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Computer Networking: A Top Down Approach lecture notes
Typology: Lecture notes
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Multimedia Networking 7 - 1
7.1 multimedia networking
applications
7.2 streaming stored video
7.3 voice-over-IP
7.4 protocols for real-time
conversational
applications
Multimedia Networking 7 - 2
Analog (Continuous) Signal
number of oscillations in
pressure per second
distance between each
successive region of high
or low pressure.
Representing waves graphically
in the medium vibrating in its location over time ( Sine Wave)
Also, Sine wave!
Wavelength (λ)
Amplitude
Crest
Trough
Representing waves graphically
Measured in db “decibels”
Multimedia Networking 7 - 13
Audio (sound) is originally
analog (continuous) wave
(signal)!
Digital Electronics can
process a limited number
of data points.
Solution:
time
audio signal amplitude
analog
signal
quantized
value of
analog value
quantization
error
sampling rate
( N sample/sec)
1 Second
Example Audio Signal
Multimedia Networking 7 - 14
Sound Source Speaker
Low-pass filter Sample and Hold Analog-to-Digital
Converter ADC
(Quantization)
Storage
Storage
Digital-to-Analog
Converter DAC
Low-pass filter Amplifier Speaker Listener
Audio recording and play-back
processes
Multimedia Networking 7 - 16 Multimedia Networking 7-
Refer to Nyquist–Shannon sampling theorem
In the note section.
Multimedia Networking 7 - 17
Using 2 bits 4 levels
Multimedia Networking 7 - 19
Showing quantization error noise
Answer: Minimize quantization error by;
1 - Sampling rate
2 - Processing power/speed
3 - Number of quantization levels
4 - Quality of Mic/Amplifiers/Speakers
Multimedia Networking 7 - 20
Example: 8,000 samples/sec,
256 (8 bits) quantized values:
64,000 bps
Electronics playing recorded
signal converts bits back to
analog signal:
some quality reduction
(Why?)
CD: 1.411 Mbps
MP3: 96, 128, 160 kbps
Internet Telephony: 5.3 kbps
and up
time
audio signal amplitude
analog
signal
quantized
value of
analog value
quantization
error
sampling rate
( N sample/sec)
