 

35. Define Power-Sum measurements. 
     i. Power-Sum testing measures the total crosstalk of all cable pairs. 
          a. This test ensures that the cable can carry data traffic on all four pairs at the same time with minimal interference. 

36. Define propagation delay. 
     i. This is a measure of the amount of time it takes for a signal to propagate from one end of the cable to the other. 

37. Signals travel in a cable at some percentage of the velocity of light. The term of this is? 
     i. Nominal Velocity of Propagation (NVP) 
          a. NVP is some percentage of the velocity of light and is dependent on the type of cable being tested. 

38. Why is delay skew critical? 
     i. It is critical in high-speed data transmission that the data on the wire pair arrive at the other end at the same time. 
          a. If the wire lengths of different wire pairs are significantly different, then the data on one wire will take longer to propagate along the wire, hence arriving at the receiver at a different time and potentially creating distortion of the data and data packet loss. The wire pair with the shortest length will typically have the least delay skew. 

39. Why are power-sum measurements critical for high-speed data communication over UTP? 
     i. The gigabit data rate capability of twisted-pair requires the use of all four wire pairs in the calbe, with each pair handling 250Mbps of data. (4x250Mbps = 1Gbps) Hence the need to obtain the combine performance measurements of all four wire pairs. 
          a. Power sum measurements provide a measure of the total crosstalk of all cable pairs, ensuring that the cable can simultaneously carry data traffic on all four wire pairs with minimal interference. 

40. The expected attenuation loss of a 20m UTP cable should be (greater or less than) a 90m UTP cable? 
     i. Less Than 

41. What is 8P8C, and what connector type is most associated with this? 
     i. Stands for 8-pin 8-conductors and is defined by ANSI/TIA-968-A and B but is commonly called RJ-45 by both professionals and end users. 

42. What are the pin assignments for 1/10 Gbps? 
     i. Can be either on a T568A or T568B wiring diagram but below corresponds the pins on each wiring diagram no matter the color. 

        Bl_DA+/Bl_DA-/Bl_DB+/Bl_DC+/Dl_DC-/Dl_DB-/Dl_DD+/Dl_DD- 
Pin     1     2       3 4   5      6        7  8 

43. What is the purpose of a lacing tool? 
     i. To match the wire colors to the proper order (T568A/T568B) displayed on the sides of the lacing tool. 

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Section 2-5

44. What is the limit on the bend radius for a UTP cable, and why is this important? 
     i. The limit on the bend radius is four times the outer jacket diameter. The reason for this is bends exceeding the limit can introduce attenuation loss. 

45. Is a high PSNEXT measurement desirable? 
     i. Yes because it indicates better cable performance. 

46. Define margin (dB) relative to cable measurements. What does it mean if the margin lists a negative value? 
     i. Each cabling standard has specific channel specifications that are used as guidelines for use in a network. Each parameter has a set margin (dB) that is used to make sure the cable can handle the traffic being sent on it. 
     ii. If the margin lists a negative value the test fails. 

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Section 2-6

47. Define Alien Crosstalk and draw a picture of how this can happen. 
     i. Alien Crosstalk - unwanted signal coupling from one permanent link to another. 
  


48. What is F/UTP, and what is its purpose? 
     i. F/UTP – Foil Twisted Pair 
          a. There are several advantages to using a shielded cable. The first is that a shielded cable offers better security because there is less chance that the data will radiate outside the cable. Additionally, the foil shield helps improve noise immunity from Electro-Magnetic Interference (EMI), Radio Frequency Interference (RFI), and most importantly, AXT. 

49. Why is balance an issue in UTP cables, and what is TCL? 
     i. The balance or symmetry of the signal over the wire pairs helps minimize unwanted leakage of the signal. 
     ii. TCL - Transverse Conversion Loss - The TCL measurement is obtained by applying a common-mode signal to the input and measuring the differential signal level on the output. 
          a. TCL is sometimes called LCL (Longitudinal Conversion Loss). The ELTCLT value (expressed in dB) is the difference between the TCTL and the differential mode insertion loss of the pair being measured. TCTL is the loss from a balanced signal at the near-end to the unbalanced signal at the far end. 

