[CCNA] CCNA1 - Chapter4

reasons for physical layer protocols to use frame encoding techniques

• to distinguish data bits from control bits
• to identify where the frame starts and ends

A network administrator notices that some newly installed Ethernet cabling is carrying corrupt and distorted data signals. The new cabling was installed in the ceiling close to fluorescent lights and electrical equipment. Which two factors may interfere with the copper cabling and result in signal distortion and data corruption?

• EMI and RFI signals can distort and corrupt data signals that are carried by copper media. These distortions usually come from radio waves and electromagnetic devices such as motors and florescent lights.
• Crosstalk is a disturbance that is caused by adjacent wires bundled too close together with the magnetic field of one wire affecting another.
• Signal attenuation is caused when an electrical signal begins to deteriorate over the length of a copper cable.

What technique is used with UTP cable to help protect against signal interference from crosstalk?

• To help prevent the effects of crosstalk, UTP cable wires are twisted together into pairs.
• Twisting the wires together causes the magnetic fields of each wire to cancel each other out.

The PC is connected to the console port of the switch. All the other connections are made through FastEthernet links. Which types of UTP cables can be used to connect the devices?

• A straight-through cable is commonly used to interconnect a host to a switch and a switch to a router.
• A crossover cable is used to interconnect similar devices together like switch to a switch, a host to a host, or a router to a router. If a switch has the MDIX capability, a crossover could be used to connect the switch to the router; however, that option is not available.
• A rollover cable is used to connect to a router or switch console port.

What is wrong with the displayed termination?

• The untwisted length of each wire is too long.

Which type of connector does a network interface card use?

• RJ-45

Why are two strands of fiber used for a single fiber optic connection?

• Light can only travel in one direction down a single strand of fiber.
• In order to allow for full-duplex communication two strands of fiber must be connected between each device.

A network administrator is designing the layout of a new wireless network. Which three areas of concern should be accounted for when building a wireless network?

• The three areas of concern for wireless networks focus on the size of the coverage area, any nearby interference, and providing network security.
• Extensive cabling is not a concern for wireless networks, as a wireless network will require minimal cabling for providing wireless access to hosts.
• Mobility options are not a component of the areas of concern for wireless networks.

Which layer of the OSI model is responsible for specifying the encapsulation method used for specific types of media?

• data link

What are two services performed by the data link layer of the OSI model

• The data link layer is responsible for the exchange of frames between nodes over a physical network media.
• Specifically the data link layer performs two basic services:
  • It accepts Layer 3 packets and encapsulates them into frames.
  • It provides media access control and performs error detection.

Which method of data transfer allows information to be sent and received at the same time?

• full duplex

star topology

• In an extended star topology, central intermediate devices interconnect other star topologies.

Which statement describes the media access control methods that are used by the networks in the exhibit?

• Network 1 represents an Ethernet LAN. Data on the wired LAN accesses the media using CSMA/CD.
• Network 2 represents a point-to-point WAN connection so no media access method is required.
• Network 3 represents a WLAN and data accesses the network using CSMA/CA.

trailer of a data-link frame

• The trailer in a data-link frame contains error detection information that is pertinent to the frame included in the FCS field.
• The header contains control information, such as the addressing, while the area that is indicated by the word “data” includes the data, transport layer PDU, and the IP header.

As data travels on the media in a stream of 1s and 0s how does a receiving node identify the beginning and end of a frame?

• The transmitting node inserts start and stop bits into the frame.

Link sublayer

• There are two data link sublayers, MAC and LLC.
• The LLC sublayer is responsible for communicating with the network layer and for tagging frames to identify what Layer 3 protocol is encapsulated.

CRC

• The CRC value in the FCS field of the received frame is compared to the computed CRC value of that frame, in order to verify the integrity of the frame.
• If the two values do not match, then the frame is discarded.

LLC

• Logical Link Control (LLC) is the data link sublayer that defines the software processes that provide services to the network layer protocols.
• LLC places information in the frame and that information identifies the network layer protocol that is encapsulated in the frame.

type of fiber

• Multimode Fiber A - LED as light source
• Multimode Fiber B - several paths of light into the fiber
• Multimode Fiber C - generally used with LANs
• Single-mode Fiber A - only one ray of light into the fiber
• Single-mode Fiber B - generally used for campus backbone
• Single-mode Fiber C - laser as light source

hybrid topology

• A physical topology that is a variation or combination of a point-to-point, hub and spoke, or mesh topology
• A hybrid topology is one that is a variation or a combination of other topologies.
• Both partial mesh and the extended star are examples of hybrid topologies.

bandwidth

• the amount of data that can flow from one place to another in a given amount of time