Transcript Before ATM - Politechnika Wrocławska

Technical Education
H.323 Components
Lesson 2
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© 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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H.323 components
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.
The Network
Click on the labels below for more information about
these components
Gatekeeper
Previous
Gateway
Endpoints
MCU
Beginning
ISDN
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Endpoints
•
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
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.
Video
Processor
Endpoints
Audio
Processor
Communications
Processor
Network
Interface
Beginning
Data
Conference
Control
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Different types of Endpoints
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
Beginning
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Endpoints - Review Question
Which of the following is not a component of an endpoint?
Video Processor
Audio Processor
Gateway
Network Interface
H.323
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Wrong Answer
 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.
H.323
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Wrong Answer
 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.
H.323
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Wrong Answer
 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.
H.323
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Correct Answer
 Well done
 A Gateway is a separate component, which will be
discussed later in this lesson.
H.323
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The Network
•
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?
H.323
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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
Beginning
•
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
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.
Routers
Routers
Layer 3
switches
The Network
Layer 2
switches
Hubs
Repeaters
Beginning
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Effects of the network on H.323 traffic
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
Beginning
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Network - Review Question
Routers have little or no impact on H.323 traffic.
True
False
H.323
Beginning
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Wrong Answer
 Routers may prevent multimedia traffic being transmitted in
useable time frames. This may be caused by the Router being
unsuitable, or incorrectly configured.
H.323
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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.
H.323
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Gatekeeper
•
What is the main function of a Gatekeeper?
•
Is the Gatekeeper mandatory in H.323?
•
What else does the Gatekeeper do?
H.323
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Is the Gatekeeper mandatory?
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?
Gatekeeper
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Gatekeeper’s main function
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.
Gatekeeper
Beginning
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
Beginning
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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.
Zone B
Zone A
Routers
Layer 3
switches
Gatekeeper
Repeaters
Layer 2
switches
Beginning
Gatekeeper A
Hubs
Gatekeeper B
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Gatekeeper - Review Question
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
H.323
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Wrong Answer
 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.
H.323
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Wrong Answer
 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
H.323
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Wrong Answer
 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
H.323
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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
H.323
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MCU
•
What does an MCU do?
•
Is the MCU mandatory in H.323?
•
How does the MCU look to the Gatekeeper?
H.323
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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.
MCU
The Ezenia MCU is The NetServer.
Beginning
•
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.
MCU
If a conference is to include data-sharing then the MCU is
also responsible for directing T.120 datastreams.
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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).
•
Where should the MCU be placed in a multi-zone network?
MCU
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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
Zone A
MCU
Zone B
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MCU - Review Question
A Multipoint Control Unit is mandatory for any multipoint H.323
conference.
True
False
H.323
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Wrong Answer
 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.
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.
H.323
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Gateway
•
What does a Gateway do?
•
Where should a Gateway be placed in a network?
H.323
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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
Beginning
•
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.
Gateway
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Gateway placement
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
H.323
Network
Gateway
ISDN
H.323
Endpoints
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MCU
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Gateway - Review Question
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
H.323
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Wrong Answer
 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.
H.323
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Wrong Answer
 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.
 This includes resolving any differences in Addressing.
 The Gatekeeper is responsible for controlling the amount
of H.323 traffic on the network.
H.323
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Wrong Answer
 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.
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.
H.323
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