Business Data Communications and Networking 7th Edition Test Bank - Chapter 06 (400 Level Course)
TRUE/FALSE
The following are possible True/False questions for tests. The statement is given and the answer is provided in square brackets. The level of difficulty (easy, moderate, difficult) and the page number(s) relevant to the topic are also furnished.
1. As discussed in this textbook, three layers of a network model are required for a typical network, including local area networks. [False, five layers are required; from previous chapters]
Moderate
2. Traditional Ethernet, switched Ethernet, and wireless Ethernet LANs account for almost 95 percent of all LANs installed today. [True; p. 172]
Easy
3. Information contained in a single database and used for decision-making can be shared by users of a LAN. [True; p.173]
Moderate
4. On a network, it is always legal to purchase one copy of software, such as a word processing package, that multiple users use simultaneously. [False, it is illegal; p. 173]
Easy
5. LAN metering software can be used to prohibit using more copies of a package than there are installed licenses. [True; p. 173]
Easy
6. Software Publishers Association has embarked upon an aggressive software audit program to check the number of illegal software copies on LANs. [True; p. 173]
Easy
7. LANs can be categorized as either dedicated (with a dedicated server) or peer-to-peer (without a dedicated server). [True; p. 173-174]
Easy
8. A Network Operating System (NOS), such as Novell or Windows NT, must be used in addition to the ‘normal’ operating system, such as Windows, on a server in a dedicated server LAN. [False, the NOS replaces/substitutes the ‘normal’ operating system; p. 174]
Easy
9. By offloading printing tasks from the main LAN server, a print server increases network efficiency. [True; p. 174]
Easy
10. The Network Interface Card (NIC) permits a computer to be physically connected to a network’s cable, which provides the network layer connection among the computers in the network. [False, it is the physical layer connection; p. 175]
Moderate
11. Some computers have a special port that enables network cards to be installed without physically opening them (PCMCIA slots). [True; p. 175]
Easy
12. LANs that run on infrared or radio frequencies use a type of conducted media. [False, these are types of radiated media; p. 176]
Moderate
13. Fiber optic cable is thicker and heavier than unshielded twisted pair. [False, it is thinner and lighter; p. 176]
Easy
14. A BALUN (Balanced Unbalanced) device permits different types of cabling (twisted pair and coax cable) to be connected together. [True; p. 176]
Easy
15. Many network hubs incorporate repeaters or amplifiers to regenerate signals so that attenuation of the signal does not occur. [True; p. 176]
Moderate
16. A hardware device that is not included in a network profile cannot be accessed by another computer on the network. [True; p. 180]
Easy
17. Traditional Ethernet is also known as shared Ethernet. [True, p. 181]
Easy
18. The NOS software for the server computer provides the physical, data link, and network layer functions.
[False, it provides the data link, network, and application software functions; p. 179]
Moderate
19. Most LANs keep audit files to track who uses which resource. [True; p. 180]
Easy
20. For security purposes, a user profile, which designates levels of access for specific devices/resources for each user of the LAN, should be developed. [True; p. 180]
Easy
21. The Ethernet standard was developed first by the IEEE. [False, it has been formalized as a standard by IEEE, but it was originally developed by DEC, Intel, and Xerox; p. 180]
Moderate
22. Topology refers to the geometric layout of the network and describes how the computers are interconnected. [True; p. 181]
Easy
23. A collision on a bus circuit means that two computers on that circuit have transmitted at the same time. [True; p. 182]
Moderate
24. On the outside, a switch looks almost identical to a hub. [True; p. 185]
Easy
25. In general, data throughput remains steady and predictable at the maximum rate in a contention approach (CSMA/CD) type of traditional hub 10Base-T large network that has high usage. [False, data throughput can drop by almost 50 percent due to collisions in a high usage network; p. 186]
Difficult
MULTIPLE CHOICE
The following are possible multiple-choice questions for tests. The question is posed and the answer is provided under the choices. The level of difficulty (easy, moderate, difficult) and the page number(s) relevant to the topic are also furnished.
