Notes on the use of RTP for shared workspace applications

The Real-time Transport Protocol, RTP, has become the dominant protocol for streaming audio and video in IP-based environments. A number of proposals have been made which attempt to build on this success and apply RTP for shared workspace applications. We discuss the needs of such applications and the features provided by RTP, with an aim to showing why RTP is not appropriate for such uses

Assessing the quality of audio and video components in desktop multimedia conferencing

This thesis seeks to address the HCI (Human-Computer Interaction) research problem of how to establish the level of audio and video quality that end users require to successfully perform tasks via networked desktop videoconferencing. There are currently no established HCI methods of assessing the perceived quality of audio and video delivered in desktop videoconferencing. The transport of real-time speech and video information across new digital networks causes novel and different degradations, problems and issues to those common in the traditional telecommunications areas (telephone and television). Traditional assessment methods involve the use of very short test samples, are traditionally conducted outside a task-based environment, and focus on whether a degradation is noticed or not. But these methods cannot help establish what audio-visual quality is required by users to perform tasks successfully with the minimum of user cost, in interactive conferencing environments. This thesis addresses this research gap by investigating and developing a battery of assessment methods for networked videoconferencing, suitable for use in both field trials and laboratory-based studies. The development and use of these new methods helps identify the most critical variables (and levels of these variables) that affect perceived quality, and means by which network designers and HCI practitioners can address these problems are suggested. The output of the thesis therefore contributes both methodological (i.e. new rating scales and data-gathering methods) and substantive (i.e. explicit knowledge about quality requirements for certain tasks) knowledge to the HCI and networking research communities on the subjective quality requirements of real-time interaction in networked videoconferencing environments. Exploratory research is carried out through an interleaved series of field trials and controlled studies, advancing substantive and methodological knowledge in an incremental fashion. Initial studies use the ITU-recommended assessment methods, but these are found to be unsuitable for assessing networked speech and video quality for a number of reasons. Therefore later studies investigate and establish a novel polar rating scale, which can be used both as a static rating scale and as a dynamic continuous slider. These and further developments of the methods in future lab- based and real conferencing environments will enable subjective quality requirements and guidelines for different videoconferencing tasks to be established

DIVE on the internet

This dissertation reports research and development of a platform for Collaborative Virtual Environments (CVEs). It has particularly focused on two major challenges: supporting the rapid development of scalable applications and easing their deployment on the Internet. This work employs a research method based on prototyping and refinement and promotes the use of this method for application development. A number of the solutions herein are in line with other CVE systems. One of the strengths of this work consists in a global approach to the issues raised by CVEs and the recognition that such complex problems are best tackled using a multi-disciplinary approach that understands both user and system requirements. CVE application deployment is aided by an overlay network that is able to complement any IP multicast infrastructure in place. Apart from complementing a weakly deployed worldwide multicast, this infrastructure provides for a certain degree of introspection, remote controlling and visualisation. As such, it forms an important aid in assessing the scalability of running applications. This scalability is further facilitated by specialised object distribution algorithms and an open framework for the implementation of novel partitioning techniques. CVE application development is eased by a scripting language, which enables rapid development and favours experimentation. This scripting language interfaces many aspects of the system and enables the prototyping of distribution-related components as well as user interfaces. It is the key construct of a distributed environment to which components, written in different languages, connect and onto which they operate in a network abstracted manner. The solutions proposed are exemplified and strengthened by three collaborative applications. The Dive room system is a virtual environment modelled after the room metaphor and supporting asynchronous and synchronous cooperative work. WebPath is a companion application to a Web browser that seeks to make the current history of page visits more visible and usable. Finally, the London travel demonstrator supports travellers by providing an environment where they can explore the city, utilise group collaboration facilities, rehearse particular journeys and access tourist information data

Multimedia data capture with multicast dissemination for online distance learning

