Modules 4 – 7: Ethernet Concepts

What is the purpose of the OSI physical layer?

• controlling access to media
• transmitting bits across the local media
• performing error detection on received frames
• exchanging frames between nodes over physical network media

Answer explanation

The Physical layer creates the electrical, optical, or microwave signals that represent the bits in each frame and transmits them across the media.

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

• The two strands allow the data to travel for longer distances without degrading.
• They prevent crosstalk from causing interference on the connection.
• They increase the speed at which the data can travel.
• They allow for full-duplex connectivity.

Answer explanation

One strand is used for transmitting (Tx) and the other for receiving (Rx), allowing simultaneous communication in both directions (full-duplex).

Which characteristic describes crosstalk?

• the distortion of the network signal from fluorescent lighting
• the distortion of the transmitted messages from signals carried in adjacent wires
• the weakening of the network signal over long cable lengths
• the loss of wireless signal over excessive distance from the access point

Answer explanation

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.

Which procedure is used to reduce the effect of crosstalk in copper cables?

• requiring proper grounding connections
• twisting opposing circuit wire pairs together
• wrapping the bundle of wires with metallic shielding
• designing a cable infrastructure to avoid crosstalk interference
• avoiding sharp bends during installation

Answer explanation

Twisting wire pairs cancels out magnetic fields and ensures that both wires are equally exposed to external interference, effectively cancelling it out.

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

Answer explanation

Throughput is the actual measure of data transfer, which is always lower than theoretical bandwidth due to factors like traffic load, packet types, and latency.

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 typically contains 4 pairs of fiber-optic wires.
• It is more expensive than UTP cabling is.

Answer explanation

Fiber optics use light pulses rather than electricity, making them immune to electromagnetic interference. However, the materials and installation are more costly than copper.

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 Physical layer accepts a complete frame from the Data Link layer and encodes it as a series of signals (electrical, optical, or radio) for transmission.

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

When current flows through a wire, a magnetic field is produced which can induce a signal (interference) in an adjacent wire.

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
• signal modulation technique
• electromagnetic interference

Answer explanation

Copper media is susceptible to external interference (EMI/RFI) and internal interference (crosstalk).

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

• Blu-ray players
• home theaters
• cordless phones
• microwaves
• incandescent light bulbs

Answer explanation

Many consumer devices, including older cordless phones and microwave ovens, operate in the 2.4 GHz frequency band, causing interference with Wi-Fi signals.