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Critical Thinking

50. Answer the following questions for the certification report shown in Figure 2-54. 
     a. What is the length of pair 7–8? 
     b. What is the length of pair 4–5? 
     c. Why did this cable fail the test? 

     a. 46ft 
     b. 72ft 
     c. Failure due to termination problem. 

51. Answer the following questions for the certification report shown in Figure 2-55. 
     a. What is the length of wire pair 7–8? 
     b. What is the delay skew for pair 4–5? 
     c. Why did this cable fail the wire-map test? 

     a. 311ft 
     b. 36 
     c. Excessive Insertion Loss (Cable is 311ft and max is 295ft for a permanent link.) 

52. Answer the following questions for the certification report shown in Figure 2-56. 
     a. Why did the cable fail the test? 
     b. Draw the wire-map diagram for this cable. 

     a. It seems that pair 3-6 are backwards. 
     b. 

Chapter 4 - Interconnecting the LANs (Questions/Answers)

Questions and Problems
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Section 4-2

1. What are the seven layer s of the OSI model? 
     i. 7-Application 
     ii. 6-Presentation 
     iii. 5-Session 
     iv. 4-Transport 
     v. 3-Network 
     vi. 2-Data Link 
     vii. 1-Physical 

2. Which OSI layer is responsible for adding a header that includes routing information? 
     i. Network Layer 

3. Which OSI layer is considered the media access control layer? 
     i. Data Link Layer 

4. Which OSI layer combines messages and segments into packets? 
     i. Transport Layer 

5. Which OSI layer is responsible for the mechanical connection to the network? 
     i. Physical Layer 

6. The OSI layer responsible for data compression and encryption is which layer? 
     i. Presentation Layer 

7. TCP functions at what layer of the OSI model? 
     i. Transport Layer 

8. HTTP functions at what layer of the OSI model? 
     i. Application Layer 

9. IP and IPX are examples of protocols that operate in what layer of the OSI model? 
     i. Network Layer 

10. The network interface card operates at what layer of the OSI model? 
     i. Physical Layer 

11. Why are the layers of the OSI model important to the network administrator? 
     i. To troubleshoot network problems by verifying functionality of each layer. 
     ii. In many cases it requires the network administrator to isolate at what layer the network problem occurs. 

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Section 4-3

12. What is a bridge? 
     i. A networking device that uses the MAC address to forward data and interconnect two LANs. 

13. Define a segment. 
     i. A section of a network separated by bridges, switches and routers. 

14. What information is stored in a bridge table? 
     i. MAC addresses and port locations for hosts connected to the bridge ports. 

15. What is an association on a bridge and how is it used? 
     i. Indicates that the destination MAC address for a host is connected to one of the ports on the bridge. 

16. Excessive amounts of broadcasts on a network are called a ___________. 
     i. Broadcast Storm 

17. What command is used on a computer to view the contents of the ARP cache? 
     i. arp -a 

18. An empty ARP cache indicates what? 
     i. The MAC addresses in the bridge table have all expired from no data traffic and have been deleted. 

19. Why do entries into the bridging table have a limited lifetime? 
     i. MAC addresses into the bridge table are temporary. The MAC address entry to the bridge table remains active as long as there is periodic data traffic activity from that host on its port. Therefore the MAC address entries have become inactive and therefore the expiration timer has expired and not renewed since no new data traffic has occurred. 

20. Which of the following are advantages of using a bridge to interconnect LANs? 
     b. Relatively inexpensive 
     d. Easy to install 
     e. Reduces collision domains 

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Section 4-4

21. The network switch operates at what layer of the OSI model? 
     i. 2: Data Link Layer 

22. Another name for a switch is 
     b. Multiport bridge 
      
23. How does a switch provide a link with minimal collisions? 
     i. Simultaneous direct data connections for multiple pairs of hosts connected to the network. 
     ii. Only two computers that established the link will be communicating over the channel. 
     iii. Their link is isolated from any other data traffic. 

24. The link for a switch connection is isolated from other data traffic except for what type of messages? 
     i. Multicast Messages – Message are sent to a specific group of hosts on the network. 
     ii. Broadcast Messages – Message is sent to all devices connected to the LAN. 

