Networking I Ch. 3: Review Questions

Which Wi-Fi standard uses beamforming to allow an AP to send data to multiple devices simultaneously? a. 802.11ac b. 802.11n c. 802.11a d. 802.11g

a. 802.11ac 802.11ac improves on the MIMO technology in 802.11n by providing up to eight data streams and introducing multiuser MIMO (MU-MIMO), which allows 802.11ac APs to send data to multiple client stations simultaneously. MU-MIMO works by using a process called "beamforming," in which the AP sends the signal in the direction of the receiving device instead of uniformly in all directions. Beamforming allows the AP to send data to multiple devices simultaneously if they aren't too close together. (pg. 129)

Which Wi-Fi standard can provide the highest bandwidth? a. 802.11ac b. 802.11b c. 802.11n d. 802.11g

a. 802.11ac Current implementations have data transfer speeds of about 1 Gbps, but future implementations will have speeds up to 6.93 Gbps. (pg. 129)

Which of the following is an advantage of a star topology? (Choose all that apply.) a. Allows faster technologies than a bus does b. Requires less cabling than a bus c. Centralized monitoring of network traffic d. No single point of failure

a. Allows faster technologies than a bus does c. Centralized monitoring of network traffic Some advantages of a physical star topology are the following: • Much faster technologies are used than in a bus topology. • Centralized monitoring and management of network traffic are possible. • Network upgrades are easier.

Which of the following is a characteristic of fiber-optic cabling? (Choose all that apply.) a. Can be used in electrically noisy environments b. Requires only a single strand of fiber for network connections c. Carries data over longer distances than UTP does d. Lower bandwidth capability

a. Can be used in electrically noisy environments c. Carries data over longer distances than UTP does Fiber-optic cabling uses extremely thin strands of glass to carry pulses of light long distances and at high data rates. It's usually used in large internetworks to connect switches and routers and sometimes to connect high-speed servers to the network. Because of its capability to carry data over long distances (several hundred to several thousand meters), it's also used in WAN applications frequently. Fiber-optic cabling isn't susceptible to electrical interference, so unlike UTP, it can be used in electrically noisy environments. It requires two strands of fiber to make a network connection: one for transmitting and one for receiving. (pg. 106)

Which of the following is a feature of 100BaseFX? (Choose all that apply.) a. Often used as backbone cabling b. Best when only short cable runs are needed c. The fastest of the Ethernet standards d. Uses two strands of fiber

a. Often used as backbone cabling d. Uses two strands of fiber In environments that aren't conducive to using copper wiring to carry network data (such as electrically noisy settings) or where the cable run length exceeds the reach of twisted-pair wiring, the only real choice in a wired network is fiber optics. 100BaseFX (with the F indicating "fiber optic"), which uses two strands of fiber-optic cable, is often the best choice of network technology in these settings. Fiber-optic cable installation is still far more expensive than twisted-pair cable, but its advantages of being impervious to electrical noise and supporting longer cable segment lengths are worth the cost if the network requires these properties. 100BaseFX is rarely used as a complete replacement for 100BaseTX; instead, it's typically used as backbone cabling between hubs or switches and to connect wiring closets between floors or buildings. It's also used to connect client or server computers to the network when immunity to noise and eavesdropping is required. (pg. 113)

Which of the following is considered a property of Ethernet? (Choose all that apply.) a. Scalable b. Best-effort delivery system c. Guaranteed delivery system d. Obsolete technology

a. Scalable b. Best-effort delivery system One reason for Ethernet's low cost and scalability is its simplicity. It's considered a best-effort delivery system, meaning that when a frame is sent, there's no acknowledgement or verification that the frame arrived at its intended destination. Ethernet relies on network protocols, such as TCP/IP, to ensure reliable delivery of data. (pg. 110)

