37 research outputs found

    Long-range dependence and performance in telecom networks

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    SUMMARY Telecommunications systems have recently undergone significant innovations. These call for suitable statistical models that can properly describe the behaviour of the input traffic in a network. Here we use fractional Brownian motion (FBM) to model cumulative traffic network, thus taking into account the possible presence of long-range dependence in the data. A Bayesian approach is devised in such a way that we are able to: (a) estimate the Hurst parameter H of the FBM; (b) estimate the overflow probability which is a parameter measuring the quality of service of a network: (c) develop a test for comparing the null hypothesis of long-range dependence in the data versus the alternative of short-range dependence. In order to achieve these inferential results, we elaborate an MCMC sampling scheme whose output enables us to obtain an approximation of the quantities of interest. An application to three real datasets, corresponding to three different levels of traffic, is finally considered

    Internet performance modeling: the state of the art at the turn of the century

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    Seemingly overnight, the Internet has gone from an academic experiment to a worldwide information matrix. Along the way, computer scientists have come to realize that understanding the performance of the Internet is a remarkably challenging and subtle problem. This challenge is all the more important because of the increasingly significant role the Internet has come to play in society. To take stock of the field of Internet performance modeling, the authors organized a workshop at Schloß Dagstuhl. This paper summarizes the results of discussions, both plenary and in small groups, that took place during the four-day workshop. It identifies successes, points to areas where more work is needed, and poses “Grand Challenges” for the performance evaluation community with respect to the Internet

    Energy-efficient wireless communication

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    In this chapter we present an energy-efficient highly adaptive network interface architecture and a novel data link layer protocol for wireless networks that provides Quality of Service (QoS) support for diverse traffic types. Due to the dynamic nature of wireless networks, adaptations in bandwidth scheduling and error control are necessary to achieve energy efficiency and an acceptable quality of service. In our approach we apply adaptability through all layers of the protocol stack, and provide feedback to the applications. In this way the applications can adapt the data streams, and the network protocols can adapt the communication parameters

    A Survey of Distributed Enterprise Network and Systems Management Paradigms

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    Since the mid 1990s, network and systems management has steadily evolved from centralized paradigms, where the management application runs on a single management station, to distributed paradigms, where it is distributed over many nodes. In this survey, our goal is to classify all these paradigms, especially the new ones, in order to help network and systems administrators design a management application, and choose between mobile code, distributed objects, intelligent agents, etc. Step by step, we build an enhanced taxonomy based on four criteria: the delegation granularity, the semantic richness of the information model, the degree of specification of a task, and the degree of automation of management

    Verteilt organisierte Mehrteilnehmer-Videokonferenzen fĂŒr geschlossene Gruppen im Internet

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    Videokonferenzen gelten als eine populĂ€re Anwendung in modernen Netzwerken. Trotz langjĂ€hriger Erfahrungen gehören sie nicht zu den alltĂ€glich genutzten Diensten. Videokonferenzdienste im Internet unterstĂŒtzen meist offene Konferenzgruppen. Jedoch haben die Mehrzahl der alltĂ€glichen Beratungen einen geschlossenen Charakter. Systeme, die geschlossene Gruppen unterstĂŒtzen, basieren meist auf spezieller Studiotechnik. Desktop-Systeme lassen nur ein begrenztes Leistungsangebot zu. Besonders beim Aufbau von Mehrteilnehmer-Gruppen ist es schwierig, eine gute DienstgĂŒte bereitzustellen. Deshalb haben Systeme fĂŒr geschlossene Gruppen bisher keine breite Anwendung gefunden. Die vorliegende Arbeit untersucht zwei AnĂ€tze zur Gestaltungsprinzipien von geschlossenen Mehrteilnehmer-Videokonferenzsystemen. Der Erste untersucht den Aufbau von globalen Konferenzen ĂŒber den Verbund lokaler Systeme. Der Zweite, ein Peer-to-Peer-Konzept, untersucht die UnterstĂŒtzung von geschlossenen Gruppen im Internet.Video conferences are considered as attractive applications in high-speed networks. But they are not broadly used. Most existing video conference systems support open group conferences for public events. However, most everyday consultations have a closed character. Systems supporting closed groups are quite expensive and mostly based on special hardware. The performance of desktop systems is limited. In particular, there are difficulties in establishing multi party video conferences with sufficient QoS. This Ph.D. thesis investigates the design principles of closed multi party video conference systems for global public networks. Two approaches are described. The first approach investigates a global video conferencing service that interconnects local systems over long distances. The second one, a Peer-to-Peer approach, deals with the design of closed multiparty conferences in the Internet. In this context the problem of ensuring the QoS of the transport of real time traffic is discussed

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

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    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

    Annual Report 1999 / Department for Computer Science

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    Selbstdarstellung des Instituts fĂŒr Informatik der BTU Cottbus und Berichte der LehrstĂŒhle fĂŒr das Jahr 1999.Presentation of the Department for Computer Science of the BTU Cottbus and reports of the chairs at the department for the year 1999

    Low Cost Video For Distance Education

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    A distance education system has been designed for Nova Southeastern University (NSU) . The design was based on emerging low cost video technology. The report presented the design and summarizes existing distance education efforts and technologies. The design supported multimedia electronic classrooms, and enabled students to participate in multimedia classes using standard telephone networks. Results were presented in three areas: management, courseware, and, systems. In the area of management, the report recommended that the University separately establish, fund, and staff the distance education project. Supporting rationale was included. In the area of courseware, the importance of quality courseware was highlighted. It was found that the development of distance education courseware was difficult; nevertheless, quality courseware was the key to a successful distance education program. In the area of systems, component level designs were presented for a student system, a university host, and a support system. Networks connecting the systems were addressed. The student system was based on widely available multimedia systems. The host system supported up to sixteen participants in a single class. The support system was designed for the development of courseware and the support of future projects in distance education. The report included supporting Proof of Principle demonstrations. These demonstrations showed that low cost video systems had utility at speeds as low as 7. 2 kbps. They also showed that high quality student images were not crucial to the system. The report included three alternate implementation strategies. The initial capability could be operational in 1997. A multi-session, 2000 user system was projected for early in the next century
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