Skip to main content
Fachgebiete
Automobil + Motoren Bauwesen + Immobilien Business IT + Informatik Elektrotechnik + Elektronik Energie + Nachhaltigkeit Finance + Banking Management + Führung Marketing + Vertrieb Maschinenbau + Werkstoffe Versicherung + Risiko
DE
EN
Themenseiten
Organisationspsychologie Projektmanagement Marketing Smart Manufacturing
Bücher
Zeitschriften
Weitere Formate
Podcasts Webinare Technik Webinare Wirtschaft Kongresse Veranstaltungskalender Awards
Jetzt Einzelzugang starten
Zugang für Unternehmen
Referenzkunden
ATZ-Fachkongress

Chassis.tech plus 2024


4 Kongresse in einer Veranstaltung

Treffen Sie in München die Fachleute von Chassis, Lenkung, Bremsen sowie Reifen/Räder.
Erweiterte Suche
Anmelden
nach oben

2007 | Buch

Netzwerkeffizienz stabiler Overlay-Streaming-Topologien Kapitel lesen Erstes Kapitel lesen

Kommunikation in Verteilten Systemen (KiVS)

15. Fachtagung Kommunikation in Verteilten Systemen (KiVS 2007) Bern, Schweiz, 26. Februar – 2. März 2007

herausgegeben von: Torsten Braun, Georg Carle, Burkhard Stiller

Verlag: Springer Berlin Heidelberg

Buchreihe : Informatik aktuell

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik" , Springer Professional "Wirtschaft"

Einloggen, um Zugang zu erhalten
insite
SUCHEN

Über dieses Buch

Die 15. GI/ITG-Fachtagung Kommunikation in Verteilten Systemen (KiVS 2007) befasst sich mit einer großen Vielfalt von innovativen und zukunftsorientierten Fragestellungen. Sie spannt dabei einen Bogen von Overlay- und Peer-to-Peer-Netzen über Sensornetze und mobile Ad-Hoc-Netze bis zu Web Services. Die KiVS 2007 dient der Standortbestimmung aktueller Entwicklungen, der Präsentation laufender Forschungsarbeiten und der Diskussion zukunftsträchtiger Ansätze für die Kommunikation in verteilten Systemen.

