Consistency in Continuous Distributed Interactive Media

In this paper we investigate how consistency can be ensured for continuous distributed interactive media, i.e. distributed media which change their state in reaction to user initiated operations as well as because of the passing of time. Existing approaches to reach consistency in discrete distributed interactive media are briefly outlined and it is shown that these fail in the continuous domain. In order to allow a thorough discussion of the problem, a formal definition of the term consistency in the continuous domain is given. Based on this definition we show that an important trade off relationship exists between the responsiveness of the medium and the appearance of short term inconsistencies. Currently this trade off is not taken into consideration for consistency in the continuous domain, thereby severely limiting the consistency related fidelity for a large number of applications. We show that for those applications the fidelity can be significantly raised by voluntarily decreasing the responsiveness of the medium. This concept is called local lag and it enables the distribution of continuous interactive media which are more vulnerable to short term inconsistencies than e.g. battlefield simulations. We prove that the concept of local lag is valid by describing how local lag was successfully used to ensure consistency in a 3D telecooperation application

The Recording of Interactive Media Streams Using a Common Framework

The development of real-time transport protocols for the Internet has been a focus ofresearch for several years. Meanwhile, the Real-Time Transport Protocol (RTP) is a well accepted standard that is widely deployed for the transmission of video and audio streams. The RTP specification, combined with a companion RTP profile, covers common aspects of real-time transmissions of video and audio in various encodings. This enabled the development of RTP recorders which record and play back video and audio streams regardless of a specific media encoding. Interactive media streams with real-time characteristics are now gaining importance rapidly. Examples are the data streams of shared whiteboards, remote Java animations and distributed VRML worlds. In this paper we present a generalized recording service that enables the recording and playback of this new class of media. In analogy to video and audio streams we have defined an RTP profile covering common aspects of the interactive media class. We discuss design principles for this recording ser-vice and describe the key mechanisms that allow to randomly access recorded interactive media streams independent of a specific media type and encoding

Access to and Encoding of VRML State Information

In this paper we propose a concept for transparent access of VRML state information. Our approach enhances VRML-browsers to provide additional functionality instead of placing the burden for state access on content developers. The enhanced functionality is realized as an extension to the External Authoring Interface (EAI). Any application which relies on a VRML-browser as 3D presentation engine can use the new EAI functionality to get and set the state of arbitrary VRML content. In order to support diverse applications, the proposed methods not only allow to retrieve the full state of a complete world, but also the state of single objects and state changes. Since the results of state access should be independent of browser implementations, we also specify an encoding for state information. Data in this form is either produced or consumed during state access. For the encoding of state information we use an easy-to-parse and efficient binary encoding

VR-LAB: A Distributed Multi-User Environment for Educational Purposes and Presentations

