Voice Over Internet Protocol (VoIP)

Copyright © 2006 Heathkit Company, Inc. All Rights Reserved

Presentation 2 – VoIP Versus PSTN

2

Objectives

At the end of this presentation, you will be able to:

3

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.

4

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.

5

Physical Circuit

Twisted Pair Wire

6

Circuit Switching

7

CentralOffice

Local Loop

8

CentralOffice

CentralOffice

Local Loop

Trunk Line

9

Central Office

Central Office

InterexchangeOffice

InterexchangeOffice

10

Central Office

Central Office

Analog

Analog

Analog

Analog

Analog

InterexchangeOffice

InterexchangeOffice

11

Voice requires only about 4kHz of bandwidth.

0 4kHzFrequency

300Hz

En

ergy

12

Central Office

Central Office

Local Loop(Analog)

Digital

Digital

Digital

Local Loop(Analog)

InterexchangeOffice

InterexchangeOffice

13

Copper Replaced with Fiber Optic Cables

14

Paths Reserved for each Digital PSTN Connection

128 Kbps

64-Kbps

64-Kbps

15

Central Office

Central Office

DistantExchange

DistantExchange

Local Loop(Copper)

Fiber

Fiber

Fiber

Local Loop(Copper)

16

This Arrangement Wastes Bandwidth

128 kbps

64-kbps

64-kbps

17

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.

18

VoIP is currently exempt from the taxes and regulations

imposed on phone companies.

19

Multiplexer Demultiplexer

Physical Circuit

Physical Circuit

PSTN

VoIP

20

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.

21

Packet Switching

Multiplexer Demultiplexer

Physical Circuit

A

B

C

1

2

3

Soft Phones Soft Phones

22

Packet Switching

Multiplexer Demultiplexer

Physical Circuit

A

B

C

1

2

3

A

B

C

23

Packet Switching

Multiplexer Demultiplexer

Physical Circuit

A

B

C

1

2

3

ABC

24

Packet Switching

Multiplexer Demultiplexer

Physical Circuit

A

B

C

1

2

3

A

B

C

25

Virtual Circuits

Physical Circuit

A

B

C

1

2

3

Virtual Circuit

Virtual Circuit

Virtual Circuit

26

Internet

InternetServiceProvider

InternetServiceProvider

27

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