The shared world of Alive on the Grid consists of the master version of the world database being maintained on one computer, with clients in CAVEs and other VR systems connecting to it and receiving a stream of continuous updates for their local copies of the database. The clients also add data for their users' avatars to the shared database, and use a streaming audio conferencing tool to allow the remote users to talk to one another.
The final, complete world for Alive on the Grid contained 1188 modeled objects, 363 recorded sounds, and many additional textures, captured motions, and other files, for a total of 2.5 gigabytes of data. The scene graph included roughly 1200 dynamic nodes, and created 14000 entries in the shared CAVERNsoft database. Ideally, we would like new clients to be able to join the running world without any preparation, and simply download all the necessary data on the fly. But, given the size of the environment, this was not practical, and instead full copies of the models, sounds, etc. were sent to participating sites in advance.
For the Ars Electronica show, the master program ran on the CAVE Onyx at the Ars Electronica Center in Linz, Austria; participants in Chicago, Buffalo, Bloomington, Umea (Sweden), Budapest, and Amsterdam, as well as an ImmersaDesk at the Center, connected at various times during the week. The Center obtained a special, added 2 megabit per second Internet connection for use during the show. However, the actual measured bandwidth from the Center to the United States was often much less than this, sometimes dropping as low as 200 kilobits/sec. Even at its maximum, this bandwidth was not sufficient to support several simultaneous clients, given the amount of dynamic data in the environment and the streaming audio communication. To get around this limitation, we ran a secondary copy of the shared database on a host at the Electronic Visualization Laboratory in Chicago with much better network connectivity. The master program in Linz linked its database to to this duplicate, and all the outside clients connected to Chicago; those in the U.S. reached it over Internet2, while the European participants came in through STAR TAP, an international networking transit point in Chicago. During the course of the show, the bandwidth used at the Chicago gateway reached roughly 5 megabits/second. Figure 8 outlines the connections that were made.
Figure 8. Network connections for Ars Electronica show