Werner Geyer

Intra- and inter-stream synchronisation for stored multimedia streams

Multimedia streams such as audio and video impose tight temporal constraints due to their continuous nature. Often, different multimedia streams must be presented in a synchronized way. We introduce a scheme for the continuous and synchronous delivery of distributed stored multimedia streams across a communications network. We propose a protocol for the synchronized playback, compute the buffer requirement, and describe the experimental results of our implementation. The scheme is very general and does not require bounded jitter or synchronized clocks and is able to cope with clock drifts and server drop outs.

Synchronized delivery and playout of distributed stored multimedia streams

Abstract. Multimedia streams such as audio and video impose tight temporal constraints for their presentation. Often, related multimedia streams, such as audio and video, must be presented in a synchronized way. We introduce a novel scheme to ensure the continuous and synchronous delivery of distributed stored multimedia streams across a communications network. We propose a new protocol for synchronized playback and compute the buffer required to achieve both, the continuity within a single substream and the synchronization between related substreams. The scheme is very general and does not require synchronized clocks. Using a resynchronization protocol based on buffer level control, the scheme is able to cope with server drop-outs and clock drift. The synchronization scheme has been implemented and the paper concludes with our experimental results.

A Model for Collaborative Services in Distributed Learning Environments

Synchronous collaborative work environments, which are mainly based on video-conferencing systems, suffer a lack of human communication channels and social awareness because mostly only audio, video, and joint editing of documents are supported. Collaborative services such as floor control, session control, and telepointers provide additional communication mechanisms to support persons co-working through computers. We propose a collaborative services model (CSM) for distributed learning environments. Our object-oriented approach includes floor and session control mechanisms and policies. Due to the realization of collaborative services as operations on the model, no specific network collaboration protocol is required. We present an optimistic synchronization scheme which provides consistency for the distributed model.

A Secure, Accountable, and Collaborative Whiteboard

This paper addresses the design issues and the security concept of the digital lecture board which is an enhanced whiteboard tailored to the specific needs of collaborative types of work, for instance, in computer-based distance education. The development of the digital lecture board emerged from our experiences with synchronous, computer-based distance education in the TeleTeaching projects of the University of Mannheim. For almost two years, we have been using video conferencing tools for transmitting lectures and seminars. These tools prove to be far from optimal for this purpose since they do not take into account the specific requirements of teaching. Security issues such as authentication, secure key exchange, and fast symmetric encryption are almost completely neglected, even though security is extremely important to allow for confidential, private sessions, and billing.

A Synchronization Scheme for Stored Multimedia Streams

Multimedia streams such as audio and video impose tight temporal constraints due to their continuous nature. Often, different multimedia streams must be played out in a synchronized way. We present a scheme to ensure the continuous and synchronous playout of stored multimedia streams. We propose a protocol for the synchronized playback and we compute the buffer required to achieve both, the continuity within a single substream and the synchronization between related substreams. The scheme is very general because it only makes a single assumption, namely that the jitter is bounded.

The design and the security concept of a collaborative whiteboard

This paper presents the design and the security concept of the digital lecture board, an enhanced whiteboard tailored to the specific needs of collaborative types of work, for instance, in computer-based distance education. The development of the digital lecture board emerged from our experiences with synchronous, computer-based distance education in the TeleTeaching projects of the University of Mannheim. For almost four years, we have been using video conferencing tools for transmitting lectures and seminars. These tools prove to be far from optimal for this purpose since they are not powerful enough to support team work, not flexible enough for the use of media, and somewhat difficult to handle for non-experts. Security issues such as authentication, secure key exchange, and fast symmetric encryption are almost completely neglected, even though security is extremely important to allow for confidential, private sessions, and billing. We discuss shortcomings of existing video conferencing tools and describe features we had in mind while designing the digital lecture board. We then present our security concept that is a user-oriented approach that takes into account the specific security requirements of different user groups. We also cover implementation issues of the current prototype.

How to Make a Digital Whiteboard Secure - Using Java-Cards for Multimedia Applications

In this paper we propose a light-weight, provable secure smart card integration for the OpenPGP secure message format. The basic idea is that the secret keys are stored on a smart card and never leave it. We have integrated this new security approach into an enhanced whiteboard, the digital lecture board (dlb). Existing whiteboards neglect security mechanisms almost completely, even though these mechanisms are extremely important to allow confidential private sessions and billing. The primary application field of our concept are small and closed groups, whereas the smart card serves to testify group membership. Our first implementation supports the JAVA i-Button which provides an additional hardware security.

Project TeleTeaching Mannheim — Heidelberg

The technology needed for teleteaching is widely available today. Interest focuses on the use of multimedia technology and high-speed networks to disseminate course content and work and deepen understanding on the part of the students. The Universities of Mannheim and Heidelberg are engaged in a joint pilot project to develop and test new technologies for teleteaching in a digital network. High-capacity multimedia workstations and PCs are linked via ATM to enable access over the network to lectures, exercises and stored teaching materials. The departments of education and psychology of the two universities are scientifically advising and evaluating the project.

Integrating support for collaboration-unaware VRML models into cooperative applications

We present the design and architecture of the distributed virtual reality service (dvr) which allows collaboration-unaware VRML animations and simulations to be integrated into cooperative applications. The dvr service realizes the distribution of VRML content to a group of participants via multicast. User interactions with the VRML model are synchronized in a manner transparent to the VRML content. To demonstrate the feasibility of our novel approach, we have successfully integrated the distributed virtual reality service into the digital lecture board which is a shared whiteboard tailored to the specific needs of collaborative work, for instance, in the area of computer-based distance education.

New paradigm for the recording of shared whiteboard streams

The number of video conferences conducted over the Internet has constantly increased during the last years. The need to archive the multimedia data streams of the conferences became apparent, and a number of tools accomplishing this task for audio and video streams were developed. In many video conferencing scenarios, shared whiteboards are used in addition to audio and video to transmit slides or to sketch ideas. However, none of the existing recording tools provides an efficient recording service for data streams of these tools. In this paper we present a new approach to the recording and playback of shared whiteboard media streams. We discuss generic design issues of a shared whiteboard recorder, and we present a novel algorithm that enables efficient random access to the recorded streams. We describe an implementation of our algorithms for the media streams of our digital lecture board.