Inhaltsverzeichnis

Frontmatter

Overlay und Peer-to-Peer Networks

Frontmatter
Netzwerkeffizienz stabiler Overlay-Streaming-Topologien
Zusammenfassung
Bei der Konstruktion von Overlay-Topologien für multimediale Live-Streaming-Anwendungen sind zwei Eigenschaften von besonderer Bedeutung: die Netzwerkeffizienz der Topologie in Bezug auf die Paketverteilung und die Stabilität der Topologie sowohl im Fall vorsätzlicher Sabotageangriffe als auch bei zufälligen Knotenausfällen. Während ein Großteil der existierenden Ansätze hauptsächlich Effizienzkriterien optimiert und nur wenige Ansätze Stabilität gegen zufällige Ausfälle betrachten, ist es uns in früheren Arbeiten gelungen, Verfahren für die Konstruktion angriffsstabiler Topologien zu entwickeln [17,3]. Da in diesen Arbeiten zum Zweck der Steigerung der Stabilitätseigenschaften der Topologie eine Verschlechterung der Effizienzeigenschaften bewusst in Kauf genommen wurde, wird in dem vorliegenden Artikel ein Verfahren vorgestellt, dass es ermöglicht, einen Kompromiss zwischen Effizienz und Stabilität bei der Konstruktion der Topologie zu finden.
Hierzu werden zunächst Stabilitäts- und Effizienzeigenschaften in Form von Kostenmetriken operationalisiert und darauf aufbauend ein verteilter Algorithmus zur dynamischen Topologieoptimierung vorgestellt, der eine Gesamtkostenfunktion optimiert, die durch eine parametrisierbare, gewichtete Kombination der Einzelmetriken definiert ist. Mit Hilfe einer Simulationsstudie wird gezeigt, dass auf diese Weise gute Kompromisse zwischen Effizienz und Stabilität bei der Topologiekonstruktion gefunden werden können.
Thorsten Strufe, Jens Wildhagen, Günter Schäfer
Improving the Performance and Robustness of Kademlia-Based Overlay Networks
Abstract
Structured peer-to-peer (p2p) networks are highly distributed systems with a potential to support business applications. There are numerous different suggestions on how to implement such systems. However, before legal p2p systems can become mainstream they need to offer improved efficiency, robustness, and stability. While Chord is the most researched and best understood mechanism, the Kademlia algorithm is widely-used in deployed applications. There are still many open questions concerning the performance of the latter. In this paper we identify the main problems of Kademlia by large scale simulations and present modifications which help to avoid those problems. This way, we are able to significantly improve the performance and robustness of Kademlia-based applications, especially in times of churn and in unstable states. In particular, we show how to increase the stability of the overlay, make searches more efficient, and adapt the maintenance traffic to the current churn rate in a self-organizing way.
Andreas Binzenhöfer, Holger Schnabel
Improved Locality-Aware Grouping in Overlay Networks
Abstract
The performance of peer-to-peer and overlay networks depends to a great extent on their awareness of the underlying network’s properties. Several schemes for estimating end-to-end network distances have been proposed to simplify this task. The mOverlay framework identifies groups of nodes that are near to each other in the network topology. Instead of distances between nodes mOverlay measures distances between groups. However, mOverlay’s locating procedure has a number of drawbacks. We propose an alternate method for identifying groups using Meridian’s closest node search. Simulation results based on PlanetLab measurements indicate that the Meridian-based approach is able to outperform mOverlay in terms of joining delay, the size of the identified groups, and their suitability for a distance estimation service.
Matthias Scheidegger, Torsten Braun
On Improving the Performance of Reliable Server Pooling Systems for Distance-Sensitive Distributed Applications
Abstract
Reliable Server Pooling (RSerPool) is a protocol framework for server redundancy and session failover, currently under standardization by the IETF RSerPool WG. While the basic ideas of RSerPool are not new, their combination into a single, unified architecture is. Server pooling becomes increasingly important, because there is a growing amount of availability-critical applications. For a service to survive localized disasters, it is useful to place the servers of a pool at different locations. However, the current version of RSerPool does not incorporate the aspect of component distances in its server selection decisions. In our paper, we present an approach to add distance-awareness to the RSerPool architecture, based on features of the SCTP transport protocol. This approach is examined and evaluated by simulations. But to also show its usefulness in real life, we furthermore validate our proposed extension by measurements in a PlanetLab-based Internet scenario.
Thomas Dreibholz, Erwin P. Rathgeb
Modeling Trust for Users and Agents in Ubiquitous Computing
Abstract
Finding reliable partners for interactions is one of the challenges in ubiquitous computing and P2P systems. We believe, that this problem can be solved by assigning trust values to entities and allowing them to state opinions about the trustworthiness of others. In this paper, we introduce our vision of trust-aided computing, and we present a trust model, called CertainTrust, which can easily be interpreted and adjusted by users and software agents. A key feature of CertainTrust is that it is capable of expressing the certainty of a trust opinion depending on the context of use. We show how trust can be expressed using different representations (one for users and one for software agents) and present an automatic mapping to change between the representations.
Sebastian Ries, Jussi Kangasharju, Max Mühlhäuser
A Decentral Architecture for SIP-based Multimedia Networks
Abstract
The Session Initiation Protocol (SIP) is a general protocol for session setup and management, e.g., for VoIP. Current SIP networks build on a fixed infrastructure that relies on static network entities. General problems with this infrastructure, e.g., in ubiquitous ad-hoc networks, lead to a trend of integrating peer-to-peer mechanisms into SIP. We propose a generic architecture for decentralised SIP networks. The SIP location service of our architecture is based on JXTA for message routing. This allows SIP networks without central location services, and in extreme even without central SIP proxies. Unlike other approaches, we do not modify SIP. Thus, standard SIP clients can be seamlessly integrated. Due to the flexibility of JXTA, various peer-to-peer algorithms can be integrated according to current requirements. Additionally, our architecture supports registration, discovery and locating of services based on SIP. This saves resources in end terminals and also benefits from the peer-to-peer approach.
Holger Schmidt, Teodora Guenkova-Luy, Franz J. Hauck

