Brutzman, D.P., et. al. Internetwork Infrastructure Requirements for Virtual Environments. In Internetwork Infrastructure Requirements for Virtual Environments, pages 13--15, San Diego, CA, December 1995. http://www.stl.nps.navy.mil/#brutzman/vrml/vrml 95.ps.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....Structures To begin with, we consider fundamental connection structures for a virtual world server and its clients. At a rough approximation, they can be categorized into structures that are built on direct server client connection [4, 9] and structures that are built on multicast mechanism [4, 5]. In the first approach, a client receives from the server all necessary update information about the world that arises from other clients. Since many clients communicate directly with the server, the server takes relatively heavy tasks and each client is given a relatively simple work. The ....

Donald P. Brutzman, Michael P. Macedonia, and Michael J. Zyda. Internetwork Infrastructure Requirements For Virtual Environments. In Symposium on the Virtual Reality Modeling Language, pages 95--104, 1995.

....to these VRML models and other extensions to VRML, such as the recommended practices for SQL database access [14] enable the development of DVEs for corporate and business applications. With standard web browsers as an execution engine for DVEs and while new networking protocols are evolving [3,4], the Internet will increasingly become the most common DVE enabler. This paper describes the concept and implementation of a Distributed Virtual Learning Centre as a site in the Internet that will provide educational multimedia material. In particular, in Section 2 we first provide general ....

D. Brutzman, M. Macedonia, M. Zyda. Internetwork Infrastructure Requirements for Virtual Environments, Computer Science Department, Naval Postgraduate School, 1995.

....multiple users can interact with each other [Roe95a] Loe95] The central problem of such systems is how to minimize communication between sites while presenting each participant a consistent view of the virtual environment. Because of the bandwidth constraints of wide area network connections [BMZ95] most systems rely on multicasting schemes where each host sends the state changes it caused to the affected group of other hosts. Locking schemes are used to guarantee a minimum amount of consistency. NPSNET of the American Naval Postgraduate School is a test bed for research and development ....

Donald P. Brutzman, Michael R. Macedonia, and Michael J. Zyda. Internetwork Infrastructure Requirements for Virtual Environments. In NII 2000 Forum of the Computer Science and Telecommunications Board, National Research Council, Washington, D.C., May 1995. ftp://taurus.cs.nps.navy.mil/pub/auv/brutzman/nii 2000.txt.

....Interface (cgi) scripts using HyperText Transfer Protocol (http) queries as inputs may be possible, and the crossplatform Java language is gaining in popularity. Crossplatform Virtual Reality Modeling Language (VRML) 3D scene generation in browsers is another possible direction of future work. [BRUT95] D. FUTURE ADVANCES IN PERSONAL COMPUTER GRAPHICS As was predicted at the start of this project, the performance of PC hardware continues to increase while the price of the hardware continues decreased dramatically. During the course of this project alone, prices of replacement components for the ....

Brutzman, Donald, Macedonia, Michael, R., Zyda, Michael J., "Internetwork Infrastructure Requirements for Virtual Environments," Presented at the VRML Symposium, San Diego California, December 1315 1995, Available at http://www.stl.nps.navy.mil/~brutzman/vrml/vrml95. html, Internet.

....this home network can now be used by different appliances without various expensive hardware based connection points. Today most distributed applications are client server based. The Internet offers an appropriate protocol suite that can be used for unicast and multicast applications [Gerf 95a] BrMZ 95] MaZy 95] However, the offered protocols are not appropriate for new kinds of application, e.g. for broadcast or large scale interactions used for virtual environments. Virtual environments are of arbitrarily large sizes, simultaneously connecting thousands of interacting players and all kinds ....

....environments, there is the potential for the establishment of large scale communication environments, which were mentioned in the previous section. The following examples concentrate on this aspect of extended interactivity and the user role as an active participant. A first example is given by [BrMZ 95] which also covers the integration of different representation levels. Sports live 3D stadium with instrumented players: Imagine that all of the ballplayers in a sports stadium wear a small device which senses location and transmits this information over a wireless network. Similar sensors are ....