You're configuring a WLAN in a long narrow ballroom. The only place you can put the AP is at the far end of the room. Which type of antenna should you use? a. Unidirectional b. Bidirectional c. Omnidirectional d. Semidirectional

a. Unidirectional With a unidirectional antenna, signals are focused in a single direction, which makes them ideal for placement at one end of long, narrow spaces or to cover distances between buildings. (pg. 125)

Which access method uses a "listen before sending" strategy? a. Token passing b. CSMA/CD c. Token bus d. Polling

b. CSMA/CD The media access method Ethernet uses in half-duplex mode is Carrier Sense Multiple Access with Collision Detection (CSMA/CD). To understand this method better, break this term down into parts. "Carrier sense" means to listen. The rules for half-duplex Ethernet state that a device can send or receive data but can't do both simultaneously. So before a device can send, it must listen to see whether the medium is already busy, much like a group of people having a conversation. (pg. 108)

Which of the following is true about full-duplex Ethernet? (Choose all that apply.) a. Stations can transmit and receive but not at the same time. b. Collision detection is turned off. c. It's possible only with switches. d. It allows a physical bus to operate much faster.

b. Collision detection is turned off. c. It's possible only with switches. Therefore, when an Ethernet NIC is operating in full-duplex mode connected to a switch, CSMA/CD isn't used because a collision can't occur in full-duplex mode. Because fullduplex mode eliminates the delays caused by CSMA/CD and allows double the network bandwidth, most Ethernet LANs now operate in this mode using switches. (pg. 111)

Which of the following is defined by the extent to which signals in an Ethernet bus topology network are propagated? a. Physical domain b. Collision domain c. Broadcast domain d. Logical domain

b. Collision domain Remember that collisions can occur only in an Ethernet shared-media environment, which means a logical bus topology is in use. In this environment, all devices interconnected by one or more hubs hear all signals generated by all other devices. The signals are propagated from hub to hub until there are no more devices or until a device is encountered that doesn't use a logical bus topology, such as a switch or a router. The extent to which signals in an Ethernet bus topology network are propagated is called a collision domain. Figure 3-13 shows a network diagram with two collision domains enclosed in circles. All devices in a collision domain are subject to the possibility that whenever a device sends a frame, a collision might occur with another device sending a frame at the same time. This fact has serious implications for the number of computers that can reasonably be installed in a single collision domain. The more computers, the more likely it is that collisions occur. The more collisions, the slower network performance is. (pg. 109)

Which of the following is a characteristic of a switched logical topology? (Choose all that apply.) a. Uses a physical bus topology b. Creates dynamic connections c. Sometimes called a shared-media topology d. Uses a physical star topology

b. Creates dynamic connections d. Uses a physical star topology A switched topology creates dynamic connections or circuits between two devices whenever data is sent. This topology is sometimes considered a switched point-to-point topology because a circuit is established between two points as needed to transfer data (like turning on a switch), and then the circuit is broken when it's no longer needed (like turning off a switch). (pg. 102)

Which of the following is a field of the most common Ethernet frame type? (Choose all that apply.) a. ARP trailer b. FCS c. Destination MAC Address d. Data e. MAC type

b. FCS c. Destination MAC Address d. Data Each frame is composed of the following (see Figure 3-12): • A 14-byte frame header composed of these three fields: A 6-byte Destination MAC Address field A 6-byte Source MAC Address field A 2-byte Type field • A Data field from 46 to 1500 bytes • A frame trailer (frame check sequence [FCS]) of 4 bytes (pg. 107)

Which of the following describes a hub-based Ethernet network? a. Physical bus b. Logical bus c. Physical switching d. Logical star

b. Logical bus A logical bus topology can be implemented as a physical bus (although this topology is now obsolete). When a logical bus is implemented as a physical star using wired Ethernet, the center of the star is an Ethernet hub. Whatever the physical topology is, data transmitted from a computer is received by all other computers. (pg. 102)