Verteilte Anwendungen und Web Services

Frontmatter
An Orchestrated Execution Environment for Hybrid Services
Abstract
Influenced by the success of web service technologies for the development and deployment of IT services, the telecommunications R&D community starts adapting and building similar service delivery platforms, trying to manage the hard constraints of telco domains, such as: existence of heterogeneous protocols, extensive use of asynchronous communications and real-time delivery requirements.
In this work we present a detailed analysis of an enhanced JAIN/SLEE architecture in which a workflow engine has been seamlessly integrated, being capable to orchestrate service entities from both telecom and IT domains.
Sandford Bessler, Joachim Zeiss, Rene Gabner, Julia Gross
A Lightweight Service Grid Based on Web Services and Peer-to-Peer
Abstract
What is The Grid? This question has been asked by many people and has been answered by many more. On our way to the One Grid, it is currently only possible to distinguish between several Computational, Data and Service Grids. This paper introduces Venice, a lightweight Service Grid that allows for easy service deployment, easy maintenance and easy service usage. It contains management services, information services and application services that can be used to build distributed applications upon. Its main focus in on providing a flexible and dependable infrastructure for deploying services that do not require special knowledge and expertise in Grid computing.
Markus Hillenbrand, Joachim Götze, Ge Zhang, Paul Müller
Semantic Integration of Identity Data Repositories
Abstract
With the continuously growing number of distributed and heterogeneous IT systems there is the need for structured and efficient identity management (IdM) processes. This implies that new users are created once and then the information is distributed to all applicable software systems same as if changes on existing user objects occur. The central issue is that there is no generally accepted standard for handling this information distribution because each system has its own internal representation of this data. Our approach is to give a semantic definition of the digital user objects’ attributes to ease the mapping process of an abstract user object to the concrete instantiation of each software system. Therefore we created an ontology to define the mapping of users’ attributes as well as an architecture which enables the semantic integration of identity data repositories. Our solution has been tested in an implementation case study.
Christian Emig, Kim Langer, Jürgen Biermann, Sebastian Abeck
Throughput Performance of the ActiveMQ JMS Server
Abstract
Communication among distributed software components according to the publish/subscribe principle is facilitated by the Java messaging service (JMS). JMS can be used as a message routing platform if the subscribers install filter rules on the JMS server. However, it is not clear whether its message throughput is sufficient to support large-scale systems. In this paper, we investigate the capacity of the high performance JMS server implementation ActiveMQ. In contrast to other studies, we focus on the message throughput in the presence of filters and show that filtering reduces the performance significantly. We present a model for the message processing time at the server and validate it by measurements. This model takes the number of installed filters and the replication grade of the messages into account and predicts the overall message throughput for specific application scenarios.
Robert Henjes, Daniel Schlosser, Michael Menth, Valentin Himmler

