Changyun Wang Under the Supervision of Dr.Turner

Changyun WangChangyun WangUnder the Supervision of Dr.TurnerUnder the Supervision of Dr.Turner

The Access Grid is an Internet-based model for video conferencing developed by the Future

Lab(FL)within the Mathematics and Computer Science (MCS) division of Argonne National

Laboratories(ANL)

DisplayComputer

Video Capture

Computer

Audio Capture

Computer Mixer

EchoCanceller

Network

RGB Video

NTSC Video

Analog Audio

Digital Video

Digital Video

Digital Audio

Shared App,Control

ControlComputer

RS232 Serial

Access Grid Component

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Basic functionality An access Grid “node” is a conference room or small auditorium

provisioned with the equipment to participate in a multipoint video conference.

. Audio

. Video

. Whiteboard

. Screen sharing

. Application

Functionality The basic functionality provided within the node is:

. Audio: encoding using one or more microphones (via a mixer)

. Video: encoding or “capture” using one or more cameras

. Audio presentation using one or more speakers

. Video display via one or more computer monitors and/or

video projection techniques

. Display of PowerPoint “slides” under the control of presenter located either on-site or at a remote site.

. Screen sharing/whiteboard via VNC.

Software components

The Access Grid model revolves around two pieces of software:

•vic: the video conferencing tool, and •rat: the robust audio tool.

and involves several other applications

•Distributed PowerPoint •a MUD •the Multicast Beacon •Virtual Venue •Virtual Network Computing

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Software componentsvic and rat were developed as part of the Internet Multicast backbone, or MBONE, which provided multicast services over the unicast Internet backbone (using "tunnels", or "bridges", between multicast nexus sites).

The Access Grid model relies upon the ability to send and receive Internet Multicast traffic to and from all conference nodes.

An individual vic stream will generate from 10Kbps to 4Mbps of network traffic. A large conference may generate 20Mbps.

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Video Conference(vic)

Vic was developed by Steve McCanne and Van Jacobson at the Lawrence Berkeley Labs. It is intended to link multiple sites with multiple simultaneous video streams over a multicast infrastructure.

vic CAN perform 2 basic functions:

• take data from video capture cards in the PC to which cameras (or other video devices) are attached and send it over the network.

• receive data from the network and display it on a video monitor or on some other attached video device such as a video projector.

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Robust Audio Tool(Rat)

rat is a recent version of the Visual Audio Tool, also developed by Steve McCanne and Van Jacobson at the Lawrence Berkely Labs. rat allows multiple users to engage in a audio conference over the Internet in multicast mode. rat can perform 2 basic functions:

• take data from the sound card in the PC to which microphones, headphones, or some other audio devices are attached and send it over the network.

• receive data from the network and send it to speakers, headphones, or other attached sound processing device, such as a tape recorder, etc.

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The MUD software

Operators at each site involved in an Access Grid conference typically keep in touch by using software originally developed for online "role-playing" games generically called Multi-User dragons and Dungeons" games, or "MUDs". (MUD functionality is similar to that of Inter net Relay Chat operating with access control.)

Argonne runs a MUD server for use by Access Grid operators who run MUD clients on their desktop systems. tkMOO-lite is currently the recommended MUD client for this purpose, but others, such as Tiny-Fugue in the Unix environment can be used as well.

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The Multicast Beacon

To help diagnose multicast network problems during conferences, Argonne promotes the use of the NLANR multicast "Beacon" monitoring system, which includes three pieces of software:

• a Beacon to be run at each AG node, • a server to collect transmission statistics from a collection of

Beacons, and • a Beacon viewer that displays data collected by the server.

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The Virtual Venue software

Coordinating multiple group conferences can be complicated. Argonne has developed a collection of web pages and Java applications that can simplify the process.

The Virtual Venue is basically a web-page that lets users select a "conference" to attend. In this context a "conference" is composed of

• a vic multicast address, • a rat multicast address, and • a MUD identifier.