Which topology is likely to be deployed in a WAN where there's a central office and three branch offices, and you want all traffic from the branch offices to go through the central office network? a. Ring b. PMP c. Mesh d. Point-to-point

b. PMP A point-to-multipoint (PMP) topology is an arrangement in which a central device communicates with two or more other devices, and all communication goes through the central device. It's often used in WANs where a main office has connections to several branch offices via a router. Instead of the router having a separate connection to each branch office, a single connection is made from the router to a switching device, which then directs traffic to the correct branch office. In drawings of PMP networks, the switching device is often shown as a cloud, as in Figure 3-6. (pg. 100)

Which of the following is true about infrastructure mode in wireless networks? (Choose all that apply.) a. Best used for temporary networks b. Uses a central device c. Resembles a physical bus and logical ring d. Most like a logical bus and physical star

b. Uses a central device d. Most like a logical bus and physical star Infrastructure mode uses a logical bus topology because all nodes hear all communications (in most cases). The physical topology is more difficult to describe because there are no physical wires; however, with a central device that all nodes communicate with, it most resembles a star topology. Ad hoc mode, sometimes called "peer-to-peer mode," is a wireless mode of operation typically used only in small or temporary installations. There's no central device, and data travels from one device to another in a line (more or less). If you want to describe ad hoc mode in terms of a physical and logical topology, it most resembles a physical and logical bus. (pg. 122)

How many channels can be used on an 802.11b network in North America? a. 7 b. 9 c. 11 d. 13

c. 11 Wi-Fi networks operate at one of two radio frequencies: 2.4 GHz and 5.0 GHz. However, this frequency is not fixed. The 2.4 GHz Wi-Fi variety operates from 2.412 GHz through 2.484 GHz, divided into 14 channels spaced 5 MHz apart, with each channel being 22 MHz wide. Because of radio frequency use restrictions, only the first 11 channels are used in North America. Other regions have channel use restrictions, too, but Japan allows using all 14 channels. The 5.0 GHz Wi-Fi variety divides frequencies between 4.915 GHZ and 5.825 GHz into 42 channels of 10, 20, 40, 80, or 160 MHz each, depending on the Wi-Fi standard in use. The remainder of the discussion on Wi-Fi channels pertains to 2.4 GHz Wi-Fi because it's the most popular, but most points also apply to the 5.0 GHz varieties. (pg. 122)

Which of the following is true of a MAC address? a. All binary 1s in the source address indicates a broadcast frame. b. It's sometimes called a logical address. c. A destination address of 12 hexadecimal Fs is a broadcast. d. It's composed of 12 bits.

c. A destination address of 12 hexadecimal Fs is a broadcast. The MAC address is stored in readonly memory (ROM) on the NIC. Because the address is said to be burned into memory, it's sometimes referred to as the "burned-in address" (BIA). The MAC address is composed of two 24-bit numbers: • A 24-bit manufacturer ID called an organizationally unique identifier (OUI) • A 24-bit serial number assigned by the manufacturer (pg. 68) A frame with a destination MAC address composed of all binary 1s or FF-FF-FF-FF-FF-FF in hexadecimal is a broadcast frame. Broadcast frames are intended to be processed by all computers on the network. (pg. 69)

Which of the following is a characteristic of unshielded twisted-pair cabling? (Choose all that apply.) a. Consists of four wires b. Commonly used in physical bus topologies c. Has a distance limitation of 100 meters d. Susceptible to electrical interference

c. Has a distance limitation of 100 meters d. Susceptible to electrical interference Unshielded twisted pair (UTP) is the most common media type in LANs. It consists of four pairs of copper wire, with each pair tightly twisted together and contained in a plastic sheath or jacket (see Figure 3-11). UTP comes in numbered categories, up to Category 8 as of this writing. The higher the category, the higher the cable's bandwidth potential. Category 5 Enhanced (Cat 5E) and Category 6 (Cat 6) are the most common in wired LANs, allowing speeds up to 10 Gbps. UTP cabling is used in physical star networks, and the maximum cable length from NIC to switch is 100 meters in LAN applications. UTP cabling is susceptible to electrical interference, which can cause data corruption, so it shouldn't be used in electrically noisy environments. (pg. 105-106)

