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Voice Over Internet Protocol (VoIP)
Copyright © 2006 Heathkit Company, Inc. All Rights Reserved
Presentation 2 – VoIP Versus PSTN
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Objectives
At the end of this presentation, you will be able to:
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Explain the difference between circuit switching and packet switching.
Explain the difference between a physical circuit and a virtual circuit.
Draw a basic block diagram of a typical PSTN voice call.
Draw a basic block diagram of a typical VoIP call.
Explain the advantages and disadvantages of VoIP versus PSTN.
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Public Switched Telephone Network (PSTN)
Plain Old Telephone System (POTS).
Available all over the world.
Basically, an analog system.
Requires analog-to-digital and digital-to-analog conversion for compatibility with the digital world.
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Physical Circuit
Twisted Pair Wire
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Circuit Switching
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CentralOffice
Local Loop
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CentralOffice
CentralOffice
Local Loop
Trunk Line
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Central Office
Central Office
InterexchangeOffice
InterexchangeOffice
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Central Office
Central Office
Analog
Analog
Analog
Analog
Analog
InterexchangeOffice
InterexchangeOffice
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Voice requires only about 4kHz of bandwidth.
0 4kHzFrequency
300Hz
En
ergy
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Central Office
Central Office
Local Loop(Analog)
Digital
Digital
Digital
Local Loop(Analog)
InterexchangeOffice
InterexchangeOffice
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Copper Replaced with Fiber Optic Cables
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Paths Reserved for each Digital PSTN Connection
128 Kbps
64-Kbps
64-Kbps
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Central Office
Central Office
DistantExchange
DistantExchange
Local Loop(Copper)
Fiber
Fiber
Fiber
Local Loop(Copper)
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This Arrangement Wastes Bandwidth
128 kbps
64-kbps
64-kbps
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Voice Over IP (VoIP)
Uses virtual circuits rather than physical circuits.
Uses packet switching rather than circuit switching.
Uses a physical circuit only when needed during a call, rather than reserving the physical circuit for the entire call.
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VoIP is currently exempt from the taxes and regulations
imposed on phone companies.
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Multiplexer Demultiplexer
Physical Circuit
Physical Circuit
PSTN
VoIP
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The IP Telephone
Soft Phone – PC with headset and proper VoIP software.
An analog phone with an Analog Telephone Adapter (ATA).
IP Phone – An analog telephone and ATA all in a single package.
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Packet Switching
Multiplexer Demultiplexer
Physical Circuit
A
B
C
1
2
3
Soft Phones Soft Phones
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Packet Switching
Multiplexer Demultiplexer
Physical Circuit
A
B
C
1
2
3
A
B
C
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Packet Switching
Multiplexer Demultiplexer
Physical Circuit
A
B
C
1
2
3
ABC
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Packet Switching
Multiplexer Demultiplexer
Physical Circuit
A
B
C
1
2
3
A
B
C
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Virtual Circuits
Physical Circuit
A
B
C
1
2
3
Virtual Circuit
Virtual Circuit
Virtual Circuit
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Internet
InternetServiceProvider
InternetServiceProvider
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VoIP Requires a Broadband Connection
Digital Subscriber Line (DSL)
Cable
ISDN
T1 Line
Voice Over Internet Protocol (VoIP)
Copyright © 2006 Heathkit Company, Inc. All Rights Reserved
End
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