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

An Improved Active Network Concept and Architecture for Distributed and Dynamic Streaming Multimedia Environments with Heterogeneous Bandwidths

A problem in todays Internet infrastructure may occur when a streaming multimedia application is to take place. The information content of video and audio signals that contain moving or changing scenes may simply be too great for Internet clients with low bandwidth capacity if no adaptation is performed. In order to satisfactorily reach clients with various bandwidth capacities some works such as receiver-driven multicast and resilient overlay networks (RON) have been developed. However these efforts mainly call for modification on router level management or place additional layer to the Internet structure, which is not recommended in the nearest future due to the highly acceptance level and widely utilization of the current Internet structure, and the lengthy and tiring standardization process for a new structure or modification to be accepted. We have developed an improved active network approach for distributed and dynamic streaming multimedia environment with heterogeneous bandwidth, such as the case of the Internet. Friendly active network system (FANS) is a sample of our approach. Adopting application level active network (ALAN) mechanism, FANS participants and available media are referred through its universal resource locator (url). The system intercepts traffic flowing from source to destination and performs media post-processing at an intermediate peer. The process is performed at the application level instead of at the router level, which was the original approach of active networks. FANS requires no changes in router level management and puts no additional requirement to the current Internet architecture and, hence, instantly applicable. In comparison with ALAN, FANS possesses two significant differences. From the system overview, ALAN requires three minimum elements: clients, servers, and dynamic proxy servers. FANS, on the other hand, unifies the functionalities of those three elements. Each of peers in FANS is a client, an intermediate peer, and a media server as well. Secondly, FANS members tracking system dynamically detects the existence of a newly joined computers or mobile device, given its url is available and announced. In ALAN, the servers and the middle nodes are priori known and, hence, static. The application level approach and better performance characteristics distinguished also our work with another similar work in this field, which uses router level approach. The approach offers, in general, the following improvements: FANS promotes QoS fairness, in which clients with lower bandwidth are accommodated and receive better quality of service FANS introduces a new algorithm to determine whether or not the involvement of intermediate peer(s) to perform media post-processing enhancement services is necessary. This mechanism is important and advantageous due to the fact that intermediate post-processing increases the delay and, therefore, should only be employed selectively. FANS considers the size of media data and the capacity of clients bandwidth as network parameters that determine the level of quality of service offered. By employing the above techniques, our experiments with the Internet emulator show that our approach improves the reliability of streaming media applications in such environment

Adaptive hypertext and hypermedia : workshop : proceedings, 3rd, Sonthofen, Germany, July 14, 2001 and Aarhus, Denmark, August 15, 2001

This paper presents two empirical usability studies based on techniques from Human-Computer Interaction (HeI) and software engineering, which were used to elicit requirements for the design of a hypertext generation system. Here we will discuss the findings of these studies, which were used to motivate the choice of adaptivity techniques. The results showed dependencies between different ways to adapt the explanation content and the document length and formatting. Therefore, the system's architecture had to be modified to cope with this requirement. In addition, the system had to be made adaptable, in addition to being adaptive, in order to satisfy the elicited users' preferences

Adaptive hypertext and hypermedia : workshop : proceedings, 3rd, Sonthofen, Germany, July 14, 2001 and Aarhus, Denmark, August 15, 2001

This paper presents two empirical usability studies based on techniques from Human-Computer Interaction (HeI) and software engineering, which were used to elicit requirements for the design of a hypertext generation system. Here we will discuss the findings of these studies, which were used to motivate the choice of adaptivity techniques. The results showed dependencies between different ways to adapt the explanation content and the document length and formatting. Therefore, the system's architecture had to be modified to cope with this requirement. In addition, the system had to be made adaptable, in addition to being adaptive, in order to satisfy the elicited users' preferences

Third international workshop on Authoring of adaptive and adaptable educational hypermedia (A3EH), Amsterdam, 18-22 July, 2005

The A3EH follows a successful series of workshops on Adaptive and Adaptable Educational Hypermedia. This workshop focuses on models, design and authoring of AEH, on assessment of AEH, conversion between AEH and evaluation of AEH. The workshop has paper presentations, poster session and panel discussions