Distance Learning Environments (DLEs) are elusive to define, difficult to successfully implement and costly due to their proprietary nature. With few open-source solutions, organizations are forced to invest large amounts of their resources in the procurement and support of proprietary products. Once an organization has chosen a particular solution, it becomes prohibitively expensive to choose another path later in the development process. The resolution to these challenges is realized in the use of open-standards, non-proprietary solutions. This thesis explores the multiple definitions of DLEs, defines metrics of successful implementation and develops open-source solutions for the delivery of multimedia in the Distance Learning Environment. Through the use of the Java Media Framework API, multiple tools are created to increase the transmission, capture and availability of multimedia content. Development of this technology, through the use of case studies, leaves a legacy of lectures and knowledge on the Internet to entertain and enlighten future generations.http://archive.org/details/multimedidatcapt109456185US Navy (USN) autho

End-to-end security in active networks

Active network solutions have been proposed to many of the problems caused by the increasing heterogeneity of the Internet. These ystems allow nodes within the network to process data passing through in several ways. Allowing code from various sources to run on routers introduces numerous security concerns that have been addressed by research into safe languages, restricted execution environments, and other related areas. But little attention has been paid to an even more critical question: the effect on end-to-end security of active flow manipulation. This thesis first examines the threat model implicit in active networks. It develops a framework of security protocols in use at various layers of the networking stack, and their utility to multimedia transport and flow processing, and asks if it is reasonable to give active routers access to the plaintext of these flows. After considering the various security problem introduced, such as vulnerability to attacks on intermediaries or coercion, it concludes not. We then ask if active network systems can be built that maintain end-to-end security without seriously degrading the functionality they provide. We describe the design and analysis of three such protocols: a distributed packet filtering system that can be used to adjust multimedia bandwidth requirements and defend against denial-of-service attacks; an efficient composition of link and transport-layer reliability mechanisms that increases the performance of TCP over lossy wireless links; and a distributed watermarking servicethat can efficiently deliver media flows marked with the identity of their recipients. In all three cases, similar functionality is provided to designs that do not maintain end-to-end security. Finally, we reconsider traditional end-to-end arguments in both networking and security, and show that they have continuing importance for Internet design. Our watermarking work adds the concept of splitting trust throughout a network to that model; we suggest further applications of this idea

Consistency Algorithms and Protocols for Distributed Interactive Applications

The Internet has a major impact not only on how people retrieve information but also on how they communicate. Distributed interactive applications support the communication and collaboration of people through the sharing and manipulation of rich multimedia content via the Internet. Aside from shared text editors, meeting support systems, and distributed virtual environments, shared whiteboards are a prominent example of distributed interactive applications. They allow the presentation and joint editing of documents in video conferencing scenarios. The design of such a shared whiteboard application, the multimedia lecture board (mlb), is a main contribution of this thesis. Like many other distributed interactive applications, the mlb has a replicated architecture where each user runs an instance of the application. This has the distinct advantage that the application can be deployed in a lightweight fashion, without relying on a supporting server infrastructure. But at the same time, this peer-to-peer architecture raises a number of challenging problems: First, application data needs to be distributed among all instances. For this purpose, we present the network protocol RTP/I for the standardized communication of distributed interactive applications, and a novel application-level multicast protocol that realizes efficient group communication while taking application-level knowledge into account. Second, consistency control mechanisms are required to keep the replicated application data synchronized. We present the consistency control algorithms “local lag”, “Timewarp”, and “state request”, show how they can be combined, and discuss how to provide visual feedback so that the session members are able to handle conflicting actions. Finally, late-joining participants need to be initialized with the current application state before they are able to participate in a collaborative session. We propose a novel late-join algorithm, which is both flexible and scalable. All algorithms and protocols presented in this dissertation solve the aforementioned problems in a generic way. We demonstrate how they can be employed for the mlb as well as for other distributed interactive applications

Smart network caches : localized content and application negotiated recovery mechanisms for multicast media distribution

