Overview
In May of 1992, we successfully submitted
a proposal for a communications
infrastructure for our Science and
Technology Center. In our proposal we specified a telecommunications system
which would allow video, audio, graphics, and data to be transmitted
bidirectionally between Center sites. We installed this system in the Fall of
1992 and have been using it continuously since January 1993.
The system network is based on dedicated
T1 lines, leased from MCI which transmit information at a rate of 1.5
Mbits/second. The network is hubbed at the
We have developed several software
applications to facilitate using the network and to enhance its functionality.
The VCC is a distributed client- server
application with a graphical user interface that allows users at all sites to
dynamically control and configure the videoconferencing network. We have also
developed a set of video widgets which provide
graphical interfaces to video cameras, tape transports, and signal routing
equipment.
One of the unique features of our multimedia network is its ability to simultaneously
transmit compressed video and digital data over the same low latency, fixed
bandwidth link. The links have sufficient bandwidth to remotely control
software programs and demonstrations in conjunction with the live video. The
ability to transmit data, graphics, and video over our dedicated network will
enable us to profile the network traffic; to study methods for appropriately
allocating bandwidth; and to develop tools to allow interactive steering of
scientific simulations.
This communications environment has
proved extremely useful thus far, and has enabled research collaborations and
the sharing of unique, site-specific resources such as the NC machining
laboratory at
Software Projects
Videoconference
Control Software (VCC): A
suite of software tools has been developed to provide simple but powerful
control of videoconferencing functions on our digital multimedia network. The
Videoconference Control Software (VCC) gives workstation users both graphical
and command-line control of videoconference configuration and scheduling from
anywhere within the Center. One application supports on-the-fly control of the
network for spontaneous interactions, another provides comprehensive
calendar-based conference scheduling, a third monitors and controls the
videoconferencing coder-decoders. The system supports up to three simultaneous
conferences on the network. Any of the conferences may be encrypted for greater
security. Motif-based graphical interfaces provide Center-wide information on
the status of the network.
Video
Widgets: We’ve developed
software tools to support end-user control of video devices on our digital
multimedia network. These tools provide close integration of graphics
workstation platforms with video production and videoconferencing environments.
Standard hardware provides for direct serial control of video signal switching,
video tape transports, robotic cameras, and conferencing equipment. The
software system provides command-line and graphical user interfaces to the
video devices, and incorporates an extensible scripting system for coordinated
control of multiple devices. The software is UNIX-based, following a
client-server model and uses Motif as the graphical interface toolkit. This
standards-compliant implementation allows remote control of any of our video
devices from graphics workstations anywhere on the Internet. It also allows
groups with similar commercially available hardware to immediately make use of
the software tools and applications.
Low-latency
Data Network Control: A
separate software system is being developed to monitor and control data
communications on our digital multimedia network. The system provides
Center-wide access to specialized instrumentation, computational resources, and
visualization systems at individual Center sites. The system ensures the
security and reliability of data connections by allocating network bandwidth on
an application-specific basis. The system’s support for the combination of
low-latency, guaranteed-bandwidth data transmission and high quality video
feedback provides a unique resource for studying a number of important research
problems including: time-critical visualization; bandwidth-latency tradeoffs in
remote interactive systems; image compression technologies for synthetic images,
and collaborative research tools.
Future Research Plans
Our long-range goal is to develop
high-quality multimedia networking systems to support interactive visualization
and collaboration at-a-distance. This kind of infrastructure must be developed
if scientific collaboratories are to become a reality. Multimedia networking is
a nascent field, so little is known about what the requirements of such systems
will be either at the network or the applications level. We propose to develop
prototype systems and study their behavior to develop hardware and software
strategies to support the needs of the research collaboratory.
At the network level much work needs to
be done on profiling the transmission characteristics of different media
(video/audio/graphics/data), to develop appropriate protocols for allocating
network bandwidth. Both packet-switched and circuit-switched approaches to
multimedia networking need to be evaluated. The different character of
local-area and wide-area networks needs to be taken into account in the design
of multimedia network systems. Appropriate strategies and protocols also need
to be developed for networks of varying bandwidth, from ISDN through Gigabit
speeds, to accommodate the different properties of the network substrate, and provide
the best service possible at any level and in heterogeneous networks.
At the applications level we need to
better understand the computational, storage, and transmission requirements of
visualization and collaboration applications. Given the "information
explosion" we see in the traditional graphics pipeline, careful thought
needs to be given to the issue of where to place the network in the pipeline.
The answer to this question is likely to vary for different classes of
applications. Support for time-critical multimedia applications is another
natural focus for research in this area.
The following is a list of specific
research investigations for the next five years.
Multimedia networking on the desktop: We are extending the functionality of our STC
network to the workstation desktop using a/v digitizing hardware, high-speed
local area networks, and software codecs. We plan to investigate the
performance differences between local area and wide area multimedia networks
and its impact on the design of interactive visualization at-a-distance
applications.
Heterogeneous multimedia networks: We are investigating ways to extend the reach of
our STC network to include a larger segment of the graphics community. We have
already successfully experimented with interfacing our system to the Internet
Multicast Backbone (MBONE). The performance of this hybrid system is limited by
the restricted bandwidth of the Internet. We would like to collaborate with
developers of the gigabit testbed networks to investigate how to extend the
functionality of our system to high-speed networks in anticipation of their
widespread deployment. The high-quality visualization applications we are
developing in our Center would provide a unique and important test of the
capabilities of the testbeds, and one that will be particularly relevant to the
requirements of scientific collaboratories.
Profiling multimedia networks: The amount of information transmitted across a
network in the course of remotely steering a scientific simulation can be vast.
Intelligent use of compression, and appropriate allocation of the modeling,
rendering, and interaction components of a simulation to local and remote
machines can greatly reduce this network load, but the load statistics of these
kinds of visualization applications are not known. We plan to conduct tests to
profile the characteristics of different media on local and wide-area networks
(video/audio/graphics/data), to develop strategies for allocating network
bandwidth to support interactive visualization at-a-distance. We will also look
at the relationships between network bandwidth, latency, and variability to
determine how to best support the demands of visualization and collaboration
applications.
Time-critical vizualization
at-a-distance: Regardless of
improvements in the technology, visualization applications will continue to
outstrip the capacity of processing, storage, and transmission systems. We plan
to develop methods to support both guaranteed quality-of-service as well as
graceful degradation in time-critical visualization applications. We will
develop methods for predicting the moment-to-moment computational demands of a
simulation to allow adaptive allocation of resources, and will conduct
experiments to develop a perceptual model which will allow us to maximize the
visual quality and interactive responsiveness of a simulation at different
levels of service.
Rendering to compressed image streams:
There is currently a great deal
of wasted overhead in rendering synthetic images sequences for dissemination
via compressed digital media (MPEG, H.261, etc.). The images are first rendered
to bitmaps and then the bitmaps are compressed for transmission. We propose to
exploit symmetries in the rendering and compression processes to greatly reduce
the computational demands of creating such compressed image streams by
completely bypassing the bitmap generation stage. This approach should greatly
facilitate generating real-time synthetic image sequences for transmission over
multimedia networks. We also plan to exploit the perceptually-based economizing
used in compression algorithms to develop a new generation of efficient
rendering algorithms.
Technical Reports
Video
Widgets (PDF 185Kb)
Videoconference
Control Software (VCC) (PDF 125Kb)
Digital Media Network (PDF 95Kb)