Chapter 15:Data Transmission Business Data Communications, 5e... Business Data Communications, 5e2 Electromagnetic Signals • Analog Signal – signal intensity varies in a smooth fashion
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Data Transmission
Business Data Communications, 5e
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Electromagnetic Signals
• Analog Signal
– signal intensity varies in a smooth fashion
over time In other words, there are no breaks
or discontinuities in the signal
Trang 3Analog Sine Wave
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Digital Square Wave
Trang 5Periodic Signal Characteristics
• Peak Amplitude (A)
– Maximum signal value, measured in volts
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s(t) = (4/ π ) × (sin (2 π ft) + (1/3) sin (2 π (3f)t))
Trang 7Frequency Domain Concepts
• Spectrum of a signal is the range of frequencies
that it contains
• Absolute bandwidth of a signal is the width of
the spectrum
• Effective bandwidth contained in a relatively
narrow band of frequencies, where most of
signal’s energy is found
• The greater the bandwidth, the higher the
information-carrying capacity of the signal
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• Greater bandwidth leads to greater costs
• Limited bandwidth leads to distortion
Trang 9Analog Signaling
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Voice/Audio Analog Signals
• Easily converted from sound frequencies
(measured in loudness/db) to electromagnetic
frequencies, measured in voltage
• Human voice has frequency components ranging from 20Hz to 20kHz
• For practical purposes, the telephone system has
a narrower bandwidth than human voice, from
300 to 3400Hz
Trang 11Image/Video: Analog Data to
Analog Signals
• Image is scanned in lines; each line is
displayed with varying levels of intensity
• Requires approximately 4Mhz of analog
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Digital Signaling
Trang 13Digital Text Signals
• Transmission of electronic pulses
representing the binary digits 1 and 0
• How do we represent letters, numbers,
characters in binary form?
• Earliest example: Morse code (dots and
dashes)
• Most common current forms: ASCII, UTF
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Trang 15Impairments and Capacity
• Impairments exist in all forms of data
transmission
• Analog signal impairments result in
random modifications that impair signal
quality
• Digital signal impairments result in bit
errors (1s and 0s transposed)
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Types of Noise
• Thermal (aka “white noise”)
– Uniformly distributed, cannot be eliminated
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