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Answers and Explanations

Objective 1.1

  1. Answer: B. In a mesh topology, each device is connected directly to every other device on the network. Such a structure requires that each device have at least two network connections. The mesh topology is not commonly implemented. In a bus topology, each device is connected to the network through a single connection. In a ring topology, each device is connected to the network through a single connection. In a star topology, each device is connected to the network through a single connection.

  2. Answer D. The layout of the network is referred to as the topology. The logical topology defines how the devices connected to the network see it, and the physical topology defines how the network is actually laid out. The term backbone is used to describe a segment of the network that acts as a connection point for other segments. Network is a generic term used to describe the network as a whole. The term physical map is not commonly used.

  3. Answer: A. In a mesh topology, all devices are connected directly to every other device on the network. If one link fails, there is always another available. It is the most fault-tolerant network topology. A hierarchical star is a variation of the standard star and is not considered a fault-tolerant implementation. A ring topology is not considered fault tolerant. In a star topology, each device is normally connected to one central device and therefore is not fault tolerant.

  4. Answer C. The most widely implemented mesh topologies are the Internet and the telephone network.

  5. Answer B. Because workstations don't contend for access to the network, access is guaranteed with a token ring network. IP addressing is a Network layer concept and isn't dependent on a Data Link layer protocol or topology. Token ring may be implemented in full-duplex, but at the workstation level, it isn't common. A ring must be broken to add a new workstation.

  6. Answer: D. A star topology consists of a central hub that is a common connection point for all nodes. The nodes connect to ports on the hub.

  7. Answer: D. The hub used in a token ring network is called a Multi-Station Access Unit, or MSAU. It may also be called a Multistation Access Unit, or MAU. An AUI is used in Ethernet coaxial networks. A switch is used to provide the full bandwidth of the network to each node. A patch panel provides a modular connection for extension of the wall cabling into the hub.

  8. Answer: B. Token ring is specified in the IEEE 802.5 standard. IEEE 802.11 describes wireless LANs. IEEE 802.3 describes CSMA/CD Ethernet. IEEE 802.2 describes the LLC sublayer of the Data Link layer.

  9. Answer: A. This is a small LAN and unless there is reason to believe it will grow drastically, a peer-to-peer arrangement should meet the needs of the three users.

  10. Answer: C. A ring must be broken to add a new node. This is a disadvantage of a ring topology. Having an excessive number of connections is a disadvantage of a large mesh network. Problems with a shorted bus may occur on a bus network. A point-to-point connection is made in a star topology.

  11. Answer: B. Each node on a star network uses its own cable, making it easy to add users without disrupting current users. Adding a node to a bus network will involve breaking the segment, which makes it inaccessible to all other nodes on the network. A ring network topology will require that the ring be broken to add a new device. A mesh topology requires that every device be connected to every other device on the network. It is, therefore, quite difficult to expand a mesh network.

  12. Answer: D. All that's required to expand a star topology is to add another node to a hub port. Star topologies usually have low overhead and high throughput.

  13. Answer: C. The most common logical topologies are the Ring, Bus, and mesh.

  14. Answer: D. A star topology consists of a central hub with spokes that connect to nodes.

  15. Answer: B. The topology of a network may affect your decision on the type of media. Bus networks, for example, require that the ends of the bus be terminated with a proper resistance so that data signals aren't reflected back through the wire thereby creating distortion.

Objective 1.2

  1. Answer: C. Carrier Sense Multiple Access/Collision Detection (CSMA/CD) is a media access method defined by the 802.3 standard. The 802.2 standard defines Logical Link Control functions. The 802.5 standard defines token ring networking. The 802.11b standard defines wireless networking for LAN systems.

  2. Answer: A. IEEE 10BASE-2 uses the coaxial cable type and has a maximum cable length of 185 meters.

  3. Answer: D. The Logical Link Control (LLC) describes the conventions a sender and receiver follow to ensure the data flow is orderly. The conventions correspond to the IEEE 802.2 standards. The LLC is a software interface situated between the software that controls network interface hardware, such as that found on the Network Interface Card (NIC), and the communication software running on a network, such as Windows NT/2000 or NetBIOS.

