Technical Education Click here to move on Index H.323 Components Lesson 2

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IndexIndexH.323 ComponentsH.323 Components

Lesson 2

2

© Copyright Ezenia Inc, 2000

Lesson objectives

This lesson is intended to give you an overview of the various parts of an H.323 system. It will introduce you to the five basic components, and give a brief description of how they work.

You will learn about the main functions of the Gatekeeper, the MCU and the Gateway.

We will also look at what components can be found inside an H.323 endpoint.

You’ll need to understand how the different components can be used and how they interact as a whole before studying each component in detail.

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ISDN

H.323 components

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Gateway

A multimedia system will consist of a number of parts. Some of these are essential, and others are required for

full functionality with multiple users.

Click on the labels below for more information about these components

MCU

Gatekeeper

The Network

Endpoints

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Endpoints

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• What does an endpoint do?

• What are the components of an endpoint?

• Can different types of endpoints connect together?

H.323

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What does an endpoint do?

An Endpoint provides the human interface to the conferencing system.

As a minimum an endpoint will have some form of audio system, which may be a simple as a telephone.

More commonly the endpoint will include a video system as well, and may even include a document camera and some method of data input (T.120).

In the market served by H.323 systems it is likely that the endpoint will be based on a PC with a integrated video camera and audio system.

From Release 2 of H.323 it is possible for endpoints to act as backup for other endpoints.

Endpoints

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Endpoint components

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VideoProcessor

ConferenceControl

Data

CommunicationsProcessor

NetworkInterface

AudioProcessor

The Network Interface will change according to the type of conference connection (for example, Ethernet for H.323, ISDN for H.320), but will exist in every system. The Communications Processor and Conference Control will also always be present, but the exact nature of these will again depend on the type of system.

Endpoints

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Different types of Endpoints

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Endpoints of different functionality may connect together to form a conference with each Endpoint receiving and sending those types of information that it is configured to use.

Endpoints

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Which of the following is not a component of an endpoint?

Video Processor

Audio Processor

Gateway

Network Interface

Endpoints - Review Question

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H.323

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The Audio Processor collects the audio signals from the microphone and prepares them for transmission across the network.

It also takes the audio signal received from the network and prepares it to play through the speakers or headphones.

A Gateway is a separate component, which will be discussed later in this lesson.

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H.323

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The Video Processor collects the video signals from the camera and prepares them for transmission across the network.

It also takes the video signal received from the network and prepares it for display on the screen.

A Gateway is a separate component, which will be discussed later in this lesson.

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H.323

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The Network Interface will vary depending on the network type, but will always be present.

It handles the network access. A Gateway is a separate component, which will be

discussed later in this lesson.

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H.323

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Correct Answer


Well done A Gateway is a separate component, which will be

discussed later in this lesson.

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H.323

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The Network

H.323

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• What kind of network does H.323 use?

• What are the components of an H.323 Network?

• How does the Network affect the H.323 traffic?

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What network does H.323 use?

H.323 does not specify the type of Local Area Network to be used, but will operate on any network type that supports IP, and has sufficient capacity. Some of the networks currently in use include:

Ethernet at 10, 100 or 1000 Mbps Token Ring at 4, 16, 32 or 100 Mbps FDDI and FDDI-II at 100 Mbps ATM at 25, 51, 100, 150, 622 and 1200 Mbps

The Network

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• So, what sort of network is best?

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What network is best?

Each type has its own advantage (for example Ethernet is the lowest cost, ATM offers managed performance), but in practice the selection criteria will be based on factors other than multimedia conferencing.

The most common network installed is Ethernet, and therefore is most likely to be the one encountered most often for conferencing applications.

The Network

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Components of the network

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The network is an essential part of an H.323 system. It connects the various elements of a conference together using various types of networking devices. Which type of device is dependent on the location, the nature and volume of the traffic, and the age of the installation.

In the same way that H.323 will work with all network types, it will also work with all network connectivity devices.

The Network

Routers

Hubs

Layer 3switches

RepeatersLayer 2switches

Routers

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Effects of the network on H.323 traffic

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Some devices (in particular Routers) can have a very major impact on the way the network operates. A Router may prevent multimedia traffic being transmitted in useable time frames, or may prevent it reaching parts of the network. This may be caused by the Router being unsuitable, or incorrectly configured.

