Networking Chapter 2: Physical Layer and Media

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Questions and Answers

What is the role of the physical layer in a network?

To determine the routing path for data

To create a signal that represents a stream of bits (correct)

To encrypt data before transmission

To provide error detection for the data

Which type of data refers to information that has discrete states?

Continuous data

Analog data

Digital data (correct)

Signal data

What must data be transformed into for transmission?

Error codes

Electromagnetic signals (correct)

Binary codes

Analog signals

Which statement about analog and digital signals is correct?

Analog signals can have an infinite number of values within a range. Signup and view all the answers

What does the physical layer control regarding the transmission medium?

Data flow directions Signup and view all the answers

Which best describes the characteristics of digital data?

It has discrete states. Signup and view all the answers

What are the two types of signals discussed in the relationship between data and transmission media?

Analog and Digital Signup and view all the answers

Which of the following best describes how analog data functions?

It represents information in a continuous manner. Signup and view all the answers

What determines the propagation speed of electromagnetic signals?

The frequency of the signal Signup and view all the answers

How is wavelength calculated?

Propagation speed / frequency Signup and view all the answers

What is the relationship between a composite signal and sine waves?

A composite signal consists of many sine waves with different frequencies. Signup and view all the answers

What happens to wavelength when a signal travels through coaxial or fiber-optic cable compared to air?

Wavelength decreases. Signup and view all the answers

What does the bandwidth of a composite signal represent?

The difference between the highest and lowest frequencies in the signal Signup and view all the answers

What does a complete sine wave in the time domain look like in the frequency domain?

A single spike Signup and view all the answers

If a composite signal is nonperiodic, what type of frequencies does its decomposition yield?

Continuous frequencies Signup and view all the answers

Which statement about the amplitude of a signal is true?

It reflects the strength or intensity of the signal. Signup and view all the answers

What do we use to describe digital signals instead of frequency?

Bit rate Signup and view all the answers

How is the bit length of a digital signal defined?

The distance one bit occupies on the transmission medium Signup and view all the answers

Which of the following factors does NOT affect data rate in data communications?

Type of signal processing used Signup and view all the answers

Which characteristic of a signal indicates that it is nonperiodic?

Bit rate used instead of frequency Signup and view all the answers

What is the relationship between bit duration and bit length?

Bit length = propagation speed x bit duration Signup and view all the answers

What happens to a signal as it travels through a transmission medium?

It gets distorted Signup and view all the answers

Why is bit rate considered more relevant than frequency for digital signals?

Frequency does not apply in digital transmission Signup and view all the answers

Which factor influences the maximum data rate over a channel?

Number of signal levels used Signup and view all the answers

What unit is frequency formally expressed in?

Hertz (Hz) Signup and view all the answers

How is frequency affected by the changes in a signal over time?

Fast changes indicate high frequency. Signup and view all the answers

If a signal does not change at all, what is its frequency?

Zero frequency Signup and view all the answers

What term describes the position of a waveform relative to time 0?

Phase Signup and view all the answers

Which of the following correctly describes wavelength?

It depends on frequency and the propagation speed of the medium. Signup and view all the answers

How can wavelength be calculated?

By knowing the propagation speed and period of the signal. Signup and view all the answers

What is the relationship between period and frequency?

Frequency is defined as the inverse of period. Signup and view all the answers

If a sine wave is offset by 1/6 cycle, what is its phase in degrees?

30° Signup and view all the answers

What is the defining characteristic of a periodic signal?

It completes a pattern within a measurable time frame and repeats it. Signup and view all the answers

What is referred to as the peak amplitude of a signal?

The maximum intensity the signal can achieve. Signup and view all the answers

Which of the following statements is true regarding frequency and period?

Frequency refers to the number of cycles per second, while period is the time for one cycle. Signup and view all the answers

What does attenuation refer to in signal transmission?

The loss of signal strength with distance Signup and view all the answers

What distinguishes a simple periodic analog signal from a composite one?

Composite signals consist of more than one sine wave. Signup and view all the answers

How is attenuation measured?

In terms of decibels (dB) Signup and view all the answers

Which form do both analog and digital signals take?

Both periodic and nonperiodic. Signup and view all the answers

What happens to a signal that experiences distortion?

Its form or shape changes Signup and view all the answers

How is peak amplitude typically measured for electric signals?

In volts. Signup and view all the answers

Which type of noise results from the random motion of electrons in a wire?

Thermal noise Signup and view all the answers

What determines the completeness of one cycle of a periodic signal?

The time it takes to complete a full pattern. Signup and view all the answers

What role do loading coils serve in the context of attenuation?