Thesis (Ph. D.)--Massachusetts Institute of Technology, Program in Media Arts & Sciences, 1998.Includes bibliographical references (p. 133-138).by Roger George Kermode.Ph.D

Supporting distributed computation over wide area gigabit networks

The advent of high bandwidth fibre optic links that may be used over very large distances has lead to much research and development in the field of wide area gigabit networking. One problem that needs to be addressed is how loosely coupled distributed systems may be built over these links, allowing many computers worldwide to take part in complex calculations in order to solve "Grand Challenge" problems. The research conducted as part of this PhD has looked at the practicality of implementing a communication mechanism proposed by Craig Partridge called Late-binding Remote Procedure Calls (LbRPC). LbRPC is intended to export both code and data over the network to remote machines for evaluation, as opposed to traditional RPC mechanisms that only send parameters to pre-existing remote procedures. The ability to send code as well as data means that LbRPC requests can overcome one of the biggest problems in Wide Area Distributed Computer Systems (WADCS): the fixed latency due to the speed of light. As machines get faster, the fixed multi-millisecond round trip delay equates to ever increasing numbers of CPU cycles. For a WADCS to be efficient, programs should minimise the number of network transits they incur. By allowing the application programmer to export arbitrary code to the remote machine, this may be achieved. This research has looked at the feasibility of supporting secure exportation of arbitrary code and data in heterogeneous, loosely coupled, distributed computing environments. It has investigated techniques for making placement decisions for the code in cases where there are a large number of widely dispersed remote servers that could be used. The latter has resulted in the development of a novel prototype LbRPC using multicast IP for implicit placement and a sequenced, multi-packet saturation multicast transport protocol. These prototypes show that it is possible to export code and data to multiple remote hosts, thereby removing the need to perform complex and error prone explicit process placement decisions

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

A web-based approach to engineering adaptive collaborative applications

Current methods employed to develop collaborative applications have to make decisions and speculate about the environment in which the application will operate within, the network infrastructure that will be used and the device type the application will operate on. These decisions and assumptions about the environment in which collaborative applications were designed to work are not ideal. These methods produce collaborative applications that are characterised as being inflexible, working on homogeneous networks and single platforms, requiring pre-existing knowledge of the data and information types they need to use and having a rigid choice of architecture. On the other hand, future collaborative applications are required to be flexible; to work in highly heterogeneous environments; be adaptable to work on different networks and on a range of device types. This research investigates the role that the Web and its various pervasive technologies along with a component-based Grid middleware can play to address these concerns. The aim is to develop an approach to building adaptive collaborative applications that can operate on heterogeneous and changing environments. This work proposes a four-layer model that developers can use to build adaptive collaborative applications. The four-layer model is populated with Web technologies such as Scalable Vector Graphics (SVG), the Resource Description Framework (RDF), Protocol and RDF Query Language (SPARQL) and Gridkit, a middleware infrastructure, based on the Open Overlays concept. The Middleware layer (the first layer of the four-layer model) addresses network and operating system heterogeneity, the Group Communication layer enables collaboration and data sharing, while the Knowledge Representation layer proposes an interoperable RDF data modelling language and a flexible storage facility with an adaptive architecture for heterogeneous data storage. And finally there is the Presentation and Interaction layer which proposes a framework (Oea) for scalable and adaptive user interfaces. The four layer model has been successfully used to build a collaborative application, called Wildfurt that overcomes challenges facing collaborative applications. This research has demonstrated new applications for cutting-edge Web technologies in the area of building collaborative applications. SVG has been used for developing superior adaptive and scalable user interfaces that can operate on different device types. RDF and RDFS, have also been used to design and model collaborative applications providing a mechanism to define classes and properties and the relationships between them. A flexible and adaptable storage facility that is able to change its architecture based on the surrounding environments and requirements has also been achieved by combining the RDF technology with the Open Overlays middleware, Gridkit