Network devices are now becoming available that are H.323 compatible. These clearly will improve the chances of building a successful multimedia network but will still need care and expertise in their configuration.

The Network

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Routers have little or no impact on H.323 traffic.

True

False

Network - Review Question

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H.323

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Routers may prevent multimedia traffic being transmitted in useable time frames. This may be caused by the Router being unsuitable, or incorrectly configured.

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Correct Answer


Well done Routers may prevent multimedia traffic being transmitted in

useable time frames. This may be caused by the Router being unsuitable, or incorrectly configured.

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H.323

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Gatekeeper

H.323

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• What is the main function of a Gatekeeper?

• Is the Gatekeeper mandatory in H.323?

• What else does the Gatekeeper do?

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Is the Gatekeeper mandatory?

Gatekeeper

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The H.323 standard states that an H.323 system does not have to include a Gatekeeper. However it also states that if one is present it must be used by all endpoints.

In practise, it is very unlikely that any multimedia conference system could operate across a LAN without one.

This is primarily because the Gatekeeper can control the quantity of H.323 traffic carried across the IP network. H.323 traffic can be very network intensive if not controlled. Since the IP network is usually already heavily loaded with other types of data, most organisations will want to limit the impact of H.323 traffic on their network.

• Is the Gatekeeper another piece of Hardware?

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Gatekeeper’s main function

Gatekeeper

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One of the main purposes of the Gatekeeper is to control the amount of network bandwidth allocated to conference traffic.

It achieves this by requiring that an endpoint first registers with the gatekeeper before starting a communication session. Once registered, an endpoint may request a connection to another endpoint, and will request bandwidth for that connection.

If there is not sufficient bandwidth available (from a configurable proportion of the total available) the request will be refused and thus bandwidth preserved for other non-conference users.

With Release 2 of H.323 it became possible for Gatekeepers to act as backup for other Gatekeepers.

• Can multiple Gatekeepers exist on a single network?

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Gatekeeper additional functions

As the Gatekeeper knows which endpoints are in the system, it can also be used to translate addresses, control who has access to the system, and monitor usage.

A Gatekeeper can provide optional additional functions including accounting information and access control. It may also provide address translation which allows users to address other conference users by H.323, user friendly names. The Gatekeeper is able to link these addresses to the underlying network numeric address (IP).

Gatekeeper

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Gatekeeper – hardware or software?

Usually the Gatekeeper is a software function that can exist on various hardware platforms.

The Ezenia Gatekeeper is a software tool which can be installed on to any NT Server platform.

Gatekeeper

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Multiple Gatekeepers

A Gatekeeper limits the amount of traffic within the part of the network allocated to it - it’s Zone - and so prevents the multimedia conference traffic from dominating. In addition Gatekeepers allow an endpoint in one zone to talk to an endpoint in another zone by understanding how the endpoints are addressed, and which endpoint is in which zone.

Gatekeeper

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HelpHubs

Layer 3switches

RepeatersLayer 2switches

Routers

Zone BZone A

Gatekeeper A

Gatekeeper B

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Which of the following is the Gatekeeper’s main function?

Controlling the amount of H.323 traffic on the network

Address Translation from H.323 to Network Address

Accounting Information

Access Control

Gatekeeper - Review Question

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H.323

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While a Gatekeeper may provide address translation services for H.323 Traffic, this is not its main function.

The Gatekeeper’s main function is to control the amount of network bandwidth available for H.323 traffic.

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H.323

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While a Gatekeeper may be able to produce accounting information about H.323 Traffic, this is not its main function.

The Gatekeeper’s main function is to control the amount of network bandwidth available for H.323 traffic

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H.323

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While a Gatekeeper may implement access control into it’s zone, this is not its main function.

The Gatekeeper’s main function is to control the amount of network bandwidth available for H.323 traffic

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Correct Answer


Well done The Gatekeeper’s main function is to control the amount of

network bandwidth available for H.323 traffic

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H.323

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MCU

H.323

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• What does an MCU do?

• Is the MCU mandatory in H.323?

