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 Central Office Local Loop

8 Central Office Central Office Local Loop Trunk Line

9 Central Office Central Office Interexchange Office Interexchange Office

10 Central Office Central Office Analog Interexchange Office Interexchange Office

11 Voice requires only about 4kHz of bandwidth. 0 4kHz Frequency 300Hz Energy

12 Central Office Central Office Local Loop (Analog) Digital Local Loop (Analog) Interexchange Office Interexchange Office

13 Copper Replaced with Fiber Optic Cables

14 Paths Reserved for each Digital PSTN Connection 128 Kbps 64-Kbps

15 Central Office Central Office Distant Exchange Distant Exchange Local Loop (Copper) Fiber Local Loop (Copper)

16 This Arrangement Wastes Bandwidth 128 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 Soft Phones

22 Packet Switching Multiplexer Demultiplexer Physical Circuit A B C A B C

23 Packet Switching Multiplexer Demultiplexer Physical Circuit A B C ABC

24 Packet Switching Multiplexer Demultiplexer Physical Circuit A B C A B C

25 Virtual Circuits Physical Circuit A B C Virtual Circuit

26 Internet Service Provider Internet Service Provider

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