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BOX 1 Summary of Internet Protocol (IP) Suite
Layer Functionality
• Process/Application Layer.
Applications invoke TCP/IP services, sending and receiving messages
or streams with other hosts. Delivery can be intermittent or
continuous.
• Transport Layer. Provides host-host
packetized communication between applications, using either
reliable delivery connection-oriented TCP or unreliable delivery
connectionless UDP. Exchanges packets end to end with other
hosts.
• Internet/Network Layer. Encapsulates
packets with an IP datagram that contains routing information;
receives or ignores incoming datagrams as appropriate from other
hosts. Checks datagram validity, handles network error and control
messages.
• Data Link/Physical Layer. Includes
physical media signaling and lowest level hardware functions;
exchanges network-specific data frames with other devices. Includes
capability to screen multicast packets by port number at the
hardware level.
Methods chosen for transfer of information must use either
reliable connection-oriented transport control protocol (TCP) or
nonguaranteed delivery connectionless user datagram protocol (UDP).
Each of these complementary protocols is part of the transport
layer. One of the two protocols is used as appropriate for the
criticality, timeliness, and cost of imposing reliable delivery on
the particular stream being distributed. Understanding the precise
characteristics of TCP, UDP, and other protocols helps the virtual
world designer understand the strengths and weaknesses of each
network tool employed. Since internetworking considerations affect
all components in a large virtual environment, additional study of
network protocols and applications is highly recommended for
virtual world designers. Suggested references include Internet NIC
(1994), Stallings (1994), and Comer (1991).
Internet Protocol
Although the variety of protocols associated with
internetworking is very diverse, there are some unifying concepts.
Foremost is "IP on everything," or the principle that every
protocol coexists compatibly within the Internet Protocol suite.
The global reach and collective momentum of IP-related protocols
make their use essential and also make incompatible exceptions
relatively uninteresting. IP and IP next generation (IPng)
protocols include a variety of electrical, radio-frequency, and
optical physical media.
Examination of protocol layers helps clarify current network
issues. The lowest layers are reasonably stable with a huge
installed base of Ethernet and fiber distributed data interface
(FDDI) systems, augmented by the rapid development of wireless and
broadband integrated services digital network (ISDN) solutions
(such as asynchronous transfer mode [ATM]). Compatibility with the
IP suite is assumed. The middle transport-related layers are a busy
research and development area. Addition of real-time reliability,
quality of service, and other capabilities can all be made to work.
Middle-layer transport considerations are being resolved by a
variety of working protocols and the competition of intellectual
market forces. From the perspective of the year 2000, lower- and
middle-layer problems are essentially solved.
Distributed Interactive
Simulation
The DIS protocol is an IEEE standard for logical communication
among entities in distributed simulations (IEEE, 1993). Although
initial development was driven by the needs of military users, the
protocol formally specifies the communication of physical
interactions by any type of physical entity and is adaptable for
general use. Information is exchanged via protocol data units
(PDUs), which are defined for a large number of interaction
types.
The principal PDU type is the Entity State PDU. This PDU
encapsulates the position and posture of a given entity at a given
time, along with linear and angular velocities and accelerations.
Special components of an entity (such as the orientation of moving
parts) can also be included in the PDU as articulated parameters. A
full
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set of identifying characteristics uniquely specifies the
originating entity. A variety of dead reckoning algorithms permits
computationally efficient projection of entity posture by listening
hosts. Dozens of additional PDU types are defined for simulation
management, sensor or weapon interaction, signals, radio
communications, collision detection, and logistics support.
Of particular interest to virtual world designers is an open
format Message PDU. Message PDUs enable user-defined extensions to
the DIS standard. Such flexibility coupled with the efficiency of
Internet-wide multicast delivery permits extension of the
object-oriented message-passing paradigm to a distributed system of
essentially unlimited scale. It is reasonable to expect that
free-format DIS Message PDUs might also provide remote distributed
connectivity resembling that of "tuples" to any information site on
the Internet, further extended by use of network pointer mechanisms
that already exist for the World Wide Web. This is a promising area
for future work.
World Wide Web
The World Wide Web (WWW or Web) project has been defined as a
"wide-area hypermedia information retrieval initiative aiming to
give universal access to a large universe of documents" (Hughes,
1994). Fundamentally the Web combines a name space consisting of
any information store available on the Internet with a broad set of
retrieval clients and servers, all of which can be connected by
easily defined HyperText Markup Language (html) hypermedia links.
