Multi-user Virtual Reality on the Internet
by Wolfgang Broll
The Computer Supported Cooperative Work/CSCW & 3D worlds project
at GMD's Institute for Applied Information Technology focuses on the development
of mechanisms and techniques to support collaborative virtual environments
on the Internet. Main issues are the representation and interaction of
multiple users distributed world-wide and the necessary enabling network
infrastructure. A prototype of a distributed Virtual Reality System and
the scaleable network protocol DWTP (Distributed Worlds Transfer and Communication
Protocol) have been realised by this project.
The realised prototype uses VRML (Virtual Reality Modelling Language)
the standard description language for the transmission of 3D data on the
Internet as a scene description language. The system consists of the multi-user
VRML browser SmallView and a number of daemons. SmallView provides support
for VRML 1.0, VRML 2.0, and extensions for the representation of users
by avatars. Support for communication between distributed users is provided
by integrated audio and text chat facilities. Sophisticated interaction
mechanisms going beyond the VRML standard in order to enable real collaboration
between users are provided. Among those are mechanisms to resolve access
conflicts and to handle multi-user interactions. The prototype system uses
DWTP for network communication.
Distributed Worlds Transfer
DWTP is an application layer protocol similar to HTTP (Hypertext Transfer
Protocol). It provides support for large scale distributed virtual worlds,
independent of the underlying network protocols. It uses various standard
network protocols of the underlying network layers to provide effective
transmission facilities for the various data types used in distributed
virtual environments. The protocol is independent of a particular Virtual
Reality System.
Screenshot of the multi-user VRML browser SmallView.
The supported data types used for communication include: the reliable
transmission of large files for virtual world descriptions between two
peers, the reliable or unreliable transfer of short messages or events
between a large number of participants, and the transfer of stream data
(eg audio). The protocol uses Internet Protocol Multicasting, UDP/IP (Internet
User Datagram Protocol/Internet Protocol) and TCP/IP (Transmission Control
Protocol/Internet Protocol) depending on the data type to transfer and
availability at the local network. The protocol forces a direct connection
between peers by Internet Protocol Multicasting thus not requiring any
central servers. Nevertheless several daemons are required to provide certain
services to the connected participants. These include download services
for new participants as well as mechanisms to make unreliable connections
- such as UDP unicast and multicast - reliable. More information on the
web at: http://orgwis.gmd.de/VR/
Please contact:
Wolfgang Broll - GMD
Tel: +49 2241 14 2715
E-mail: wolfgang.broll@gmd.de
