Acknowledgments, sequencing, and flow control are characteristics of which OSI layer?
Answer: C
A reliable Transport layer connection uses acknowledgments to make sure all data is transmitted and received reliably. A reliable connection is defined by a virtual circuit that uses acknowledgments, sequencing, and flow control, which are characteristics of the Transport layer (layer 4).
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Routers operate at layer _____. LAN switches operate at layer _____. Ethernet hubs operate at layer _____. Word processing operates at layer _____.
Answer: B
Routers operate at layer 3. LAN switches operate at layer 2. Ethernet hubs operate at layer 1. Word processing applications communicate to the Application layer interface, but do not operate at layer 7, so the answer would be none.
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Which layer 1 devices can be used to enlarge the area covered by a single LAN segment?
1.Switch
2.NIC
3.Hub
4.Repeater
5.RJ45 transceiver
Answer: C
Correct answer: 3 and 4
A hub and a repeater both work at the physical layer: they regenerate and retime the signal so it can travel further, extending the reach of a single segment without dividing it. A switch is a layer 2 device and creates separate collision domains rather than enlarging one; a network card is an endpoint; and a transceiver converts between media rather than extending the distance.
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Which of the following are unique characteristics of half-duplex Ethernet when compared to full-duplex Ethernet?
1.Half-duplex Ethernet operates in a shared collision domain.
2.Half-duplex Ethernet operates in a private collision domain.
3.Half-duplex Ethernet has higher effective throughput.
4.Half-duplex Ethernet has lower effective throughput.
Answer: C
Correct answer: 1 and 4
Half-duplex Ethernet cannot send and receive at once, so every station shares one collision domain and must use CSMA/CD to detect and recover from collisions. Full duplex has a separate path each way, so collisions cannot occur and collision detection is switched off.
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Which three statements are true about the operation of a full-duplex Ethernet network?
1.There are no collisions in full-duplex mode.
2.A dedicated switch port is required for each full-duplex node.
3.Ethernet hub ports are preconfigured for full-duplex mode.
4.In a full-duplex environment, the host network card must check for the availability of the network media before transmitting.
5.The host network card and the switch port must be capable of operating in full-duplex mode.
Answer: A
Full-duplex means you are using both wire pairs simultaneously to send and receive data. You must have a dedicated switch port for each node, which means you will not have collisions. Both the host network card and the switch port must be capable and set to work in full-duplex mode.
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Which of the following types of connections can use full duplex?
1.Hub to hub
2.Switch to switch
3.Host to host
4.Switch to hub
5.Switch to host
Answer: D
Hubs cannot run full-duplex Ethernet. Full duplex must be used on a point-to-point connection between two devices capable of running full duplex. Switches and hosts can run full duplex between each other, but a hub can never run full duplex.
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How does a host on an Ethernet LAN know when to transmit after a collision has occurred?
1.In a CSMA/CD collision domain, multiple stations can successfully transmit data simultaneously.
2.In a CSMA/CD collision domain, stations must wait until the media is not in use before transmitting.
3.You can improve the CSMA/CD network by adding more hubs.
4.After a collision, the station that detected the collision has first priority to resend the lost data.
5.After a collision, all stations run a random backoff algorithm. When the backoff delay period has expired, all stations have equal priority to transmit data.
Answer: D
Once transmitting stations on an Ethernet segment hear a collision, they send an extended jam signal to ensure that all stations recognize the collision. After the jamming is complete, each sender waits a predetermined amount of time, plus a random time. After both timers expire, they are free to transmit, but they must make sure the media is clear before transmitting and that they all have equal priority.
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Which of the following are types of flow control?
1.Buffering
2.Cut-through
3.Windowing
4.Congestion avoidance
Answer: B
Correct answer: 1, 3 and 4
Flow control keeps a fast sender from overwhelming a slow receiver, and the three methods are buffering the excess, windowing to limit how much may be outstanding, and signalling congestion avoidance when the receiver falls behind. Cut-through is a switching method, describing when a frame is forwarded, not a means of flow control.
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What is the purpose of flow control?
Answer: C
Correct answer: To provide a means for the receiver to govern the amount of data sent by the sender.
Flow control exists so that a fast sender does not overwhelm a slow receiver: the receiver advertises how much it can accept, and the sender respects that window. It is distinct from the other three mechanisms listed - retransmission on a missing acknowledgement is reliability, reassembly in order is sequencing, and segment size is set by the maximum segment size negotiation.
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Which of the following describe router functions?
Answer: E
Correct answer: All of the above
All four are router functions. It switches packets between interfaces, filters them against access lists, provides communication between different networks - which is the definition of internetworking - and selects the path by consulting its routing table. Path selection is the one that distinguishes a router from a switch, since a switch forwards on a single flat topology.
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