This globally accessible combination of media, client programs,
servers, and hyperlinks can be conveniently used by humans or
autonomous entities. The Web has fundamentally shifted the nature
of information storage, access, and retrieval (Berners-Lee et al.,
1994). Current Web capabilities are easily used despite rapid
growth and change. Directions for future research related to the
Web are discussed in (Foley and Pitkow, 1994). Nevertheless,
despite tremendous variety and originality, Web-based interactions
are essentially client-server: A user can push on a Web resource
and get a response, but a Web application can't independently push
back at the user.
Multicast
IP multicasting is the transmission of IP datagrams to an
unlimited number of multicast-capable hosts that are connected by
multicast-capable routers. Multicast groups are specified by unique
IP Class D addresses, which are identified by 11102 in the high-order bits and correspond to
Internet addresses 224.0.0.0 through 239.255.255.255. Hosts choose
to join or leave multicast groups and subsequently inform routers
of their membership status. Of great significance is the fact that
individual hosts can control which multicast groups they monitor by
reconfiguring their network interface hardware at the data link
layer. Since datagrams from unsubscribed groups are ignored at the
hardware interface, host computers can solely monitor and process
packets from groups of interest, remaining unburdened by other
network traffic (Comer, 1991; Deering, 1989).
Multicasting has existed for several years on local area
networks such as Ethernet and FDDI. However, with IP multicast
addressing at the network layer, group communication can be
established across the Internet. Since multicast streams are
typically connectionless UDP datagrams, there is no guaranteed
delivery and lost packets stay lost. This best-effort unreliable
delivery behavior is actually desirable when streams are high
bandwidth and frequently recurring, in order to minimize network
congestion and packet collisions. Example multicast streams include
video, graphics, audio, and DIS. The ability of a single multicast
packet to connect with every host on a local area network is good
since it minimizes the overall bandwidth needed for large-scale
communication. Note, however, that the same multicast packet is
ordinarily prevented from crossing network boundaries such as
routers. If a multicast stream that can touch every workstation
were able to jump from network to network without restriction,
topological loops might cause the entire Internet to become
saturated by such streams. Routing controls are necessary to
prevent such a disaster and are provided by the recommended
multicast standard (Deering, 1989) and other experimental
standards. Collectively the resulting internetwork of communicating
multicast networks is called the Multicast Backbone (MBone)
(Macedonia and Brutzman, 1994).
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Improved real-time delivery schemes are also being evaluated
using the real-time transport protocol (RTP), which is eventually
expected to work independently of TCP and UDP (Schulzrinne and
Casner, 1993). Other real-time protocols are also under
development. The end result available today is that even with a
time-critical application such as an audio tool, participants
normally perceive conversations as if they are in ordinary real
time. This behavior is possible because there is actually a small
buffering delay to synchronize and resequence the arriving voice
packets. Research efforts on real-time protocols and numerous
related issues are ongoing, since every bottleneck conquered
results in a new bottleneck revealed.
The MBone community must manage the MBone topology and the
scheduling of multicast sessions to minimize congestion. Currently
over 1,800 subnets are connected worldwide, with a corresponding
host count equivalent to the size of the Internet in 1990. Topology
changes for new nodes are added by consensus: A new site announces
itself to the MBone mail list, and the nearest potential providers
decide who can establish the most logical connection path to
minimize regional Internet loading. Scheduling MBone events is
handled similarly. Special programs are announced in advance on an
electronic mail list and a forms-fed schedule home page. Advance
announcements usually prevent overloaded scheduling of
Internet-wide events and alert potential participants. Cooperation
is key. Newcomers are often surprised to learn that no single
person or authority is "in charge" of either topology changes or
event scheduling.
Software Infrastructure Needs
We believe that the "grand challenges" of computing today are
not large static gridded simulations such as computational fluid
dynamics or finite element modeling. We also believe that
traditional supercomputers are not the most powerful or significant
platforms. Adding hardware and dollars to incrementally improve
existing expensive computer designs is a well-understood exercise.
What is more challenging and potentially more rewarding is the
interconnection of all computers in ways that support global
interaction of people and processes. In this respect, the Internet
is the ultimate supercomputer, the Web is the ultimate database,
and any networked equipment in the world is a potential
input/output device. Large-scale virtual environments attempt to
simultaneously connect many of these computing resources in order
to recreate the functionality of the real world in meaningful ways.
Network software is the key to solving virtual environment grand
challenges.