Brutzman D.P., Macedonia M.R., Zyda M.J., Internetwork Infrastructure Requirements for Virtual Environments, Proceedings of the Virtual Reality Modeling Language (VRML) Symposium, San Diego Supercomputing Center (SDSC), San Diego, CA, Dec. 1995

....(e.g. into a wall) or it can decide to limit sending the user s message to a subset of other users. These systems scale reasonably well, but are limited by the load that the servers can handle as every piece of user data is sent through the servers. Some systems such as VERN, SIMNET and NPSNET [Mace95b, Brutz] reduce the bandwidth required by using predictive motion. In what is called dead reckoning, users send their initial location, destination and speed to other users. No further updates are sent until the user has reached the destination, hence reducing the number of updates sent by that user. ....

D. P. Brutzman, et. al, Internetwork Infrastructure Requirements for Virtual Environments, Proceedings of the Virtual Reality Modeling Language (VRML) Symposium, San Diego Supercomputer Center (SDSC), San Diego, CA, December 13-15, 1995. http://www.stl.nps.navy.mil/brutzman/vrml/vrml 95.ps

....at the server. Problems can arise, when a large number of participants connect to a single server, since the network, as well as the server load, increases by the square of the number of clients. 4.2. Multicast Approach An approach to realize multi user capabilities for VRML based on multicasting [5][9] was developed at W. Broll, T. Koop VRML: Today and Tomorrow 6 GMD [4] Multicasting provides a flexible and powerful way of distributing data between a large dynamic group of participants. Nevertheless the current multicast protocol is not reliable and many users still do not have ....

Brutzman, Donald P., Macedonia, Michael R., and Zyda, Michael J.: Internetwork Infrastructure Requirements for Virtual Environments. In Proceedings of the VRML'95 Symposium, (San Diego, Ca., Dec. 13-15, 1995) ACM, 1995, 95-104.

....prototype of a shared virtual environment. 2. Network connections Existing networked virtual environments either use unicast or multicast network connections. While unicast connections are based on TCP IP or UDP IP, multicast based solutions use the experimental multicasting IP addresses [11] [6]. TCP IP connections realize a reliable transmission of data. In contrast UDP IP and IP multicast (UDP) are connectionless services. This means, that each packet transmitted might be routed a different way, might get lost or duplicated the transmission is not reliable. The general problem of ....

....the infrastructure to transmit messages reliable, which ensures that all participants receive this event, or each object which might change state, sends its state from time to time over the network. The second approach is used in DIS [13] which is the multicast based protocol used in NPSNET [6] [14] In a general purpose virtual world however, there might be a very large number of objects which somehow could be modified. All these objects would have to transmit their state at least every few seconds, even if sporadically or never modified. This is not feasible due to the already high ....

D. P. Brutzman, M. R. Macedonia, and M. J. Zyda, "Internetwork Infrastructure Requirements for Virtual Environments", Proceedings of the VRML'95 Symposium, ACM, 1995, pp. 95104.

....Interface (cgi) scripts using HyperText Transfer Protocol (http) queries as inputs may be possible, and the crossplatform Java language is gaining in popularity. Crossplatform Virtual Reality Modeling Language (VRML) 3D scene generation in browsers is another possible direction of future work. [BRUT95] D. FUTURE ADVANCES IN PERSONAL COMPUTER GRAPHICS As was predicted at the start of this project, the performance of PC hardware continues to increase while the price of the hardware continues decreased dramatically. During the course of this project alone, prices of replacement components for the ....

Brutzman, Donald, Macedonia, Michael, R., Zyda, Michael J., "Internetwork Infrastructure Requirements for Virtual Environments," Presented at the VRML Symposium, San Diego California, December 1315 1995, Available at http://www.stl.nps.navy.mil/~brutzman/vrml/vrml95. html, Internet.

....would very soon exceed the capacity of a server as well as the network [8] Additionally the delay time would be very high, since all events had to be sent over the network twice. A more reasonable approach for the distribution of messages to a large number of recipients is required. Multicasting [5] [7] has already proven to be very suitable for this task. By sending W.Broll and J.Fechter Interaction and Behavior in Web Based Shared Virtual Environments 5 a message to a multicast group address, it is distributed to all hosts which have connected to the particular group. Since messages ....

Brutzman, Donald P., Macedonia, Michael R., and Zyda, Michael J.: Internetwork Infrastructure Requirements for Virtual Environments. In Proceedings of the VRML'95 Symposium, ACM, 1995, 95-104.