Which best describes a typical wireless LAN? a. Logical ring topology b. Logical switching topology c. Logical bus topology d. Logical star topology

c. Logical bus topology Most Wi-Fi networks operate in infrastructure mode, meaning wireless stations connect through a wireless AP before they can begin communicating with other devices. Infrastructure mode uses a logical bus topology because all nodes hear all communications (in most cases). The physical topology is more difficult to describe because there are no physical wires; however, with a central device that all nodes communicate with, it most resembles a star topology. Ad hoc mode, sometimes called "peer-to-peer mode," is a wireless mode of operation typically used only in small or temporary installations. There's no central device, and data travels from one device to another in a line (more or less). If you want to describe ad hoc mode in terms of a physical and logical topology, it most resembles a physical and logical bus. (pg. 122)

Which topology most likely uses coaxial cabling? a. Physical star b. Logical ring c. Physical bus d. Logical switching

c. Physical bus Best known for its use in cable TV, coaxial cable is obsolete as a LAN medium, but it's used as the network medium for Internet access via cable modem. Coaxial cable was the original medium used by Ethernet in physical bus topologies, but its limitation of 10 Mbps half-duplex communication made it obsolete for LAN applications after star topologies and 100 Mbps Ethernet became the dominant standard. Coaxial cable in LANs can be around 200 meters long (pg. 106)

Which of the following describes the arrangement of network cabling between devices? a. Logical topology b. Networking technology c. Physical topology d. Media access method

c. Physical topology The arrangement of cabling and how cables connect one device to another in a network are considered the network's physical topology, and the path data travels between computers on a network is considered the network's logical topology. (pg. 94)

Which media access method does Wi-Fi use? a. CSMA/CD b. Token bus c. Demand priority d. CSMA/CA

d. CSMA/CA If a station transmits data, it can't hear whether any other station is transmitting, so if a collision does occur, the sending station doesn't detect it. For this reason, 802.11 specifies the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) access method, in which an acknowledgement is required for every packet sent, as explained in Chapter 2. With this requirement, if a collision occurs, the sending station knows the packet didn't arrive safely because there's no acknowledgement. (pg. 125)

Which of the following is true of IEEE 802.3an? a. Requires two pairs of wires b. Uses Category 5 or higher cabling c. Currently best for desktop computers d. Operates only in full-duplex mode

d. Operates only in full-duplex mode The 2006 IEEE 802.3an standard defines 10 Gigabit Ethernet as running over four pairs of Category 6A or Category 7 UTP cabling. Unlike the other BaseT Ethernet standards, 10GBaseT operates only in full-duplex mode, so you won't find any 10 Gbps hubs—only switches. [...] Although this cost might still be a lot for a desktop computer, you might need to equip network servers with 10 Gigabit Ethernet NICs so that they can keep up with desktop systems that commonly operate at 1 Gbps. (pg. 113)

Which type of Wi-Fi signal interference is most likely to be caused by leaves on trees? a. Diffraction b. Reflection c. Refraction d. Scattering

d. Scattering Scattering is caused by small, irregular objects, such as leaves, chain-link fences, dust, water droplets, and so forth. The signal changes direction in unpredictable ways, causing a loss in signal strength. (pg. 127)

Which technology is likely to be implemented as a point-to-point physical topology? a. Wi-Fi infrastructure mode b. FDDI c. Ethernet d. Wireless bridge

d. Wireless bridge Point-to-point topologies are also used with wireless networks in what's called a wireless bridge. This setup can be used to connect two buildings without using a wired network (see Figure 3-5) or to extend an existing wireless network. (pg. 100)