Four Key Communication Methods
Large-scale virtual world internetworking is possible through
the application of appropriate network protocols. Both bandwidth
and latency must be carefully considered. Distribution of virtual
world components using point-to-point sockets can be used for tight
coupling and real-time response of physics-based models. The DIS
protocol enables efficient live interaction between multiple
entities in multiple virtual worlds. The coordinated use of
hypermedia servers and embedded Web browsers allows virtual worlds
global input/output access to pertinent archived images, papers,
datasets, software, sound clips, text, or any other
computer-storable media. Multicast protocols permit moderately
large real-time bandwidths to be efficiently shared by an
unconstrained number of hosts. Applications developed for multicast
permit open distribution of graphics, video, audio, DIS, and other
streams worldwide in real time. Together these example components
provide the functionality of lightweight messages, network
pointers, heavyweight objects, and real-time streams (Box 2).
Integrating these network tools in virtual worlds produces
realistic, interactive, and interconnected 3D graphics that can be
simultaneously available anywhere (Brutzman, 1994a,b; Macedonia,
1995; Macedonia et al., 1995).
Application Layer Interactivity
It is application layer networking that needs the greatest
attention in preparing for the information infrastructure of the
year 2000. DIS combined with multicast transport provides solutions
for many
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BOX 2 Four Key Communications Components Used
in Virtual Environments
• Lightweight Interactions. Messages
composed of state, event, and control information as used in DIS
Entity State PDUs. Implemented using multicast. Complete message
semantics is included in a single packet encapsulation without
fragmentation. Lightweight interactions are received completely or
not at all.
• Network Pointers. Lightweight
network resource references, multicast to receiving groups. Can be
cached so that repeated queries are answered by group members
instead of servers. Pointers do not contain a complete object as
lightweight interactions do, instead containing only a reference to
an object.
• Heavyweight Objects. Large data
objects requiring reliable connection-oriented transmission.
Typically provided as a WWW query response to a network pointer
request.
• Real-time Streams. Live video,
audio, DIS, 3D graphics images, or other continuous stream traffic
that requires real-time delivery, sequencing, and synchronization.
Implemented using multicast channels.
SOURCE: Macedonia (1995).
application-to-application communications requirements.
Nevertheless DIS is insufficiently broad and not adaptable enough
to meet general virtual environment requirements. To date, most of
the money spent on networked virtual environments has been by, for,
and about the military. Most of the remaining work has been in
(poorly) networked games. Neither is reality. There is a real
danger that specialized high-end military applications and chaotic
low-end game ''hacks" will dominate entity interaction models. Such
a situation might well prevent networked virtual environments from
enjoying the sustainable and compatible exponential growth needed
to keep pace with other cornerstones of the information
infrastructure.
Next-generation DIS
We believe that a successor to DIS is needed that is simpler,
open, extensible, and dynamically modifiable. DIS has proven
capabilities in dealing with position and posture dead reckoning
updates, physically based modeling, hostile entity interactions,
and variable latency over wide-area networks. DIS also has several
difficulties: awkward extendibility, requiring nontrivial
computations to decipher bit patterns, and being a very "big"
standard. DIS protocol development continues through a large and
active standards community. However, the urgent military
requirements driving the DIS standard remain narrower than general
virtual environment networking requirements.
A common theme that runs through all network protocol
development is that realistic testing and evaluation are essential,
because the initial performance of distributed applications never
matches expectations or theory. A next-generation DIS research
project ought to develop a "dial-a-protocol" capability, permitting
dynamic modifications to the DIS specification to be transmitted to
all hosts during an exercise. Such a dynamically adjustable
protocol is a necessity for interactively testing and evaluating
both the global and local efficiency of distributed entity
interactions.
Other Interaction Models
Many other techniques for entity interaction are being
investigated, although not always in relation to virtual
environments. Intelligent agent interactions are an active area of
research being driven by artificial intelligence and user interface
communities. Rule-based agents typically communicate via a
message-passing paradigm that is a natural extension of
object-oriented programming methods. Common Gateway Interface (cgi)
scripts function similarly, usually using hypertext transfer
protocol (http) (Berners-Lee et al., 1994) query extensions as
inputs. Ongoing research by the Linda project uses "tuples" as the
communications unit for logical entity interaction, with particular
emphasis on scaling up (Gelernter, 1992). MUDs (multiuser dungeons)
and MOOs (MUDs object-oriented) provide a powerful server
architecture and text-based interaction paradigm that is
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well suited to support a variety of virtual environment
scenarios (Curtis and Nichols, 1994). Passing scripts and
interpretable source code over the network for automatic client use
has been widely demonstrated for the multiplatform tool control
language (Tcl) (Ousterhout, 1994). Recently the Java language has
provoked interest over the possibility of simple and secure passing
of precompiled program object files for multiplatform execution
(Sun, 1995).