• How does the MCU look to the Gatekeeper?

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Multipoint Control Unit main functions

Where more than two endpoints are involved in a conference it is necessary to mix the audio signals, and select the appropriate video signal for each endpoint to receive. This is one of the prime functions of an MCU - some times also known as a Multimedia Bridge.

When multiple endpoints wish to join together in a conference the MCU will combine their audio, data and video streams so that a common conference stream is created which is sent to all participants in the conference.

The Ezenia MCU is The NetServer.

MCU

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• What else does an MCU do?

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Multipoint Control Unit

While H.323 conferences are governed by a set of standards, there are a range of options that are often dictated by the endpoints in use. For example there are a number of different audio encoding standards that offer differing compromises between quality and bandwidth. To allow these possibly different systems to communicate a series of negotiations between the various endpoints has to be conducted - the MCU undertakes that function.

If a conference is to include data-sharing then the MCU is also responsible for directing T.120 datastreams.

MCU

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Multipoint Control Unit – mandatory?

It is possible for an H.323 multipoint conference to exist without an MCU - however such an arrangement is very inefficient and is unlikely to support more than 6 users.

MCU

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Multipoint Control Unit

The MCU is known to the Gatekeepers. It registers with the Gatekeeper as an endpoint(MCU).

MCU

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• Where should the MCU be placed in a multi-zone network?

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Multipoint Control Unit Placement

In this example the location of the MCU is the most practical if those endpoints within Zone B are the ones that most frequently form a conference. Those within Zone A may, of course, join a conference; should they frequently have conferences with endpoints within their own zone then an additional MCU within Zone A may be desirable.

MCU

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Zone B

Zone A MCU

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A Multipoint Control Unit is mandatory for any multipoint H.323 conference.

True

False

MCU - Review Question

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H.323


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A multipoint conference can run without an MCU. However such an arrangement is unlikely to support

more than 6 users. A Multipoint Control Unit is not Mandatory in the H.323

Standard.

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H.323


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Correct Answer


Well done A multipoint conference can run without an MCU. However such an arrangement is unlikely to support more

than 6 users. A Multipoint Control Unit is not Mandatory in the H.323

Standard.

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H.323

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Gateway

H.323

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• What does a Gateway do?

• Where should a Gateway be placed in a network?

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Gateway function

Not all endpoints will necessarily be attached to a LAN. For example an existing H.320 WAN system may need to be connected into a common conference, or a remote site may not justify the provision of adequate LAN internetworking capacity. To allow for these types of situation, a Gateway has been specified that will allow the interconnection between H.320 and H.323 systems.

Gateway

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• Are H.323 and H.320 very different standards?

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H.320 to H.323

Many of the encoding and control standards are common to H.320 and H.323, but just about everything associated with transporting the information is different. The Gateway resolves these differences.

The Gateway will translate operating parameters, resolve addressing issues and converts information transport from one protocol suite to the other.

For example, a Gateway would be necessary when transferring conference information from the Ethernet/IP environment to ISDN.

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Gateway

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Gateway placement

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Gateways may be placed in the network wherever is appropriate to the highest volume of traffic.

In the example below most of the conference traffic is managed through the MCU on the H.323 network. However two remote offices need occasional access to conferences, and can connect through the Gateway.

Gateway

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H.323Network

MCUH.323Endpoints

Gateway

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Which of the following is not a Gateway Function?

Translating operating parameters

Resolving addressing issues

Converting information transport from one protocol suite to the other

Controlling the amount of H.323 traffic on the network

Gateway - Review Question

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H.323

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The Gateway is responsible for taking information from the H.323 network, and preparing it for transmission over the H.320 network.

It also takes information from the H.320 network, and preparing it for transmission over the H.323 network.

The Gatekeeper is responsible for controlling the amount of H.323 traffic on the network.

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H.323

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This includes resolving any differences in Addressing. The Gatekeeper is responsible for controlling the amount of

H.323 traffic on the network.

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H.323

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The Gatekeeper is responsible for controlling the amount of H.323 traffic on the network.

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H.323

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Correct Answer


Well done The Gatekeeper is responsible for controlling the amount of

H.323 traffic on the network.

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H.323

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