uoa/cnl tnc 2000 potential and limitations of a teleteaching environment based on h.323 audio-visual...

UoA/CNL UoA/CNL TNC 2000TNC 2000

Potential and Limitations of a Potential and Limitations of a Teleteaching Environment based on Teleteaching Environment based on H.323 Audio-Visual Communication H.323 Audio-Visual Communication

Systems.Systems.

P. Balaouras, I. Stavrakakis, L. MerakosP. Balaouras, I. Stavrakakis, L. Merakos

Communication Networks Laboratory (Communication Networks Laboratory (CNLCNL))

University of Athens (University of Athens (UoAUoA))


IntroductionIntroduction• Teleteaching services

• Networked multimedia applications– MJPEG/ATM– Mbone tools medium quality, desktop– H.323 systems classroom settings

• H.323 are mature for videoconferencing; what

about teleteaching (TT) ?• TT requir. are a superset of VC requir.


OutlineOutline

• Introduction

• The ITU-T H.323 Recommendations

• Capabilities of present H.323 products

• Teleteaching Environment

• Functional requirements

• Conclusions


The ITU-T H.323 RecommendationsThe ITU-T H.323 Recommendations

• H.323 entities

• Capabilities of H.323 terminals– audio, video, data exchanging and processing– controls issues and device control

• H.323 Multipoint Conferences

• Capabilities of the H.323 MCU

• Control issues


H.323 EntitiesH.323 Entities• H.323 terminal

• H.323 Multipoint Control Unit end-points

• H.323/H.32* Gateway

• H.323 Gatekeeper


Defined audio capabilities of H.323 Defined audio capabilities of H.323 terminalsterminals

H.323 terminal

Audiocodec(s)

Audiochannel(s)

G.711 A-law, G.711 A-law, μ-μ-lawlaw

G.722, G.723, G.722, G.723, G.728, G.729,G.728, G.729,MPEG-1 audio

Coding schemes

Green for mandatory featuresGreen for mandatory features

Orange for optional featuresOrange for optional features

H.323 terminal

Audio mixing

multicast

multicast

G.729G.729

G.728G.728

Assymetric operationAssymetric operation


Defined visual capabilities of H.323 Defined visual capabilities of H.323 terminalsterminals

H.323 terminal

Videocodec(s)

Videochannel(s)

H.261 QCIFH.261 QCIF

H.261 CIF,H.261 CIF, H.263 SQCIF,QCIF,H.263 SQCIF,QCIF, CIFCIF, , 4CIF, 16CIF

Coding schemes



H.323 terminal

Videomixing

orswitching

multicast

multicast

QCIFQCIF

CIFCIF

Assymetric operationAssymetric operation


Defined data capabilities of H.323 terminalsDefined data capabilities of H.323 terminals

H.323 terminal

T.120 entity

Data channel(s)

T.120T.120



H.323 terminal

- One or more data channel(s)- Unidirectional or bi-directional channel(s)


Audio-visual capabilities of H.323 terminalsAudio-visual capabilities of H.323 terminals

Audio Video Data#streams 1 0 0Manda-

tory Codingschemes

A-law, μ-law, G.711

H.261 QCIF T.120

#streams N>1 N>0 N>0optionalCodingschemes

G.722, G.723,G.728, G.729,MPEG1 audio.

- H.261 CIF- H.263 SQCIF,QCIF,

CIF, 4CIF 16CIF


Capability set (CS) of an H.323 terminalCapability set (CS) of an H.323 terminal

• H.245 procedure to exchange CS

• Decoder capability set – video & audio bit rate,– video, audio format, – algorithm options accepted by decoder

• Number of simultaneous audio, video decoding

• Encoder: is free to transmit anything in the agreed set.