Electronic Business in traditional structures – new services as forerunner of cooperation exemplified in a network for textile design development

Seit dem ersten häufigeren Auftauchen des Begriffes "Internetökonomie" oder auch "New Economy" und dem vorläufigen Höhepunkt der Entwicklung entsprechender Konzepte und Technologien vergingen nur wenige Jahre, in denen wissenschaftliche Arbeiten und praxisorientierte Ratgeber und Erfahrungsberichte in großer Zahl erschienen. Vor allem die technologischen Innovationen erwiesen sich zu Beginn als Treiber dieser Entwicklungen. Faktoren wie Macht-, Wert-, und Investitionsneutralität erlaubten ein schnelles Umsetzen von Ideen in unterschiedliche Anwendungen bzw. Geschäftsmodelle. Dem rasanten Aufschwung folgte allerdings eine noch schnellere Phase der Ernüchterung, denn viele der neuen Spielregeln der "Internetökonomie" erwiesen sich als nicht haltbar und wenig erfolgversprechend. Der Internetökonomie werden als primäre Eigenschaften die Digitalität, die Vernetzung und die Globalität zugeschrieben. Der daraus resultierende orts- und zeitunabhängige Zugriff auf Daten und Informationen – eine Möglichkeit, die mit dem Begriff Ubiquität beschrieben wird – charakterisiert den Wandel von der postmodernen Industriegesellschaft hin zur Informationsgesellschaft. Insbesondere der Zugriff auf ein in dieser Form bisher nicht verfügbares Maß an Informationen, die bisher verteilt vorlagen, erlaubt neue Formen der Zusammenarbeit in neuen, aber vor allem auch in traditionellen Strukturen. Erschwerend für die Eingrenzung des Begriffes "Internetökonomie" ist seine Verwendung für volkswirtschaftliche Zusammenhänge einerseits und für betriebswirtschaftliche Anwendungen oder Geschäftsmodelle andererseits. Gerade mit Letzteren setzt sich die vorliegende Untersuchung ausführlich auseinander. Im Rahmen dieser Arbeit wird der Bereich des Electronic Business (auch als „business-to-business“ bezeichnet) näher betrachtet und durch folgende konstituierende Elemente bestimmt: a) die digitale Abwicklung von Kommunikationsprozessen und Geschäftstransaktionen, b) die Fähigkeit, eine Alternative zu traditionellen Koordinationsmechanismen zu generieren und c) die Schaffung eines informationellen Mehrwertes. Neben der herausragenden Rolle, die das Vertrauen unter den Akteuren im Electronic Business spielt, werden die Entwicklungen bzw. Entwicklungsstufen im Electronic Business beschrieben. Unterschiedliche Rahmenmodelle bzw. Leitfäden und Implementierungsvorgaben können so voneinander – etwa über die umfassende Darstellung von Anwendungen und Geschäftsmodellen – abgegrenzt werden. Bislang erfolgt allerdings bei keinem dieser Rahmenmodelle oder Leitfäden eine systematische Zuordnung von Methoden oder Werkzeugen zu den entsprechenden Entwicklungsstufen und Anwendungen. Aus diesem Grund wird ein eigener Ansatz zur Beschreibung der Entwicklungsstufen des Electronic Business vorgestellt, wo den Stufen "Information", "Interaktion" sowie "Kooperation und Integration" unterschiedliche "Services" und damit auch Methoden und Werkzeuge zugeordnet werden. Diese "Services" können sowohl von Anwendungen in Unternehmen in Anspruch genommen werden als auch einzelne Geschäftsmodelle unterstützen, wie die Praxisbeispiele in Anhang 1 aufzeigen. Eine eigene Kategorisierung der Geschäftsmodelltypen wird durch Beispiele, vornehmlich aus der Textil- und Bekleidungsindustrie, illustriert. Die Arbeit liefert Anregungen für die unternehmerische Praxis, indem konzeptionelle Entwicklungsstufen dem Grad des Engagements der Unternehmen im Electronic Business in einem Portfolio einander gegenübergestellt werden. Die Entwicklung und Einführung eines "Intelligence Services" in traditionellen Strukturen wird in einem Textildesign-Netzwerk – im Rahmen des europäischen Forschungsprojektes CREATIV ("Commercial Retrieval for Fabrics and Design Patterns", IST-1999-20534) – erprobt. Durch die räumliche Trennung der Partner dieses Netzwerkes kann bei der Produktentwicklung der Prozess der Mustererstellung durch die Digitalisierung und die Nutzung des Internets für den Informationsaustausch vereinfacht, beschleunigt