In the last three years our research was focused on a new distributed multi-user environment. Finally, all components were integrated in a system called the VR-Lab, which will be described on the following pages. The VR-Lab provides Hard- and Software for a distributed presentation system. Elements which are often used in environments called Computer Supported Cooperative Work (CSCW). In contrast to other projects the VR-Lab integrates a distributed system in a common environment of a lecture room and does not generate a virtual conference room in a computer system. Thus, allowing inexperienced persons to use the VR-LAB and benefit from the multimedia tools in their common environment. To build the VR-LAB we developed a lot of hard- and software and integrated it into a lecture room to perform distributed presentations, conferences or teaching. Additionally other software components were developed to be connected to the VR-LAB, control its components, or distribute content between VR-LAB installations. Beside standard software for video and audio transmission, we developed and integrated a distributed 3D-VRML-Browser to present three dimensional content to a distributed audience. One of the interesting features of this browser is the object oriented distributed scene graph. By coupling a high-speed rendering system with a database we could distribute objects to other participants. So the semantic properties of any geometrical or control object can be kept and used by the remote participant. Because of the high compression achieved by the transport of objects instead of triangles a lot of bandwidth could be saved. Also each participant could select a display quality appropriate to its hardware.Diese Arbeit beschreibt ein integriertes Virtual-Reality System, das VR Lab. Das System besteht aus verschiedenen Hard- und Softwarekomponenten die eine verteiltevirtuelle Multi-User Umgebung darstellen die vor allem im Bereich verteilter Präsentationen verwendet werden kann. Im Gegensatz zu anderen Systemen dieser Art, die oft im Bereich des Computer Supported Cooperative Work (CSCW) eingesetzt werden dient unser System nicht dazu eine Präsentationsumgebung im Computer nachzubilden sondern eine reele Umgebung zu schaffen in der verteilte Präsentationen durchgeführt werden können. Dies soll vor allem ungeübten Personen die Arbeit mit verteilten Umgebungen erleichtern. Dazu wurden verschiedene Hard- und Softwarekomponenten entwickelt. Darunter der verteilte 3D Browser MRT-VR, der es ermöglicht 3D Daten an verschiedenen Stellen gleichzeitig zu visualisieren. MRT-VR zeichnet sich insbesondere dadurch aus, daß die 3D Objekte nicht als Polygondaten transportiert werden, sonderen als Objekte und so deren Objekteigenschaften beibehalten werden. Dies spart nicht nur sehr viel Bandbreite bei der Übertragung sondern ermöglicht auch Darstellungen in unterschiedlichen Qualitätsstufen auf den unterschiedlichen Zielrechnern der Teilnehmer. Ein weiterer Teil der Arbeit beschreibt die Entwicklung einer preiswerten imersiven 3D Umgebung um die 3D Daten in ansprechender Qualität zu visualisieren. Alle Komponenten wurden in einer gemeinsamen Umgebung, dem VR-Lab, integriert und mt Steuerungskomponenten versehen

Transparent Access to and Encoding of VRML State Information

In this paper we propose a concept for transparent access to VRML state information. Our approach enhances VRML browsers to provide additional functionality instead of plac-ing the burden for state access on content developers. The enhanced functionality is realized as an extension to the Ex-ternal Authoring Interface (EAI). Any application which re-lies on a VRML browser as the 3D presentation engine can use the new EAI functionality to get and set the state of arbi-trary VRML content. In order to support diverse applica-tions, the proposed methods allow not only retrieval of the full state of a complete world, but also of the state of single objects and state changes. Since the results of state access should be independent of browser implementations, we also specify an encoding for state information. Data in this form are either produced or consumed during state access. For the encoding of state information we use an efficient, easy-to-parse binary encoding

Transparent Access to and Encoding of VRML State Information

Abstract. In this paper we propose a concept for transparent access to VRML state information. Our approach enhances VRML browsers to provide additional functionality instead of placing the burden for state access on content developers. The enhanced functionality is realized as an extension to the External Authoring Interface (EAI). Any application which relies on a VRML browser as the 3D presentation engine can use the new EAI functionality to get and set the state of arbitrary VRML content. In order to support diverse applications, the proposed methods allow not only retrieval of the full state of a complete world, but also of the state of single objects and state changes. Since the results of state access should be independent of browser implementations, we also specify an encoding for state information. Data in this form are either produced or consumed during state access. For the encoding of state information we use an efficient, easy-to-parse binary encoding

Abstract Transparent Access To And Encoding Of VRML State Information

In this paper we propose a concept for transparent access to VRML state information. Our approach enhances VRML browsers to provide additional functionality instead of placing the burden for state access on content developers. The enhanced functionality is realized as an extension to the External Authoring Interface (EAI). Any application which relies on a VRML browser as the 3D presentation engine can use the new EAI functionality to get and set the state of arbitrary VRML content. In order to support diverse applications, the proposed methods allow not only retrieval of the full state of a complete world, but also of the state of single objects and state changes. Since the results of state access should be independent of browser implementations, we also specify an encoding for state information. Data in this form are either produced or consumed during state access. For the encoding of state information we use an efficient, easy-toparse binary encoding