Voice Over Internet Protocol (VoIP) Copyright © 2006 Heathkit Company, Inc. All Rights Reserved Presentation 3 – VoIP: An Overview

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

3 Define signaling, encoding, transport, and gateway control as they apply to VoIP. Identify the protocols associated with signaling, encoding, transport, and gateway control in VoIP. Define jitter, latency, and packet loss. Describe techniques designed to overcome these problems.

4 Levels of VoIP Computer to Computer – One softphone connects to another directly over the Internet. Via a VoIP Service Provider Enterprise System – An organization acts as its own VoIP Service provider

5 Computer to Computer VoIP VoIP over Instant Messaging Microsoft – MSN Messenger and Windows Messenger AOL – AIM Yahoo! – Yahoo! Messenger Google – Google Talk

6

7 VoIP via a Service Provider Great for homes and small businesses. Monthly fee or per call fee. Provide services which are not available or cost extra through PSTN. Generally better quality than IM.

8 VoIP Providers AT&T Cablevision Vonage Verizon EarthLink Nortel Comcast Communications Time Warner Cox Communications SBC Communications Bell South Quest Communications

9 Typical Services Provided Connect to PSTN Call Waiting Caller ID Voice Mail Unlimited long Distance Select your Area Code Call Forwarding Online Account Management Conference Calls

10 Vonage The largest VoIP Service provider Requires a broadband connection to the Internet. Signaling Protocol is SIP.

11 Soft-phone

12 IP Phone Analog Phone Analog Telephone Adapter

13 Enterprise System IP PBX Internet PSTN IP Phones VoIP to PSTN Gateway Proxy Server Admin Server

14 Major VoIP Issues Signaling Voice Coding Packet Delivery Gateway Control

15 Signaling Find the called party. Determine the status of the called party – busy or not. Create and manage calls.

16 Voice Coding Voice is inherently analog. Microphones produce an analog signal. Speakers require an analog signal to reproduce voice. The Internet requires digital data packets. The conversion of voice to digital data packets at the transmitting end and the conversion of the digital data packets back into voice at the receiving end.

17 Packet delivery Moving the voice data packets to their intended recipient while ensuring acceptable voice quality. Rearranging the order of the received data packets back to the order in which they were transmitted. Controlling the rhythm of the packets.

18 Gateway Control A gateway is a device that converts from one protocol to another. Common gateway conversions include: H.323 to SIP and vice versa VoIP to PSTN VoIP to ATM VoIP to ISDN

19 VoIP creates two paths within the IP network. Signaling Path – Carries information needed to establish and maintain the media path. Media Path – The path used by the voice packets.

20 VoIP Protocols Signaling Path protocols – SIP, H.323, MGCP, and Megaco/H.248 Media Path protocol – Real Time Protocol (RTP)

21 VoIP Challenges Latency Jitter Packet loss

22 Latency The delay between the instant a voice fragment is produced and the later instant at which the listener hears it. The amount of time that the packet spends in the network. Latency greater than 150 milliseconds becomes noticeable and may degrade voice quality.

23 Contributors to Latency Encoder delay Transport delay Jitter Buffer delay Decoder delay

24 Jitter Changes in latency from one packet to the next. Packets may take different paths with different overall delays.

25 Packet Jitter Internet A B

Jitter Buffer

27 Lost Packets Ignore the problem – “transmit” an instant of silence. Repeat the last packet transmitted. Predict the contents of the lost packet by examining the contents of previous packets. Insert an instant of noise.

Voice Over Internet Protocol (VoIP) Copyright © 2006 Heathkit Company, Inc. All Rights Reserved End