  4. Answer: B. The maximum number of stations permitted on an IEEE 802.3 network is 1,024.

  5. Answer: A. IEEE 802.3 is the standard specification for 100BASE-T.

  6. Answer: C. Because the transmission times of nodes can be predicted, token ring has a huge advantage over Ethernet. Token ring has a huge advantage over CSMA/CD networks in that it's deterministic. This means that the nodes transmit at specific, predictable times. Because the transmission times of nodes can be predicted, so can the delivery times. Without contention on the network, there are no collisions. Ultimately, this has led to a general consensus that token ring networks offer a higher degree of reliability, and integrity than Ethernet networks.

  7. Answer: A. The IEEE 802.5 standard was adapted from token ring access methods developed by IBM in the early 1970s. Token ring networks are specified for 4Mbps and 16Mbps operation, with the latter being used in all modern networks.

  8. Answer: B. A CSMA/CD, Ethernet LAN has a bandwidth of 10Mbps, while a token ring network operates at 4 or 16Mbps. Ethernet is available at 1000Mbps, but only with a contention access method. 100VG-AnyLAN operates on ring topologies, but isn't widely deployed. Although token ring only runs at 16Mbps, the good thing about it is that node access can be made deterministic, an option not available with Ethernet. What's needed is a technology that offers the access advantages of token ring, and the speed of Ethernet.

  9. Answer: D. The farther a workstation is moved away from an AP, the lower the data rate. The minimum data rate is 1Mbps. The maximum distance at any data rate varies with the material that the radio waves must pass through between workstation and AP. Commercial cards can transmit up to about a quarter mile at the lowest data rates in an open-air setting.

  10. Answer: B. A wireless network is implemented with a wireless card installed into an expansion slot of a computer, and that communicates with an access point.

  11. Answer: A. In 2000, the IEEE approved the IEEE 802.11a standard. This standard offers even higher data rates, peaking at 54Mbps. Commercial products began shipping for 802.11a later in 2001.

  12. Answer: A. A connection-oriented protocol assigns sequence numbers to frames passed into the LLC, and tracks them at the receiving node. At the Data Link layer, it's the same as Type II LLC. Because the frames are tracked, connection-oriented protocols are also called reliable.

  13. Answer: D. Bit-oriented protocols have high efficiency and low overhead. SDLC (Synchronous Data Link Control), HDLC (High-Level Data Link Control), and LAPB (Link Access Protocol-Balanced) are bit-oriented protocols. Conversely, character-oriented protocols, such as IBM Binary Synchronous Communication (BCS), frame and send blocks of characters at a time.

Objective 1.3

  1. Answer: B. A 10BASE-T network has a maximum data rate of 10Mbps. The 10 in 10BASE-T indicates the data rate. 100Mbps refers to 100BASE-T. 500Mbps doesn't apply to any standard data rate. 1000Mbps refers to 1000BASE-T.

  2. Answer: A. The maximum segment length is 100 meters for 10BASE-T networks. Because the cable media is UTP and a hub is being used, a segment refers to the media length from hub port to NIC card of a workstation. 10BASE2 networks have a maximum segment length of 185 meters. 10BASE5 networks have a maximum segment length of 500 meters. 10 meters doesn't apply to any standard segment lengths.

  3. Answer: B. 10 BASE2 network operates at 10Mbps and uses coaxial cable with segment lengths from node to hub of 185 meters.

  4. Answer: C. 100BASE-TX suffers from the same 100-meter distance limitations as other UTP-based networks.

  5. Answer: C. The 10BASE2 standard specifies a limit of 185 meters per segment (that is, 607 feet).

  6. Answer: D. A 100BASE-FX fiber-optic NIC will not work with 10BASE-T copper cabling.

  7. Answer: B. 802.5 defines token ring networking.

  8. Answer: A. 10BASE-T has a maximum segment length of 100 meters. The maximum length of a 10BASE2 segment is 185 meters. The maximum length of a 10BASE5 segment is 500 meters. 10BASEYX is not a valid networking standard.

