in the Proceedings of the 1995 Symposium on Interactive 3D Graphics, 9 - 12 April 1995, Monterey, California.Accepted/Published Conference Pape

Barham, Paul T.

Brutzman, Donald P.

Falby, John

Locke, John

Macedonia, Michael R.

Pratt, David R.

Zyda, Michael J.

Calhoun, Institutional Archive of the Naval Postgraduate School

Calhoun: The NPS Institutional ArchiveFaculty and Researcher Publications Faculty and Researcher Publications1995NPSNET: A Multi-Player 3D VirtualEnvironment Over the InternetMacedonia, Michael R.Macedonia, Michael R., Brutzman, Donald P., Zyda, Michael J., Pratt, David R., Barham, Paulþÿ T . ,   F a l b y ,   J o h n   a n d   L o c k e ,   J o h n    N P S N E T :   A   M u l t i - P l a y e r   3 D   V i r t u a l   E n v i r o n m e n t   O v e r   t h eþÿ I n t e r n e t ,    i n   t h e   P r o c e e d i n g s   o f   t h e   1 9 9 5   S y m p o s i u m   o n   I n t e r a c t i v e   3 D   G r a p h i c s ,   9   -   1 2   A p r i l1995, Monterey, California.http://hdl.handle.net/10945/41582Networked Virtual WorldsThe development of multi-user networked virtual worlds hasbecome a major area of interest to the graphics community. The re-alization of high bandwidth wide area communications, the successof World Wide Web applications such as the National Center forSupercomputing Application’s Mosaic browser, and governmentfunding of Distributed Interactive Simulation (DIS) has fueled thedesire to expand networked virtual worlds beyond local area net-works. However, the Internet has proved a challenging environ-ment for real-time applications such as interactive virtual worldsand multimedia.Our group has been motivated to expand the capabilities of sim-ulations and virtual environments (VEs) by exploiting multicastnetworks to serve medium to large numbers (more than 1,000) ofsimultaneous users. To understand and meet these challenges wehave developed the Naval Postgraduate School Networked VehicleSimulator IV (NPSNET-IV) -- a 3D virtual environment suitablefor multi-player participation over the Internet.Key TechnologiesNPSNET-IV is used for the following research areas:• Dynamic IP Multicast for network group communication tosupport large scale distributed simulation over the Internet.• Wireless (mobile) and remote (Integrated Services Digital Net-work, ISDN, and low-rate analog) communications technolo-gy for VEs.• Human, instrumented figures in VEs for medical and emergen-cy training applications.• Distributed Interactive Simulation protocol development forapplication level communication among independently devel-oped simulators (e.g. legacy aircraft simulators, constructivemodels, and real field instrumented vehicles).• Networked real-time hypermedia within 3D VEs such as videoand audio.• Autonomous players or entities for populating virtual worlds.• Low-cost 3D sound.• Simulation-based design.NPSNET: A MULTI-PLAYER 3D VIRTUAL ENVIRONMENT OVER THEINTERNETMichael R. Macedonia, Donald P. Brutzman, Michael J. Zyda*, David R. Pratt, Paul T. BarhamJohn Falby, John LockeNaval Postgraduate SchoolDepartment of Computer ScienceMonterey, California 93943-5100{zyda,pratt}@cs.nps.navy.milNPSNETNPSNET-IV runs on commercial, off-the-shelf Silicon Graph-ics workstations and employs the Performer graphics library[8].Developed at the Naval Postgraduate School’s (NPS) Departmentof Computer Science in the Graphics and Video Laboratory, thesimulator uses Simulation Network (SIMNET) databases. NPS-NET-IV participants communicate with other virtual environment“players” located across the United States via IP multicast networkprotocols, the IEEE 1278 Distributed Interactive Simulation appli-cation protocol and the Internet Multicast Backbone(MBONE)[4,6].NPSNET-IV is the first DIS application to use the IP Multicastprotocol. IP Multicast, developed by Steve Deering, is an Internetstandard (RFC 1112), and is supported by a variety of operatingsystems including SGI’s Irix and Sun’s Solaris [3].Multicast provides one-to-many and many-to-many deliveryservices for applications such as teleconferencing and distributedsimulation in which there is a need to communicate with severalother hosts simultaneously. For example, a multicast teleconfer-ence allows a host to send voice and video simultaneously to a setof (but not necessarily all) locations. With broadcast, data is sent toall hosts while unicast or point-to-point routes communication be-tween only two hosts.Most distributed VEs have employed some form of broadcast(hardware-based or IP) or point-to-point communications. Howev-er, these schemes are bandwidth inefficient and broadcast, which isused in SIMNET and most DIS implementations, is not suitable forMulticast Group 224.11.22.33Multicast Group 224.11.22.56Player X Player BPlayer CPlayer YPlayer APlayer ZMBONEFigure 1. The MBONE allows different large-scale networkedvirtual environments to exist simultaneously over the Internet.In the Proceedings of the ACM - 1995 Symposium on Interactive 3D Graphics, 9 - 12 April 1995,Monterey, California.internetworks.IP broadcast, which is commonly used in DIS environments,cannot be used over the Internet unless it is encapsulated. It alsoadds an additional burden because it requires that all nodes examinea packet even if the information is not intended for that receivinghost, incurring a major performance penalty for that host because itmust interrupt operations in order to perform this task at the operat-ing system level.Point-to-point communication requires the establishment of aconnection or path