Virtual Reality Modeling Language
The Web is being extended to three spatial dimensions thanks to
virtual reality modeling language (VRML), a specification based on
Silicon Graphics Inc. Open Inventor scene description language
(Wernicke, 1994). Key contributions of the VRML 1.0 standard are a
core set of object-oriented graphics constructs augmented by
hypermedia links, all suitable for scene generation by browsers on
PCs, Macintoshes, and Unix workstations. The current interaction
model for VRML browsers is client-server, similar to most other Web
browsers. Specification development has been effectively
coordinated by mail list, enabling consensus by a large, active,
and open membership (Pesce and Behlendorf, 1994; Pesce and
Behlendorf, 1994–1995; and Bell et al., 1994).
Discussion has already begun on incorporating interaction,
coordination, and entity behaviors into VRML 2.0. A great number of
issues are involved. We expect that in order to scale to
arbitrarily large sizes, peer-to-peer interactions will be possible
in addition to client-server query-response. Although behaviors are
not yet formally specified, the following possible view of
behaviors extends the syntax of existing "engine" functionality in
Open Inventor (Figure 2). Two key points in this representation
follow. First, engine outputs only operate on the virtual scene
graph, and so behaviors do not have any explicit control over the
host machine (unlike CGI scripts). Second, behaviors are engine
drivers, while engines are scene graph interfaces. This means that
a wide variety of behavior mechanisms might stimulate engine
inputs, including Open Inventor sensors and calculators, scripted
actions, message passing, command line parameters, or DIS. Thus it
appears that forthcoming VRML behaviors might simultaneously
provide simplicity, security, scalability, generality, and open
extensions. Finally, we expect that as the demanding bandwidth and
latency requirements of virtual environments begin to be exercised
by VRML, the client-server design assumptions of the HyperText
Transfer Protocol (http) will no longer be valid. A Virtual Reality
Transfer Protocol (vrtp) will be needed once we better understand
how to practically deal with the new dynamic requirements of
diverse interentity virtual environment communications.
Vertical Interoperability
A striking trend in public domain and commercial software tools
for DIS, MBone, and the Web is that they can seamlessly operate on
a variety of software architectures. The hardware side of vertical
interoperability for virtual environments is simple: access to
IP/Internet and the ability to render real-time 3D graphics. The
software side is that information content and even applications can
be found that run equivalently under PC, Macintosh, and a wide
variety of Unix architectures. One important goal for any virtual
environment is that human users, artificial entities, information
streams, and content sources can interoperate over a range that
includes highest-performance machines to least-common-denominator
machines. Here are some success metrics for vertical
interoperability: "Will it run on my supercomputer?" Yes.
"Will it run on my Unix workstation?" Yes. ''Will it also
run on my Macintosh or PC?" Yes. This approach has been
shown to be a practical (and even preferable) software requirement.
Vertical interoperability is typically supported by open
nonproprietary specifications developed by standardization groups
such as the Internet Engineering Task Force (IETF).
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Figure 2
Proposed behavior interaction model for VRML.
Hardware Infrastructure Needs
Research Testbed
The National Research Council report on virtual reality (Durlach
and Mavor, 1995) made few recommendations for funding virtual
environment hardware research due to active commercial development
in most critical technologies. We agree with that assessment.
However, the report also has a notable hardware-related
recommendation regarding networks:
RECOMMENDATION: The committee recommends that
the federal governmentprovide funding for aprogram (to be conducted
with industry and academia in collaboration) aimed atdeveloping
networkstandards that support the requirements for implementing
distributed VEs[virtual environments] on alarge scale. Furthermore,
we recommended funding of an open VE network thatcan be used
byresearchers, at a reasonable cost, to experiment with various VE
networksoftware developments andapplications. (Durlach and Mavor,
1995, p. 83)
The cost of high-speed network connections has precluded most
academic institutions from conducting basic research in
high-performance network applications. Those sites with
high-performance connections are rarely free from the reliability
requirements of day-to-day network operations. A national VE
Network Testbed for academia and industry is proposed as a feasible
collaboration mechanism. If rapid progress is expected before 2000,
it is clearly necessary to decouple experimental network research
from campus electronic mail and other essential services. The
International Wide-Area Year (I-WAY) project is a proposed
experimental national network that is applications-driven and
ATM-based (I-WAY 95). It will connect a number of high-performance
computing centers and supercomputers together. I-WAY may well serve
as a first step in the direction of a national testbed, but
additional efforts will be needed to connect institutions with
lesser research budgets. Finally, it must be noted that design
progress and market competition are bringing the startup costs of
high-speed local
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area networks (e.g., FDDI, ATM) within reach of institutional
budgets. At most schools, it is the off-campus links to the
Internet that need upgrading and funding for sustained use.
