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- KonferenzbeitragFederated Identity Management: Die Notwendigkeit zentraler Koordinationsdienste(Kommunikation in Verteilten Systemen (KiVS), 2005) Hommel, Wolfgang; Reiser, HelmutIdentity & Access Management (I&AM) Systeme bilden eine moderne Basis f ür die organisationsinterne Verwaltung von Mitarbeitern und Kunden sowie deren Zugriff auf lokale Ressourcen. Ihr Wirkungsbereich endet allerdings an den Organisationsgrenzen. Im Rahmen von B2B-Szenarien, beispielsweise beim Supply Chain Management, wächst jedoch der Bedarf, auch die Accounts und Rechte der Mitarbeiter und Kunden von Partnerunternehmen effizient verwalten zu können, d.h. diese Organisationsgrenzen zu überschreiten. Die zentrale Idee des Federated Identity Managements (FIM) ist, die Partnerunternehmen als autoritative Quelle für die Identitätsinformationen zu nutzen und die damit zusammenhängenden Management-Aufgaben an diese zu delegieren. In diesem Artikel zeigen wir, dass die drei derzeit fortgeschrittensten FIM-Ansätze – SAML, Liberty Alliance und WS-Federation – mehrere methodische und funktionale Defizite aufweisen, die einen effizienten Aufbau von FIM-Szenarien in der Praxis erschweren. Als Lösung eines Teils dieser Probleme stellen wir einen zentralen Koordinationsdienst für Identitätsföderationen vor, der im Rahmen unserer Forschung prototypisch implementiert wird.
- KonferenzbeitragParlay PAM in 3GPP's IP-multimedia subsystem(Kommunikation in Verteilten Systemen (KiVS), 2005) Klaus, Jens-Michael; Magedanz, ThomasThe document will give a brief overview of the Presence and Availability -specification in general, protocols used in the IP Multimedia Subsystem - namely SIP and Diameter - and will show a possible mapping for PAM-methods to the underlying infrastructure. In addition it will describe the IMS infrastructure developed at Fraunhofer Fokus and the implementation of the PAM-server
- KonferenzbeitragFrom location to position management: User tracking for location-based services(Kommunikation in Verteilten Systemen (KiVS), 2005) Küpper, Axel; Treu, GeorgThis paper compares traditional location management, which focuses on tracking mobile subscribers in the topology of a cellular network, with position management, which we define to be a set of functions for tracking mobile targets in terms of geographic positions as needed for LBSs. As the air interface is the most limited resource in a mobile network, location management has been optimized with regard to signaling overhead caused by updating location data (and paging) between the terminal and the network. Position management is exposed to the same limitations, but, on the other hand, imposes much stronger requirements with regard to accuracy of position data as well as flexibility of tracking. This paper presents an architecture for tailoring the tracking process according to the special LBS requirements on the one hand and limiting the resulting update traffic at the air interface on the other. The architecture is shared between mobile terminals and an application server, for which we present first details of our implementation.
- KonferenzbeitragThe FOKUS open SIP AS - A service platform for NGN(Kommunikation in Verteilten Systemen (KiVS), 2005) Fasel, Elmar; Knüttel, Karsten; Magedanz, ThomasEvolutionary, a Next Generation Network (NGN) is a significant improvement of a successfully existing network. The third Generation Partnership Project (3GPP) aimed to merge two of the most successful paradigms in communications: cellular networks and the Internet. Within the IP Multimedia Subsystem (IMS) the 3GPP specified a comprehensive and service oriented architecture that includes session based Quality of Service in IP, charging mechanisms and offers standardized interfaces for application service integration and seamless interactions with legacy services. Under this technical premise a variety of promising value added services suppose to attend our entire communication life. Fraunhofer Institute FOKUS designed and implemented a 3GPP compliant Application Server for converged services called the 'Open SIP AS' which is deploying services within the 'National Host for 3Gb Applications Testbed' on top of an IMS architecture. This paper describes details of the implementation and the usage of the 'Open SIP AS' and gives an example of a NGN service.