H.323 Multipoint ConferencesH.323 Multipoint Conferences

• Multipoint Controller (MC)– control functions (e.g., chair control) – controls MP

• Multipoint Processor (MP) – video switching, mixing, transcoding– audio mixing, transcoding– T.120 data distribution


Types of multipoint conferencesTypes of multipoint conferences

• Centralized

• Decentralized

• Hybrid


Centralized multipoint conferencesCentralized multipoint conferences

unicast

MCUMCU

MPMP

MCUMCU

H.323 terminal

MCUMCU MPMP

MPMPMPMP

MPMPMPMP

MPMPMPMPMCMCMCMC

MCMCMCMC

MCMCMCMC

Audio & Video unicasting

Audio & Video unicasting

Audio & Video multicasting


Decentralized multipoint conferencesDecentralized multipoint conferences

Audio & Video Multicasting

MPMP

MPMPMPMP

MPMP

MCMC

GWGW

H.323 terminal

MCUMCU MCMCMCMC

MCMCMCMC

- 1 MP @ every H.323 terminal - 1 MC/session @ any H.323 end-point

IP IP


Hybrid multipoint, centralized audioHybrid multipoint, centralized audio

Video Multicasting

MPMP

MPMPMPMP

MPMP

H.323 terminal

MCUMCU

- 1 MP for video @ every terminal - 1 MC/session @ MCU

IP IP

Audio unicasting

MCMCMCMC


Hybrid multipoint, centralized videoHybrid multipoint, centralized video

Audio Multicasting

MPMP

MPMPMPMP

MPMP

H.323 terminal

MCUMCU

- 1 MP for audio @ every terminal - 1 MC/session @ MCU

IP IP

Video unicasting

MCMCMCMC


Characteristics and potential location Characteristics and potential location of MC and MPof MC and MP

ConferenceType

Centralized Decentralized Hybrid-centralizedaudio

Hybrid-centralizedvideo

Capability * M** O** O OCommunication modesAudio P2P Multicast P2P MulticastVideo P2P Multicast Multicast P2PT.120 Data P2P P2P P2P P2PPotential locations ofMC MCU MCU, terminal,

GK, GatewayMCU MCU

MP MCU Terminals MP-audio: MCUMP-video: TerminalsT.120 MP: All endpoints

MP-audio: terminalsMP-video: MCUT.120MP: All endpoints

Hints: (*)Capability of Terminals and MCU in supporting the conference type, (**)M for mandatory, O forOptional.


Defined capabilities of the H.323 MCUDefined capabilities of the H.323 MCU

• Must Support centralized Mult. conferences• MP

– video switching, – synchronization and video mixing – synchronization and audio mixing,– transcoding, – T.120 data distribution

• MC– control functions

MCMCMCMCMCUMCU

MPMPMPMP


MP functionsMP functions

sw

MP@MCU

Sa

Sa

Sa

Sa

Video/audio switching function

Sb

Sb

mix

Audio/video mixing function

Sa

Sb

Sd

Sc

Mixed(Sa,Sb,Sc,Sd)

MP@MCUSd

Sc

Waste of bandwidth


MP functionsMP functions

sw

MP@MCU

Da

Da

Da

Da

Data distribution function

Audio/video transcoding function

trans

MP@MCU

Sa

Sa

Sa

Sa @ QCIF

Sb

Sb

CIF

QCIF

CIF

CIF


Control issues performed by MC (H.243Control issues performed by MC (H.243)

• Automatic video selection mode• Chair-control mode

– video broadcast visualization forcing capability – multipoint visualization– video selection

• Any terminal can have the chair token• Floor control - only in chair-control mode • Camera control


sw

MP@MCU

Sa

Sa

Sa

Sa Sb

Sb

Sd

Sc

Automatic video switching mode Automatic video switching mode

The selection mechanism is voice-activated


CC - Video broadcast (VCB)CC - Video broadcast (VCB)• To determine which one of the available video streams will

be transmitted to all terminals, except chairman’s

Sa

Sb

Sd

Sc

MCU

VCB Sb

Sb

Sb

MCMCMCMC

MPMPMPMPChair-control terminal


CC - Video select (VCS)CC - Video select (VCS)• To determine which video stream will be transmitted to

chairman’s terminal

Sa

Sb

Sd

Sc

MCU

VCS Sc

Sc

MCMCMCMC

MPMPMPMP


CC - Multipoint visualization (MCV)CC - Multipoint visualization (MCV)• To broadcast chairman’s terminal video to all participants

Sa

Sb

Sd

Sc

MCU

MCV

Sa

Sa

Sa MCMCMCMC

MPMPMPMP


Floor Control issues performed by MCFloor Control issues performed by MC

• Floor control is possible only in chair-control mode.• Any terminal may request the floor by sending command

TIF to the MCU.• The MCU forwards the request to the chair-control

terminal.