  9. Answer: A. 100BASE-TX uses Category 5 cabling. Fiber optic is a type of cable. 10BASE5 is an Ethernet networking standard that uses thick coaxial cable. 10BASE2 is an Ethernet networking standard that uses thin coaxial cable.

  10. Answer: B. 10BASE-T networks use twisted-pair cable and RJ-45 connectors. RJ-11 connectors are associated with telephone cabling. RJ-T is not a valid type of connector. A BNC connector is associated with coaxial cabling, not twisted-pair cabling.

  11. Answer: C. For thick or thinnet coaxial cable, it's 10 MHz; and for cable television coaxial cable the maximum rates are in the hundreds of megahertz.

  12. Answer: C. It's important to make a distinction between how frequency affects signal loss, and how the resistance of copper cable affects signal loss. Losses due to frequency changes are the result of line inductance and capacitance. Resistance has a negligible impact when the frequency changes. However, the resistance of the wiring dissipates electrical energy in the form of heat. The higher the resistance, the greater the signal energy loss. Resistance is directly proportional to the length of the wire.

  13. Answer: D. The proper termination for unshielded twisted-pair network cable is 100 ohms.

  14. Answer: B. The solid center wire is separated from the braided conductor by a polyurethane insulator. The wires act like capacitor plates across the entire cable length. Twisted pairs are separated from one another by the insulating jacket. Similar to coax, the wire pairs represent capacitor plates, and the insulation represents a capacitor dielectric.

  15. Answer: D. The reactive components of cables cause Intersymbol Interference (ISI).

  16. Answer: B. Adaptive equalization adds expense and complexity to a data communication system. A signal that has been conditioned with an adaptive equalizer is also difficult to evaluate from a troubleshooting standpoint, because it may have very little resemblance to the square waves associated with digital logic. An adaptive equalizer constantly samples and evaluates data for ISI.

  17. Answer: C. An equalizer separates signal frequencies through filtering and incorporates phase shifts to counter the effects of the channel.

  18. Answer: B. In addition to lightning, sunspot activity creates atmospheric noise. On the sun, a sunspot is an explosion that releases a tremendous amount of energy that travels through the solar system, striking the earth, and creating noise in a way similar to lightning strikes. Sunspots are cyclical, occurring about every 11 years, and can therefore be anticipated.

  19. Answer: B. 100BASE-FX uses a fiber-optic cable and has a segment length of 412 meters.

  20. Answer: C. Impulse noise is sporadic and of short duration, usually caused by periodic use of electromechanical equipment or from a glitch that occasionally appears. Mechanical switches, motors, generators, and engine ignition systems all contribute to the distortion of data bits, and are collectively called "impulse noise." It's generally of short duration and in close proximity to the affected data system.

  21. Answer: D. Frequency noise originates from 60 Hz wire, system clocks, or carrier frequencies. Frequency noise is of a constant time but of variable amplitude. The most common type of frequency noise is the 60 Hz radiated from fluorescent lights and the associated wiring.

  22. Answer: A. Crosstalk is the electromagnetic induction (transmitted noise) that results from unshielded cables laying in parallel.

  23. Answer: C. You may have been talking on the telephone and have heard another conversation. Crosstalk is a frequent problem in the telephone system because hundreds of cables may run in parallel. The energy from a cable radiates and cuts across adjacent cables, inducing a signal into them. Although crosstalk in a telephone conversation is annoying, it generally doesn't prevent you from continuing your own conversation. But crosstalk between data signals can blur the distinction between logic levels and introduce a considerable error component into data.

  24. Answer: B. Noise and distortion are expressed in decibels. The decibel results from the ratio of an actual value to a reference value. Reference values for data communications are 1 mW and 6 mW.

