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Data must be transformed into electromagnetic signals prior to transmission
across a network.
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Data and signals can be either analog or digital.
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A signal is periodic if it consists of a continuously repeating pattern.
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Each sine wave can be characterized by its amplitude, frequency, and phase.
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Frequency and period are inverses of each other.
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A time-domain graph plots amplitude as a function of time.
*
A frequency-domain graph plots each sine wave’s peak amplitude against its
frequency.
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By using Fourier analysis, any composite signal can be represented as a
combination of simple sine waves.
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The spectrum of a signal consists of the sine waves that make up the signal.
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The bandwidth of a signal is the range of frequencies the signal occupies.
Bandwidth is determined by finding the difference between the highest and
lowest frequency components.
*
Bit rate (number of bits per second) and bit interval (duration of 1 bit) are
terms used to describe digital signals.
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A digital signal is a composite signal with an infinite bandwidth.
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Bit rate and bandwidth are proportional to each other.
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The Nyquist formula determines the theoretical data rate for a noiseless
channel.
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The Shannon capacity determines the theoretical maximum data rate for a noisy
channel.
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Attenuation, distortion, and noise can impair a signal.
*
Attenuation is the loss of a signal’s energy due to the resistance of the
medium.
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The decibel measures the relative strength of two signals or a signal at two
different points.
*
Distortion is the alteration of a signal due to the differing propagation
speeds of each of the frequencies that make up a signal.
*
Noise is the external energy that corrupts a signal.
*
We can evaluate transmission media by throughput, propagation speed, and
propagation time.
*
The wavelength of a frequency is defined as the propagation speed divided by
the frequency.
Reference:
Data Communication and Networking
Fourth Edition
Behrouza A. Forouzan
Fourth Edition
Behrouza A. Forouzan
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