CCNA 640-802 Ver 22-09-2008 page11
QUESTION 101
The Certkiller internetwork shown in the diagram is experiencing network delays. On the basis of the information provided in the exhibit above, what is the problem?
A. The connection between Switch1 and Switch2 should be half-duplex.
B. The cable between Router1 and Switch1 should be a crossover.
C. The cable connecting Host A to Switch2 is too long.
D. The server is on a different subnet than router interface Fa0/0.
E. The cable between Switch1 and Switch2 should be straight-through.
F. None of the above
Answer: C
Explanation:
According to IEEE specifications, the maximum segment length of an Ethernet cable should not exceed 100 meters. The total distance between an Ethernet Transmitter and Receiver at the absolute end points of the network (maximum diameter from origin to final destination, if the wires were stretched out to form a straight line) should be no more than100 Meters (328 ft., 109 yards, or about the length of a football field). This limitation results from the timing of the Ethernet signals on the cable and not necessarily the cable characteristics, and is, therefore, a "hard" number.
QUESTION 102
What is the IEEE standard associated with Gigabit Ethernet? (Select two answer choices)
A. 802.11
B. 802.5
C. 802.3ab
D. 802.3ae
E. 802.3z
F. 802.3u
Answer: C, E
Explanation:
The IEEE 802.3z standard describes 1000BASE-SX. The 1000BaseT standard was released in June 1999, defined by IEEE 802.3ab. Incorrect Answers:
A. This describes the standard used for wireless networks.
B. This is the standard for token ring networks.
D. On June 17, 2002 the IEEE 802.3ae specification for 10 Gigabit Ethernet was approved as an IEEE standard by the IEEE Standards Association (IEEE-SA) Standards Board.
F. IEEE 802.3u describes the standard for 100BASE-TX.
QUESTION 103
Which of the following can lead to the contribution of LAN traffic congestion? (Select all that apply)
A. Too many hosts in a bro
adcast domain
B. Full duplex operation
C. Broadcast storms
D. Multicasting
E. Segmentation
F. Low bandwidth
Answer: A, C, F
Explanation:
Choice A is correct because the more hosts on a broadcast domain, the more traffic that is created. Choice Ccontributes to congestion because broadcast storms can become very problematic, and lead to complete network saturation. Multicasts are similar to broadcasts in their use on a LAN. Finally, if there is not enough bandwidth, traffic sessions can time out. This leads to new transmissions and the re-sending of data, which can lead to more congestion.
Incorrect Answers:
B, E. These are incorrect because full duplex operation and segmented networks actually result in less congestion.
D. Multicasting can actually alleviate congestion issues, as single streams of information can reach multiple hosts at the same time, instead of using a series of point to point connections.
QUESTION 104
On a half-duplex Ethernet LAN, two hosts attempt to send data simultaneously, resulting in a collision. Following this collision, what will the hosts do? (Select all valid answers)
A. The destination host sends a request to the source for retransmission.
B. The jam signal indicates
that the collision has been cleared.
C. The hosts will attempt to resume transmission after a time delay has expired.
D. An electrical pulse indicates that the collision has cleared.
E. The router on the segment will signal that the collision has cleared.
F. The hosts will do nothing, as the higher layers are responsible for data error correction and re-transmission.
Answer: C
Explanation:
When a host on an Ethernet LAN has information to send, the following steps are taken:
1. A device with a frame to send listens until Ethernet is not busy.
2. When the Ethernet is not
busy, the sender begins sending the frame.
3. The sender listens to make sure that no collision occurred.
4. Once the senders hear the collision, they each send a jamming signal, to ensure that all stations recognize the collision.
5. After the jamming is complete, each sender randomizes a timer and waits that long.
6. When each timer expires, the process starts over with step 1.
QUESTION 105
Which of the following statements correctly describe the differences between half-duplex and full-duplex Ethernet? (Select two answer choices.)
A. Full-duplex Ethernet uses CSMA/CD to prevent collisions.
B. Half-duplex Ethernet uses a loopback circuit to detect collisions.
C. A full-duplex Ethernet
card allows 20Mbps for data transmission.
D. Full-duplex Ethernet makes use of two pairs of wires for data.
E. An Ethernet hub can operate both half and full duplex simultaneously.
Answer: B, D
Explanation:
Half-duplex Ethernet send and receives on the same line, so a loopback needs to be set to detect collisions. Alternatively, full-duple Ethernet doesn't have to because it uses two pairs of wire, one to send and the other to receive. Collisions are not possible on full duplex Ethernet networks.
Incorrect Answers:
A. Full duplex uses both pairs of wires, so transmissions are sent on the first pair, and data that is received come in on the other pair. This prevents collisions.
C. Full duplex allows for data to be sent and received at the same time. It will not double the amount of bandwidth at any given
time. The speed of the Ethernet link will remain at 10/100.
E. Hubs are shared devices and can only support one mode, unlike switches.
QUESTION 106
Why is full-duplex Ethernet superior to its single-duplex counterpart? (Select two answer choices.)