  25. Answer: B. The signal-to-noise ratio is a measure of the desired signal power relative to the noise signal power at the same point in a circuit. It's expressed mathematically as: SNR = Ps/Pn where Ps = the power of the desired signal and Pn = the power of the noise. It's often expressed in decibels as:

    SNR =10 log (P s/P n) dB

    By replacing Ps and Pn with the given numbers, we can rewrite the expression as

    SNR =10 log (50 mW/5 mW) dB

    SNR =10 log (10) dB

    SNR =10 (1) dB

    SNR =10 dB

  26. Answer: C. An acceptable SNR for digital Communications 40 dB.

  27. Answer: C. The maximum segment length of a 100BASE-FX network is 412 meters. The maximum number of nodes for this type of network is 1024 and the maximum length of the network is 5 kilometers.

  28. Answer: A. The IEEE 100BASE-TX standard speed is 100Mbps.

  29. Answer: C. Thinnet (also called cheapernet, RG-58A/U, 10BASE2 or thin coaxial) coaxial cable has less shielding than thicknet, and consequently, smaller permissible segment lengths in a LAN.

  30. Answer: A. The standard is 802.10 and covers LAN Security.

  31. Answer: B. 100VG-AnyLAN was given its own IEEE 802.12 subgroup heading.

  32. Answer: C. The 802.3 standard for bus networks is based on the joint efforts of Digital Equipment Corporation, Intel, and Xerox. The original standard was called Ethernet, and the name has been retained although the current versions are not the same as the original. The original is now called Ethernet I, or simply "the DIX standard" after the founding companies.

  33. Answer: A. The maximum length of a 10BASE-T segment is 100 meters. The segment length in the question is 105 meters. By reducing the length of the NIC to wall outlet patch cable, the total segment length meets the standard. This reduces the number of service calls to this particular workstation because the connection should no longer be intermittent. It's not likely to have an effect on collisions because network collisions are more affected by the volume of network traffic than by segment length.

  34. Answer: D. The maximum cable length for a 10BASE-T (STP) is 200 meters.

  35. Answer: C. A 10BASE-T network operates at a maximum of 10Mbps.

  36. Answer: D. The maximum segment length for 10BASE-T4 is 100 meters.

  37. Answer: C. 100BASE-TX uses the full bandwidth capabilities of category 5 cable to achieve 100Mbps data rates.

  38. Answer: A. 100BASE-FX is the fiber-optic version 100Mbps Ethernet. The connection between devices includes only two fiber strands: a transmit strand and a receive strand. Both are running at 100Mbps.

  39. Answer: A. The maximum segment length for 10BASE-TX is 100 meters.

  40. Answer: B. 100BASE-T4 is an alternate version of 100BASE-TX. It uses category 3 (or better), voice-grade twisted pairs for cable links to hubs. Unlike 100BASE-TX, T4 will use all eight wires (4 pairs) that are attached to an RJ-45 connector.

  41. Answer: C. 100BASE-FX is the fiber-optic version 100Mbps Ethernet. It uses any of the common fiber-optic connectors. The connection between devices includes only two fiber strands, a transmit and a receive strand. Both are running at 100Mbps.

Objective 1.4

  1. Answer: A. Category 5 UTP cables use RJ-45 connectors. RJ-11 connectors are used to connect phone wires. BNC connectors are associated with thin coaxial cabling. ST connectors are associated with fiber-optic cabling.

  2. Answer: B. An AUI port is typically used to connect an external transceiver to a device such as a router. An MSAU is a type of network device used on token ring networks. RJ-11 is a connector type associated with telephone cabling. BNC is a type of network connector used on coaxial networks.

  3. Answers: D, B. A hardware loopback plug connects the 2 and 6 wires and 1 and 3 wires to simulate a live network connection. The remaining possible answers are not correct for the cabling in a hardware loopback adapter.

  4. Answer: C. The Presentation Layer is responsible for, among other things, encryption and decryption of data. The Network Layer protocols are responsible for route discovery and network addressing tasks. The Session Layer protocols are responsible for establishing, maintaining, and breaking communication sessions between applications. The Physical Layer defines the physical characteristics of the network connection.