25. Explain what data traffic is sent across a network when a computer pings another computer. A hub is used to interconnect the computers. 
     i. And echo request is sent, the HUB broadcasts the request to all computers connected to the LAN, The computer that holds the IP address replies with its MAC address to the HUB, the HUB then sends the requests back to the computer that initiated the ping command and a direct line of communication is established between the two computers. The computer that initiated the ping command then receives the data packets from the destination computer. 

26. Explain what data traffic is seen by computer 3 when computer 1 pings computer 2 in a LAN. A switch is used to interconnect the computers. 
     i. Computer 3 only sees/receives an ARP request asking who has the specific IP address because after that a direct line of communication between computer 1 and 2 is established by the switch that prevents computer 3 from seeing the data traffic between computers 1 and 2. 

27. Explain the concept of dynamic assignment on a switch. 
     i. MAC addresses are assigned to a port when a host is connected. 

28. Define aging time on a switch. 
     i. The length of time a MAC address remains assigned to a port. 

29. Explain how a switch learns MAC addresses, and where does a switch store the address. 
     i. By extracting the MAC address information from the headers of Ethernet data packet header of transmitted data packets. 
     ii. The switch then maps the extracted MAC address to the port where the data packet came in and stores it in the Content Addressable Memory (CAM). 
     iii. Content Addressable Memory (CAM) – A table of MAC addresses and port mapping used by the switch to identify connected networking devices. 

30. What happens if a MAC address is not stored in CAM on a switch? 
     i. Flooding – Term used to describe what happens when a switch doesn’t have the destination MAC address stored in CAM. 
     ii. The packet is transmitted out all switch ports except for the port where the packet is received. 

31. What two modes are used by a switch to forward frames? 
     i. Store- and-Forward 
     ii. Cut-Through 

32. What switch mode offers minimum latency? 
     i. Cut-Through 

33. What is error threshold, and what mode is it associated with? 
     i. Error Threshold – The point where the number of errors in the data packets has reached a threshold and the switch changes from the cut-through to the store-and-forward mode. 
     ii. Adaptive Cut-Through mode – Switches when the errors in the data packets has been exceeded 

34. Explain the difference in store-and-forward and the cut-through mode on a switch. 
     I. Store-and-Forward – The entire frame of data is received before any decision is made regarding forwarding the data packet to its destination. (The switch checks the data packet for errors before it is sent on to the destination.) 
     II. Cut-Through – The data packet is forwarded to the destination as soon as the destination MAC address has been read.  (No error checking) 
          i. Fast-Forward- Minimum switch latency 
          ii. Fragment-Free – Fragment collision are filtered out by the switch. 
               1. Fragments occur within the first 64 bytes of a data packet and if the packet is not 64 bytes it is discarded. Therefore no fragments. 

35. How does a layer 3 switch differ from a layer 2 switch? 
     i. They still work at layer 2 of the OSI model but additionally work at Layer 3 Network and use IP addressing for making decision s to route a data packet to the best direction. 
     ii. They use ASICs (application specific integrated circuits) – Hardware to handle the packet switching. 
     iii. They do Wire Speed Routing – Data packets are processed as fast as they are arriving. 

36. What is mean by the term wire-speed routing? 
     i. Data packets are processed as fast as they are arriving. 

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Section 4-5

37. A router uses the network address on a data packet for what purpose? 
     i. To make routing decisions regarding forwarding data packets. 

38. What is the logical address? 
     i. Describes the IP address location of the network and the address location of the host in the network. 

39. The physical connection where a router connects to the network is called the . . . 
     d. Router interface 

40. The connection to the router’s console input is typically which of the following? 
     a. RS-232 
    
41. AUI stand for . . . 
     d. Attachment Unit Interface 

42. The AUI port on a router connects to what networking protocol? 
     d. Ethernet 

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Section 4-6

43. Define Enterprise Network. 
     i. A term used to describe the network used by a large company. 

44. The router interface most commonly used to interconnect LANs in a campus network is. . . 
     c. Ethernet 
    
45. Serial interfaces on a router are typically used to 
     c. Connect to communication carriers 
    
46. The designation E0 indicates. . . 
     a. Ethernet port 0 
    
47. Routing  tables on a router keep track of 
     d. Routes to use for forwarding data to its destination 

48. The convention used for naming of the serial port 0 n a router is . . . 
     a. S0 
      
49. Define the term gateway 
     i. Describes the networking device that enables hosts in a LAN to connect to networks (and hosts) outside the LAN. 