They equalize attenuation across frequencies Signup and view all the answers

Which statement is false regarding nonperiodic signals?

They are always composed of sine waves. Signup and view all the answers

What effect does noise have on a transmitted signal?

It alters the original signal Signup and view all the answers

Crosstalk occurs when:

Two wires interfere with each other's signals Signup and view all the answers

What distinguishes amplified signals from attenuated signals in terms of decibels?

Amplified signals are always greater than 0 dB Signup and view all the answers

Study Notes

Chapter 2: Physical Layer and Media

This chapter discusses the relationship between data created by devices and electromagnetic signals transmitted over a medium.
It covers digital and analog transmission, conversion of data to signals, efficient bandwidth usage, and characteristics of transmission media (guided and unguided).
Transmission media, though operating under the physical layer, are controlled by it.

Physical Layer

The physical layer interacts with the transmission medium and connects network components.
One of its tasks is creating a signal representing a stream of bits.
The physical layer also manages the transmission medium, including data flow direction and logical channel allocation for data from different sources.

Analog and Digital Data

Data can be analog or digital.
Analog data are continuous and take on continuous values.
Digital data have discrete states and take on discrete values.

Analog and Digital Signals

Signals can be analog or digital.
Analog signals have an infinite number of values in a range.
Digital signals have only a limited number of values.

Periodic and Nonperiodic Signals

Signals can be periodic or nonperiodic.
A periodic signal repeats a pattern over time intervals (called a period). Completing the full pattern is a cycle.
A nonperiodic signal doesn't repeat a pattern over time.

Periodic Analog Signals

Periodic analog signals can be simple (e.g., a sine wave) or composite (multiple sine waves).
Sine waves are fundamental and cannot be further decomposed.
Composite signals are composed of multiple sine waves.
Topics covered include sine wave, wavelength, time and frequency domain, composite signals, and bandwidth.

Signal Characteristics

Peak amplitude is the absolute value of the highest intensity, proportional to the energy carried.
Peak amplitude is typically measured in volts for electrical signals.
Time period and frequency are inverse of each other.
Frequency is the rate of change over time (high frequency = short time span, low frequency = long time span)
Phase is the position of the waveform relative to time 0.

Wavelength

Wavelength is a property of any signal.
It's the distance a signal travels in one period.
Wavelength ties the period or frequency of a sine wave to the propagation speed of the medium.
In data communications, wavelength is used to describe light transmission in optical fibers. The speed of light and the frequency of the signal determine the wavelength.

Bandwidth and Signal Frequency

Bandwidth is the difference between the highest and lowest frequencies in a composite signal.
It represents the range of frequencies used in a signal.

Transmission Impairment

Signals weaken (attenuate), change shape (distort), or are mixed with unwanted signals (noise) during transmission.

Attenuation

Attenuation is signal strength loss over distance. It depends on the medium and increases with frequency.
To overcome attenuation, amplifiers or repeaters are used to increase signal strength.
Attenuation is measured in decibels (dB).

Distortion

Distortion is the change in a signal's shape due to different propagation speeds for different frequency components.
This results in different phase shifts at the receiver.

Noise

Noise is unwanted signals interfering with the original signal.
Types of noise include thermal noise, induced noise, crosstalk, and impulse noise.
Signal-to-noise ratio (SNR) measures the strength of the signal relative to the noise. A higher SNR indicates better quality.

Digital Signals

Digital signals can convey information using different voltage levels (e.g., 0V, 5V) to represent bits (1 or 0). Digital signals may have more than two levels (e.g., different voltages for 1 and 0)
Bit rate is the number of bits sent in one second.
Bit length is the distance one bit travels on a transmission medium.

Data Rate Limits

Data rate depends on bandwidth, signal levels, and channel quality (noise).

Capacity of a System

Bit rate, or the rate at which data is sent, depends on the increase in the signal levels to encode a symbol, and this increases the probablity of an error.

Nyquist Theorem

Nyquist theorem gives the upper bound for the bit rate of a noiseless transmission system, directly related to the number of bits in a symbol, or signal levels, and the bandwidth.

Shannon's Theorem

Shannon's theorem provides the capacity of a system given the presence of noise.
The formula relates capacity (C) to bandwidth (B) and signal-to-noise ratio (SNR).

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Description

This chapter delves into the physical layer of networking, exploring how data and electromagnetic signals interact through different transmission media. It focuses on both digital and analog transmission, the conversion of data into signals, and the managing of bandwidth usage. Learn about signal characteristics and media types that affect data flow direction and logical channel allocation.