  5. Answer: A. A NIC might have a BNC connector, an RJ-45 connector, or both types. A BNC connector is used with coaxial cable. An RJ-45 connector is used with any UTP category.

  6. Answers: B, C, D. The following connector types may be used with SCSI devices: 50-pin SCSI connector, 68-pin Wide SCSI-3 primary connector pinout. In addition, a common, though nonstandard connector is DB-25 SCSI.

  7. Answer: D. A Centronics 50-pin connector works with SCSI.

  8. Answer: B. An RJ-45 connector is a eight-pin connector that can be used with any UTP category.

  9. Answer: C. To connect a transceiver, the cable is cut and the ends prepared for BNC connectors and a T-connector installed at the break. One of the leads from the T connects back to the NIC card of the computer (which contains the transceiver circuitry), while the other two leads form an Ethernet bus. Barrel connectors can be used to join two short RG-58 cables, if necessary.

Objective 1.5

  1. Answer: C. Communication channels that allow communication to occur in both directions at the same time are called duplex. Simplex transmissions occur in one direction at a time. Multiplexing is the process of combining multiple communication channels on a single cable. In a full-duplex scenario, communications occur in both directions at the same time but on different wires.

  2. Answer: A. Fiber cable is immune to EMI because it propagates light signals rather than electrical signals. Fiber-optic cable requires specialized training and tools to install. The cost of fiber cable is higher than UTP and coaxial. Fiber uses light waves and not microwaves.

  3. Answer: D. Category 5 UTP cable is the most appropriate media for a small 100BASE-T network. RG-58 coaxial and category 3 UTP cannot carry the data throughput required by a 100BASE-T network. Fiber-optic cable is too expensive for a small implementation.

  4. Answer: A. Because the card is functioning at half-duplex 10Mbps, the transfer rate is going to be 10Mbps.

  5. Answer: B. Fiber-optic cable provides the most resistance to EMI and therefore is often used in environments where there is a risk of interference. Although cheap, UTP cabling has a very low resistance to EMI. Therefore, it is unsuitable for running near high voltage electric cables. Thin coax has a low resistance to EMI. Therefore, it is unsuitable for running near high-voltage electric cables. STP has a good level of resistance to EMI, but is still not as resistant as fiber optic. Not factoring in the cost, fiber optic is the most suitable solution.

  6. Answers: A, C. Fiber-optic cable can either use SC or ST type connectors. An RJ-45 connector is used with copper UTP cable. An RJ-11 connector is used with standard copper telephone wire.

  7. Answer: C. The shielding—when grounded properly—causes a current to be induced in it from the interference. This same current will generate electromagnetic flux that induces an opposite polarity current into the twisted pairs. Because the two noise signals are of opposite polarities, they cancel, thereby eliminating the interfering noise.

  8. Answer: B. Even though it's an expensive choice, there are several reasons to install fiber in a network. Because no copper is used in the cable, data bits won't be corrupted by electromagnetic interference (EMI), crosstalk, or other external noise that may garble bits in a UTP or coaxial system.

  9. Answer: B. The 802.8 is the standard for fiber-optic cable.

  10. Answer: A. Fiber optics has been hailed as the transmission media totally immune from EMI interference. Fiber-optic cable can be run side-by-side with industrial-grade motors and not be affected by radiated noise. However, fiber remains an expensive option when compared to alternative, copper-based media. In addition, there are problems created during the installation of fiber-optic cable that affect signal integrity.

  11. Answer: C. Connection losses contribute to signal degradation. Connection losses result from fiber splices, the interface of light source to fiber, and of fiber to light detector. The actual amount of signal attenuation is measured with a photometer.

  12. Answer: D. When injected into a perfectly straight fiber cable, the rays travel as axial beams through the cable, neither reflecting nor refracting. In a bent cable, the axial rays will strike the core/cladding interface and reflect along the remaining distance to the receiver. Some of the energy will refract into the cladding and be lost. A bind in a fiber-optic cable will produce losses and signal attenuation. This is true of all optical cable types, so cable runs should be kept as straight as possible.