A. It uses inexpensive hubs
B. It operates without collisions
C. It operates on switches
D. It provides faster data transfer
E. It utilizes fewer wiring pairs
Answer: B, D
Explanation:
Full duplex Ethernet allows concurrent sending and receiving, which allows the full bandwidth to be used for both sending and receiving. The result is a collision free network with increased throughput.
Incorrect Answers:
A, C. These are incorrect because full duplex doesn't require hubs or switches. Full duplex operation can be used on switch and router ports, as well as PC hosts.
E. This is incorrect because full duplex actually uses more wiring pairs. In full duplex, both wire pairs are used. Half duplex uses only a single pair.
QUESTION 107
When you compare the differences between half-duplex and full-duplex Ethernet, which of the following characteristics are exclusi
ve to half-duplex? (Select two answer choices)
A. Half-duplex Ethernet operates in a shared collision domain.
B. Half-duplex Ethernet operates in an exclusive broadcast domain.
C. Half-duplex Ethernet has efficient throughput.
D. Half-duplex Ethernet has lower effective throughput.
E. Half-duplex Ethernet operates in an exclusive collision domain.
Answer: A, D
Explanation:
A single device could not be sending a frame and receiving a frame at the same time because it would mean that a collision was occurring. So, devices simply chose not to send a frame while receiving a frame. That logic is called half-duplex logic. Ethernet switches allow multiple frames to be sent over different ports at the same time. Additionally, if only one device is connected to a switch port, there is never a possibility that a collision could occur. So, LAN switches with only one device cabled to each port of the switch allow the use of full-duplex operation. Full duplex means that an Ethernet card can send and receive concurrently.
Incorrect Answers:
B. Full duplex effectively doubles the throughput of half-duplex operation, because data can be both sent and received at the full 10/100 speed.
C, E. In half duplex operation, the network is shared between all devices in the collision domain.
QUESTION 108
Two stations on the Certkiller LAN transmit at the same time, resulting in a collision. What happens when a collision occurs on t
he network? (Choose all that apply)
A. Each device on the Ethernet segment stops transmitting for a short time.
B. A jam signal informs all devices that a collision occurred.
C. When data transmission resumes, the devices that were involved in the collision have priority to transmit.
D. The devices that are involved in the collision stops transmitting for a short time.
E. The collision invokes a random back-off algorithm.
Answer: B, D, E
Explanation:
When a host on an Ethernet LAN has information to send, the following steps are taken:
1. A device with a frame to send listens until Ethernet is not busy.
2. When the Ethernet is not busy, the sender begins sending the frame.
3. The sender listens to make sure that no collision occurred.
4. Once the sender
s hear the collision, they each send a jamming signal, to ensure that all stations recognize the collision.
5. After the jamming is complete, each sender randomizes a timer and waits that long.
6. When each timer expires, the process starts over with step 1. Incorrect Answers:
A. Only the stations involved in the collision stop transmitting for a short time, not all stations on the LAN.
C. No priority is given to any stations once a collision has occurred.
QUESTION 109
Which of the following are true of Ethernet technology?
A. Hosts use a logical ring topology.
B. Hosts use a logica
l bus topology
C. Hosts must wait for an electronic signal to transfer data.
D. Hosts are directly connected to a wiring concentrator called a MSAU.
E. None of the above
Answer: B
Explanation:
LAN topologies define the manner in which network devices are organized. Four common LAN topologies exist: bus, ring, star, and tree. These topologies are logical architectures, but the actual devices need not be physically organized in these configurations. Logical bus and ring topologies, for example, are commonly organized physically as a star. A bus topology is a linear LAN architecture in which transmissions from network stations propagate the length of the medium and are received by all other stations. Of the three most widely used LAN implementations, Ethernet/IEEE 802.3 networks, including 100BaseT, implement a bus topology, which is illustrated in Figure 2-3.
Figure2-3: Some networks implement a local bus topology.
QUESTION 110
With regard to Ethernet media access methods, which of the following are true? (Choose all that apply.)
A. A device waits for an electronic signal before transmitting.
B. A device listens and waits until the media is not busy before transmitting.
C. All devices on an Ethernet segment see data that passes on the network medium.
D. Only the sender and the receiver devices see data that passes on the network medium.
E. Ethernet networks allow you to configured devises with higher transmission priority.
Answer: B, C
Explanation:
Ethernet uses the CSMA/CD access method. CSMA/CD logic helps prevent collisions and also defines how to act when a collision does occur. The CSMA/CD algorithm words like this:
1. A device with a frame to send listens until the Ethernet is not busy.
2. When the Ethernet is not busy, the sender begins sending the frame.
3. The sender listens to make sure that no collision occurred.
4. Once the senders hear the collision, they each send a jamming signal, to ensure that all stations recognize the collision.
5. After the jamming is complete, each sender randomizes a timer and waits that long. 6 When each timer expires, the process starts over with Step 1. So, all devices on the Ethernet need to use CSMA/CD to avoid collisions and to recover when inadvertent collisions occur.
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