1. _____________ refers to having users who access the same data files, exchange information via electronic mail, or search the Internet for information.
a. Resource sharing
b. User grouping
c. User profiling
d. Information sharing
e. Data pirating
Answer: d, Easy, p. 173
2. ____________ refers to one computer legally sharing a software package, such as Microsoft Word, with other computers on the network to save costs.
a. Software metering
b. Information sharing
c. Resource sharing
d. Software pirating
e. Network routing
Answer: c, Easy, p. 173
3. A dedicated server LAN:
a. can only use simple LAN software
b. is limited to handling small databases
c. has one or more permanently assigned servers that can enable users to share files, for example
d. can not connect with other networks
e. is limited to handling small files
Answer: c, Moderate, p. 174
4. Which of the following is not a critical software component in a dedicated server LAN?
a. application software on server computers
b. network operating system in the dedicated server
c. network communication software on the client
d. LAN metering software
e. application software on client computers
Answer: d, Moderate, p. 174
5. A(n) _____________ is not a common type of dedicated server.
a. file server
b. print server
c. database server
d. collision server
e. remote access server
Answer: d, Moderate, p. 174
6. A(n) ____________ can permit users calling into a LAN remotely to retrieve their email, for example.
a. print server
b. database server
c. file server
d. piconet server
e. remote access server
Answer: e, Moderate, p. 174
7. A peer-to-peer LAN:
a. has more capability than a dedicated server
b. supports a higher number of computers than a dedicated server
c. is generally cheaper in hardware and software than a dedicated server
d. is not appropriate for sharing resources in a small LAN
e. is often much faster than dedicated server networks
Answer: c, Moderate, p. 174-175
8. Which of the following is not a basic LAN component?
a. client
b. PAD
c. server
d. network interface card
e. network operating system
Answer: b, Moderate, p. 175-180
9. Which of the following is not an advantage of using Cat5 unshielded twisted pair for cabling LANs?
a. cost (relative to fiber)
b. thickness (relative to coax)
c. weight (relative to coax)
d. flexibility (relative to coax)
e. security (relative to fiber)
Answer: e, Moderate, p. 176
10. Of the following, which is not true about fiber optic cable?
a. it is thinner than unshielded twisted pair cable
b. it is lighter than unshielded twisted pair cable
c. it has a very low capacity
d. it is more expensive than CAT5 unshielded twisted pair cable
e. it is a type of guided media
Answer: c, Moderate, p. 176-177
11. Which of the following is not a purpose for using hubs in a network?
a. to act as a communications server
b. to connect network cables
c. to prevent attenuation
d. to act as a junction box
e. none of the above
Answer: a, Moderate, p. 176-177
12. Which of the following type of media is most commonly used in backbone networks because of its high capacity?
a. fiber
b. infrared frequencies
c. coax cable
d. unshielded twisted pair
e. shielded twisted pair
Answer: a, Easy, p. 176
13. Hubs:
a. usually incorporate repeaters or amplifiers
b. have connection points called handles
c. limit the distance of a network to a few meters in length
d. are a difficult method to connect network cables
e. operate at the application layer
Answer: a, Moderate, p. 177
14. __________ is not true with respect to network hubs.
a. Each port in a hub has a unique number.
b. A good network plan includes hubs in areas, such as a telecommunications wiring closet, in which a network may expand
c. Simple hubs are commonly available in 4-, 8-, 16-, and 24-port sizes
d. Many hubs act as repeaters or amplifiers
e. Hubs provide a complicated way to connect network cables
Answer: e, Moderate, p. 176-177
15. The server version of the Network Operating System does not:
a. provide the software that performs the functions associated with the physical layer
b. provide the software that performs the functions associated with the data link layer
c. provide the software that performs the functions associated with the application layer
d. provide the software that performs the functions associated with the network layer
e. usually provide the software that performs the functions associated with the computer’s own operating system
Answer: a, Moderate, p. 179
16. A __________ indicates what resources on each server are available on the network for use by other computers and what people are allowed what access to the network.