Other Problems
In order to achieve broad vertical integration, it is
recommended that proprietary and vendor-specific hardware be
avoided. Videoteleconferencing (VTC) systems are an example of a
market fragmented by competing proprietary specifications. Broad
interoperability and Internet compatibility are essential. Closed
solutions are dead ends. In the area of new network services such
as asynchronous transfer mode (ATM) and integrated services digital
network (ISDN), some disturbing trends are commonplace. Supposedly
standardized protocol implementations often do not work as
advertised, particularly when run between hardware from different
vendors. Effective throughput is often far less than maximum bit
rate. Latency performance is highly touted and rarely tested.
Working applications are difficult to find. Network operating costs
are often hidden or ignored. Application developers are advised to
plan and budget for lengthy delays and costly troubleshooting when
working with these new services.
Applications
We believe that working applications—not theories and not
hype—will drive progress. In this section we present feasible
applications that are exciting possibilities or existing works in
progress. Many new projects are possible and likely to occur by the
year 2000 if virtual environment requirements are adequately
supported in the information infrastructure.
Sports: Live 3D Stadium with
Instrumented Players
Imagine that all of the ballplayers in a sports stadium wear a
small device that senses location (through the Global Positioning
System or local electrical field sensing) and transmits DIS packets
over a wireless network. Similar sensors are embedded in gloves,
balls, bats, and even shoes. A computer server in the stadium feeds
telemetry inputs into a physically based, articulated human model
that extrapolates individual body and limb motions. The server also
maintains a scene database for the stadium complete with textured
images of the edifice, current weather, and representative pictures
of fans in the stands. Meanwhile, Internet users have browsers that
can navigate and view the stadium from any perspective. Users can
also tune to multicast channels providing updated player positions
and postures along with live audio and video. Statistics,
background information, and multimedia home pages are available for
each player. Online fan clubs and electronic mail lists let fans
trade opinions and even send messages to the players. Thus any
number of remote fans might supplement traditional television
coverage with a live interactive computer-generated view. Perhaps
the most surprising aspect of this scenario is that all component
software and hardware technologies exist today.
Military: 100,000-Player Problem
"Exploiting Reality with Multicast Groups" describes
groundbreaking research on increasing the number of active entities
within a virtual environment by several orders of magnitude
(Macedonia, 1995; Macedonia et al., 1995). Multicast addressing and
the DIS protocol are used to logically partition network traffic
according to spatial, temporal, and functionally related entity
classes. "Exploiting Reality" further explains virtual environment
network concepts and includes experimental results. This work has
fundamentally changed the distributed simulation community, showing
that very large numbers of live and simulated networked players in
real-world exercises are feasible.
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Science: Virtual Worlds as
Experimental Laboratories for Robots and People
In separate work, we have shown how an underwater virtual world
can comprehensively model all salient functional characteristics of
the real world for an autonomous underwater vehicle (AUV) in real
time. This virtual world is designed from the perspective of the
robot, enabling realistic AUV evaluation and testing in the
laboratory. Real-time 3D computer graphics are our window into that
virtual world. Visualization of robot interactions within a virtual
world permits sophisticated analyses of robot performance that are
otherwise unavailable. Sonar visualization permits researchers to
accurately "look over the robot's shoulder" or even "see through
the robot's eyes" to intuitively understand sensor-environment
interactions. Theoretical derivation of six-degrees-of-freedom
hydrodynamics equations has provided a general physics-based model
capable of replicating a highly nonlinear (yet experimentally
verifiable) response in real time. Distribution of underwater
virtual world components enables scalability and rapid response.
Networking allows remote access, demonstrated via MBone audio and
video collaboration with researchers at distant locations.
Integrating the World Wide Web allows rapid access to resources
distributed across the Internet. Ongoing work consists primarily of
scaling up the types of interactions, datasets, and live streams
that can be coordinated within the virtual world (Brutzman,
1994a,b).
Interaction: Multiple CAVEs using ATM
and VRML
A CAVE is a type of walk-in synthetic environment that replaces
the four walls of a room with rear-projection screens, all driven
by real-time 3D computer graphics (Cruz-Neira et al., 1993). These
devices can accommodate 10 to 15 people comfortably and render
high-resolution 3D stereo graphics at 15-Hz update rates. The
principal costs of a CAVE are in high-performance graphics
hardware. We wish to demonstrate affordable linked CAVEs for remote
group interaction. The basic idea is to send graphics streams from
a master CAVE through a high-speed, low-latency ATM link to a less
expensive slave CAVE that contains only rear-projection screens.
