Module 4-7

A network administrator is measuring the transfer of bits across the company backbone for a mission critical financial application. The administrator notices that the network throughput appears lower than the bandwidth expected. Which three factors could influence the differences in throughput? (Choose three.)

• the amount of traffic that is currently crossing the network

• the sophistication of the encapsulation method applied to the data

• the type of traffic that is crossing the network

• the latency that is created by the number of network devices that the data is crossing

• the bandwidth of the WAN connection to the Internet

What are two characteristics of fiber-optic cable? (Choose two.)

• It is not affected by EMI or RFI.

• Each pair of cables is wrapped in metallic foil.

• It combines the technique of cancellation, shielding, and twisting to protect data.

• It is more expensive than UTP cabling is.

What is a primary role of the Physical layer in transmitting data on the network?

• create the signals that represent the bits in each frame on to the media

• provide physical addressing to the devices

• determine the path packets take through the network

• control data access to the media

Answer explanation

The OSI physical layer provides the means to transport the bits that make up a frame across the network media. This layer accepts a complete frame from the data link layer and encodes it as a series of signals that are transmitted to the local media.

With the use of unshielded twisted-pair copper wire in a network, what causes crosstalk within the cable pairs?

• the magnetic field around the adjacent pairs of wire

• the use of braided wire to shield the adjacent wire pairs

• the reflection of the electrical wave back from the far end of the cable

• the collision caused by two nodes trying to use the media simultaneously

Answer explanation

Crosstalk is a type of noise, or interference that occurs when signal transmission on one wire interferes with another wire. When current flows through a wire a magnetic field is produced. The produced magnetic field will interface the signal carried in the adjacent wire.

Refer to the graphic. What type of cabling is shown?

• STP

• UTP

• coax

• fiber

Answer explanation

Network cabling include different types of cables:

UTP cable consists of four pairs of color-coded wires that have been twisted together and then encased in a flexible plastic sheath.

STP cable uses four pairs of wires, each wrapped in a foil shield, which are then wrapped in an overall metallic braid or foil.

Coaxial cable uses a copper conductor and a layer of flexible plastic insulation surrounds the copper conductor.

Fiber cable is a flexible, extremely thin, transparent strand of glass surrounded by plastic insulation.

In addition to the cable length, what two factors could interfere with the communication carried over UTP cables? (Choose two.)

• crosstalk

• bandwidth

• size of the network

• electromagnetic interference

Answer explanation

Copper media is widely used in network communications. However, copper media is limited by distance and signal interference. Data is transmitted on copper cables as electrical pulses. The electrical pulses are susceptible to interference from two sources: Electromagnetic interference (EMI) or radio frequency interference (RFI) - EMI and RFI signals can distort and corrupt the data signals being carried by copper media.Crosstalk - Crosstalk is a disturbance caused by the electric or magnetic fields of a signal on one wire interfering with the signal in an adjacent wire.

Refer to the graphic. What type of cabling is shown?

• STP

• UTP

• coax

• fiber

Answer explanation

Network cabling include different types of cables: UTP cable consists of four pairs of color-coded wires that have been twisted together and then encased in a flexible plastic sheath.STP cable uses four pairs of wires, each wrapped in a foil shield, which are then wrapped in an overall metallic braid or foil.Coaxial cable uses a copper conductor and a layer of flexible plastic insulation surrounds the copper conductor.Fiber cable is a flexible, extremely thin, transparent strand of glass surrounded by plastic insulation.

Which two devices commonly affect wireless networks? (Choose two.)

• Blu-ray players

• home theaters

• cordless phones

• microwaves

Answer explanation

Radio Frequency Interference (RFI) is the interference that is caused by radio transmitters and other devices that are transmitting in the same frequency.

Which two statements describe the services provided by the data link layer? (Choose two.)

• It defines the end-to-end delivery addressing scheme.

• It maintains the path between the source and destination devices during the data transmission.

• It manages the access of frames to the network media.

• It packages various Layer 3 PDUs into a frame format that is compatible with the network interface.

Answer explanation

The data link layer is divided into two sub layers, namely Logical Link Control (LLC) and Media Access Control (MAC). LLC forms a frame from the network layer PDU into a format that conforms to the requirements of the network interface and media. A network layer PDU might be for IPv4 or IPv6. The MAC sub layer defines the media access processes performed by the hardware. It manages the frame access to the network media according to the physical signaling requirements (copper cable, fiber optic, wireless, etc.)

What is the function of the CRC value that is found in the FCS field of a frame?

• to verify the integrity of the received frame

• to verify the physical address in the frame

• to verify the logical address in the frame

• to verify the logical address in the frameto compute the checksum header for the data field in the frame

Answer explanation

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.