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Section 4-7

50. What is the purpose of the fast link pulse? 
     i. The auto negotiation protocol uses the (FLP) to carry the information between each end of a data link. 
     ii. (FLP) Fast Link Pulse – Carries the configuration information between each end of a data link. 

51. Define full duplex. 
     i. The communication device can transmit between each end of a data link. 

52. Define half duplex. 
     i. The communication device can transmit and receive at the same time. 

53. Which of the following is a disadvantage of the auto-negotiation protocol? 
     b. A failed negotiation on a functioning link can cause a link failure. 
    


Chapter 5 - TCP/IP (Questions/Answers)

Questions and Problems
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Section 5.2

1. What are the four layers of the TCP/IP model? 
     i. Application – Defines the applications used to process requests and what ports and sockets are used. 
          I. (This layer is used to process requests from hosts and to make sure a connection is made to an appropriate port.) 
     ii. Transport – Defines the type of connection established between hosts and how acknowledgements are sent. 
     iii. Internet – Defines the protocols used for addressing and routing the data packets. 
     iv. Network Interface – Defines how the host connects to the network. 

2. Which layer of the TCP/IP model processes requests from hosts to make sure a connection is made to the appropriate port? 
     i. Application Layer 

3. What are well known ports? 
     i. Also known as “reserve ports”, which are ports 1 – 1023 that are reserved by ICANN (Internet Corporation for Assigned Names and Numbers). 

           Port Number Assignments
        Port Numbers          Description 
           1 - 1023          The “well known” ports 
       1024 – 49,151            Registered ports 
      49,152 – 65,535        Private Ports 


4. Identify the port numbers for the following applications. 
     a. Telnet – 23 
     b. HTTP – 80  (Hypertext Transfer Protocol) 
     c. FTP – 20, 21 (File Transfer Protocol) 
     d. DNS – 53 (Domain Name Server) 
     e. DHCP – 67, 68 (Dynamic Host Control Protocol) 


      Common Applications and Their Port Numbers
    Port Number                        Application Description 
       20, 21                                            FTP - (File Transfer Protocol) 
          22                                            SSH - (Secure Shell) 
          23                                          Telnet - (Virtual Terminal Connection) 
          25                                           SMTP - (Simple Mail Transfer Protocol) 
          53                                               DNS  - (Domain Name Server) 
       67, 68                                           DHCP  - (Dynamic Host Control Protocol) 
                                                           (BOOTP-Client)
                                                           (BOOTP-Server)
          69                                            TFTP  - (Trivial File Transfer Protocol) 
          80                                            HTTP  - (Hypertext Transfer Protocol) 
         110                                            POP3  - (Post Office Protocol) 
         161                                            SNMP  - (Simple Network Management Protocol) 
         443                                           HTTPS  - (Secure HTTP) 
         445                                            SMB    - (Server Message Block) 
        1701                                            L2TP  - (Layer 2 Tunneling Protocol) 
        1720                                       H.323/Q.931  - (Voice Over Protocol) 
        1723                                            PPTP  - (Point-To-Point Tunneling Protocol) 

5. Define the purpose of a connection oriented protocol. Give an example. 
     i. Establishes the network connection, manages the data transfer, and terminates the connection. 
          I. Connection Oriented Protocol – Establishes a network connection, manages the delivery of data, and terminates the connection. 
     ii. The TCP (Transport Control Protocol) protocol within the TCP/IP transport layer. 
          I. TCP protocol establishes a set of rules or guidelines for establishing the connection. 

6. What three packets are exchanged between two hosts when establishing a TCP connection? 
     i. SYN – (Synchronizing Packet) 
     ii. SYN ACK – (Synchronizing Acknowledgement Packet) 
     iii. ACK– (Acknowledgement Packet) 

7. What is the purpose of a sequence number (SEQ=) in TCP data packets? 
     i. SEQ (Sequence Number) is used to keep track of the data packets being transferred from Host A to Host B. 