Automatic generation of VRML scene graphs and simultaneous
replication of state information over standard multicast links will
permit both CAVEs and networked computers to interactively view
results generated in real time by a supercomputer. Our initial
application domain is a gridded virtual environment model of the
oceanographic and biological characteristics of Chesapeake Bay. To
better incorporate networked sensors and agents into this virtual
world, we are also investigating extensions to IP using underwater
acoustics (Reimers and Brutzman, 1995). As a final component, we
are helping establish an ambitious regional education and research
network that connects scientists, students from kindergartens
through universities, libraries, and the general public. Vertically
integrated Web and MBone applications and a common theme of live
networked environmental science are expected to provide many
possible virtual world connections (Brutzman, 1995a,b).
Conclusions
•
Virtual environments are an all-inclusive superset
of NII 2000.
•
Any workable solution must address scaling up to
arbitrarily large sizes.
•
Lower- and middle-network layer problems are
basically solved.
•
Four key communications components are used in
virtual environments:
—
Lightweight entity interactions (e.g., DIS
PDUs);
—
Network pointers (e.g., URLs), usually passed
within a lightweight entity interaction that includes identifying
context;
—
Heavyweight objects (e.g., terrain databases or
large textured scene graphs) which require reliable connections for
accurate retrieval; and
—
Real-time streams (e.g., audio and video), usually
via MBone.
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•
The Virtual Reality Modeling Language (VRML) will
take the Web into three dimensions and make powerful applications
available across platforms that were previously restricted to
expensive graphics workstations.
Recommendations
•
It is the upper network application layers
relating to entity interactions that need funded research work.
•
A Virtual Environment Network Testbed is needed to
enable research schools to cheaply connect and test experimental
services without jeopardizing production networks.
•
Behaviors are needed in VRML that allow 3D
graphics objects to be driven by
—
Internal algorithms (e.g., Open Inventor
sensors),
—
Scripted actions (embedded or live via network
streams),
—
Message passing (by user or agent, e.g.,
MUDs/MOOs),
—
Open extension mechanism (e.g., http attributes),
and
—
DIS (or superior) entity interaction protocol.
•
Virtual Reality Transport Protocol (VRTP) will
soon be needed:
—
Bandwidth, latency, and efficiency requirements
will change relative to the design assumptions of current http
servers;
—
Lightweight objects, heavyweight objects,
multicast real-time streams;
—
Small sets of servers will combine to serve very
large client/peer base.
•
Compelling applications, not protocols, will drive
progress. some examples:
—
Sports: live 3D stadium with instrumented
players; user chooses view;
—
Military: 100,000-player problem;
—
Science: virtual worlds as experimental
laboratories for robots, people; and
—
Interaction: affordable linked CAVEs for
remote group interaction.
Projections
If one considers the evolving nature of the global information
infrastructure, it is clear that there is no shortage of basic
information. Quite the opposite is true. Merely by reading the
New York Times daily, any individual can have more information
about the world than was available to any world leader throughout
most of human history! Multiply that single information stream by
the millions of other information sources becoming openly available
on the Internet, and it is clear that we do not lack
content. Mountains of content have become accessible. What is
needed now is context, a way to interactively locate,
retrieve, and display the related pieces of information and
knowledge that a user needs in a timely manner.
Within two lifetimes we have seen several paradigm shifts in the
ways that people record and exchange information. Handwriting gave
way to typing, and then typing to word processing. It was only a
short while afterwards that preparing text with graphic images was
easily accessible, enabling individuals to perform desktop
publishing. Currently people can use 3D real-time interactive
graphics simulations and dynamic "documents" with multimedia hooks
to record and communicate information. Furthermore such documents
can be directly distributed on demand to anyone connected to the
Internet. In virtual environments we see a further paradigm shift
becoming possible. The long-term potential of virtual environments
is to serve as an archive and interaction medium, combining massive
and dissimilar data sets and data streams of every conceivable
type. Virtual environments will then enable comprehensive and
consistent interaction by humans, robots, and software agents
within those massive data sets, data streams, and models that
recreate reality. Virtual environments can provide meaningful
context to the mountains of content that currently exist in
isolation without roads, links, or order.
What about scaling up? Fortunately there already exists a model
for these growing mountains of information content: the real world.
