Technical Education Click here to move on Index Types of Conference Lesson 7.

Technical Education

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IndexIndexTypes of ConferenceTypes of Conference

Lesson 7

2

© Copyright Ezenia Inc, 2000

Lesson Objectives

This lesson will look at the two main types of H.323 conferences, and the components necessary to make them work.

It will look more closely at the role of the MCU within centralised conferences.

The advantages and disadvantages of using different conference types will also be discussed.

An understanding of how H.323 conferences are set up and operated, and the reasons for choosing the type of conference setup, is necessary when planning and designing a conference environment. It is also useful to understand the underlying reason why the setup to be supported has been designed in a particular way.

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Conference types

Conferences will involve two, or more than two endpoints. To allow for maximum efficiencies, H.323 defines three types of conferences; Centralised, De-centralised and Hybrid.

Before considering each type further, it is necessary to introduce two additional control functions into a conference; Multipoint Controller and Multipoint Processor. Explore what these are first.

Ok, now we can look at each type of conference –Centralised, De-centralised and Hybrid.

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Multipoint Controller

The Multipoint Controller decides which audio and video streams should be sent to all endpoints in the conference. It also negotiates between all parties as they join a conference to try to ensure compatible standards are used.

An MC is required for all multipoint conference types. It does not have to be a separate device and can be located in an endpoint for small conferences.

The MC operates the H.245 channel. An MCU will be used for a large conference and that will

contain an MC. Conference Types

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Multipoint Processor

The Multipoint Processor receives and mixes the audio, and determines the selected video and data during the conference. It is essential for a centralised conference, and may be located within an endpoint. In practice the amount of processing by an MP in all but the smallest conference will dictate that the MP is in a separate specialist device - the MCU.

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Conference Types

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Centralised conference

Each endpoint transmits its conference control, audio, video and data streams to the MCU which contains both the MP and MC. The MP processes the incoming information and produces an audio conference mix which it transmits to all endpoints. The MP selects which of the incoming video streams is to be used and broadcasts that to all endpoints. Using RTCP, two video signals will be received by the MCU (the loudest and next loudest), these will be retransmitted, all other video signals will be stopped at source until the loudest site changes.

The MC manages the conference operating parameters.

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Conference Types

• How does this work?

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Centralised conference

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MCU

MPMC

Audio, Video and Data

H.245 Control

Centralised conferences use Unicast transmission, that is one way, single destination. I.e. from originator to MCU and from MCU to each individual endpoint that requires the signal. This is the most efficient system in terms of network bandwidth available with most currently installed routers.

• Can I see this in more detail?

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Step 1 An endpoint registers with the Gatekeeper. Step 2 At some time in the future a conference is required. “MC” in the MCU calls the Gatekeeper to register conference “meeting96”. Step 3 Gatekeeper registers and responds that conference may proceed.

How a centralised conference happens

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2. Register conference ‘meeting96’

3. Conference ‘meeting96’ may proceed

1. Register ‘Dave’

Dave

LegendH.225/Q.931H225/RAS H.245RTPother

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Dave

4. Name of conference?

Step 4 Dave” is a participant in the conference. He uses the Browser interface to establish the name of the conference.

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5. Can I connect to ‘meeting96’ at 384 kbps

6. Yes; use IP address 23.46.147.11


Step 5 Endpoint calls Gatekeeper to request connection to “Meeting96”, and indicates required bandwidth.

Step 6 Gatekeeper negotiates with the endpoint over bandwidth if necessary and able, then responds positively (in this example), and provides the IP address to be used.

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Step 7 Endpoint calls MCU conference “Meeting96” directly.

Step 8 “Meeting96” checks with Gatekeeper that it can accept the call.

Step 9 Gatekeeper responds positively if sufficient bandwidth is available.

7. Hello ‘meeting96’

8. Can I accept call from ‘Dave’ at 384 kbps

9. yes

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Step 10 MCU confirms “Dave” is a participant in the conference “Meeting96”.

Step 11 MC in MCU communicates with “Dave” and agrees standards to be used for audio and video. (H.245)

11. Hello ‘Dave’ What parameters can you use?

10. Is ‘Dave’ in ‘meeting

96’

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Step 12 Endpoint “Mary” requires to join conference.Conducts conversation with Gatekeeper to gain admission. (H.225/Q.931/RAS)

Step 13 “Mary” requests connection to “MCU” at 768 kbps. (H.225/Q.931/RAS)

Mary

13. Hello ‘meeting96’

Dave

12a. Can I connect to ‘meeting96’ at 768 kbps?