MCU

TIF MCMCMCMC

TIF


Camera control (H.281)Camera control (H.281)

• A moderator is able to control the local and remote cameras that are connected to an H.323 terminal that supports H.281 standard (FECC: Far-End Camera Control)


Capabilities Capabilities of presentof presentH.323 H.323 terminalsterminals

Characteristics H.323 roomterminals

H.323 desktopterminals

Audio & videoinputs

1xAudio,2xS-video,

1xcomposite

1xAudio,1xS-video or composite,

1xComposite orproprietary

Video sourceselection

Yes

Audio CodingSchemes

{G.711,G.722,G.723,G.728}

Video CodingSchemes

{H.261 Sub-QCIF, H.261 QCIF, H.263 Sub-QCIF,H.263 QCIF, H.263}

Type ofsessions

Centralized by H.323 MCU

Comm. mode point to pointDisplaywindows

Small, medium, Full screen,PIP modes

Outputs Audio, RGB, s-video Audio, RGB

Far-end cameracontrol

Y some

Floor control only via chair control noChair control Y noDisplayDevices

TV PC monitorPC speakers

Data Support Yes, by T.120 Application Sharing ServicesNetworkSupport

IP, ISDN, MVIP IP and some ISDN

Platform PC based Windows


Teleteaching Environment (TE)Teleteaching Environment (TE)• An TE enables synchronous participation in a lecture

of dispersed set of students located at workspaces.

• The supported interaction among the workspaces

constitute a teleteaching scenario.

• Set of interactions supported by present H.323

products potential teleteaching scenario.


Available sources as teaching materialAvailable sources as teaching material

Teaching mediaTeaching media Input DevicesInput Devices

Students’ Students’ voicevoice

Instructor’s Instructor’s voicevoice

Tape/CD player

Source analog audio signals

Students’ mic

Instructor’s wireless mic

Music, sounds, Music, sounds, recorded coursesrecorded courses

Sa

Ia

Ma


Real object Visual Presenter

Camera for Instructor

Camera for students

Instructor

Student(s)

VCRVideo recorded material

Sourceanalog video

signals

V

Iv

Sv

Mv




Computer System

digital streams of data,

video and audio files

Still media forpresentations and docs

Continuous audio and video media

Applications

Broadcast application

Appl.Sharing S/W

DpDvDa




Required H.323 entitiesRequired H.323 entities

IP

H.323 & T.120 Multipoint Conference Unit (MCU)

H.323Terminal

H.323/H.320GatewayISDN

H.323Gatekeeper

H.323Terminal

H.323Terminal

H.320Terminal

H.323Terminal

Wz

Wy

WxWi


Number of H.323 terminalsNumber of H.323 terminals

• Multiple audio and video streams are to transmitted multiple H.323 terminals

H.323 terminal(s)Camera for Instructor

Camera for students

Iv

Sv

H.323 terminal(s)Camera for Instructor

Camera for students

Iv

Sv

H.323 room terminal

Video matrix


Potential interactions among workspacesPotential interactions among workspaces

Automatic video switching mode

Wi

Wx

Wy

Wz

sw

sw

mixIa(Wi)

Sa(Wz)

Sa(Wx)

Sa(Wy)

MixedA

mixedAMixedA

Sa(Wi)

mixedA

MCU



Chair control mode

Wi

Wx

Wy

Wz

sw

sw

swIa(Wi)

Sa(Wz)

Sa(Wx)

Sa(Wy)

Sel-A

Sel-ASel-A

Sa(Wi)

Sel-A

MCU



Wi

Wx

Wy

Wz

mix

sw

swIv/V(Wi)

Sv(Wz)

Sv(Wx)

Sv(Wy)

Sel-V

Sel-V*Sel-V

Sv(Wi)

Sel-V

MCU

Sel-V: one of Iv/V(Wi),Sv(W*), selected by chair control or automatic video switching

*: if Wy is the source then a stream other than Sv(Wy):=Sel-V is transmitted to Wy



Wi

Wx

Wy

Wz

mix

sw

swDp(Wi)

MCU

Dp(Wi)

Dp(Wi)

Dp(Wi)


Summary of potential interactionsSummary of potential interactions

Iv/V(Wi) or /Sv*

Dp(Wi)Wi

Wx

Wy

Wz

Dp(Wi)

Dp(Wi)

sw

sw

Iv/V(Wi)Sv(Wy)

Sv(Wz)

Sv(Wx)

Dp(Wi)

mix

Sv(Wi)

Ia(Wi)

Sa(Wz)

Sa(Wx)

Sa(Wy)

Sel-A

Sel-A

Sel-A

Sa(Wi)

Sel-A

Sel-V

MCU

Sel-V

Sel-V


Teleteaching functional Teleteaching functional requirementsrequirements

• Presentation of a set of TT requirements.