Sensornetze und Mobile Ad-Hoc-Netze

Frontmatter
Titan: A Tiny Task Network for Dynamically Reconfigurable Heterogeneous Sensor Networks
Abstract
Context recognition, such as gesture or activity recognition, is a key mechanism that enables ubiquitous computing systems to proactively support users. It becomes challenging in unconstrained environments such as those encountered in daily living, where it has to deal with heterogeneous networks, changing sensor availability, communication capabilities, and available processing power.
This paper describes Titan, a new framework that is specifically designed to perform context recognition in such dynamic sensor networks. Context recognition algorithms are represented by interconnected data processing tasks forming a task network. Titan adapts to different context recognition algorithms by dynamically reconfiguring individual sensor nodes to update the network wide algorithm execution.
We demonstrate the applicability of Titan for activity recognition on Tmote Sky sensor nodes and show that Titan is able to perform processing of sensor data sampled at 100 Hz and can reconfigure a sensor node in less than 1ms. This results in a better tradeoff between computational speed and dynamic reconfiguration time.
Clemens Lombriser, Daniel Roggen, Mathias Stäger, Gerhard Tröster
Key Exchange for Service Discovery in Secure Content Addressable Sensor Networks
Abstract
Secure Content Addressable Network (SCAN) is an architecture for service discovery in service centric sensor networks that enables dynamic service composition. This paper proposes two new security mechanisms for SCAN: Single Path Key Exchange (SPX) and Multi Path Key Exchange (MPX). Both security mechanisms allow two arbitrary nodes of SCAN to exchange a symmetric key for secure communication. We also propose to use replication service information and majority vote to achieve security.
We evaluated the performance and security of Secure Content Addressable Networks with Single Path Key Exchange, Multi Path Key Exchange and replication using a worst case attack model. It has been found, that in a network with 1000 nodes and 5% malicious nodes the probability of a successful lookup operation is still 80%. The results of the simulation indicate, that the overhead and the security level of SCAN with SPX and MPX scale with an increasing number of nodes. The simulation results also show that SCAN is suitable for networks with 100 to 1000 nodes.
Hans-Joachim Hof, Ingmar Baumgart, Martina Zitterbart
NIDES: Ein Verfahren zur Multihop-Distanzschätzung mittels Nachbarschaftsanalyse
Zusammenfassung
Die Bestimmung räumlicher Entfernungen zwischen einzelnen Knoten ist ein wichtiger Aspekt in drahtlosen Sensornetzwerken. In diesem Beitrag präsentieren wir ein neuartiges Verfahren zur Abstandsschätzung, welches auf dem Vergleich von Nachbarschaftslisten basiert. Es nutzt die Tatsache aus, dass zwei dicht zusammen liegende Knoten mehr gemeinsame Nachbarn haben als solche, die weiter voneinander entfernt liegen. Das Verfahren bietet zwei besondere Vorteile gegenüber anderen Ansätzen. Zum einen kommt es gänzlich ohne zusätzliche Hardware aus und zum anderen basiert es nicht auf der Messung physikalischer Größen, wie etwa der Funksignalstärke, welche durch Umwelteinflüsse oft stark verfälscht werden. Wir erläutern die grundlegende Funktionsweise dieses Schätzverfahrens zwischen direkt benachbarten Knoten und präsentieren anschließend ausführliche Untersuchungen zur Anwendung dieser Technik über mehrere Hops hinweg. Anhand von Simulationsergebnissen demonstrieren wir, dass diese Art der Abstandsschätzung auch im Multihopfall zuverlässige Ergebnisse liefert.
Carsten Buschmann, Christian Werner, Horst Hellbrück, Stefan Fischer
Verhaltensbeobachtung und -bewertung zur Vertrauensbildung in offenen Ad-hoc-Netzen
Zusammenfassung
Die Beobachtung des Verhaltens anderer Teilnehmer anhand mitgehörten Netzverkehrs ist in offenen Ad-hoc-Netzen die einzige ohne Vorwissen anwendbare Methode, durch welche Einschätzungen über die Kooperationsbereitschaft und Vertrauenswürdigkeit Anderer gewonnen werden können. Dieser Beitrag beschreibt die Problematik der Verhaltensbeobachtung und entwickelt auf der Basis einer grundlegenden Bedrohungsanalyse ein konkretes Verfahren für die zuverlässige Bewertung des Weiterleitungsverhaltens teilnehmender Knoten in Ad-hoc-Netzwerken. Anhand von Simulationsergebnissen wird nachgewiesen, dass mit dem Verfahren eine ausreichende Anzahl an Bewertungsereignissen gewonnen werden kann.
Daniel Kraft, Günter Schäfer

