Do I Know This Already Quiz

1. Which of the following network topologies is characterized by attachments from many devices to a single linear cable?

Answer: A

2. Which of the following types of networks is considered to be a logical bus topology?

Answer: A and B. 10BASE5 is a physical bus, and it behaves like a bus, making it a logical bus topology. Because a 10BASE-T hub repeats incoming transmissions out all other ports, effectively creating a bus, it is considered to be a logical bus topology.

3. Which pins typically are used on an RJ-45 connector by an Ethernet card to support Fast Ethernet over UTP cabling?

Answer: C

4. Which part of an optical cable reflects the light back into the cable as a result of a different refractive index?

Answer: A

5. Which of the following UTP cable types support Gigabit Ethernet? Answer: C, D, and E.

6. Which of the following Ethernet standards call for the use of 802.3 MAC and 802.2 LLC standards?

Answer: E. All the Ethernet standards call for the use of 802.3 framing, including the 802.3 MAC and 802.2 LLC sublayers.

Q&A

Which of the following Ethernet standards refer to Gigabit Ethernet?

Answer: B and C. 802.3z refers to Gigabit over optical, and 802.3ab refers to Gigabit over copper cabling.

Which of the following IEEE standards define framing used when transmitting wireless LAN traffic?

Answer: A and D. Wireless LANs use the IEEE 802.11 standard instead of 802.3 for the MAC sublayer header, and also use IEEE 802.2 for the LLC sublayer header.

Describe why a 10BASE-T network using a hub is considered to be a logical bus topology.

Answer: A physical bus causes the transmitted electrical signal to be propagated to all devices connected to the bus. A 10BASE-T hub repeats a signal entering one port out all the other ports, ensuring that all devices receive the same signal. Hubs do not have any logic to prevent some frames from being sent out ports (all signals are repeated), creating a single collision domain, just like a physical bus.

Compare and contrast full-mesh versus partial-mesh topologies, in relation to physical topologies.

Answer: In a full mesh, for a particular set of networking devices, a direct cable connects each pair of devices. For a partial mesh, some pairs of devices are not directly connected.

Compare and contrast full-mesh versus partial-mesh topologies, in relation to logical topologies.

Answer: Regardless of the physical topology, a topology is considered a logical full mesh if each pair of devices can communicate directly, and is considered a partial mesh if some pairs cannot communicate directly. A Frame Relay network uses a star physical topology. Depending on what VCs have been defined, it might use a logical full mesh or a logical partial mesh.

What is the main motivation for using a dual-ring physical topology versus a single ring? Why?

Answer: For better network availability. With dual rings, if a cable or a device fails, the devices near the failure can loop the signals from the two different cables together, thereby creating a single phyiscal path that loops to each node.

5. What two methods are used to reduce the amount of electromagnetic emissions emanating from copper Ethernet cabling? Why do they help reduce emissions?

Answer: By using two pairs of wires for transmission, with differing currents, and twisting the wires, the magnetic fields generated when the electrical current flows are cancelled. The other method is to put insulating material around the wires, which shields the emissions to a great degree.

6. Which wires are used by a typical Ethernet CAT5 cable? Which ones are used for transmit, and which ones are used to receive, by an Ethernet card?

Answer: Ethernet cards transmit on the pair using pins 1 and 2, and receive on the pair at pins 3 and 6.

7. Which TIA standards for UTP cabling support 10BASE-T? Answer: CAT3, 5, 5e, and 6.

8. What are the maximum lengths for coaxial cables as used by 10BASE5? 10BASE2? Answer: 500 m and 185 m, respectively.

9. What are key differences between multimode and single-mode optical cabling?

Answer: Multimode cabling typically supports shorter distances than single-mode. Single-mode uses a much smaller diameter for the glass fiber, which allows for the greater distances.

10. What types of cabling are least susceptible to having someone eavesdrop and somehow discover what is being transmitted over the cable?

Answer: Optical cables do not emit any EM radiation outside the cable, as do metallic copper cables. So, you cannot simply sense what signal is crossing over an optical cable without physically breaking into the cable, which makes the cable unusable.

11. What are the IEEE standards for 10BASE-T, Fast Ethernet, Gigabit Ethernet, and 10-Gigabit Ethernet?

Answer: 802.3, 802.3u (Fast Ethernet), 802.3z and 802.3ab (Gigabit Ethernet), and 802.3ae (10 Gigabit).

12. Which variations on the Fast Ethernet standard, which use names like "10BASE-something," specifically state the need for four pairs of wires in the cable? What about for Gigabit Ethernet?

Answer: 100BASE-T4 for Fast Ethernet, and 1000BASE-T for Gigabit Ethernet.

13. Which variations on the Fast Ethernet and Gigabit standard use IEEE 802.3 MAC and 802.2 LLC framing?

Answer: All of them.

14. What were some of the differences between 10-Gigabit Ethernet, as compared with other types of Ethernet, as outlined in this chapter?

Answer: The speed, of course, is the obvious difference. Additionally, 10-Gigabit Ethernet is allowed to be used in a point-to-point topology only, it supports full-duplex only, and today it supports only optical cabling.

15. What IEEE standards are used by an 802.11 access point?

Answer: The access point uses 802.11 standards for communication across the wireless LAN, including 802.2 LLC. It also connects to a wired LAN, so it uses 802.3 for its wired Ethernet.

16. What does the term line-of-sight mean in relation to wireless communications?

Answer: Line-of-sight means that you could stand beside one device, and see the other device. Some wireless technologies require a line-of-sight, and others do not.

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