8. Explain how a host knows whether a data packet was not received 
     i. A SYN ACK packet is sent back to the host– The ACK is an acknowledgement that Host B received the pack from Host A. There is a number attached to the ACK with a value of (x+1) [where “x” is the SEQ (Sequence Number).] that should be the sum of the SEQ# from packet 1 plus the length (LEN) of packet 1. 

9. Describe how a TCP connection is terminated. 
     i. The host sends a FIN (Finish) packet to the other connected host. 
          1. Host B sends a FIN packet to Host A indicating the data transmission is complete. 
          2. Host A responds with an ACK packet acknowledging the reception of the FIN packet. 
          3. Host A then sends Host B a FIN packet indicating that the connection is being terminated. 
          4. Host B replies with an ACK packet. 

10. What is a connectionless protocol? Give an example. 
     i. UDP (User Datagram Protocol) Protocol is a connectionless protocol. 
     ii. UDP packets are transported over the network without a connection being established and without any acknowledgment that the data packets arrived at the destination. 

11. What is the purpose of the Internet layer in the TCP/IP protocol suite? 
     i. It defines the protocols used for addressing and routing the data packets. 
          I. Examples – IP, ARP, ICMP, & IGMP. 
               1. IP (Internet Protocol) – Defines the addressing used to identify the source and destination addresses of data packets being delivered over an IP network 
               2. ARP (Address Resolution Protocol) – Used to map an IP address to its MAC address. 
               3. ICMP (Internet Control Message Protocol) – Used to control the flow of data in the network, for reporting error, and for performing diagnostics. 
                    a. Contains “Ping” (packet Internet groper) troubleshooting tool. 
               4. IGMP (Internet Group Message Protocol) – Used when one host needs to send data to many destination hosts. 
                    a. This process is called Multicasting. 
                    b. Example - Streaming (audio and video) - data is sent without waiting for an acknowledgement that the data packets were delivered. 

12. What is the purpose of an ARP request? 
     i. A BROADCAST message is sent to all networking devices asking which network interface has the specific IP address detailed in the ARP query that was sent. 
          I. ARP – is used to resolve an IP address to a hardware address for final delivery of data packets to the destination. ARP issues a query in a network called an ARP request asking which network interface has this IP address 

13. What is the purpose of an ARP reply? 
     i. A reply from the host assigned the IP address replies with an ARP reply. 
          I. ARP Reply - The protocol that contains the hardware address (MAC address) for the destination host that sent the ARP request. 

14. What important networking –troubleshooting tool is part of ICMP, and how does it test a network connection? 
     i. Ping – Packet Internet Groper 
          I. The ping command uses a series of echo requests, and the networking device receiving the echo requests responds with a series of echo replies to test a network connection. 

15. When is IGMP used? 
     i. IGMP is used when multicasting (when one host wants to send data to many destination hosts). The source doesn’t care whether the destination receives a packet. 
          I. Example – Steaming audio and video files over the internet. 

16. The network interface layer of the TCP/IP model defines how the host connects to what network? 
     i. Ethernet, Token-Ring network, or a router connected to a frame relay wide area network. 
          I. Not dictated by the TCP/IP protocol 
          II. Every TCP/IP data packet must have a destination and source MAC address in the TCP/IP header. 

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Section 5-3

                     128 –  64 –  32 –  16 – 08  –  04 –  02   – 01 
                     ___ -____-____-____-____-____- ____ -____ 

17. Convert the following 8-bit binary number to decimal: 10010011? 
     i. 147 

18. Convert the following octet to decimal: 11000000? 
     i. 192 

19. Convert the following 8-bit number to decimal 11111100? 
     i. 252 

20. Convert the following binary number to decimal 11111111? 
     i. 255 

21. Convert the number 192 to its binary equivalent? 
     i. 11000000 

22. Convert the number 65 to its binary equivalent? 
     i. 01000001 

23. Convert the number 96 to its binary equivalent? 
     i. 01100001 

24. What is the equivalent hexadecimal number for 13? 
     i. 1101 

25. Convert 0x5AF3 to binary. Use Table 5-5. 
     i. 0101101011110011 

26. Convert 1011011011110001 to hexadecimal. 
     i. B6F1 



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Section 5-4 

27. What is the IP address range for class C addresses? 
     i. 192.0.0.0 – 223.255.255.255 

28. What is the purpose of class D IP addresses? 
     i. Reserved for Multicast groups 
          I. Example – Skype for video conferencing 

