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Introduction

Potential and Limitations of a Teleteaching Environment based on H.323 Audio-Visual Communication Systems. P. Balaouras, I. Stavrakakis, L. Merakos Communication Networks Laboratory ( CNL ) University of Athens ( UoA ). Introduction. Teleteaching services Networked multimedia applications

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Introduction

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  1. Potential and Limitations of a Teleteaching Environment based on H.323 Audio-Visual Communication Systems. P. Balaouras, I. Stavrakakis, L. Merakos Communication Networks Laboratory (CNL) University of Athens (UoA)

  2. Introduction • 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.

  3. Outline • Introduction • The ITU-T H.323 Recommendations • Capabilities of present H.323 products • Teleteaching Environment • Functional requirements • Conclusions

  4. The 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

  5. H.323 Entities • H.323 terminal • H.323 Multipoint Control Unit end-points • H.323/H.32* Gateway • H.323 Gatekeeper

  6. Defined audio capabilities of H.323 terminals Coding schemes Audio codec(s) Audio mixing G.711 A-law, μ-law G.722, G.723, G.728, G.729, MPEG-1 audio Audio channel(s) multicast H.323 terminal multicast H.323 terminal G.729 G.728 Assymetric operation Green for mandatory features Orange for optional features

  7. Defined visual capabilities of H.323 terminals Coding schemes Video codec(s) Video mixing or switching H.261 QCIF Video channel(s) H.261 CIF, H.263 SQCIF,QCIF, CIF, 4CIF, 16CIF multicast H.323 terminal multicast H.323 terminal QCIF CIF Assymetric operation Green for mandatory features Orange for optional features

  8. Defined data capabilities of H.323 terminals T.120 entity T.120 Data channel(s) H.323 terminal H.323 terminal - One or more data channel(s) - Unidirectional or bi-directional channel(s) Green for mandatory features Orange for optional features

  9. Audio-visual capabilities of H.323 terminals

  10. Capability 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.

  11. H.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

  12. Types of multipoint conferences • Centralized • Decentralized • Hybrid

  13. MP MC MC MC MP MP MP MP Centralized multipoint conferences Audio & Video unicasting Audio & Video unicasting MCU MCU unicast MCU Audio & Video multicasting H.323 terminal

  14. MC MC MC MP MP MP MP Decentralized multipoint conferences Audio & Video Multicasting MCU GW IP - 1 MP @ every H.323 terminal - 1 MC/session @ any H.323 end-point H.323 terminal

  15. MP MP MP MP MC Hybrid multipoint, centralized audio Audio unicasting Video Multicasting MCU IP - 1 MP for video @ every terminal - 1 MC/session @ MCU H.323 terminal

  16. MP MP MP MP MC Hybrid multipoint, centralized video Video unicasting Audio Multicasting MCU IP - 1 MP for audio @ every terminal - 1 MC/session @ MCU H.323 terminal

  17. Characteristics and potential location of MC and MP

  18. MP MC Defined 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 MCU

  19. mix sw MP functions Video/audio switching function Audio/video mixing function Sa Sb Sb Sa Sa Sc Sa Sc Sb MP@MCU MP@MCU Sd Sd Sa Mixed(Sa,Sb,Sc,Sd) Waste of bandwidth

  20. sw trans MP functions Audio/video transcoding function Data distribution function QCIF Da Sb Sa @ QCIF CIF CIF Sa Da Da Sa Sb MP@MCU MP@MCU Sa Da CIF

  21. Control 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

  22. sw Automatic video switching mode Sa Sb Sa Sc Sa Sb MP@MCU Sd Sa The selection mechanism is voice-activated

  23. MP MC CC - Video broadcast (VCB) • To determine which one of the available video streams will be transmitted to all terminals, except chairman’s Sb MCU Sb Sa Chair-control terminal Sc VCB Sb Sd Sb

  24. MP MC CC - Video select (VCS) • To determine which video stream will be transmitted to chairman’s terminal Sb MCU Sc Sa Sc VCS Sc Sd

  25. MP MC CC - Multipoint visualization (MCV) • To broadcast chairman’s terminal video to all participants Sb Sa MCU Sa Sa Sc MCV Sa Sd

  26. MC Floor 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 TIF

  27. 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)

  28. Capabilities of presentH.323 terminals

  29. 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.