12b.yes - use IP address 23.46.147.11

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Step 14 MCU requests acceptance from Gatekeeper. Step 15 MCU specifies audio and video operating parameters. Step 16 “Mary” joins conference. (H.245)

Note - “Mary” has joined the conference at 768 kbps; “Dave” is operating at 384 kbps, and this has set the ruling speed for the conference video to 384k.

DaveMary

15. Use these parameters

14a. Can I talk to ‘Mary’

14b. yes

16. ‘Mary’ joins conference

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Step 17 Dave chooses to leave the conference, and notifies the MCU and the Gatekeeper. (H.225/RAS)

Step 18 MCU advises the Gatekeeper that the connection to “Dave” has ended. (H.225/RAS)

DaveMary

17. End connection to “meeting 96”

17. End connection

18. Connection to “Dave” ended

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Decentralised conference

Each endpoint transmits its audio, video and data to every other endpoint in the conference.An MC must be present (it may be co-located with an endpoint, in an MCU, or other device). The MC manages the H.245 control channel with each endpoint in the conference. No MP is required because each endpoint is sending the audio, video and data streams to everyone else in the conference. Each endpoint manages the received input and selects a video stream and mixes the audio.Conference control is unicast in this case, but everything else can be multicast. This means that decentralised is only suitable for very small conferences

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Conference Types

• Why is this not suitable for large conferences?

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Decentralised conference

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While there is not very much H.323 traffic associated with this 4 seat conference, just adding 1 More user dramatically increases the amount of traffic.


H.245 Control

MC

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Hybrid conference

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MCU

MPMC


H.245 Control

MC

In this mixed conference some endpoints are in a centralised conference, while others are in a decentralised conference. The endpoints are not aware of the mixed nature of the conference. In the decentralised part of the conference the MCU acts as a composite endpoint for all those endpoints that are in the centralised conference.

Conference Types

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An MCU is not necessary for a de-centralised conference.

True

False

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Conference Types

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An MC is necessary for any type of conference. An MCU is not necessary for a de-centralised conference.

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Correct Answer


Well done An MCU is not necessary for a de-centralised conference.

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Conference Types

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Which of the following is not a benefit of running centralised conferences?

Less network bandwidth used for H.323 traffic

Less overhead in endpoints as MP is centrally located

Gatekeeper is not used

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As all traffic in a centralised conference is unicast, between MCU and endpoints, there is less traffic in such a conference. Also, as the MP in the MCU sorts out the audio and video streams, and source quenches any video that is not needed, there is less H.323 data on the network.

The Gatekeeper is always involved in any H.323 conference set up, if there is a Gatekeeper present.

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In any type of conference there must be an MC function. If there is no MCU, one of the endpoints must perform that function. This could have a detrimental effect on that endpoint’s performance.

The Gatekeeper is always involved in any H.323 conference set up, if there is a Gatekeeper present.

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Correct Answer


Well done The Gatekeeper is always involved in any H.323

conference set up, if there is a Gatekeeper present.

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Which of the following is a function of a Multipoint Controller?

Registering endpoints

Source Quenching unwanted Video streams

Negotiating conference operating parameters

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This is a function of the Gatekeeper. The MC must be present in all conference and it decides

which audio and video streams will be used in a conference, and negotiates the operating parameters of that conference.

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This is a function of the MP, found in centralised conferences.

The MC must be present in all conference and it decides which audio and video streams will be used in a conference, and negotiates the operating parameters of that conference.

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Correct Answer

Well done The MC must be present in all conference and it decides

which audio and video streams will be used in a conference, and negotiates the operating parameters of that conference.

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The MCU appears as another endpoint to the endpoints in the decentralised part of a hybrid conference?

True

False

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Endpoints in a de-centralised conference will not recognise what an MCU is. As an MCU mixes the signals for the endpoints it manages, it has to present that information to those endpoints outside its area.

The MCU will appear as a composite endpoint for all those endpoints that are in the centralised conference.

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Correct Answer


Well done The MCU will appear as a composite endpoint for all those

endpoints that are in the centralised conference.

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