Dienstgüte und Sicherheit

Frontmatter
A Priori Detection of Link Overload due to Network Failures
Abstract
Restoration or protection switching mechanisms are triggered by link or node failures to redirect traffic over backup paths. These paths then carry the normal and the backup traffic which may lead to overload and thereby to quality of service (QoS) violations, i.e. to excessive packet loss and delay. In this paper, we present a method to assess the potential overload of the links due to network failures. We calculate the complementary cumulative distribution function (CCDF) of the relative load for each link in the network. We discuss various performance measures that condense this information to a single value per link which is suitable for a link ranking. This helps to identify weak spots of the network and to appropriately upgrade the bandwidth of links although they are not overloaded during normal operation. We implemented the concept in a software tool which helps network providers to anticipate the potential overload in their networks prior to failures and intended modifications (new infrastructure, new routing, new customers,...) and to take appropriate actions.
Jens Milbrandt, Michael Menth, Frank Lehrieder
Analysis of a Real-Time Network Using Statistical Network Calculus with Approximate Invariance of Effective Bandwidth
Abstract
The modern industrial network traffic consists of an increasing amount of soft real-time flows, which can tolerate very small delay and losses. Allowing probabilistic Quality of Service (QoS) violation for these flows can greatly help to improve resource utilization. However, the improvement depends on the statistical properties of competing independent flows. The notion of effective bandwidth, summarizes the statistical properties and QoS requirements of a flow. This paper suggests the usage of effective bandwidth to describe the arrival process of the flow along its path in a. network within the framework of the statistical network calculus. Further, we improve the existing formal relationship between effective envelope and effective bandwidth to achieve a better bound for the arrival process. This new approach enables efficient utilization of statistical multiplexing of independent flows both at the ingress of the network and along the path of the flow.
Kishore Angrishi, Shu Zhang, Ulrich Killat
Comparison of Preemptive and Preserving Admission Control for the UMTS Enhanced Uplink
Abstract
The UMTS enhanced uplink provides high bit rate radio bearers with fast rate control for packet switched radio traffic. Resource Managament in UMTS networks with the enhanced uplink has to consider the requirements of the dedidated channel users and the enhanced uplink users on the shared resource, i.e. the cell load. We propose an analytical model for such a system and evaluate the impact of two resource management strategies, one with preemption for dedicated channels and one without, on key QoS-indicators like blocking and dropping probabilities as well as user and cell throughput.
Andreas Mäder, Dirk Staehle
A New Model for Public-Key Authentication
Abstract
PGP’s Web of Trust, Maurer’s model of a PKI, Jøsang’s Certification Algebra, Haenni’s key validation method, and Credential Networks provide techniques for authenticating a public key in a decentralized public-key infrastructure. They allow to compute a degree of confidence for the authenticity of someone else’s public key. The computations are generally based on a reasoner’s trust assumptions and evidence such as public-key certificates and recommendations. In this paper, a new model and a formal language applicable to decentralized public-key authentication are introduced. The model is intended to serve as a basis for more sophisticated public-key authentication methods, as it incorporates some important points neglected so far. For example, the possibility of a physical entity to use different keys, to act under different names, or to share a key with others is considered.
Reto Kohlas, Jacek Jonczy, Rolf Haenni
A Proof of Concept Implementation of SSL/TLS Session-Aware User Authentication (TLS-SA)
Abstract
Most SSL/TLS-based e-commerce applications employ conventional mechanisms for user authentication. These mechanisms—if decoupled from SSL/TLS session establishment—are vulnerable to man-in-the-middle (MITM) attacks. In this paper, we elaborate on the feasibility of MITM attacks, survey countermeasures, introduce the notion of SSL/TLS session-aware user authentication (TLS-SA), and present a proof of concept implementation of TLS-SA. We think that TLS-SA fills a gap between the use of public key certificates on the client side and currently deployed user authentication mechanisms. Most importantly, it allows for the continued use of legacy two-factor authentication devices while still providing high levels of protection against MITM attacks.
Rolf Oppliger, Ralf Hauser, David Basin, Aldo Rodenhaeuser, Bruno Kaiser
Secure TLS: Preventing DoS Attacks with Lower Layer Authentication
Abstract
SSL/TLS has been designed to protect authenticity, integrity, and confidentiality. However, considering the possibility of TCP data injection, as described in [Wa04], it becomes obvious that this protocol is vulnerable to DoS attacks just because it is layered upon TCP. In this paper, we analyze DoS-attacks on SSL/TLS and describe a simple, yet effective way to provide protection for SSL/TLS by protecting the underlying TCP connection. We focus on a simple, feasible, and efficient solution, trying to balance security and usability issues by using the built-in key exchange of SSL/TLS to initialize TCP’s MD5 option.
Lars Völker, Marcus Schöller