Virtual worlds can address the context issue by providing
information links similar to those that exist in our understanding
of the real world. When our virtual constructs cumulatively
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approach realistic levels of depth and sophistication, our
understanding of the real world will deepen correspondingly. In
support of this goal, we have shown how the structure and scope of
virtual environment relationships can be dynamically extended using
feasible network communications methods. This efficient
distribution of information will let any remote user or entity in a
virtual environment participate and interact in increasingly
meaningful ways.
Open access to any type of live or archived information resource
is becoming available for everyday use by individuals, programs,
collaborative groups, and even robots. Virtual environments are a
natural way to provide order and context to these massive amounts
of information. Worldwide collaboration works, for both people and
machines. Finally, the network is more than a computer, and
even more than your computer. The Internet becomes
our computer as we learn how to share resources, collaborate,
and interact on a global scale.
References
Bell, Gavin, Anthony Parisi, and Mark
Pesce, "The Virtual Reality Modeling Language (VRML) Version 1.0
Specification," draft,
http://www.eit.com/vrml/vrmlspec.html, November 3, 1994.
Berners-Lee, Tim, Luotonen Cailliau, Ari
Nielsen, Henrik Frystyk, and Arthur Secret, "The World-Wide Web,"
Communications of the ACM, vol. 37, no. 8, August 1994, pp.
76–82.
Brutzman, Donald P., "A Virtual World for
an Autonomous Underwater Vehicle," Visual Proceedings,
Association for Computing Machinery (ACM) Special Interest Group on
Computer Graphics (SIGGRAPH) 94, Orlando, Florida, July
24–29, 1994a, pp. 204–205.
Brutzman, Donald P., A Virtual World
for an Autonomous Underwater Vehicle, Ph.D. Dissertation, Naval
Postgraduate School, Monterey, California, December 1994b.
Brutzman, Donald P., "Remote Collaboration
with Monterey Bay Educators," Visual Proceedings, Association
for Computing Machinery (ACM) Special Interest Group on Computer
Graphics (SIGGRAPH) 95, Los Angeles, California, August
7–11, 1995.
Brutzman, Donald P., "Networked Ocean
Science Research and Education, Monterey Bay, California,"
Proceedings of International Networking (INET) 95 Conference,
Internet Society, Honolulu, Hawaii, June 27–30, 1995.
Available at
ftp://taurus.cs.nps.navy.mil/pub/i3la/i3laisoc.html.
Comer, Douglas E., Internetworking with
TCP/IP, Volume I: Principles, Protocols and Architecture,
second edition, Prentice Hall, Englewood Cliffs, New Jersey,
1991.
Cruz-Neira, Carolina, Jason Leigh, Michael
Papka, Craig Barnes, Steven M. Cohen, Sumit Das, Roger Engelmann,
Randy Hudson, Trina Roy, Lewis Siegel, Christina Vasilakis, Thomas
A. DeFanti, and Daniel J. Sandin, "Scientists in Wonderland: A
Report on Visualization Applications in the CAVE Virtual Reality
Environment," IEEE 1993 Symposium on Research Frontiers in
Virtual Reality, San Jose, California, October 25–26,
1993, pp. 59–66 and CP-3.
Curtis, Pavel, and David A. Nichols, "MUDs
Grow Up: Social Virtual Reality in the Real World," Xerox Palo Alto
Research Center, Palo Alto, California, 1994. Available at
ftp://ftp.parc.xerox.com/pub/MOO/papers/MUDsGrowUp.ps.
Deering, Steve, "Host Extensions for IP
Multicasting," Request for Comments (RFC) 1112,
ftp://ds.internic.net/rfc/rfc1112.txt, August 1989.
Durlach, Nathaniel I., and Anne S. Mavor,
eds., Virtual Reality: Scientific and Technological
Challenges, National Research Council, National Academy Press,
Washington, D.C., 1995.
Foley, Jim, and James Pitkow, eds.,
Research Priorities for the World-Wide Web, National Science
Foundation (NSF) Information, Robotics and Intelligent Systems
Division Workshop, Arlington, Virginia, October 31, 1994. Available
at
http://www.cc.gatech.edu/gvu/nsf-ws/report/Report.html.
Gelernter, David, Mirror World—Or
the Day Software Puts the Universe in a Shoebox … How It
Will Happen and What it Will Mean, Oxford University Press, New
York, 1992.
Hughes, Kevin, "Entering the World-Wide
Web (WWW): A Guide to Cyberspace," Enterprise Integration
Technology Inc., May 1994. Available at
http://www.eit.com/web/www.guide/.
IEEE Standard for Information
Technology—Protocols for Distributed Interactive Simulation
(DIS) Applications, version 2.0, Institute for Simulation and
Training report IST-CR-93-15, University of Central Florida,
Orlando, Florida, May 28, 1993.