29. How many bits are in an IPv4 address? How many octets? 
     i. Bits – 32 

Example –     {xxxxxxxx}     |          {xxxxxxxx}          |         {xxxxxxxx}           |          {xxxxxxxx} 
               1,2,3,4,5,6,7,8   |  9,10,11,12,13,14,15,16 | 17,18,19,20,21,22,23,24 | 25,26,27,28,29,30,31,32 

     ii. Octets – 4 
          I. Example - xxxxxxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx 
                                1           2          3          4 

30. The IP address is typically expressed in what format for the user? 
     i. A dotted-decimal format. 
          I. Example – X.X.X.X 

31. The IP address 192.168.12.2 is an example of what format? 
     i. Dotted decimal format and is a Class C network. 

32. How many network bits are in each of the following classes? 
     i. Class A – 8 Network bits and 24 Host Bits 
     ii. Class B -  16 Network bits and 16 Host Bits 
     iii. Class C – 24 Network bits and 8 Host Bits 

33. How many network and host bits are in a class C network address? 
     i. 24 Network bits and 8 Host Bits 

34. What is the purpose of a private IP address? 
     i. Have been set aside for private use. 
          I. Are not used for Internet data traffic but are intended to be used specifically on internal networks called intranets. 

35. Can private IP address be routed? 
     i. No, They  are Non- Internet Routable IP Addresses and not routed on the internet 
          I. Non- Internet Routable IP Addresses - IP addresses not routed on the internet and are blocked by the ISP. 

36. How are private IP addresses handled on the Internet? 
     i. They are blocked by the ISP. 

37. What organization assigns IP addresses? 
     i. The ARIN (American Registry for Internet Numbers) 


Wireless Networking (Questions/Answers)

Questions and Problems
------------------------------------------------------------------------------------------------------- 
Section 11-2

1. List two advantages of wireless networking. 
     i. User mobility in the workplace. 
     ii. A cost-effective networking media for use in areas that are difficult or too costly to wire. 

2. What are the three areas defined for the IEEE 802.11 standard? 
     i. Physical Layer (PHY) 
          I. The method of transmitting the data, which may be either RF or infrared (although infrared is rarely used.) 
     ii. Medium Access Control (MAC) 
          I.The reliability of the data service. 
          II. Access control to the shared wireless medium. 
          III. Protecting the privacy of the transmitted data. 
     iii. MAC management protocols and services 
          I.Authentication, association, data delivery, and privacy. 

3. What is an ad hoc network? 
     i. In this network, the wireless clients (stations) communicate directly with each other. This means the clients have recognized the other stations in the WLAN and have established a wireless data link. 
     ii. The fundamental topology of the WLAN is the Basic Service Set (BSS). This is also called the independent Basic Service Set, or ad hoc network. 

4. What is the purpose of an Extended Service Set? 
     i. By adding multiple access points to the network, the range of mobility of a wireless client in the LAN is extended. 
     ii. Definition - The use of multiple access points to extend user mobility Hand-off. 

5. What are the four physical layer technologies being used in 802.11 wireless 
networking? 
     i. Direct Sequence Spread Spectrum (DSSS) 
     ii. Frequency Hopping Spread Spectrum (FHSS) 
     iii. Infrared 
     iv. Orthogonal Frequency Division Multiplexing (OFDM) 

6. Describe the frequency spectrum for the DSSS channels in 802.11b wireless 
networking. 
     i. implements 14 channels (each consuming 22 MHz) over approximately 90 MHz of RF spectrum in the 2.4 GHz ISM (industrial, scientific, and medical) band. 