a. user profile
b. user access log
c. network profile
d. network operating system
e. server allocation list
Answer: c, Easy, p. 180
17. The cheapest time to install network cabling is:
a. during the construction of the building
b. as soon as the building is completed
c. as soon as the building is occupied
d. about five years after the building is occupied so that the exact office locations for each network computer is known
e. any time that a network needs to be installed
Answer: a, Moderate, p. 178
18. Most buildings under construction today have a separate:
a. LAN cabling plan
b. telephone cabling plan
c. electrical cabling plan
d. all of the above
e. none of the above
Answer: d, Easy, p. 178
19. Media access control refers to:
a. the price of fiber optic cable
b. security over floppy disks in a user environment
c. the ability for a user to use multimedia equipment in a LAN
d. controlling access to a media by more than one computer in a LAN
e. the control over coax cable installed by a cable service provider
Answer: d, Moderate, p. 182
20. Ethernet LAN was developed by:
a. IBM
b. ARPANET
c. DEC, Xerox, and Intel
d. University of Minnesota
e. CERN laboratory in Geneva
Answer: c, Easy, p. 180
21. The type of logical topology that Ethernet uses is a:
a. ring
b. bus
c. star
d. mesh
e. interconnected
Answer: b, Easy, p. 181
22. The type of physical topology that Ethernet uses is a:
a. ring
b. bus
c. star
d. mesh
e. interconnected
Answer: c, Easy, p. 181
23. A logical bus topology:
a. is always used by token ring protocol LANs
b. has all computers connected to each other in point-to-point connections
c. is limited to short distances since devices like a hub or repeater cannot be used with this type of topology
d. permits every message to be received by every computer on the bus, even when those messages are intended for other computers
e. has a central control device, such as a mainframe
Answer: d, Moderate, p. 181
24. Which of the following is not true about CSMA/CD?
a. The acronym refers to Carrier Sense Multiple Access with Collision Detection
b. It is used in token ring protocol LANs
c. It is a contention-based media access control technique
d. When a collision has occurred, the computers that wish to transmit wait a random amount of time after a colliding message before attempting to retransmit
e. Computers on the circuit ‘listen’ while transmitting
Answer: b, Moderate, p. 182
25. _________ is not a type of Ethernet specification.
a. Thinnet
b. Thicknet
c. 1000Base-T (1GbE)
d. 10Base-T
e. Securenet
Answer: e, Moderate, p. 183
26. 10Base-5:
a. supports 10 Mbps data rate
b. was the original Ethernet specification
c. is known as Thicknet
d. is capable of running 500 meters between hubs
e. all of the above
Answer: e, Moderate, p. 183
27. 1000 Base-T:
a. can run at either full- or half-duplex
b. is one of the oldest forms of Ethernet
c. is one of the slowest forms of Ethernet
d. can only be used over coaxial cables
e. has only one version, 1000Base-SLCX
Answer: a, Moderate, p. 183-184
28. ________ is a hybrid version of Ethernet that uses either 10Base-T or 100Base-T.
a. Mullion Ethernet
b. Base-T Ethernet
c. 10/100 Ethernet
d. Token ring Ethernet
e. FDDI Ethernet
Answer: c, Easy, p. 184
29. 10/100 Ethernet:
a. uses 100 Mbps throughout the entire network
b. is not useful in the short run for organizations that are uncertain about which Ethernet standard to use
c. uses 10 Mbps throughout 100% of the entire network
d. provides traditional 10 Mbps Ethernet connections to client computers utilizing traditional 10Base-T, with 100 Mbps generally used to the server
e. uses 10 Gbps throughout 100% of the entire network
Answer: d, Moderate, p. 184
30. Which of the following is not true about 10/100 Ethernet?
a. It is not a hybrid type of Ethernet.
b. It provides flexibility for organizations that want to use both the 10Base-T and 100Base-T standards at the same time.
c. 10/100 autosense hubs (and/or switches) are able to detect the signal transmitted by the client’s NIC and use 10 Mbps or 100 Mbps, depending on what the client uses.
d. Depending upon how it is configured, a 10/100 Ethernet NIC can run at either 10 Mbps or at 100 Mbps.
e. It provides flexibility for organizations that are uncertain about which Ethernet standard to use in the short term.
