Voice Over Internet Protocol (VoIP)

Copyright © 2006 Heathkit Company, Inc. All Rights Reserved

Presentation 6 – The H.323 Protocol

2

Objectives

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

3

Explain why H.323 involves much more than just VoIP.

Identify the four components or entities in an H.323 network and explain the purpose of each.

Explain the main operations involved in establishing, maintaining, and terminating a voice communications session using the H.323 protocol.

Identify the control signaling, media control, and media transport protocols employed in the H.323 suite of protocols and briefly explain the purpose of each.

Explain how H.323 integrates with the PSTN.

4

International Telecommunications Union (ITU)

An international organization within the United Nations System where governments and the private sector coordinate global telecom networks and services.

The leading publisher of telecommunication technology, regulatory and standards information.

Released the first major protocol for VoIP called H.323.

5

The H.323 protocol is much broader than just VoIP.

A set of protocols designed for voice, video, and data conferencing.

A set of protocols designed to operate over a range of packet-based networks.

6

Components of an H.323 System

Terminals

Gateways

Multipoint Control Units (MCU)

Gatekeepers

End points

7

H.323 terminal

Provides real-time, two-way voice, video and/or data communications with another terminal.

Common VoIP examples include computers acting as soft phones, IP phones, and PSTN telephones equipped with Analog Telephone Adapters (ATA).

May also communicate with a gateway or a multipoint control unit.

8

H.323 Gateway

A device that translates between an H.323 terminal and a non-H.323 terminal.

Common examples include translating from H.323 to: PSTN

ATM

ISDN

9

Multipoint Control Unit (MCU)

Allows conferences between three or more endpoints.

Required for multipoint conferences.

Not required for single-endpoint to single endpoint communications.

10

Gatekeeper

May authorize network access to terminals or gateways.

May control bandwidth allocation to terminals.

May offer address translation services.

11

Data Link Layer

Physical Layer

Internet Protocol (IP)

TCP UDP

Call Control RTP/RTCP

Audio CodecH.245

H.225

H.323

TCP/IP

Control Media Transport

12

Data Link Layer

Physical Layer

Internet Protocol (IP)

TCP UDP

Call Control RTP/RTCP

Audio CodecH.245

H.225

Control

TCP/IP

H.323

13

H.225 Control Signaling

Establishes and tears down connections between H.323 endpoints.

Handles registration, admission, and status signals.

14

H.245 Media Control

Manages the media streams between H.323 endpoints.

Insures that the media sent by one end can be understood by the other end.

15

Data Link Layer

Physical Layer

Internet Protocol (IP)

TCP UDP

Call Control RTP/RTCP

Audio CodecH.245

H.225

H.323

TCP/IP

Media Transport

16

Data Link Layer

Physical Layer

Internet Protocol (IP)

TCP UDP

Call Control RTP/RTCP

Audio CodecH.245

H.225

H.323

TCP/IP

Media Transport

17

Major H.323 OperationsDiscovery

Registration

Connection Setup

Capability Exchange

Logical Channel Exchange

Payload Transfer

Termination

18

Discovery

The endpoint determines which gatekeeper to register with.

Gatekeepers act as traffic cops.

The endpoint sends a multicast message asking: “Is my gatekeeper out there?”

The gatekeeper replies: “I’m your gatekeeper and here is my address”

19

Registration

Endpoint: “Can I join your zone?”

Gatekeeper: “First, tell me all about yourself.”

Endpoint: “Well I am an end-user terminal, my IP address is ____ and my aliases are _____ and _______.”

Gatekeeper: “Okay, your qualifications look good, so you’re in.”

20

A

B

GatekeeperInternetInternet

Endpoint

RAS Signaling

21

Connection Setup

Calling Endpoint: “Hey my human needs to talk with your human.”

Called Endpoint : “Okay, I have initiated the call establishment procedure.”

Calling Endpoint : “Great. I’m ringing your number.”

Called Endpoint : “I have answered and am ready to proceed.”

22

Capability Exchange

Endpoints reveal their capabilities to each other.

Endpoints agree on a media transfer format that both sides can understand and handle.

Examples; Codec, bit rate, etc.

23

Logical Channel Exchange

The two endpoints set up the media transport channels.

With two-party VoIP calls, two logical channels are established, one in each direction.

These are the channels that will carry the voice packets back and forth.

24

Payload Transfer

Voice data from the codec is processed by the Real-Time Protocol (RTP) into RTP packets.

These packets are transported from the caller endpoint to the called endpoint via UDP and IP over the logical media channels established in the prior step.

25

Termination

Occurs when the phone conversation is eventually finished.

Both sides release the logical channel and any other resources such as bandwidth that was set aside for the call.

26

Major H.323 OperationsDiscovery

Registration

Connection Setup

Capability Exchange

Logical Channel Exchange

Payload Transfer

Termination

27

A

Gateway

Internet

Internet

Endpoint

PSTNPSTN

28

A

MultipointControl

Unit (MCU)

InternetInternet

Endpoint

1

2

3

29

H.323 Capabilities

Video Voice DataMulti-media

Packet-BasedTransport

IP ATM ISDN Other

30

H.323 Criticisms

Too complex

Not easy to scale up

Not designed specifically with Internet Protocol (IP) in mind.

Voice Over Internet Protocol (VoIP)

Copyright © 2006 Heathkit Company, Inc. All Rights Reserved

End