  13. Answer: A. dB = 10 log (Po/Pi)

    dB = 10 log (20 mW/200mW)

    dB = 10 log (.1)

    dB = 10 (–1.)

    dB = –10

  14. Answer: D. A loss of signal strength is indicated by a negative dB.

  15. Answer: C. The wires are twisted together to reduce noise and, in particular, crosstalk. Recall that crosstalk is the magnetic induction of a signal from wires lying in a parallel plane. The twisting of the wires causes the unwanted crosstalk signals to cancel. Twisted pair is the most widely installed media. Unshielded twisted pair (UTP) is the preferred cabling for LANs. UTP is classified by the EIA/TIA according to categories. Whenever possible, use category 5 UTP.

Objective 1.6

  1. Answer: A. MDI-X (Media Dependent Interface-Crossover) means that a cable connected to the port should be wired using straight-through pinning. An IEEE-compliant hub labels ports with MDI-X if the hub does not perform the crossover internally. A BNC connector is used with coaxial cable. AUI refers to a 15-pin connector. The X in MDI-X is an instruction not to use a crossover cable.

  2. Answer: A. The router link light can be checked at a glance to determine whether there's a connection to the hub. The self-test lights on the hub and the power-on lights on the router provide information about the operation of the hub and router, but not about the connection between router and hub. A NIC is associated with servers and workstations.

  3. Answer: D. Bridges specifically interconnect LANs that don't use the same access protocols. Bridges aren't routinely used for either rerouting data around LANs or replacing multiple repeaters.

  4. Answer: C. The Gateway represents too much power for this size of LAN. MAU and transceiver are associated with coaxial cable.

  5. Answer: C. A router is used to connect networks.

  6. Answer: B. MDI-X, or Media Dependent Interface-Crossover, is an indication that a crossover cable must be used between the hub port and connected workstation or another hub.

  7. Answer: D. A gateway is any device, system, or software application that can perform the function of translating data from one protocol/format to another.

  8. Answer: A. The 16550 UART chip will provide a modem connection at 115200 bps.

  9. Answer: B. A transparent bridge is a device that can be used to divide up an Ethernet network to reduce collisions. Switches can also be used but the network in the question is a 10BASE2 network and uses coaxial cable and not twisted pair cabling. Ethernet switches can only be used on networks that are created with twisted pair cabling. 10BASE2 is a networking standard that uses thin coaxial cabling. A source-route bridge is used on token ring networks. 10BASE2 is an Ethernet networking standard. An MSAU is used on token ring networks. 10BASE2 is an Ethernet networking standard.

  10. Answer: C. A gateway is used to translate between networks using dissimilar protocols. In this question it is used to translate between an AppleTalk and a token ring network. A source-route bridge is used on token ring networks. A router is use to connect two networks. Strictly speaking a router does not perform translational tasks, though the gateway functionality can be implemented on some routers. A transparent bridge is used to segregate Ethernet networks.

  11. Answer: B. When a new card is installed on a token ring network, the speed of the card has to be set to match the speed used by the network. Token ring networks operate at either 4 or 16Mbps. Full-duplex connections are not used on token ring networks. Although it is possible, it is not most likely that the card is faulty.

  12. Answer: C. Because the card is functioning at half-duplex 10Mbps, the transfer rate is going to be 10Mbps.

  13. Answer: D. The base I/O port is a hexadecimal number used by the system microprocessor to identify the destination of data sent to a peripheral device. Because the bus in a computer is shared by all peripherals, the base I/O port identifies where data is to be sent within the computer. The base I/O port for all devices must be unique. Common 32-bit base I/O ports are 0300 and 031F.

  14. Answer: B. A gateway is a device that converts one communication system to another or from one protocol to another.

  15. Answer: B. The hub used in a token ring network is called a Multi-Station Access Unit, or MSAU. It may also be called a Multistation Access Unit, or MAU. An AUI is used in Ethernet coaxial networks. A switch is used to provide the full bandwidth of the network to each node. A patch panel provides a modular connection for extension of the wall cabling into the hub.