Preisträger

Frontmatter
Traffic Shaping in a Traffic Engineering Context
Abstract
Modern communication networks carry a broad range of various applications such as data, voice, and video, and network providers are increasingly faced to the problems of traffic and resource management in order to meet the increasing quality of service (QoS) requirements. In particular, multi-media and realtime applications are sensitive with respect to QoS. In this paper we propose novel traffic engineering concepts for QoS that, in contrast to already existing solutions, need no intelligent functionality inside the core network and furthermore provide access to resource dimensioning in a comfortable way.
Dirk Abendroth
Routing and Broadcasting in Ad-Hoc Networks
Abstract
In this paper, we introduce two protocols - a routing and a broadcasting protocol - for ad-hoc networks which are based on a new paradigm enabled by the broadcast property of the wireless propagation medium. Nodes simply broadcast packets such that forwarding decisions are no longer taken at the sender of a packet, but in a completely distributed manner at the receivers. Consequently, nodes do not require knowledge about their neighbors. In this way, control traffic can be eliminated almost completely which in turn conserves scarce network resources such as battery power and bandwidth. Furthermore, as these two protocols are almost stateless and nodes do not store network topology information they remain unaffected by even very high rates of topology change and prove highly scalable in terms of number of nodes.
Marc Heissenbüttel
Benutzerorientierte Leistungs- und Verfügbarkeitsbewertung von Internetdiensten am Beispiel des Portals hamburg.de
Zusammenfassung
Der vorliegende Beitrag gibt einen Überblick über die Inhalte der Diplomarbeit „Benutzerorientierte Leistungs- und Verfügbarkeitsbewertung von Internetdiensten am Beispiel des Portals hamburg. de“, die in der Arbeitsgruppe TKRN unter Betreuung von Prof. Dr. Bernd E. Wolfinger entstand. Die Arbeit zeigt auf, wie durch eine Kombination von System-, Last-, Leistungs- und Verfügbarkeitsmessungen sowie durch die Vermessung adäquat gewählter Teilsysteme in sehr gezielter Weise nicht nur Engpässe in komplexen Internetkonfigurationen aufgedeckt und präzise eingegrenzt werden können, sondern auch, welche Optimierungsentscheidungen daraus betreiberseitig abgeleitet werden können.
Martin Gaitzsch
A System for in-Network Anomaly Detection
Abstract
Today, the Internet is used by companies frequently since it simplifies daily work, speeds up communication, and saves money. But the more popular the Internet gets the more it suffers from various challenges like DDoS attacks. This work, therefore, proposes an anomaly-based system that is able to detect adverse events caused by such challenges. The detection of network anomalies, in contrary to signature-based systems, ensures that previously unknown adverse events can be detected, too. Furthermore, the proposed system is designed for deployment within the network to allow a detection of adverse events as fast as possible, i.e., not only at the victim’s edge of the network. To achieve such an in-network anomaly detection the system is designed hierarchically and applies refinement of detection granularity.
Thomas Gamer
Simulation-Based Evaluation of Routing Protocols for Vehicular Ad Hoc Networks
Abstract
Information exchange between vehicles on the road is an important issue for future automotive applications. In vehicular ad hoc networks (VANETs), vehicles can be interconnected without the need of additional infrastructure along the roadside. Since these networks are highly dynamic, routing of data packets is a challenging task. In order to analyze and compare the performance of routing protocols, we developed realistic mobility models for typical traffic scenarios. These were used for a simulation-based evaluation of four routing protocols: AODV, DSR, FSR and TORA. AODV and FSR showed promising results in our simulations, while TORA is completely inapplicable for VANETs.
Sven Lahde
Dynamic Algorithms in Multi-user OFDM Wireless Cells
Abstract