Answer: a, Easy, p. 184
31. Switched Ethernet:
a. uses a hub to connect computers
b. has a physical topology of a ring
c. has a logical topology of a ring
d. has a logical topology of a bus
e. usually enables all attached circuits to send or receive packets simultaneously
Answer: e, Moderate, p. 184-185
32. A switch uses a _____________ that is very similar to a routing table used in a router.
a. cable plan
b. forwarding table
c. network server
d. reversing table
e. switching mullion
Answer: b, Moderate, p. 185
33. Which of the following is not true about layer-2 switched Ethernet?
a. A switch replaces the hub.
b. The physical topology is the same as the physical topology of shared Ethernet: a ring.
c. The logical topology is a star.
d. The switch uses a forwarding table to route the packet to the correct circuit/computer.
e. The switch chooses which packet to transmit first if it receives more than one packet destined for the same computer at the same time, and stores the other packet(s) temporarily.
Answer: b, Easy, p. 185
34. Switched Ethernet:
a. always has a lower capacity than shared Ethernet.
b. operates at 50% of capacity before performance becomes a problem.
c. operates at about 95% of capacity before performance becomes a problem.
d. is affected by the increased collisions caused by using a switched LAN design.
e. decreases network performance because each computer is connected via a common multipoint circuit.
Answer: c, Moderate, p. 186
35. Which of the following is not true about switched Ethernet?
a. The probability of collision is higher than with shared Ethernet.
b. It uses a switch instead of a hub.
c. It has faster connections (almost immediate) than traditional Ethernet.
d. It essentially provides a point-to-point connection between computers.
e. It has forwarding tables in which entries are learned over time.
Answer: a, Moderate, p. 186
36. LAW is an acronym for:
a. Local Area Wireless Network
b. Lean Access Wiring
c. Local Area Wide Network
d. Logical Access Wireless
e. Logical Area Wiring
Answer: a, Moderate, p. 187
37. Wireless Ethernet:
a. has a physical topology of a bus
b. uses an Access Point (AP) as a radio transmitter that acts as a hub
c. is composed of devices that use different radio frequencies to communicate
d. have extremely high levels of security
e. use exactly the same media access control (CSMA/CD) as shared Ethernet
Answer: b, Moderate, p. 187-188
38. Which of the following is not true about the media access control for wireless Ethernet?
a. It is optional to use both physical carrier sense method and virtual carrier sense method simultaneously.
b. It requires use of both physical carrier sense method and virtual carrier sense method simultaneously.
c. It is known as carrier sense multiple access with collision avoidance.
d. A hidden node problem may exist when computers are on opposite edges of the WLAN.
e. With virtual carrier sense method, the AP manages the shared circuit using a controlled-access approach.
Answer: b, Moderate, p. 188-190
39. IEEE 802.11b, one type of wireless Ethernet, has been defined:
a. with only one basic form, Frequency-Hopping Spread Spectrum (FHSS)
b. with only one basic form, Direct-Sequence Spread Spectrum (DSSS)
c. with two basic forms, FHSS and DSSS
d. as a switched media implementation only
e. to always operate at its top-rated speeds
Answer: c, Easy, p. 191
40. Which of the following is not true about spread spectrum LAN devices?
a. Other devices, such as cordless phones, that rely on radio waves could interfere with the signal
b. Speed can be reduced in case the distance between the AP and the computer is too far for a strong signal.
c. These are a switched media implementation.
d. Either DSSS or FHSS operate at frequencies in the 2.4 Ghz band.
e. FHSS is considered to have good security because it is difficult for an outside listener to know what frequencies will be hopped to next, and in what sequence.