  16. Answer: C. A hub is a device used to provide centralized access to the network. Hubs are used in a physical star topology. The network nodes connect to ports in the hub via a cable such as UTP or coaxial. One end of the cable plugs into the node NIC card while the other end plugs into a port on a hub.

  17. Answer: A. MDI-X: Media Independent Interface-Crossover, when engaged, allows you to use the port for connecting to a NIC card in a PC (or similar device) using straight-through pinning.

  18. Answer: A. A bridge is primarily used to connect networks that use different network access protocols. For example, a bridge is used to connect users on an Ethernet LAN and users on a token ring LAN. Wireless access points that have an Ethernet port employ a bridge to connect the IEEE 802.11b users and the Ethernet users.

  19. Answer: D. A network interface card (NIC) contains a transceiver that sends and receives data frames on and off the network.

  20. Answer: C. A bridge is primarily used to connect networks that use different network access protocols. For example, a bridge is used to connect users on an Ethernet LAN and users on a token ring LAN.

  21. Answer: B. A router is used to connect different networks and, occasionally, different network segments. A "network" in this context refers to a group of nodes that share the same network portion of an IP address. If two groups of nodes don't have the same network portion of an IP address, they are located on different networks. The router interconnects data packets across a network running TCP/IP. The network consists of an Ethernet, a token ring, and a Token Bus LAN. Notice that the router allows computers on all three LANs to communicate, regardless of the topology and access protocols.

  22. Answer: C. A router is used to connect different networks and, occasionally, different network segments. A "network" in this context, refers to a group of nodes that share the same network portion of an IP address. Routers operate at the Network layer of the OSI model. A router isn't concerned if the data it receives originated from a token ring LAN or an Ethernet LAN. The router is only concerned with getting the data to the correct destination network.

  23. Answer: D. A dynamic router learns addressing information automatically, without intervention from the network administrator. Dynamic routers broadcast the addressing information in their tables in the form of advertisements.

  24. Answer: D. At each router hop, the router will compare its list of MAC addresses to the destination IP address. If they aren't the same, it will reframe the MAC addresses and pass it on.

  25. Answer: B. Replacing hubs with switches is a practical, economical, and very effective way to improve performance on twisted-pair networks. It is the accepted upgrade path in hub-based networks. Although implementing switches is a valid approach, the cost of doing so may be prohibitive and it is not the best option of those given. Implementing a router is not the most likely approach and would require extensive reconfiguration of the network. Implementing a bridge is not the most likely approach.

  26. Answer: A. Integrated Services Digital Network (ISDN) is a set of digital services that are available over telephone lines. ISDN is a complete digital solution from end-user to end-user. Because the connection is all digital, data rates can be much higher than on an analog telephone connection—as high as 128 kbps.

  27. Answer: D. A modem provides a computer user with a tremendous amount of access. Literally, a good modem makes the difference in working at an isolated PC and accessing the great, wide-open spaces of the Internet. Nearly all data communications utilize modems—from the single user at home with a PC, to internationally distributed networks of conglomerate corporations.

  28. Answer: C. As ISDN frame carries data in a Bearer channel (B channel) that has a 64 kbps bandwidth. On older telephone systems, B channels may drop to 56 kbps. A Data channel (D channel) carries supervisor and signaling information at 16 kbps (and sometimes at 64 kbps).

  29. Answer: B. An active hub operates under its own power supply. Data signals may be amplified in an active hub to restore signal losses, or to remove noise. Active hubs are also called repeaters.

  30. Answer: B. A crossover cable may be necessary to troubleshoot NICs or hub ports. A crossover allows you to directly connect two stations, without a hub. A crossover is merely a means of connecting the proper transmit pins of one NIC card to the corresponding receive pins of another NIC card, and vice versa.

  31. Answer: A. The regenerator, or repeater, is an in-line amplifier that boosts the signal level and restores the square wave to its original shape.

  32. Answer: C. The routing tables in a dynamic router are updated automatically.

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