- KonferenzbeitragA flexible reflector for media streams(Kommunikation in Verteilten Systemen (KiVS), 2005) Brandt, Jens; Kahmann, Verena; Wolf, LarsReflectors mapping multicast to unicast sessions have been proposed to enable multicast media distribution for clients in non-multicast capable networks. However, existing implementations do not allow clients to modify the session by using VCR-like commands in a flexible way. In this paper we describe the design and implementation of a reflector mapping a multicast or unicast session to several downstream unicast sessions. We show that by applying a separation of control and data path such a flexible reflector can handle true media-on-demand functionality for several scenarios, even for group communication, more efficiently than several unicast sessions.
- KonferenzbeitragLastregelung von web services mittels Proof-of-Work Funktionen(Kommunikation in Verteilten Systemen (KiVS), 2005) Golze, Sebastian; Mühl, Gero; Weis, Torben; Jäger, Michael C.Kostenlos frei angebotene Web Services sind anfällig für Überlastsituationen, die beispielsweise durch eine zu große Anzahl von Clients oder durch zu häufig anfragende Clients verursacht werden können. Auch Denial-of-Service Angriffe durch bösartige Clients können Überlastsituationen verursachen. Eine Lösung wäre, den betroffenen Web Service kostenpflichtig zu machen. Dies scheitert jedoch in der Praxis meist an der umständlichen Erhebung. In diesem Artikel erläutern wir, wie mittels Proof-of-Work Funktionen eine Lastregelung von Web Services realisiert werden kann. Proof-of-Work Funktionen er- möglichen Clients nachzuweisen, dass sie eine gewisse Menge von Rechenleistung oder anderen Ressourcen erbracht haben. Durch die Regelung wird sichergestellt, dass alle Clients weiterhin Zugriff haben, aber die Zugriffe von zu häufig nachfragenden Clients eingeschränkt werden.
- KonferenzbeitragRevenue maximisation in peer-to-peer networks(Kommunikation in Verteilten Systemen (KiVS), 2005) Eger, Kolja; Killat, UlrichBitTorrent is a peer-to-peer (p2p) protocol for file-sharing. Its improvement over other file-sharing protocols is its tit-for-tat strategy to decide to whom a peer should upload. This means that an upload to a peer depends on the download from that peer. This paper investigates the BitTorrent upload algorithm and proposes a new algorithm which is based on a distributed optimisation problem where each peer maximises its own revenue. First simulation results show that the proposed algorithm outperforms the BitTorrent choking algorithm with respect to efficiency and fairness.
- KonferenzbeitragMaking chord go mobile(Kommunikation in Verteilten Systemen (KiVS), 2005) Zöls, Stefan; Schollmeier, Rüdiger; Kellerer, WolfgangThe Chord protocol is a structured Peer-to-Peer (P2P) protocol based on distributed hash tables (DHT). By using hash keys to identify the nodes in the network and also the shared objects, it can significantly reduce the signaling overhead in a P2P overlay network, as flooding of query messages can be avoided. However, when nodes join or leave the Chord network, object references have to be rearranged in order to maintain the hash key mapping rules. This leads to high maintenance traffic, especially when nodes stay in the Chord ring only for a short time. In mobile environments, the resources and data rates of mobile devices are limited, so the maintenance traffic generated by shifting object references may cause problems when using Chord in a mobile scenario. In this work, we present a solution to the problem of frequent joins and leaves of nodes. By distinguishing static nodes and temporary nodes, we can decrease the maintenance traffic generated by shifting object references significantly.
- KonferenzbeitragA generic and modular accounting and charging system for peer-to-peer applications(Kommunikation in Verteilten Systemen (KiVS), 2005) Hausheer, David; Gerke, Jan; Stiller, BurkhardAccountability is one of the keys to success for emerging P2P systems. In the absence of appropriate accounting and charging mechanisms, P2P applications may suffer from free-riders which benefit from other peers without contributing themselves. This paper describes a new Accounting and Charging system for P2P applications which separates generic accounting and charging functionality from individual underlying accounting mechanisms. The presented approach enables the design and implementation of different accounting schemes, independently from core accounting functionality. The approach has been implemented and successfully used with several accounting schemes in different P2P applications.
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