und kostengünstiger gestaltet werden.Since the emergence of the "Internet Economy" or "New Economy" and its preliminary summit regarding concepts and technologies, it has been only over a couple of years that a great deal of scientific articles and practical guidelines or codes of practice have been published. Especially in the beginning of the "Internet Economy" technological innovations proved to be drivers of development. Several factors like neutrality of power, neutrality of value and neutrality of capital investment permitted a fast implementation of ideas regarding both business applications and business models. However, this rapid boom was followed by an even faster period of disillusion and consolidation: most of the "new" rules of the "Internet Economy" were not valid in businesses in order to generate profit and success. The main characteristics of the "New Economy" are: being digital, being networked and being global. These characteristics point up the change from post-modern society to information society by providing the means to retrieve ubiquitously as many data and information as never before. By now there are ways to use huge amounts of data and information that were distributed before and however could not be retrieved. So new kinds of cooperation in newly arranged and in traditional structures are possible. It is difficult to give a sound definition the "Internet Economy" because of its use for economical questions, business applications and business models. In particular the latter are concerned here and will be analysed in detail. The present thesis focuses on Electronic Business (so-called "business-to-business"), which can be characterised by the following points: a) digital processing of communication processes and business transactions, b) realisation of alternatives regarding traditional mechanisms of coordination and c) creation of an informational added value. Besides the outstanding role of trust among the actors doing Electronic Business the thesis describes the evolutions, respectively developments, of Electronic Business. General Frameworks or guidelines can be distinguished - for instance by the extent applications and business models are described. So far none of these frameworks - and none of the guidelines and codes for practice - offer a consistent assignment of methods, tools or applications to the steps of their actual framework. Therefore an original conceptual framework has been created including the steps "information", "interaction" as well as "cooperation and integration", assigning to these steps different "services" (methods and tools). All those "Services" can be used either for supporting business applications or business models (examples of already established ones are shown in Annex 1). A categorisation of business models (and types of business models) using a new set of criteria is illustrated by examples of textile and apparel companies. Suggestions for entrepreneurial activities are made in a portfolio by classifying the steps of the conceptual framework and the engagement of entrepreneurs in Electronic Business. The development and implementation of an "Intelligence Service" in a network of cooperative product development of textile and apparel companies is presented, which has been tested within the frame of the project CREATIV ("Commercial Retrieval for Fabrics and Design Patterns", IST-1999-20534) funded by the European Commission. The European wide network showed to have potentials in the phase of making samples in order to improve the processing, the speed and the cost situation by using digitised samples and exchanging the needed information via the Internet. Moreover, this realisation exemplifies that there is no serious difference in the economic rules of the "New Economy" and the "Old Economy". Different impacts result basically from the particularity of production of goods and services, depending on the use of the new production factor (information), from the deployment of digitised exchange processes and the use of "Services" as well as from the associated possible (re-)organisation of the institutional arrangements

