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Computer Networking: A Top Down Approach lecture notes, Lecture notes of Computer Networks

Computer Networking: A Top Down Approach lecture notes

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Chapter 7 Part 1
Multimedia Networking
Computer
Networking: A Top
Down Approach
6th edition
Jim Kurose, Keith Ross
Addison-Wesley
March 2012
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
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Chapter 7 – Part 1

Multimedia Networking

Computer

Networking: A Top

Down Approach

th

edition

Jim Kurose, Keith Ross

Addison-Wesley

March 2012

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: audio signal

Multimedia Networking 7 - 2

 Audio signal:

 Analog (Continuous) Signal

Fundamentals of Sound Waves

 Frequency

number of oscillations in

pressure per second

 Wavelength

distance between each

successive region of high

or low pressure.

Sound waves are longitudinal waves!

Frequency= waves/time

Sound Wave Motion:

No Matter Transfer – Only Energy Transfer

Representing waves graphically

Vibration with time in same place:

displacement – time graph shows what happens to a single particle

in the medium vibrating in its location over time (Sine Wave)

‘Period’, T, is time for one complete cycle. Gives frequency,

T

f

Also, Sine wave!

 Wavelength (λ)

  • distance in one cycle

 Amplitude

  • Displacement

 Crest

  • high point

 Trough

  • low point

 Note: λ  Lambda

Representing waves graphically

Vibration moving in space:

Mathematical representation

 Measured in db “decibels”

  • Volume; Loudness
  • Strength of the wave; Energy of the wave

Measuring Amplitude of Sound

Multimedia: audio

Multimedia Networking 7 - 13

 Audio (sound) is originally

analog (continuous) wave

(signal)!

 Digital Electronics can

process a limited number

of data points.

 Solution:

 Audio signal must be

sampled (Why?)

 Usually at constant rate

(Why?)

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

Recording Process

Storage

Digital-to-Analog

Converter DAC

Low-pass filter Amplifier Speaker Listener

Play-back Process

Audio recording and play-back

processes

Multimedia Networking 7 - 16 Multimedia Networking 7-

Sampling and Hold Example

Refer to Nyquist–Shannon sampling theorem

In the note section.

Multimedia Networking 7 - 17

Quantization Example

Using 2 bits4 levels

Multimedia Networking 7 - 19

Original Signal vs Re-constructed Signal

Showing quantization errornoise

How to improve the recording and output voice quality?

Answer: Minimize quantization error by;

1 - Sampling rate

2 - Processing power/speed

3 - Number of quantization levels

4 - Quality of Mic/Amplifiers/Speakers

Multimedia: audio

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?)

example rates

 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)