• In which degree these requirements are

fulfilled by present H.323 products.

• Possible solutions are proposed for

requirements that are partly or not fulfilled.


Lecture delivery phase requirementsLecture delivery phase requirements

R1a: high quality audio-visual communication– Audio:G.711 audio coding @ 64 kbps– Video: H.263 CIF bite rate > 768 kbps

R1b:R1b: one way lecture delivery without any interference– Use of terminals and MCU that support chair control

feature.– In automatic video switching, interference is possible.



Wi

Wx

Wy

Wz

swIv/V(Wi)

Iv/V(Wi)

Iv/V(Wi)Sel-V

Iv/V(Wi)

MCU

Ia(Wi)

Ia(Wi)

Ia(Wi)

Ia(Wi)

Dp(Wi)

Dp(Wi)

Dp(Wi)

Dp(Wi)

- G.711 audio coding @ 64 kbps- H.263 CIF bite rate > 768 kbps

- Terminals and MCU that support chair control.



R2:R2: Presentation of Iv(Wi) and Dp(Wi) in separate

display device (i.e., projector)

1 H.323, T.120, PIP

Iv(Wi)

Dp(Wi)

1 H.323

1 T.120

Iv(Wi)

Dp(Wi)

1 H.323 & T.120, dual monitor

PC with dual VGA output card



R3:R3: Instructor should be free to move around as

in a conventional classrooms

– Wireless microphone.

– Pan-Tilt-Zoom camera with auto-tracking feature.


R4,R5 - Instructor’s interaction with studentsR4,R5 - Instructor’s interaction with students

R4:R4: Interaction with local or remote students.

All participants should be able to listen and watch the speaker.

R5:R5: How a student request the floor to ask a question.


Chair controlChair control

Wi

Wx

Wy

Wz

swIv/V(Wi)

Iv/V(Wi)

Iv/V(Wi)

Iv/V(Wi)

MCU

Ia(Wi)

Ia(Wi)

Ia(Wi)

Ia(Wi)

Dp(Wi)

Dp(Wi)

Dp(Wi)

Dp(Wi)

The operator of the chair-control capable terminal shall request the floor on behalf of a student.Complementary floor control system: terminals, camera and MIC


Chair controlChair control

Wi

Wx

WyWy

Wz

swIv/V(Wi)

Iv/V(Wi)Sa(Wy)Sv(Wy)

MCU

Ia(Wi)Ia(Wi)

Sa(Wy)

Dp(Wi)

Dp(Wi)

Dp(Wi)

Dp(Wi)

Sv(Wy)

Sv(Wy)

Sv(Wy)Sa(Wy)

Sa(Wy)


Automatic video switchingAutomatic video switching

Wi

Wx

Wy

Wz

swIv/V(Wi)

Iv/V(Wi)Sa(Wy)Sv(Wy)

MCU

Ia(Wi)MixedA

Dp(Wi)

Dp(Wi)

Dp(Wi)

Dp(Wi)

Iv(Wi) or Sv(Wy)

Sv(Wy)Sa(Wy)

Mixed(Ia(Wi),Sa(Wy)

Mixed(Ia(Wi),Sa(Wy)

Iv(Wi) or Sv(Wy)

Social rules e.g. hand raising are used.