  30. Available sources as teaching material Teaching media Input Devices Students’ mic Students’ voice Sa Ia Ma Source analog audio signals Instructor’s voice Instructor’s wireless mic Tape/CD player Music, sounds, recorded courses

  31. Available sources as teaching material Teaching media Input Devices Visual Presenter Real object V Iv Sv Mv Camera for Instructor Instructor Source analog video signals Camera for students Student(s) Video recorded material VCR

  32. Available sources as teaching material Teaching media Input Devices Computer System Still media for presentations and docs Continuous audio and video media digital streams of data, video and audio files Dp Dv Da Appl.Sharing S/W Applications Broadcast application

  33. IP ISDN Required H.323 entities Wx Wi H.323 Terminal H.323 Terminal H.323 & T.120 Multipoint Conference Unit (MCU) H.320 Terminal H.323 Wy Terminal H.323/H.320 Gateway H.323 H.323 Terminal Gatekeeper Wz

  34. Camera for Instructor H.323 terminal(s) Iv Sv H.323 room terminal Camera for Instructor H.323 terminal(s) Camera for students Iv Sv Video matrix Camera for students Number of H.323 terminals • Multiple audio and video streams are to transmitted  multiple H.323 terminals

  35. mix Potential interactions among workspaces Sa(Wx) MixedA Wx Wi Wy sw Sa(Wi) Sa(Wy) Ia(Wi) mixedA MixedA sw MCU mixedA Sa(Wz) Wz Automatic video switching mode

  36. sw Potential interactions among workspaces Sa(Wx) Sel-A Wx Wi Wy sw Sa(Wi) Sa(Wy) Ia(Wi) Sel-A Sel-A sw MCU Sel-A Sa(Wz) Wz Chaircontrolmode

  37. sw Potential interactions among workspaces Sv(Wx) Sel-V Wx Wi Wy sw Sv(Wi) Sv(Wy) Iv/V(Wi) Sel-V* Sel-V mix MCU Sel-V Sv(Wz) Wz 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

  38. sw Potential interactions among workspaces Dp(Wi) Wx Wy sw Dp(Wi) Dp(Wi) Wi mix MCU Dp(Wi) Wz

  39. Sel-V Wx Sv(Wx) Sa(Wx) Dp(Wi) Sel-A sw mix Wy Wi Dp(Wi) Dp(Wi) sw Sel-V Iv/V(Wi) Sv(Wy) Sv(Wi) Sa(Wy) MCU Sa(Wi) Ia(Wi) Sel-A Sel-A Dp(Wi) Sa(Wz) Sel-A Sel-V Sv(Wz) Wz Summary of potential interactions Iv/V(Wi) or /Sv*

  40. Teleteaching functional requirements • 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.

  41. Lecture 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: one way lecture delivery without any interference • Use of terminals and MCU that support chair control feature. • In automatic video switching, interference is possible.

  42. sw Lecture delivery phase requirements Ia(Wi) Iv/V(Wi) Wx Dp(Wi) Wi Dp(Wi) Wy Dp(Wi) Ia(Wi) Ia(Wi) Iv/V(Wi) Iv/V(Wi) Sel-V MCU Ia(Wi) Dp(Wi) Iv/V(Wi) Wz - G.711 audio coding @ 64 kbps - H.263 CIF bite rate > 768 kbps - Terminals and MCU that support chair control.

  43. Lecture delivery phase requirements R2: Presentation of Iv(Wi) and Dp(Wi) in separate display device (i.e., projector) 1 H.323 & T.120, dual monitor PC with dual VGA output card Iv(Wi) Dp(Wi) 1 H.323 1 T.120 Iv(Wi) Dp(Wi) 1 H.323, T.120, PIP

  44. Lecture delivery phase requirements R3: Instructor should be free to move around as in a conventional classrooms • Wireless microphone. • Pan-Tilt-Zoom camera with auto-tracking feature.

  45. R4,R5 - Instructor’s interaction with students R4: Interaction with local or remote students. All participants should be able to listen and watch the speaker. R5: How a student request the floor to ask a question.

  46. sw Chair control Ia(Wi) Iv/V(Wi) Wx Dp(Wi) Wi Dp(Wi) Wy Dp(Wi) Ia(Wi) Ia(Wi) Iv/V(Wi) Iv/V(Wi) MCU Ia(Wi) Dp(Wi) Wz Iv/V(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

  47. sw Chair control Sa(Wy) Sv(Wy) Wx Dp(Wi) Wi Wy Dp(Wi) Dp(Wi) Ia(Wi) Ia(Wi) Iv/V(Wi) Iv/V(Wi) Sa(Wy) Sv(Wy) Sv(Wy) Sa(Wy) MCU Sa(Wy) Dp(Wi) Wz Sv(Wy)

  48. sw Automatic video switching Mixed(Ia(Wi),Sa(Wy) Iv(Wi) or Sv(Wy) Wx Dp(Wi) Wi Wy Dp(Wi) Dp(Wi) Ia(Wi) MixedA Iv/V(Wi) Iv/V(Wi) Sa(Wy) Sv(Wy) Sv(Wy) Sa(Wy) MCU Mixed(Ia(Wi),Sa(Wy) Dp(Wi) Iv(Wi) or Sv(Wy) Wz Social rules e.g. hand raising are used.

  49. R6 - 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

  50. R7 - Interference of an external person … just as an another workspace H.323 Terminal Wx Wi H.323 Terminal H.323 Multipoint H.323 & T.120 Terminal Conference Unit (MCU) H.320 Terminal H.323 Wy IP Terminal H.323/H.320 ISDN Gateway H.323 H.323 Terminal Gatekeeper Wz

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