         North American DSSS Channels 
Channel Number                  Frequency (GHz) 
         1                                    2.412 
         2                                    2.417 
         3                                    2.422 
         4                                    2.427 
         5                                    2.432 
         6                                    2.437 
         7                                    2.442 
         8                                    2.447 
         9                                    2.452 
        10                                    2.457 
        11                                    2.462 

7. Define a pseudorandom sequence as it applies to FHSS. 
     i. Pseudorandom means the sequence appears to be random but in fact does repeat, typically after some lengthy period of time. 
     ii. FHSS uses 79 channels (each 1 MHz wide) in the ISM 2.4 GHz band. FHSS requires that the transmitting and receiving units know the hopping sequence (the order of frequency changes) so that a communication link can be established and synchronized. 

8. What must the FHSS transmitting and receiving units know to communicate? 
     i. Hopping Sequence - The order of frequency changes. 

9. What is the frequency range used by 802.11a, and what modulation technique is used? 
     i. 5 GHz 
     ii. Orthogonal Frequency Division Multiplexing (OFDM) 

10. What is the maximum data rate for the following: 
     a. 802.11b 
     b. 802.11a 
     c. 802.11g 
     d. 802.11n 

     a. 11 Mbps 
     b. 54 Mbps 
     c. 54 Mbps 
     d. 200+ Mbps 

11. Define MIMO as it applies to 802.11n. 
     i. Multiple Input Multiple Output (MIMO) 
     ii. MIMO uses a technique called space-division multiplexing, where the data stream is split into multiple parts called spatial streams. The different spatial streams are transmitted using separate antennas. With MIMO, doubling the spatial streams doubles the effective data rate. 

12. What is the purpose of the power-save mode in 802.11n? 
     i. 802.11n only uses multiple data paths when faster data transmission is required—thus saving power. 

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Section 11-3

13. What is the purpose of an access point? 
     i. Provides a bridge between the wireless LAN and the wired network. 

14. How does the access point know if a wireless data packet is intended for its network? 
     i. The answer is the 802.11 wireless LAN devices use an SSID to identify what wireless data traffic is allowed to connect to the network. 
          I. The SSID is the wireless service set identifier, basically a password that enables the client to join the wireless network. 

15. What is an association, and what is its purpose? 
     i. The access point uses the SSID to determine whether the client is to become a member of the wireless network. 
          I. The term association is used to describe that a wireless connection has been obtained. 

16. Draw a picture of a point-to-point wireless connection. 
     i.

17. Draw a picture of a point-to-multipoint wireless network. 
     i.

18. What are the key issues to be obtained from conducting a site survey for each of the following? 
     a. indoor 
          i. Electrical Power 
          ii. Wired network connection point(s) 
          iii. Access point placement 
          iv. RF coverage - user mobility 
          v. Bandwidth supported 
          vi. Identify any significant RF interference 
     b. outdoor 
          i. Electrical power (base access point) 
          ii. Connection back to the home network 
          iii. Antenna selection 
          iv. Bandwidth supported 
          v. RF coverage 
          vi. Identigy any significant RF interference. 

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Section 11-4

19. In what frequency band does Bluetooth operate? 
     i. 2.4 GHz ISM 

20. How many output power classes does Bluetooth have? List the power level and 
the operating range for each class. 
     i. 3 
     ii.  Power Class     Maximum Output Power     Operating Distance 
                1                      20 dBm                        ~ 100 m 
                2                      4 dBm                          ~ 10 m 
                3                      0 dBm                           ~ 1 m 

21. What is a piconet? 
     i. An ad hoc network of up to eight Bluetooth devices. 
          I. Examples: Computer, Mouse, Headset, Earpiece, and so on. 

22. What is the purpose of the inquiry procedure in Bluetooth? 
     i. When a Bluetooth device is enabled, it uses an inquiry procedure to determine whether any other Bluetooth devices are available. 
     ii. This procedure is also used to allow itself to be discovered. 

23. What is the purpose of the paging procedure in Bluetooth? 
     i. The paging procedure is used to establish and synchronize a connection between two Bluetooth devices. 

24. Define the term backscatter. 
     i. Refers to the reflection of the radio waves striking the RFID tag and reflecting back to the transmitter source with its stored unique identification information. 

25. What are the three parameters that define an RFID system? 
     i. Means of powering the tag 
     ii. Frequency of operation 
     iii. Communications protocol (also called the air interface protocol) 

26. Explain how power is provided to a passive RFID tag. 
     i. Power is provided to the tag by rectifying the RF energy, transmitted from the reader, that strikes the RF tag antenna. 
          I.The rectified power level is sufficient to power the ICs on the tags and also provides sufficient power for the tag to transmit a signal back to the reader. 