R6 - Open conversationR6 - Open conversation

R6: Open conversation among all the participants

• Microphone system in open mode

• MCU on automatic video selection mode– audio mixing – selection of the video stream of the participant who

talks more than two seconds


R7 - Interference of an external personR7 - Interference of an external person

IP

H.323 & T.120 Multipoint

Conference Unit (MCU)

H.323Terminal

H.323/H.320GatewayISDN

H.323Gatekeeper

H.323Terminal

H.323Terminal

H.320Terminal

H.323Terminal

Wz

Wy

WxWi

… just as an another workspaceH.323 Terminal


R8 - Projection of the remote workspace’s signalsR8 - Projection of the remote workspace’s signals

• Permanent display mode on dedicated display device(s)

• Periodic display mode, on the same device(s)

• Instant display mode, on the same device(s)

One remote workspace each time or panorama

R8:R8: Students should be able to attend thereactions and gestures of remote students. This helps in avoiding the sensory deprivation.



Presently, Presently, only periodic or instant display can be implemented

by using the chair-control capability.

Permanent display an be implemented by using other

technology such as MBONE tools in parallel to H.323 terminals.

No simultaneous view of instructor’s video and workspaces’ is

feasible by using H.323 because:•video mixing function is not supported by H.323 MCU•reception and display of multiple video streams is not

supported by H.323 terminals



In future, In future, H.323 products should support this

requirement by enhancing H.323 MCU and

terminal.


Display of Multiple workspaces

Wi

Wx

Wy

Wz

sw

Iv/V(Wi) M

SpeakerMCU

M:=Mixed(Iv(Wi),Sv(W*)-SpeakerM:=Mixed(Iv(Wi),Sv(W*)-Speaker

M

Speaker

Speaker M

Speaker:= Sv(Wy)

mix

MSv(Wx)

Sv(Wi)

Sv(Wz)


Display of single workspace

Wi

Wx

Wy

Wz

sw

Iv/V(Wi) Sel-V

SpeakerMCU

Sel-V: one of Sv(W*)

Sel-V

Speaker

Speaker Sel-V

Speaker:= Sv(Wy)

sw

Sel-V Sv(Wx)

Sv(Wi)

Sv(Wz)


R9 - Projection of the remote classroom on R9 - Projection of the remote classroom on the instructor’s small size monitorthe instructor’s small size monitor

Instructor should attend the remote classrooms in small size monitor(s).

Similar requirement to the previous one (R8)

- MBONE tools

- video mixing @ H.323 MCU


R10 - Lecture broadcastingR10 - Lecture broadcasting

Broadcasting the lecture to a large number of passive participants

H.323 MCUH.323 MCU

Audio & Video multicasting

to passive participants

Active participants

H.323 MCUH.323 MCU

Active participants

BEBE MBONE or commercial product


R11-Session recordingR11-Session recording

A session should be recorded to be available for latter asynchronous access.

• Recording is not supported by H.323 Recom.

• A complementary system should be used, possibly in conjunction with the broadcast system.

H.323 H.323 MCUMCU

Active participants

BE BE + recording+ recording

MBONE or commercial product


R12 - Session managementR12 - Session management

A teleteaching environment should provide a way for:

• session announcement, scheduling and

management.

• Active participants should be invited.

• Passive participants should be able to join.

• Authentication mechanism is optional.

• Statistics for billing and accounting reasons.


Conclusions (1/3)Conclusions (1/3)• Present H.323 products partly fulfil the teleteaching

requirements.• H.323 products should be enhanced.• H.323 MCU:

– stream distribution in multicast (R1,R4,R6)

– disable stream transmission of non participating terminals in processing function(s) in MP@MCU (R4,R6)

– video mixing, transcoding (R8,R9)

– allow video switching of multiple streams (R8,R9)

– enable concurrent video mixing and switching (R8,R9).


Conclusions (2/3)Conclusions (2/3)• H.323 terminals:

– support multicast communication mode (R1,R4, R6)

– be capable of receiving and decoding multiple (at least 2) video streams and displaying them in dual monitor(R8)

– support chair control (only for desktop terminals) (R1,R4,R6)

• Co-operation of H.323 terminals with camera system and microphone system.– Submit and cancel floor requests (R5).


Conclusions (3/3)Conclusions (3/3)OPEN QuestionOPEN Question

How flexible and cost-effective is the deployment

of teleteaching environments based on H.323

products?

in comparison to:

Scalable and composable architectures for

distributed multimedia collaboration such as

Mbone tools.


Thank youThank you

QuestionsQuestions

??

uoa/cnl tnc 2000 potential and limitations of a teleteaching environment based on h.323 audio-visual...

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