Distributed interactive media

In this thesis distributed interactive media are shown to form a class of media that share many important attributes. The key characteristic of media belonging to this class is that they are distributed media which involve direct user interactions with the medium itself. Typical examples of distributed interactive media are shared whiteboards, networked computer games, and distributed virtual environments. In order to prove that the idea of a common media class is valid, an abstract media model for the distributed interactive media class is given. Furthermore, existing distributed interactive media are investigated and it is shown that these are covered by the media model. With the definition of a distributed interactive media class it becomes feasible to create a common foundation for the development of shared functionality that is usable by many or all media belonging to this media class. The development of an application level protocol as such a foundation for common functionality constitutes the key contribution of this thesis. The application level protocol is called “Real-Time Application Level Protocol for Distributed Interactive Media” (RTP/I). It was inspired by the “Real Time Transport Protocol” (RTP), which is commonly used for the transmission of audio and video over the Internet. The design decisions and the specification of RTP/I are discussed in detail. In order to show that RTP/I can indeed serve as a common foundation for shared functionality, three generic and reusable services are presented: a consistency service, a service which supports latecomers who wish to join an ongoing session, and a recording service for distributed interactive media. Moreover, it is discussed how the media model, RTP/I, and the generic services have been used to develop a complex real world application for a distributed interactive medium. This application is known as TeCo3D (3D TeleCooperation). It allows a distributed group of users to view and interact with dynamic 3D models that are specified using the Virtual Reality Modeling Language.