27. Cite three advantages for using an active RFID tag. 
     i. The power consumption of the G2C501 is 10μA in the sleep mode and uses two AA batteries with an expected lifetime of five years. 
     ii. The G2C501 also works in the standard 915 MHz range. 
     iii. The G2C501 also has location capability. 
          I. This is accomplished by making Receive Signal Strength Indicator (RSSI) measurements from three separate access points. 

28. What are the three frequency bands typically used for RFID tags? 
     i. Low Frequency (LF) 
     ii. High Frequency (HF) 
     iii. Ultra-high Frequency (UHF) 

29. What is the WiMax frequency standard for the United States? 
     i. United States - Unlicensed 5.8GHz and licensed 2.5 GHz spectrum. 
     ii. Internationally 3.5 GHz 
     iii. Worldwide Interoperability for Microwave Access (WiMax) 

30. Why was OFDM selected for WiMax? 
      i. This signaling format was selected for the WiMAX standard IEEE 802.16a standard because of its improved NLOS (non line-of-sight) characteristics in the 2 GHz to 11 GHz frequency range. 
          I. An OFDM system uses multiple frequencies for transporting the data, which helps minimize multipath interference problems. Some frequencies may be experiencing interference problems, but the system can select the best frequencies for transporting the data. 
          II. Orthogonal Frequency Division Multiplexing (OFDM) 

31. How does WiMax differ from Wi-Fi? 
     i. The WiMAX (IEEE 802.16e) media access control (MAC) layer differs from the IEEE 802.11 Wi-Fi MAC layer in that the WiMAX system has to compete only once to gain entry into the network. 

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Section 11-5

32. What is the most important thing to do if using a wireless network? 
     i. The wireless security features are turned on. 

33. What is the purpose of wireless beacons? 
     i. In WLAN equipment, the beacons are transmitted so that a wireless user can identify an access point to connect to. 
     ii. Definition - Used to verify the integrity of a wireless link. 

34. What information can be obtained from a wireless beacon? 
     i. The Service Set Identifier (SSID) of the network. 

35. What is the purpose of WEP? 
     i. Wired Equivalent Privacy (WEP) is used to encrypt and decrypt wireless data packets. 
          I. The exchange and the return of the encrypted text verifies that the client has the proper WEP key and is authorized to be a member of the wireless network. 

36. List four guidelines for wireless security. 
     i. Make sure the wireless security features are turned on. 
     ii. Use firewalls and intrusion detection on your WLAN. 
     iii. Improve authentication of the WLAN by incorporating 802.1x features. 
     iv. Consider using third-party end-to-end encryption software to protect the data that might be intercepted by an unauthorized user. 
     v. Whenever possible, use encrypted services such as SSH and Secure FTP. 

37. Describe the steps used by WPA2 to authenticate a user. 
     i. WPA2 is an improved version of WPA. The 802.1x standard enhances wireless security by incorporating authentication of the user. Cisco Systems uses an 802.1x authentication system called LEAP. In Cisco LEAP, the user must enter a password to access the network. This means that if the wireless client is being used by an unauthorized user, the password requirement will keep the unauthorized user out of the network. 

38. What is a RADIUS server? 
     i. A Remote Authentication Dial-In User Service (RADIUS) service is sometimes used to provide authentication. This type of authentication helps prevent unauthorized users from connecting to the network. Additionally, this authentication helps to keep authorized users from connecting to rouge of unauthorized access points. 
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Section 11-6

39. What type of wireless connection is used to connect the home network to a multi-point distribution site? 


40. Use the Internet to find a source of omnidirectional and directional antennas for 
each of the following standards. 
     a. 802.11b 
     b. 802.11a 
     c. 802.11g 
     d. 802.11n 
Prepare a list of three manufacturers for each antenna type. Include cost figures. 

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Critical Thinking

41. A wireless network receiving site is experiencing occasional loss of signal due 
to interference. Discuss the steps you would take to correct this problem. 


42. Prepare a memo to your supervisor explaining why it is important to run encryption 
on your wireless network. 

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