- 1. An Instantaneous Introduction to theAlliance Access
GridMichael Grobe Assistant DirectorAcademic Computing ServicesThe
University of KansasSeptember 2000
2. 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. 3.
- As described on the Access Grid web site:
- "The Access Grid is the ensemble of resources that can be used
to support human interaction across the grid. It consists of:
-
- multimedia display, presentation and interaction
environments,
-
- interfaces to grid middleware,
-
- interfaces to visualization environments
4. The Access Grid will support large-scale distributed
meetings, collaborative work sessions, seminars, lectures,
tutorials and training. The Access Grid 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 accessible to a wide audience of users
on an ad hoc basis 5.
- An AccessGrid "node" will be a small conference room or
auditorium, provisioned with the equipment to participate in a
multipoint video conference. 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.
6. To achieve this functionality the Access Grid model relies
upon the ability to send and receive Internet Multicast traffic to
and from all conference nodes.The Access Grid is based on software
(vic and rat) 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). 7.
- 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
-
- Virtual Network Computing
8.
- 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.
9. Note that vic may be run in such a way that it only receives
video transmissions or only sends transmissions; it is not required
to do both at the same time.For more information about vic see:
http://www-mice.cs.ucl.ac.uk/multimedia/software/vic 10.
- 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.
11. rat displays a list of connected participants and identifies
who is speaking and who is listening at any given time.For more
information about rat seehttp://www-mice. cs . ucl .ac. uk
/multimedia/software/rat and the Access Grid web site. 12. 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 theGentnerCommunications 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. 13.
- The Gentners can use 3 different connectivity
infrastructures:
-
- a point-to-point telephone connection,
-
- a telephone connection to a telephone bridge,
-
- 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).
14. 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. 15. 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. 16.
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. tkMOO will run on both Windows and Linux systems,
so it may be be run on any of the AG component systems described
below. 17.
- 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.
18. The Beacon at each node connects to a Multicast group and
collects latency, loss, and packet misordering statistics from all
other beacons connected to that Multicast group and sends them to
the Beacon server. The Beacon viewer displays these traffic
statistics as a matrix showing traffic to and from each Beacon
attached to the server. (There is also a web-based Beacon.)At KU
the Beacon is running on the AG node's video capture system.
19.
- 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 rat multicast address, and
20. 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. 21. 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. 22.
Although not part of the original Access Grid canon, VNC has been
employed during several Access Grid conferences, and shows promise
for future applications. VNC eliminates the coordination effort
required to display Distributed PowerPoint slide sets. (No files
need to be downloaded ahead of time and no slide synchronization is
required.)In general, update times are a function of the number of
pixels changed and the number of remote viewers (as well as avaible
bandwidth), so VNC will not be appropriate for all
applications.Instructions for setting up a VNC relay, are presented
in Using Unix-based VNC to relay other VNC traffic . 23. 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:
24.
- This section shows one such configuration:
-
- 1 computer system running Linux for audio capture and
presentation
-
- 1 computer system running Linux for video capture
-
- 1 computer running Windows2000 video display through 1 or more
video cards controlling one or more video projectors illuminating 1
or more screens.
-
- 1 computer system running Win98 for controlling the audio
echo-canceller/mixer
-
- 1 speaker's podium computer running Windows2000 or NT to
control remote PowerPoint displays and/or give real-time
demonstrations using some Windows application
25.
- 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 .
-
- AudioResourceManager from the Virtual Venue suite
26.
- The video capture computer system converts analog video from
cameras and/or VCRs, etc. to digital for transmission by vic over
the multicast network.
-
- Stock kernel with the BTTV drivers
-
- VideoResourceMonitor from the Virtual Venue suite
27.
- 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)
-
- Runs collaboration applications such as Distributed PowerPoint
and the VNC viewer
28.
-
- Argonne Distributed PowerPoint client
-
- EventServerMonitor and DisplayResourceManager from the Virtual
Venue suite
29. 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.comfor
more details. Within the KU ACS node, this function is provided by
a 133MHz PC. 30.
- Speaker's podium computer
- The speaker's podium computer runs:
-
- the Argonne Distributed PowerPoint master software, and
the
- Configuration suggested by Argonne: Some laptop powerful enough
to run PowerPoint
31. The KU ACS Podium laptop is connected to a "scan converter"
that can convert the VGA/SVGA signal generated by the laptop to
NTSC video expected by video capture cards. The CORIOscan Select
from TVONE is lists for around $495, and can be used to produce a
reasonably high-resolution image (1280x860). 32.
- Alternatives for displaying speaker slidesets
- As mentioned earlier, the Access Grid provides several methods
for displaying speaker slidesets.
-
- use Distributed PowerPoint.
-
- This is the "standard" method and provides high quality
representation at every site with very little network traffic.
Using DPPT means getting each slide set prior to use, stripping it
of special PPT features and publishing it on a Web server for
distribution to each remote site.This approach may not work well if
the speaker relies on special features (such as fancy animations)
or launches other applications during the talk.
33.
-
- use a VNC server running on the Podium laptop and a VNC relay
(as discussed earlier).
This approach provides high quality video including simple
animations and all PowerPoint features, but introduces some update
delay, and generates much more network traffic than the other
alternatives. (If a version of VNC were produced to employ
Multicast for image distribution network traffic would be
significantly reduced.) 34.
-
- 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 from the
video capture machine.
-
- This will give excellent update speed both locally and
remotely, but relatively poor image quality at remote sites. Text
smaller than 20 points is usually not legible, but animations and
videos present well (as long as high resolution is not necessary).
This approach could be a very effective, general solution IF vic
could be used with a higher quality codec than the usual H.261. An
MPEG-1 codecs is apparently under development and should provide a
significant improvement.
35.
-
- use commercial streaming video package.
-
- For example, during the Kansas issue of Alliance Chautauqua
2000, Cisco IPTV was employed to present full-motion animations at
high resolution. However, setting up for IPTV broadcasts is complex
and requires access to an IPTV server, so this alternative will not
be available to all.
36.
- 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,
-
- Virtual Venue server (should you wish to define your own
Virtual Venues).
37.
- 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:
- 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.
38. 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/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.