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The Virtual Venue software

If your systems are Virtual Venue-enabled, the display system operator can click on a conference room name and the vic, rat and MUD applications running on the video display, video capture and audio processing systems will all be started with target addresses and settings appropriate to the selected conference room.

This coordination is accomplished by running an "event server" and the event controller on the display system, along with "event listeners" on the video capture and audio processing systems.

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Virtual Network Computing

• VNC allows users to share monitor screens over the Internet in a variety of modes. In the Access Grid environment, VNC allows a speaker to share his/her podium laptop with Access Grid display systems which can then project it at remote nodes. This is useful when a speaker wishes to give real-time demonstrations or present PowerPoint slides that include "fancy" features, such as animations, that cannot be displayed using Distributed PowerPoint.

• VNC employs a client server architecture, and there are clients and servers available for Windows98/NT/2000 and Unix operating systems.

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Basic system configurations

• The AG model uses a collection of commodity components to provide various services. To assure optimal responsiveness individual functions (video capture, video display, audio capture and presentation) are placed on separate computer systems.

• There is a variety of hardware and software configurations that can provide the required video conferencing functionality.

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Here is one possible configuration:

• 1 computer system running Linux for audio capture and presentation

• 1 computer system running Linux for video capture

• 1 computer running Windows2000 for video display through 1 or more video cards

• 1 audio echo-canceller/mixer (e.g., Gentner AP400)

• 1 computer system running Win98 for controlling the echo-canceller

• 1 speaker's podium computer running Windows2000 or NT to control remote PowerPoint displays and/or give real-time Windows-based demonstrations

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The Gentner AP400 Echo Canceller

• Within the Access Grid model, signals from and to attached audio equipment are funneled through an "echo canceller" made by the Gentner Communications Corporation, to eliminate certain kinds of echoes produced during networked conferencing.

• It is probably fair to say that the Gentner echo canceller is the major component of the audio conferencing system Networks of Gentners work together to provide useful audio signal exchanges.

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The Gentners can use 3 different connectivity infrastructures:

•a point-to-point telephone connection,

•a telephone connection to a telephone bridge (used as a backup during some conferences),

•a computer network, or

•Gentner's own local area network, called G-link.

When a Gentner uses a computer network to connect to other Gentners, it connects to the computer just as it would to a simple Codec (compression/decompression device).

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Echo Canceller control computer

• The audio control computer runs Windows 98 and uses custom Genter Control Software to control the Gentner mixer/echo canceller. See http://www.gentner.com for more details.

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Audio capture and presentation computer

The audio capture computer:• Converts analog audio from mixers and mics to digital form for

transmission by rat over the multicast network • Converts digital audio to analog audio for distribution to room

speakers and/or headsets .

Software • RedHat Linux version 7.n • rat • AudioResourceManager from the Virtual Venue suite

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Video capture computer

The video capture computer system converts analog video from cameras and/or VCRs, etc. to digital for transmission by vic over the multicast network.

Software • RedHat Linux version 7.n• Stock kernel with the BTTV drivers • vic • VideoResourceMonitor from the Virtual Venue suite

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Video display computer

Receives video content over the network and displays it on the PC monitor as well as one or more other monitors and/or video projectors if desirable (using the ability of Win2K to display its console screen across multiple video cards)

• Decodes Video streams • Runs collaboration applications such as Distributed PowerPoint

and the VNC viewer

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Software on the video computer

. Windows 2000

• vic

• PowerPoint

• Argonne Distributed PowerPoint client

• EventServerMonitor and DisplayResourceManager from the Virtual Venue suite

• VNC viewer

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Speaker’s podium computer

The speaker's podium computer runs:

• Windows98/NT/2000 • PowerPoint • the Argonne Distributed PowerPoint master software, and the • VNC server

Configuration suggested by Argonne: Some laptop powerful enough to run PowerPoint

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References

www.cc.ku.edu/acs/docs/access-grid-node/access-grid-ku.html http://www.osc.edu/accessgriddoc/room/roomconfig.html http://mrccs.man.ac.uk/global_supercomputing/hardware.html