(Download)

The Alliance Access Grid

Michael Grobe, Assistant Director

Academic Computing Services The University of Kansas

[email protected] 2001

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).

The Access Grid is an extension of the Alliance Computational Grid which is a distributed computing environment designed to provide convenient access to high performance computer systems to any network user.

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 sharing

The basic functionality provided within the node is:

•Audio encoding using one or more microphones•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 a presenter located either on-site or at a remote site

•Screen sharing/whiteboard via VNC

The Access Grid will support distributed meetings, collaborative work sessions, seminars, lectures, tutorials and training, scaling from 2 to 20 sites exchanging up to ~80 video streams.

The “design point” is group-to-group communication (thus differentiating it from desktop to desktop based tools that are focused on individual communication).“

The Access Grid includes the notion of a "persistent" video conferencing venue, a conferencing site operating continuously (and comfortably), accessible to a wide audience of users on an ad hoc basis.

Open source and multi-platform software is employed almost exclusively.

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

vic 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.

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.

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.

The Distributed PowerPoint software

The Argonne Distributed PowerPoint software allows a single presenter at one node to control PowerPoint applications running on computer systems located at other Access Grid nodes.

For example, a conference speaker can run PowerPoint along with the Distributed PowerPoint master software on her laptop computer at the podium of one of the AG sites. When the speaker changes slides, the master will notify the DPPT server, which will notify DPPT clients running on systems at other nodes which will, in turn, direct their local PowerPoint programs to change slides.

Note that this approach requires that some PowerPoint features be removed or disabled prior to presentation, because Distributed PowerPoint cannot deal with them. (See later discussions of VNC and "scan conversion" for alternatives.)

The DPPT clients can operate on PowerPoint slidesets published on a Web server, or on local copies of the slidesets.

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.

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.

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.

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.

Virtual Network Computing (VNC)

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.

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.

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

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. (We leave our mics on.)

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.

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).

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.

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

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

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

Software on the video display computer

•Windows 2000

•vic

•PowerPoint

•Argonne Distributed PowerPoint client

•EventServerMonitor and DisplayResourceManager from the Virtual Venue suite

•VNC viewer

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

Alternatives for displaying speaker slidesets

As mentioned earlier, the Access Grid provides several methods for displaying speaker slidesets.

1. use Distributed PowerPoint.

2. use a VNC server running on the Podium laptop and a VNC relay (as discussed earlier).

3. split the Podium laptop video output, send one channel to a local projector for the local audience, and one to a scan converter and then to a video capture card for distribution over vic.

4. use vic modified by Chinese AA University.

5. use a commercial streaming video package.

Ancillary Servers

You may need to run some of the ancillary servers mentioned earlier on separate computer systems. For example, you may need boxes to run a

•Distributed PowerPoint server, •VNC relay server, •MUD, and/or a •Virtual Venue server (should you wish to define your own Virtual Venues).

Operators

You will need from 1 to 4 operators, depending on how you apportion duties, to run an Access Grid node. With one operator per basic function you will need an operator for:

•video display, •video capture, •audio control, and •network monitoring.

To some degree there is a trade-off between system costs and operator costs, and the staffing requirements will vary with the complexity of the presentations being offered at a site. (Telephone backchannels for operators are used for some conferences.)

Experimentation and research

The Access Grid provides a platform for:

1. experimenting with the tools currently included,

2. combining existing tools from other domains and for

3. developing new tools.

Effort is currently going into integrating virtual environments, such as (3D) visualizations, shared immersive collaboration environments (e.g., AGAVE, the Access Grid Augmented Virtual Environment from UIC), etc.

Additional Info

The Access Grid web site:http://www.fp.mcs.anl.gov/fl/accessgrid/

For a more detailed version of this talk see: http://www.cc.ukans.edu/~acs/docs/access-grid-node/

For more information about vic and rat see:

http://www-mice.cs.ucl.ac.uk/multimedia/software/vic http://www-mice.cs.ucl.ac.uk/multimedia/software/rat

Acknowledgments

Some of the material for this web page has been taken from the Argonne Labs web site listed above, or from documents provided via that site.