Transcript Before ATM - Politechnika Wrocławska
Types of Conference
Lesson 7
Technical Education
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Lesson Objectives
This lesson will look at the two main types of H.323 conferences, and the component 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.
And 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;
,
and
.
Before considering each type further, it is necessary to introduce two additional control functions into a conference;
and
Review Questions Previous Beginning Help 3
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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.
Ezenia NetServer contains an MC. Conference Types Beginning Help 4
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.
Ezenia NetServer contains an MP.
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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.
Conference Types Beginning Help 6
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Centralised Conference
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.
MCU
MP MC Audio, Video and Data H.245 Control
Can I see this in more detail?
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How a Centralised Conference Happens
Step 1 An Endpoint registers with the Gatekeeper. Step 2 Step 3 At some time in the future a conference is required. “MC” calls the Gatekeeper to register conference “meeting96”. Gatekeeper registers and responds that conference may proceed.
2. Register conference ‘meeting96’ Legend
H.225/Q.931
H225/RAS H.245
RTP other Next
3. Conference ‘meeting96’ may proceed
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1. Register ‘Dave’
Beginning
Dave
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How a Centralised Conference Happens
Step 4 Dave” is a participant in the conference. He uses the Browser interface to establish the name of the conference.
Legend
H.225/Q.931
H225/RAS H.245
RTP other
4. Name of conference?
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Dave
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How a Centralised Conference Happens
Step 5 Step 6 Endpoint calls Gatekeeper to request connection to “Meeting96”, and indicates required bandwidth. Gatekeeper negotiates with the Endpoint over bandwidth if necessary and able, then responds positively, and provides the IP address to be used.
Legend
H.225/Q.931
H225/RAS H.245
RTP other Next Previous
5. Can I connect to ‘meeting96’ at 384 kbps 6. Yes; use IP address 23.46.147.11
Beginning
Dave
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How a Centralised Conference Happens
Step 7 Step 8 Step 9 Dave” calls MCU conference “Meeting96” directly. “Meeting96” checks with Gatekeeper that it can accept the call. Gatekeeper responds positively if sufficient bandwidth is available.
Legend
H.225/Q.931
H225/RAS H.245
RTP other
8. Can I accept call from ‘Dave’ at 384 kbps
Next
9. yes
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7. Hello ‘meeting96’ Dave
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How a Centralised Conference Happens
Step 10 Step 11 MCU confirms “Dave” is a participant in the conference “Meeting96”.
MC in MCU communicates with “Dave” and agrees standards to be used for audio and video. (H.245)
Legend
H.225/Q.931
H225/RAS H.245
RTP other
10. Is ‘Dave’ in ‘meeting 96’
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11. Hello ‘Dave’ What parameters can you use?
Beginning
Dave
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How a Centralised Conference Happens
Step 12 Step 13 Endpoint “Mary” requires to join conference.
Conducts conversation with Gatekeeper to gain admission. (H.225/Q.931/RAS) “Mary” requests connection to “MCU” at 768 kbps. (H.225/Q.931/RAS)
Legend
H.225/Q.931
H225/RAS H.245
RTP other Next
12a. Can I connect to ‘meeting96’ at 768 kbps?
13. Hello ‘meeting96’ 12b.yes - use IP address 23.46.147.11
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Mary
Help 13
Dave
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How a Centralised Conference Happens
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 data flow.
14a. Can I talk to ‘Mary’ Legend
H.225/Q.931
H225/RAS H.245
RTP other Next
14b. yes
Previous
15. Use these parameters
Beginning
16. ‘Mary’ joins conference Dave Mary
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How a Centralised Conference Happens
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)
Legend
H.225/Q.931
H225/RAS H.245
RTP other
18. Connection to “Dave” ended
Conference Types Previous
17. End connection to “meeting 96”
Beginning
17. End connection Dave Mary
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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
Why is this not suitable for large conferences?
Conference Types Beginning Help 16
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Decentralised Conference
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.
This page is animated. Please wait for the Conference Types button to appear.
MC Conference Types Beginning Audio, Video and Data H.245 Control Help 17
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Hybrid Conference
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.
MCU
MP MC Conference Types Beginning Audio, Video and Data H.245 Control Help 18
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Review Question 1
An MCU is not necessary for a de-centralised conference.
True False
Choose your answer
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Wrong Answer
An MC is necessary for any type of conference.
An MCU is not necessary for a de-centralised conference. © Copyright Ezenia Inc, 2000 Review that information again Move on to the next question Conference Types Beginning Help 20
Correct Answer
Well done An MCU is not necessary for a de-centralised conference.
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Review Question 2
Which of the following is not a benefit of running centralised conferences?
Choose your answer
Less network bandwidth used for H.323 traffic Less overhead in Endpoints as MP is centrally located Gatekeeper is not used Previous Question Beginning Review that information again Move on to the next question Help 22
Wrong Answer
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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Wrong Answer
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.
Review that information again Move on to the next question Previous Question Beginning Help 25
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Review Question 3
Which of the following is a function of a Multipoint Controller?
Registering Endpoints Source Quenching unwanted Video streams Negotiating conference operating parameters
Choose your answer
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Wrong Answer
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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Wrong Answer
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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Review Question 4
The MCU appears as another Endpoint to the Endpoints in the decentralised part of a hybrid conference?
True False Review that information again
Choose your answer
Previous Question Beginning Help 30
Wrong Answer
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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