Answer: c, Moderate, p. 191
41. The primary advantage of a wireless LAN is that:
a. higher speed data transmissions than using fiber optics can be achieved
b. no cabling need be installed
c. it is very secure from eavesdropping
d. there is much less opportunity to disrupt transmissions
e. it is a new technology so it provides leading edge ‘prestige’ for the organization that uses it
Answer: b, Easy, p. 192
42. Most infrared wireless LANs are:
a. more flexible than IEEE 802.11 WLANs
b. faster than LANs that use fiber optics throughout the LAN
c. require line of sight between transmitting and receiving devices in the LAN
d. always completely wireless throughout the entire LAN
e. are extremely expensive because they do not require the use of cables throughout the LAN
Answer: c, Easy, p. 192
43. Diffuse infrared LANs operate without a direct line of sight because:
a. all devices are connected using fiber optics
b. infrared light is bounced around a single room
c. this type of infrared can operate through walls
d. all devices communicate using piconets
e. all devices communicate using radio waves
Answer: b, Easy, p. 192
44. A piconet is another name for:
a. a spread spectrum LAN network
b. a Bluetooth network
c. a shared hub-based Ethernet network
d. a type of coaxial cable
e. a radio AP
Answer: b, Easy, p. 193
45. Bluetooth:
a. provides full 1 Mbps shared circuit because its data link protocol is extremely efficient
b. consists of expensive, large devices
c. uses a master/slave media access control
d. uses contention-based media access control
e. uses DSSS in a 2.4 GHz range
Answer: c, Moderate, p. 193
46. LAN bottlenecks are usually found at the:
a. data entry keyboard and client video monitors
b. LAN server and network circuit
c. hub repeaters and transducer circuit modules
d. client operating system and diskette drive
e. client hard drive and processor
Answer: b, Easy, p. 193-194
47. Which of the following is not a potential bottleneck for LAN performance?
a. number and speed of hard disks in the server
b. amount of memory in the server
c. speed of server’s CPU
d. network interface card
e. all of the above are potential bottlenecks for LAN performance
Answer: e, Easy, p. 193-196
48. If your LAN server is overloaded, which of the following should you not consider (to solve the server problem)?
a. adding one or more additional servers
b. upgrading the server’s CPU with a faster CPU
c. increasing the amount of memory of the server
d. increasing the number and speed of hard disks in the server
e. replacing the cable with fiber optic cable
Answer: e, Moderate, p. 193-196
49. To increase the volume of simultaneous messages the LAN circuit can transmit from network clients to the server(s), you can:
a. increase the CPU of the server
b. upgrade to a bigger circuit
c. increase the number of hard disks on the server
d. increase the amount of disk capacity of the server
e. increase the amount of memory of the server
Answer: b, Easy, p. 196-197
50. Breaking a network into smaller parts is called network:
a. fragmentation
b. segmentation
c. localization
d. allocation
e. mitigation
Answer: b, Easy, p. 196
51. Which of the following is not an effective way to reduce LAN network demand:
a. move files to client computers
b. use disk caching on the client machines
c. find an application that places a large demand on the network and run it a time when the network is lightly loaded
d. add hidden nodes
e. shift the users’ routines
Answer: d, Moderate, p. 196-197
Short Answer Questions
1. Describe the major components of a LAN and what function each performs.
Answer: The Network Interface Card (NIC) enables the computer to be physically connected to the network cable, which provides the physical layer connection among the computers in the network. Most LANs are formed with unshielded twisted pair (UTP) wires, shielded twisted pair (STP), coaxial cable, and/or fiber optic cable. Network hubs provide an easy way to connect network cables and act as repeaters or amplifiers. Most new buildings built today have a separate LAN cable plan as they do for telephone cables and electrical cables. Wireless LANs use the same protocols (Ethernet, for example) as other LANs, but they transmit data through the air rather than by cable. The network operating system (NOS) is the software that performs the functions associated with the data link and the network layers, and interacts with the application software and the computer’s own operating system. Every NOS provides two sets of software: one that runs on the network server(s), and one that runs on the network client(s). A network profile specifies what resources on each server are available for network use by other computers and which devices or people are allowed what access to the network.
2. How does a logical topology differ from a physical topology?
Answer: A logical topology is how the network works conceptually, similar to a logical ERD in database design. A physical topology is how the network is physically installed, similar to a physical ERD in databases.
3. How does direct-sequence spread-spectrum (DSSS) WLANs differ from frequency-hopping spread-spectrum (FHSS) LANs?
Answer: DSSS systems transmit signals through a wide spectrum of radio frequencies simultaneously (in the 2.4 GHz band). This signal is divided into many different parts and sent on different frequencies simultaneously. Because several radio devices could be operating in these same frequency bands, devices add a special code to each bit transmitted that uniquely identifies the signal and enables the intended receiver to identify it.
FHSS systems transmit signals through the same wide spectrum of radio frequencies, but use each frequency in turn. A short burst of data is sent on one frequency and then the sender changes to another pseudorandom frequency and broadcasts another burst of data before changing to another frequency. That transmitter and receiver are synchronized so that they both know which frequencies will be used at which point. This approach minimizes jamming and eavesdropping.