....which smother the network over its capacity. Also, at the lowerperformance platform this plethora of update messages continuously accumulates waiting for being processed, hence makes (Problem 2) worse. As the number of participants increases, this phenomenon results in more degenerate situation[2]. Problem 3 (Large number of update messages) The inefficient message exchange protocol produces large number of messages, and the network with limited bandwidth and long transmission delay, becomes a bottleneck easily. This problem is not confined to low end systems, and has been tackled by ....

M. R. Macedonia D. P. Brutzman and M. J. Zyda. "Internetwork infrastructure requirements for virtual environments". In Proceedings of the Virtual Reality Modeling Language Symposium.

....appliances without various expensive hardware based connection points. Figure 4 Virtual infrastructure [TLGK 95] 11 Today most distributed applications are client server based. The Internet offers an appropriate protocol suite which can be used for unicast and multicast applications [Gerf 95a] BrMZ 95] MaZy 95] However, the offered protocols are not appropriate for new kinds of application, e.g. for broadcast or large scale interactions used for virtual environments. Virtual environments are of arbitrarily large sizes, simultaneously connecting thousands of interacting players and all kinds ....

....environments their is the potential for the establishment of large scale communication environments, which were mentioned in the previous section. The following examples concentrate on this aspect of extended interactivity and the user role as a active participant. A first example is given by [BrMZ 95] which covers the integration of different representation levels, too. Sports live 3D stadium with instrumented players: Imagine that all of the ballplayers in a sports stadium wear a small device which senses location and transmits this information over a wireless network. Similar sensors are ....

Brutzman D.P., Macedonia M.R., Zyda M.J., Internetwork Infrastructure Requirements for Virtual Environments, Proceedings of the Virtual Reality Modeling Language (VRML) Symposium, San Diego Supercomputing Center (SDSC), San Diego, CA, Dec. 1995

....the passing of initial states must be done reliably, but speed is not as important. The type of message (light weight object, network pointer, heavy weight or real time stream) as well as the recipients of the message (multi casting) must be accessible to the programmer as a simple abstraction. BMZ95] MZP 95] If VEs are only to receive pertinent messages, the run time environment must have the logic to decide which entities get which messages. In a simulation such as this example, multi casting is not critical, but if there were a brigade s worth of BIFVs instead of a platoon the Apache ....

Donald P. Brutzman, Micheal Macedonia, and Micheal Zyda. Internetwork Infrastructure Requirements for Virtual Environments. In Proceedings, VRML Symposium, San Diego, CA, December 13-15 1995.

....IP Multicast protocol is neither reliable nor order preserving. Thus packets might get lost, be duplicated or arrive in different orders. The reason is, that multicasting is a connectionless service similar to UDP IP. Several approaches exist to build reliable protocols on top of IP Multicast [14] [8]. Although some of them (e.g. RMP [9] 20] or ISIS HORUS [18] can even provide a total ordering of all messages within a distributed system, they do not fit very well for the task. The reasons are: virtual environments require high interactivity, which can not be provided, if all messages have ....

D. P. Brutzman, M. R. Macedonia, and M. J. Zyda. Internetwork Infrastructure Requirements for Virtual Environments. In Proceedings of the VRML'95 Symposium, ACM, 1995, 95-104.

....minimize communication on network tail links and localize reliability problems. The partitioning may be performed based on spatial, functional, or timing properties, and partitions are mapped to network multicast groups. The communication model for large scale virtual environments proposed in [13, 37] is based on four types of communications: ffl Lightweight interactions (state, event and control PDUs as in DIS, distributed using multicast) ffl Network pointers (references to resources, similar to URL for World Wide Web) ffl Heavyweight objects (objects requiring reliable ....

....yes yes netw. prot. UDP IP IPmc IPmc SRM IPmc (nack) IPmc TCP IP SRM IPmc Table 6: The VEs review summary (networking issues) The inadequacy of existing communication protocols and architectures for distributed multimedia and virtual reality has been recognized and criticized by many researchers [13, 19, 29, 43, 53]. In this area there is a lot of ongoing activities, both in improving the existing protocols, and defining the requirements and proposing for new protocols (such as the virtual reality transfer protocol (vrtp) 12] Another problem is a lack of standards in the area. In 1994, National Research ....