from each node to every other node in the net-work for a total of N*(N-1) virtual connections in a group. For ex-ample, with a 1000 member group each individual host would haveto separately address and send 999 identical packets. If a client-server model is used, such as that typically found in networkedgames and multi-user domains (MUDs), the server manages all theconnections and rapidly becomes an input/output bottleneck.Dead-reckoningThe networking technique used in NPSNET-IV, evolved fromSIMNET, and embodied in DIS follows the players and ghosts par-adigm presented in [1][7]. In this paradigm, each object is con-trolled on its own host workstation by a software object called aPlayer. On every other workstation in the network, a version of thePlayer is dynamically modeled as an object called a Ghost.The Ghost objects on each workstation update their own posi-tion each time through the simulation loop, using a dead-reckoningalgorithm. The Player tracks both its actual position and the predict-ed position calculated with dead-reckoning. An updated EntityState Protocol Data Unit is sent out on the network when the twopostures differ by a predetermined error threshold, or when a fixedamount or time has passed since the last update (nominally 5 sec-onds). When the updated posture (location and orientation) and ve-locity vectors are received by the Ghost object, the Ghost’s is cor-rected to the updated values, and resumes dead-reckoning from thisnew posture.This dead-reckoning technique helps in overcoming a majorproblem found in a number of networked simulations -- excessivenetwork utilization. For example, each networked participant play-ing the popular game DOOM generates a packet on every graphicsframe. On an SGI, this translates into 30 packets per second, evenwhen an entity is inactive. This not only wastes bandwidth, it alsooverloads the ability of network devices to process packets. On theother hand, a high performance aircraft in a DIS environment typi-cally produces about 8 packets per second --a dramatic difference.MBONEMBONE is a virtual network that originated from an effort tomulticast audio and video from the Internet Engineering Task Force(IETF) meetings [2]. MBONE today is used by several hundred re-searchers for developing protocols and applications for group com-munication.We have used MBONE to demonstrate the feasibility of IPMulticast for distributed simulations over a wide area network. Inthe past, participation with other sites required prior coordinationfor reserving bandwidth on the Defense Simulations Internet (DSI).DSI, funded by ARPA, is a private line network composed of T-1(1.5 Mbps) links, BBN switches and gateways using the ST-II net-work protocol. It had been necessary to use DSI because ARPAsponsored DIS simulations use IP broadcast - requiring a uniquewide-area bridged network. With the inclusion of IP Multicast in NPSNET-IV, sites con-nected via the MBONE can immediately participate in a simulation.MBONE uses a tool developed by Van Jacobson and Steven Mc-Canne called the Session Directory (SD) to display the advertise-ments by multicast groups. SD is also used for launching multicastapplications like NPSNET-IV and for automatically selecting anunused address for a new group session. Furthermore, we can inte-grate other multicast services such as video with NPSNET-IV. Forexample, participants are able to view each other’s simulation witha video tool, NV, developed by Ron Fredrickson at Xerox Parc [5].AcknowledgmentsWe wish to express our thanks to the Air Force Institute ofTechnology, George Mason University, the Naval Research Labsand all those who participated in the demonstrations of NPSNET-IV.This work would not have been possible without the support ofour research sponsors: USA ARL, DMSO, USA STRICOM, USAHQDA AI Center-Pentagon, USA TRAC, ARPA.ResourcesMany of the references noted below are available via the NPS-NET Research Group’s WWW home page:file://taurus.cs.nps.navy.mil/pub/NPSNET_MOSAIC/npsnet_mosaic.htmlReferences1.Blau, Brian, Hughes, Charles E., Moshell, J. Michael and Lisle,Curtis “Networked Virtual Environments,” Computer Graphics,1992 Symposium on Interactive 3D Graphics (March 1992),pp.157.2.Casner, Steve. “Frequently Asked Questions on the MulticastBackbone”. (6 May 1993). Available at venrera.isi.edu:/mbone/faq.txt.3.Deering, Stephen. Host Extensions for IP Multicasting. RFC1112. (August 1989).4.Institute of Electrical and Electronics Engineers, InternationalStandard, ANSI/IEEE Std 1278-1993, Standard for InformationTechnology, Protocols for Distributed Interactive Simulation,(March 1993).5.Macedonia, Michael R. and Donald P. Brutzman. “MBone Pro-vides Audio and Video Across the Internet”. In IEEE Computer.(April 1994). pp. 30-36.6.Pope, Arthur, BBN Report No. 7102, “The SIMNET Networkand Protocols”, BBN Systems and Technologies, Cambridge, Mas-sachusetts, (July 1989).7.Pratt, David R. “A Software Architecture for the Constructionand Management of Real Time Virtual Environments”. Disserta-tion, Naval Postgraduate School, Monterey, California (June 1993).8.Zyda, Michael J., Pratt, David R., John S. Falby, Chuck Lombar-do, Kelleher, Kristen M. “The Software Required for the ComputerGeneration of Virtual Environments”. In Presence. 2, 2. (Spring1993). pp. 130-140.

NPSNET: A Multi-Player 3D Virtual Environment Over the Internet

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NPSNET: A Multi-Player 3D Virtual Environment Over the Internet

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