4. Compare and contrast 10Base-T, 10Base-5, and 10Base-2.
10Base-T is the most commonly used type of Ethernet. The name means 10 Mbps, baseband, and the “T” means it uses (very cheap) twisted pair wiring (actually unshielded twisted pair). It was the 10Base-T standard that revolutionized Ethernet, and made it the most popular type of LAN in the world.
The original Ethernet specification was a 10 Mbps data rate using baseband signaling on thick coaxial cable, called 10Base-5 (or “Thicknet”), capable of running 500 meters between hubs.
10Base-2 (or “Thinnet”) uses thinner cheaper coaxial cable than Thicknet. Thinnet is capable of running 200 meters between hubs.
5. Compare traditional Ethernet and switched Ethernet in terms of performance.
Answer: It is generally accepted that traditional hub-based 10Base-T LANs can run effectively only to about 50% of their capacity because many collisions affect response time. The diminished capacity (effectively being 5 Mbps on a 10 Mbps network) is shared by all computers on the LAN. However, as speeds of a LAN increase, the probability of collisions decreases, so a 100Base-T can run close to 80% of capacity with few problems.
Switched Ethernet dramatically improves network performance because each computer has its own dedicated point-to-point circuit, rather than the one common shared multipoint circuit in traditional hub-based Ethernet. The probability of a collision is lower because there are only 2 devices on each point-to-point circuit. Some experts believe that we can effectively use up to about 95% of the switched Ethernet capacity before performance becomes a problem. Therefore, on a 10Base-T switched circuit, each computer would effectively run at about 9.5 Mbps on average.
6. You arrive at your new job and your manager asks you to explain two important technical differences between traditional hub-based Ethernet and wireless Ethernet. Remember that your manager does not understand technical buzzwords; use language your manager will understand.
Answer: Traditional Ethernet and wireless LANs are different in terms of media, and media access control (handles when the message gets sent).
Both types of Ethernet use a logical bus topology and a star physical topology. Shared Ethernet can use a variety of guided media (such as various types of coaxial cable). On the other hand, Wireless Ethernet use radio frequencies (unguided media) as circuits. In both cases, computers must take turns using the one circuit.
Traditional Ethernet uses a contention-based technique media access technique called Carrier Sense Multiple Access with Collision Detection (CSMA/CD). Computers listen while transmitting (collision detection). If a collision occurs, all computers stop transmitting and wait for the circuit to become free before trying to retransmit.
Wireless Ethernet uses CSMA/CA, a contention-based technique that is similar to CSMA/CD. It uses both physical and virtual carrier sense methods to avoid collision.
7. You arrive at your new job and your manager asks you to explain two important technical or business factors we need to consider in choosing between two types of LANs for your organization? Don't make a choice (you don't have enough information to make a choice) just discuss two factors that would influence your choice. For example, suppose you decided that the color of the network hubs was important. I would expect you to explain why it was important, and explain how it would affect your choice (e.g., If we have blue carpet, I would buy the blue ones). Remember that your manager does not understand technical buzzwords; use language your manager will understand.
Answer: Important technical or business factors to consider in choosing between two types of LANs for an organization are cost, market share changes, size of network for traffic, data rate, and fit with existing network. Cost is a typical factor when considering most anything. The organization’s market share could change depending if the market is sensitive enough to react to the network decision. The size and kind of network depends upon how many messages will be sent on the network and if there are certain times of the business day in which the network will be flooded with messages (i.e., the network decision will depend upon the expected traffic of the network). The decision based on network traffic will also determine the data rate that will be needed for the network. An existing network will also be a factor in the decision because compatibility with components and vendors is a noteworthy consideration.
8. Compare and contrast radio and infrared wireless LANs. Under what circumstances would you use radio? Under what circumstances would you use infrared?
Answer: In general, infrared LANs are the least flexible because most require a direct line of sight between the transmitters and receivers. Transmitters and receivers are usually mounted in fixed positions. Therefore, most direct line of sight infrared LANs are wireless only between the hubs. The NICs inside the computers are connected via traditional wires to a network hub that contains the transmitter.