D. P. Brutzman, M. R. Macedonia, and M. J. Zyda. Internetwork infrastructure requirements for virtual environments. In Proceedings of the Virtual Reality Modeling Language Symposium, pages 95--104, San Diego Supercomputing Center, San Diego, CA, Dec. 13-15 1995.

....and artifacts) have to be transmitted to the site of the user to build up the local copy of virtual world. When using regular VRML browsers or Web browser plug ins, this task is realized via HTTPD servers by the existing HTTP protocol. Other approaches as used in distributed virtual environments [Brutzman 95] are based on a limited number of different objects which might populate the virtual world. Thus the object descriptions can be stored within a local database and only the information about the current instances of these objects in the virtual world has to be distributed. However, this approach ....

Brutzman, Donald P., Macedonia, Michael R., and Zyda, Michael J.: Internetwork Infrastructure Requirements for Virtual Environments. In Proceedings of the VRML'95 Symposium, (San Diego, Ca., Dec. 13-15, 1995) ACM, 1995, 95-104.

....number identify a single world. This allows the daemon as well as the participating host, to receive messages from this group and port only. Future extensions might even use several groups or ports for update messages of a single world, in order to support the subdivision of large virtual worlds [Brutzman et al. 95] The multicast address as well as the port number are transmitted to the clients (browsers) as part of the initial world distribution. Avatar Distribution As already mentioned, avatars of users participating at a shared virtual world are added to the world file and distributed by the HTTPD ....

Brutzman, D. P., & Macedonia, M. R., & Zyda, M. J. (1995). Internetwork Infrastructure Requirements for Virtual Environments, VRML'95 Symposium, 1995, ACM SIGGRAPH, 95-104.

....throughout the global Internet and in most private TCP IP networks around the world. However, the Internet community does not intend for this transition to take place precipitously. Rather, it is expected that IPv6 and IPv4 will coexist for years with transition rates driven by user requirements. [13] We intend to take advantage of IPv6 capabilities as they become publicly available, especially regarding router resource reservation, quality of service, mobility and security. Most importantly we will build and deploy vrtp using today s technology (IPv4) while designing with tomorrow s ....

....(MBone) Distributed Interactive Simulation (DIS) and other) behavior protocols, VRML etc. Four minimum and sufficient requirements for LSVE connectivity have already been specified and demonstrated (nonfragmented message passing, URL pointers, heavyweight objects and real time streams) 2][13][14] An efficient combined implementation is needed: vrtp. vrtp is not a transport layer protocol. vrtp refers to transfer, an application layer protocol that includes the services of http in combination with efficient real time functionality provided by multicast. Specification and ....

Brutzman, Donald P., Macedonia, Michael R. and Zyda, Michael J., "Internetwork Infrastructure Requirements for Virtual Environments, " NII 2000 Forum of the Computer Science and Telecommunications Board, National Research Council, Washington DC, May 23-24 1995. Available at ftp://taurus.cs.nps.navy.mil/ pub/auv/brutzman/nii_2000.ps.Z

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Brutzman, D.P., et. al. Internetwork Infrastructure Requirements for Virtual Environments. In Internetwork Infrastructure Requirements for Virtual Environments, pages 13--15, San Diego, CA, December 1995. http://www.stl.nps.navy.mil/#brutzman/vrml/vrml 95.ps.

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Michael R. Macedonia Donald P. Brutzman and Michael J. Zyda. Internetwork infrastructure requirements for virtual environments. Proceedings of the VRML Symposium, San Diego Supercomputer Center (SDSC), San Diego, CA, December 13-15 1995.

No context found.

Brutzman D., Macedonia M., Zyda M. (1995) Internetwork Infrastructure Requirements for Virtual Environments, Computer Science Department, Naval Postgraduate School

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D. Brutzman, M. Macedonia, M. Zyda (1995). Internetwork Infrastructure Requirements for Virtual Environments, Computer Science Department, Naval Postgraduate School.

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BRU95 Brutzman, Donald, Macedonia, Michael and Zyda, Michael, Internetwork Infrastructure Requirements for virtual Environments, submitted to the First VRML Symposium, 1995.

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