Internet Network Information Center (NIC),
Request for Comments (RFC) archive,
ftp://ds.internic.net, 1994.
International Wide-Area Year (I-WAY)
project, 1995, information available at
http://www.iway.org.
OCR for page 122
Page 122
Macedonia, Michael R., and Donald P.
Brutzman, "MBone Provides Audio and Video Across the Internet,"
IEEE COMPUTER, April 1994, pp. 30–36. Available at
ftp://taurus.cs.nps.navy.mil/pub/i3la/mbone.html.
Macedonia, Michael R., A Network
Software Architecture for Large Scale Virtual Environments,
Ph.D. Dissertation, Naval Postgraduate School, Monterey,
California, June 1995.
Macedonia, Michael R., Michael J. Zyda,
David R. Pratt, Donald P. Brutzman, and Paul T. Barham, "Exploiting
Reality with Multicast Groups: A Network Architecture for
Large-Scale Virtual Environments," IEEE Computer Graphics and
Applications, 1995, to appear.
Ousterhout, John K., Tcl and the Tk
Toolkit, Addison-Wesley, Reading, Massachusetts, 1994.
Pesce, Mark, and Brian Behlendorf,
moderators, "Virtual Reality Modeling Language (VRML)," working
group home page, http://www.wired.com.vrml,
1994–1995.
Reimers, Stephen, and Donald P. Brutzman,
"Internet Protocol over Seawater: Towards Interoperable Underwater
Networks," Unmanned Untethered Submersibles Technology 95,
Northeastern University, Nahant, Massachusetts, September
25–27, 1995, to appear.
Schulzrinne, Henning, and Stephen Casner,
"RTP: A Transport Protocol for Real-Time Applications," Audio-Video
Transport Working Group, Internet Engineering Task Force, working
draft, Oct. 20, 1993, available as
ftp://nic.ddn.mil/internet-drafts/draft-ietf-avt-rtp-04.ps.
Stallings, William, Data and Computer
Communications, fourth edition, Macmillan, New York, 1994.
Sun Microsystems Corporation, Java
language home page, 1995, http://java.sun.com/.
Wernicke, Josie, The Inventor Mentor:
Programming Object-Oriented 3D Graphics with Open Inventor™, Release 2, Addison-Wesley
Publishing, Reading, Massachusetts, 1994.
Zyda, Michael J., David R. Pratt, John S.
Falby, Paul T. Barham, Chuck Lombardo, and Kirsten M. Kelleher,
"The Software Required for the Computer Generation of Virtual
Environments," PRESENCE: Teleoperators and Virtual
Environments, vol. 2, no. 2, MIT Press, Cambridge,
Massachusetts, Spring 1993, pp. 130–140.
Author Information
Don Brutzman is a computer scientist working in the
Interdisciplinary Academic Group at the Naval Postgraduate School.
His research interests include underwater robotics, real-time 3D
computer graphics, artificial intelligence, and high-performance
networking. He is a member of the Institute of Electrical and
Electronic Engineers (IEEE), the Association for Computing
Machinery (ACM) Special Interest Group on Computer Graphics
(SIGGRAPH), the American Association for Artificial Intelligence
(AAAI), the Marine Technology Society (MTS), and the Internet
Society (ISOC).
Mike Macedonia is an active duty Army officer and Ph.D.
candidate at the Naval Postgraduate School. He received a M.S.
degree in telecommunications from the University of Pittsburgh and
a B.S. degree from the U.S. Military Academy. His research
interests include multicast data networks, real-time computer
graphics, and large-scale virtual environments. His leadership on
the Joint Electronic Warfare Center and CENTCOM staffs was
instrumental in successfully deploying and integrating advanced
computers, networks, and telecommunications systems during
Operations Desert Shield and Desert Storm.
Mike Zyda is professor of computer science at the Naval
Postgraduate School. His research interests include computer
graphics, virtual world systems, and visual simulation systems. He
is executive editor of the journal PRESENCE: Teleoperators and
Virtual Environments, published by MIT Press. His recent
accomplishments include organizing and serving as general chair for
the 1995 ACM SIGGRAPH Symposium on Interactive 3D Graphics.
Representative terms from entire chapter:
virtual world
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Figure
Correspondence between OSI and IP protocol layer models, and
objects passed between corresponding layers on separate hosts.
These diagrams and definitions are merely an overview but help
illustrate the logical relationship and relative expense of
different network interactions. In general, network operations
consume proportionately more processor cycles at the higher layers.
Minimizing this computational burden is important for minimizing
latency and maintaining virtual world responsiveness.