Interoperability of wireless communication technologies in hybrid networks: Evaluation of end-to-end interoperability issues and quality of service requirements

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Hybrid Networks employing wireless communication technologies have nowadays brought closer the vision of communication “anywhere, any time with anyone”. Such communication technologies consist of various standards, protocols, architectures, characteristics, models, devices, modulation and coding techniques. All these different technologies naturally may share some common characteristics, but there are also many important differences. New advances in these technologies are emerging very rapidly, with the advent of new models, characteristics, protocols and architectures. This rapid evolution imposes many challenges and issues to be addressed, and of particular importance are the interoperability issues of the following wireless technologies: Wireless Fidelity (Wi-Fi) IEEE802.11, Worldwide Interoperability for Microwave Access (WiMAX) IEEE 802.16, Single Channel per Carrier (SCPC), Digital Video Broadcasting of Satellite (DVB-S/DVB-S2), and Digital Video Broadcasting Return Channel through Satellite (DVB-RCS). Due to the differences amongst wireless technologies, these technologies do not generally interoperate easily with each other because of various interoperability and Quality of Service (QoS) issues. The aim of this study is to assess and investigate end-to-end interoperability issues and QoS requirements, such as bandwidth, delays, jitter, latency, packet loss, throughput, TCP performance, UDP performance, unicast and multicast services and availability, on hybrid wireless communication networks (employing both satellite broadband and terrestrial wireless technologies). The thesis provides an introduction to wireless communication technologies followed by a review of previous research studies on Hybrid Networks (both satellite and terrestrial wireless technologies, particularly Wi-Fi, WiMAX, DVB-RCS, and SCPC). Previous studies have discussed Wi-Fi, WiMAX, DVB-RCS, SCPC and 3G technologies and their standards as well as their properties and characteristics, such as operating frequency, bandwidth, data rate, basic configuration, coverage, power, interference, social issues, security problems, physical and MAC layer design and development issues. Although some previous studies provide valuable contributions to this area of research, they are limited to link layer characteristics, TCP performance, delay, bandwidth, capacity, data rate, and throughput. None of the studies cover all aspects of end-to-end interoperability issues and QoS requirements; such as bandwidth, delay, jitter, latency, packet loss, link performance, TCP and UDP performance, unicast and multicast performance, at end-to-end level, on Hybrid wireless networks. Interoperability issues are discussed in detail and a comparison of the different technologies and protocols was done using appropriate testing tools, assessing various performance measures including: bandwidth, delay, jitter, latency, packet loss, throughput and availability testing. The standards, protocol suite/ models and architectures for Wi-Fi, WiMAX, DVB-RCS, SCPC, alongside with different platforms and applications, are discussed and compared. Using a robust approach, which includes a new testing methodology and a generic test plan, the testing was conducted using various realistic test scenarios on real networks, comprising variable numbers and types of nodes. The data, traces, packets, and files were captured from various live scenarios and sites. The test results were analysed in order to measure and compare the characteristics of wireless technologies, devices, protocols and applications. The motivation of this research is to study all the end-to-end interoperability issues and Quality of Service requirements for rapidly growing Hybrid Networks in a comprehensive and systematic way. The significance of this research is that it is based on a comprehensive and systematic investigation of issues and facts, instead of hypothetical ideas/scenarios or simulations, which informed the design of a test methodology for empirical data gathering by real network testing, suitable for the measurement of hybrid network single-link or end-to-end issues using proven test tools. This systematic investigation of the issues encompasses an extensive series of tests measuring delay, jitter, packet loss, bandwidth, throughput, availability, performance of audio and video session, multicast and unicast performance, and stress testing. This testing covers most common test scenarios in hybrid networks and gives recommendations in achieving good end-to-end interoperability and QoS in hybrid networks. Contributions of study include the identification of gaps in the research, a description of interoperability issues, a comparison of most common test tools, the development of a generic test plan, a new testing process and methodology, analysis and network design recommendations for end-to-end interoperability issues and QoS requirements. This covers the complete cycle of this research. It is found that UDP is more suitable for hybrid wireless network as compared to TCP, particularly for the demanding applications considered, since TCP presents significant problems for multimedia and live traffic which requires strict QoS requirements on delay, jitter, packet loss and bandwidth. The main bottleneck for satellite communication is the delay of approximately 600 to 680 ms due to the long distance factor (and the finite speed of light) when communicating over geostationary satellites. The delay and packet loss can be controlled using various methods, such as traffic classification, traffic prioritization, congestion control, buffer management, using delay compensator, protocol compensator, developing automatic request technique, flow scheduling, and bandwidth allocation

Designing new network adaptation and ATM adaptation layers for interactive multimedia applications