This paper presents several results on dynamic OFDMA systems. It addresses especially the algorithmic complexity involved with several resource allocation approaches, sub-optimal heuristics for the use in practical systems, the related signaling overhead and modifications to the IEEE 802.11 protocol stack. It is argued that for the generation of dynamic OFDMA resource allocations very good sub-optimal methods exist while the loss due to signaling can be kept low for a large range of system parameters. Finally, an outline of the integration of dynamic OFDMA schemes into OFDM-based IEEE 802.11 systems is presented, providing significant performance benefits for such wireless local area networks.
James Gross
Self-Organizing Infrastructures for Ambient Services
Abstract
The vision of Ambient Intelligence (AmI) as a new paradigm for supporting the mobile user in his daily activities is currently entering the focus of European research efforts. A high degree of autonomy on the part of the supporting software system is inherent to this vision of omnipresent and continuously running services. However, adequate concepts for creating respective infrastructures that may operate autonomously and in a self-organized fashion are still largely unexplored. We propose the Ad hoc Service Grid (ASG) as a dedicated AmI infrastructure that may be deployed in an ad hoc fashion at arbitrary medium-sized locations (shopping malls, construction sites, trade fairs, etc.). In this paper, we give an overview over our results thus far. We focus on the problems of service placement, discovery and lookup, and data consistency within an ASG environment and show how we have solved these problems with new self-organizing and adaptive algorithms. These vital functions are the basis for the realization of ASG systems and represent an essential contribution to AmI research in general.
Klaus Herrmann
Bereitstelhmg von Dienstgüte für aggregierte Multimedia-Ströme in lokalen ‘Broadcast’-Netzen
Zusammenfassung
Mit der zunehmenden Bedeutung von echtzeitkritischen Audio- und Videoapplikationen wächst die Wichtigkeit von Dienstgütegarantien in Rechnernetzen. Als eine Möglichkeit Dienstgüte zu gewährleisten, bietet sich die Ressourcenreservierung, wobei sich eine statische Reservierung als ineffizient herausgestellt hat. In der vorgestellten Arbeit wurde ein dynamisches Reservierungssystem auf seine Eignung für aggregierte Audio- und Videolasten untersucht. Durch analytische Untersuchungen konnte zunächst gezeigt werden, dass sich mit zunehmender Aggregation die Abschätzung der zu erwartenden Last verbessert. Hierzu wurde der bei der Lastschätzung entstehende Fehler für reale Lasten und verschiedene stochastische Beschreibungsmethoden untersucht. Die Untersuchung des Gesamtsystems zeigte weiterhin, dass sich die Effizienz in fast alien Fallen durch Aggregation erhöhen lässt.
Stephan Heckmüller
Ein heuristisches Verfahren zur dienstgütebasierten Optimierung flexibler Geschäftsprozesse
Zusammenfassung
Im Zusammenhang mit der unternehmensübergreifenden Integration externer Partner in Geschäftsprozesse, haben serviceorientierte Architekturen zunehmend an Bedeutung gewonnen. Mit zunehmender Existenz von Servicen gleicher oder ähnlicher Funktionalität steigt die Relevanz nichtfunktionaler Eigenschaften als Selektionskriterium bei der Serviceauswahl. Geschäftsprozesse derart automatisiert aus Servicen zu orchestrieren, dass hierbei definierte Präferenzen und Restriktionen hinsichtlich ihrer nicht-funktionalen Eigenschaften bestmöglich erfüllt werden, führt zu einem Kompositionsproblem, welches sich als NP-schweres Optimierungsproblem formulieren lässt. Gegenstand dieses Beitrages ist die Vorstellung eines heuristischen Verfahrens zur Lösung des Service-Kompositionsproblems, welches mit geringer Laufzeit nahezu optimale Lösungen erzeugt, sowie gut mit der Problemgröße skaliert. Aufgrund der hohen Performanz eignet sich das Verfahren in besonderem Maße für zeitkritische Anwendungen.
Michael Spahn
Backmatter
Metadaten
Titel
Kommunikation in Verteilten Systemen (KiVS)
herausgegeben von
Torsten Braun
Georg Carle
Burkhard Stiller
Copyright-Jahr
2007
Verlag
Springer Berlin Heidelberg
Electronic ISBN
978-3-540-69962-0
Print ISBN
978-3-540-69961-3
DOI
https://doi.org/10.1007/978-3-540-69962-0

Premium Partner

    Bildnachweise