The primary advantage of a wireless LAN is the reduction in wiring. Infrared-based LANs are sometimes used for communication between buildings where installing underground cable would be expensive. In an old building where wiring is difficult and costs are extremely high, wireless LANs offer a low cost alternative by enabling communication without the installation of cables. The primary disadvantage is the low speed, only 1-4 Mbps.
A new version of infrared, called diffuse infrared, operates without a direct line of sight by bouncing infrared light around a room. Most diffuse infrared systems have extremely short ranges (usually only 50-75 feet) and will only operate in the same room because the light cannot travel through walls.
Radio waves travel in all directions and through non-metal objects and thus are more flexible than infrared systems. Most radio LANs have a NIC inside the computer that is connected to an external transmitter. The external transmitter transmits radio signals to a receiver that acts like a network hub and enables wireless computers to communicate with each other and with traditional wired networks. Most radio LANs have a range of 100-500 feet and may even reach 1000 feet in open areas without obstructions or sources of interference.
Wireless LANs are also being used increasingly with laptop computers, permitting new capabilities for mobile computing. When configured with a wireless network, a set of laptops becomes an effective way to provide a portable groupware configuration or to enable workers to walk through a facility and have constant network access at any point (e.g., warehouse, factory).
9. Suppose an Ethernet 10BaseT LAN in your office is starting to have slower and slower response time. What would you do?
Answer: Every LAN has a bottleneck, a narrow point in the network that limits the number of messages that can be processed. Generally speaking, the bottleneck will lie either in the network server or the network circuit. Server performance can be improved with a faster NOS that provides better disk caching and disk elevatoring, by buying more servers and spreading applications among them, or by upgrading the server’s CPU, memory, NIC, and the speed and number of its hard disks. Circuit capacity can be improved by using token ring rather than Ethernet, and by segmenting the network into several separate LANs. Overall LAN performance also can be improved by reducing the demand for the LAN by moving files off the LAN, using disk caching on the client computers, and by shifting the user’s routines. Additionally, an Ethernet LAN could be segmented. By carefully identifying how much each computer contributes to the demand on the server, and carefully spreading those computers to different network segments, the network bottleneck can often be broken.
10. You arrive at your new job and your manager asks you to explain the role of network segmentation in improving performance. Remember that your manager does not understand technical buzzwords; use language your manager will understand.
Answer: If there is more traffic on a LAN than the network circuit and media access protocol can handle, the solution is divide the LAN into several smaller segments. Breaking a network into smaller parts is called network segmentation. By carefully identifying how much each computer contributes to the demand on the server, and carefully spreading those computers to different network segments, the network bottleneck can often be broken.
Most servers can support up to as many as 16 separate networks or network segments, simply by adding one NIC into the server for each network. As the number of NICs in the server increase, however, the server spends more of its processing capacity monitoring and managing the NICs, and has less capacity left to process client requests. Most experts recommend no more than three or four NICs per server. There are two ways to create more network segments: one is to use more servers, each dedicated to one or more segments; and the other is to use a backbone network to connect different segments.
11. Explain the two most important issues in selecting a LAN and justify why they are the most important.
Answer: There are a host of issues to be considered in selecting a LAN including: protocol (Ethernet vs. token ring, for example), configuration/topology, network operating system, vendor service and support, application systems, number and type of servers, client computers and users, and network interface cards. The most important issues in selecting a LAN are fit with the existing network, future prospects of the network, cost, and data rate.
The marketplace is crowded with vendors, all claiming their products are the best. To complicate matters, the small, simple LAN you start with today may turn into a large multi-floor, multi-building, or enterprise-wide network in the future. You should start by asking some basic questions: how many users are expected, how much data will be stored and transmitted, how easy it will be to add workstations, what cabling is needed, whose software should be selected, and how much security is needed.
The following lists important factors and decisions to consider when selecting a LAN.
Network Needs
• Number of client computers
• Number of dedicated severs
• Distance between computers
• Internetworking requirements
• Specific application needs
• User training, documentation, and network policies
• Future growth
Technology
• Protocol
• Cabling/Wireless
• Network Operating System
• Reliability
• Ease of use
• Performance
• LAN management software
• LAN backup software and hardware
Vendor
• Experience with network hardware and software
• Experience with your network application
• Vendor service and support
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