ActualTests.Cisco.640-802.Exam.Q.and.A.08.15.08-DDU (1130589), страница 13
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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 allstations 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:Actualtests.com - The Power of Knowing640-802A. Only the stations involved in the collision stop transmitting for a short time, not allstations 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 logical bus topologyC. 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 aboveAnswer: BExplanation:LAN topologies define the manner in which network devices are organized. Fourcommon LAN topologies exist: bus, ring, star, and tree.
These topologies are logicalarchitectures, but the actual devices need not be physically organized in theseconfigurations. Logical bus and ring topologies, for example, are commonly organizedphysically as a star. A bus topology is a linear LAN architecture in which transmissionsfrom network stations propagate the length of the medium and are received by all otherstations. Of the three most widely used LAN implementations, Ethernet/IEEE 802.3networks, including 100BaseT, implement a bus topology, which is illustrated in Figure2-3.Figure2-3: Some networks implement a local bus topology.Reference: http://www.pulsewan.com/lanintro.htmQUESTION 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, CActualtests.com - The Power of Knowing640-802Explanation:Ethernet uses the CSMA/CD access method.CSMA/CD logic helps prevent collisions and also defines how to act when a collisiondoes 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 allstations 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 recoverwhen inadvertent collisions occur.Reference: Cisco CCNA intro 640-821 p.55QUESTION 111:Which two statements describe the operation of the CSMA/CD access method,which is in use on the Certkiller network? (Choose two)A. After a collision, the station that detected the collision has first priority to resend thelost data.B. In a CSMA/CD collision domain, stations must wait until the media is not in usebefore transmitting.C. In a CSMA/CD collision domain, multiple stations can successfully transmit datasimultaneously.D. The use of hubs to enlarge the size of collision domains is one way to improve theoperation of the CSMA/CD access method.E.
After a collision, all stations run a random backoff algorithm. When the backoff delayperiod has expired, all stations have equal priority to transmit data.F. After a collision, all stations involved run an identical backoff algorithm and thensynchronize with each other prior to transmitting data.Answer: B, EExplanation:Ethernet networking uses Carrier Sense MultipleAccess with Collision Detect (CSMA/CD), a protocolthat helps devices share the bandwidth evenlywithout having two devices transmit at the same timeon the network medium.
CSMA/CD was created toovercome the problem of those collisions that occur whenpackets are transmitted simultaneously from different nodes. And trust me, good collisionmanagement is crucial, because when a node transmits in a CSMA/CD network, all theActualtests.com - The Power of Knowing640-802other nodes on the network receive and examine that transmission. Only bridges androuters can effectively prevent a transmission from propagating throughout the entirenetwork! So, how does the CSMA/CD protocol work? Like this: when a host wants totransmit over the network, it first checks for the presence of a digital signal on the wire.If all is clear (no other host is transmitting), the host will then proceed with itstransmission. But it doesn't stop there.
The transmitting host constantly monitors the wireto make sure no other hosts begin transmitting. If the host detects another signal on thewire, it sends out an extended jam signal that causes all nodes on the segment to stopsending data (think, busy signal). The nodes respond to that jam signal by waiting a whilebefore attempting to transmit again. Backoff algorithms determine when the collidingstations can retransmit. If collisions keep occurring after 15 tries, the nodes attempting totransmit will then time out.QUESTION 112:Which three statements are true about the operation of a full-duplex Ethernetnetwork, which is being used in the Certkiller LAN? (Choose three)A.
Ethernet hub ports are preconfigured for full-duplex mode.B. The host network card and the switch port must be capable of operating in full-duplexmode.C. There are no collisions in full-duplex mode.D. In a full-duplex environment, the host network card must check for the availability ofthe network media before transmitting.E. A dedicated switch port is required for each full-duplex node.Answer: B, C, EExplanation:Half-duplex Ethernet is defined in the original 802.3 Ethernet and Cisco says you onlyuse one wire pair with a digital signal running in both directions on the wire. It also usesthe CSMA/CD protocol to help prevent collisions and to permit retransmitting if acollision does occur.
If a hub is attached to a switch, it must operate in half-duplex modebecause the end stations must be able to detect collisions. Half-duplex Ethernet-typically10BaseT-is only about 30 to 40 percent efficient as Cisco sees it, because a large10BaseT network will usually only give you 3- to 4Mbps-at most.Full-duplex Ethernet uses two pairs of wires, instead of one wire pair like half duplex.Also, full duplex uses a point-to-point connection between the transmitter of thetransmitting device and the receiver of the receiving device, which means that withfull-duplex data transfer, you get a faster data transfer compared to half duplex.
Andbecause the transmitted data is sent on a different set of wires than the received data, nocollisions occur. The reason you don't need to worry about collisions is because nowFull-duplex Ethernet is like a freeway with multiple lanes instead of the single-lane roadprovided by half duplex. Full-duplex Ethernet is supposed to offer 100 percent efficiencyActualtests.com - The Power of Knowing640-802in both directions; this means you can get 20Mbps with a 10Mbps Ethernet running fullduplex, or 200Mbps for FastEthernet.QUESTION 113:Exhibit:You work as a network technician at Certkiller .com. Please study the exhibitcarefully.
Which statement describes the operational state of the Certkiller 2FastEthernet 0/0 interface?A. The interface is operational and currently handling traffic.B. The interface has failed because of a media error.C. The interface requires a no shutdown command to be issued.D.
The interface is generating protocol errors.E. None of the above.Answer: AExplanation:The interface is up indicates whether the interface hardware is currently active andwhether it has been taken down by an administrator. "Disabled" indicates that the routerhas received more than 5,000 errors in a keepalive interval, which is 10 seconds, bydefault.The line protocol indicates whether the software processes that handle the line protocolbelieve that the interface is usable (that is, whether keepalives are successful) or if it hasbeen taken down by an administrator.For a complete list of the field descriptions of this command as well as troubleshootinginformation for Ethernet interfaces refer to the reference link listed below.Actualtests.com - The Power of Knowing640-802Reference: "Troubleshooting Ethernet"http://www.cisco.com/en/US/docs/internetworking/troubleshooting/guide/tr1904.htmlQUESTION 114:The Certkiller network administrator wants to use a router named CK1 to segmentthe local network.
What are some of the advantages of using CK1 to segment thenetwork? (Choose two)A. Routers generally cost less than switchesB. Filtering can occur based on Layer 3 informationC. Broadcasts are not forwarded across the routerD. Broadcasts are eliminatedE. Adding a router to the network decreases latencyF. Routers can generally support more LAN ports than switchesAnswer: B, CExplanation:When the router's interface receives the broadcast, it discard the broadcast withoutforwarding it on to other networks.
Even though routers are known for breaking upbroadcast domains by default, it's important to remember that they break up collisiondomains as well.There are two advantages of using routers in your network:* They don't forward broadcasts by default.* They can filter the network based on layer 3 (Network layer) information (e.g., IPaddress) by using IOS based firewall ie.
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