Multimedia services, audiovisual applications composed of a combination of discrete and continuous data streams, will be a major part of the traffic flowing in the next generation of high speed networks. The cornerstones for multimedia are Asynchronous Transfer Mode (ATM) foreseen as the technology for the future Broadband Integrated Services Digital Network (B-ISDN) and audio and video compression algorithms such as MPEG-2 that reduce applications bandwidth requirements. Powerful desktop computers available today can integrate seamlessly the network access and the applications and thus bring the new multimedia services to home and business users. Among these services, those based on multipoint capabilities are expected to play a major role.    Interactive multimedia applications unlike traditional data transfer applications have stringent simultaneous requirements in terms of loss and delay jitter due to the nature of audiovisual information. In addition, such stream-based applications deliver data at a variable rate, in particular if a constant quality is required.    ATM, is able to integrate traffic of different nature within a single network creating interactions of different types that translate into delay jitter and loss. Traditional protocol layers do not have the appropriate mechanisms to provide the required network quality of service (QoS) for such interactive variable bit rate (VBR) multimedia multipoint applications. This lack of functionalities calls for the design of protocol layers with the appropriate functions to handle the stringent requirements of multimedia.    This thesis contributes to the solution of this problem by proposing new Network Adaptation and ATM Adaptation Layers for interactive VBR multimedia multipoint services.    The foundations to build these new multimedia protocol layers are twofold; the requirements of real-time multimedia applications and the nature of compressed audiovisual data.    On this basis, we present a set of design principles we consider as mandatory for a generic Multimedia AAL capable of handling interactive VBR multimedia applications in point-to-point as well as multicast environments. These design principles are then used as a foundation to derive a first set of functions for the MAAL, namely; cell loss detection via sequence numbering, packet delineation, dummy cell insertion and cell loss correction via RSE FEC techniques.    The proposed functions, partly based on some theoretical studies, are implemented and evaluated in a simulated environment. Performances are evaluated from the network point of view using classic metrics such as cell and packet loss. We also study the behavior of the cell loss process in order to evaluate the efficiency to be expected from the proposed cell loss correction method. We also discuss the difficulties to map network QoS parameters to user QoS parameters for multimedia applications and especially for video information. In order to present a complete performance evaluation that is also meaningful to the end-user, we make use of the MPQM metric to map the obtained network performance results to a user level. We evaluate the impact that cell loss has onto video and also the improvements achieved with the MAAL.    All performance results are compared to an equivalent implementation based on AAL5, as specified by the current ITU-T and ATM Forum standards.    An AAL has to be by definition generic. But to fully exploit the functionalities of the AAL layer, it is necessary to have a protocol layer that will efficiently interface the network and the applications. This role is devoted to the Network Adaptation Layer.    The network adaptation layer (NAL) we propose, aims at efficiently interface the applications to the underlying network to achieve a reliable but low overhead transmission of video streams. Since this requires an a priori knowledge of the information structure to be transmitted, we propose the NAL to be codec specific.    The NAL targets interactive multimedia applications. These applications share a set of common requirements independent of the encoding scheme used. This calls for the definition of a set of design principles that should be shared by any NAL even if the implementation of the functions themselves is codec specific. On the basis of the design principles, we derive the common functions that NALs have to perform which are mainly two; the segmentation and reassembly of data packets and the selective data protection.    On this basis, we develop an MPEG-2 specific NAL. It provides a perceptual syntactic information protection, the PSIP, which results in an intelligent and minimum overhead protection of video information. The PSIP takes advantage of the hierarchical organization of the compressed video data, common to the majority of the compression algorithms, to perform a selective data protection based on the perceptual relevance of the syntactic information.    The transmission over the combined NAL-MAAL layers shows significant improvement in terms of CLR and perceptual quality compared to equivalent transmissions over AAL5 with the same overhead.    The usage of the MPQM as a performance metric, which is one of the main contributions of this thesis, leads to a very interesting observation. The experimental results show that for unexpectedly high CLRs, the average perceptual quality remains close to the original value. The economical potential of such an observation is very important. Given that the data flows are VBR, it is possible to improve network utilization by means of statistical multiplexing. It is therefore possible to reduce the cost per communication by increasing the number of connections with a minimal loss in quality.    This conclusion could not have been derived without the combined usage of perceptual and network QoS metrics, which have been able to unveil the economic potential of perceptually protected streams.    The proposed concepts are finally tested in a real environment where a proof-of-concept implementation of the MAAL has shown a behavior close to the simulated results therefore validating the proposed multimedia protocol layers