Contributions published at Communication Systems Group (Burkhard Stiller)

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Voting in distributed systems is a thoroughly researched subject within the domain of computer science since more than two decades. Surprisingly, little attention has been paid to the subject of voting during he last years media hype of peer-to-peer (P2P) networks. This is in spite of the fact that voting could be used to implement decentralized decision making, which has many useful applications in self-organizing P2P systems. A voting mechanism for fully decentralized P2P networks needs to be scalable, secure, robust and incentive-compatible. The properties of existing voting mechanisms prevents them from being used in fully decentralized systems, as these mechanisms are either centralized or do not scale. This thesis proposes a fully decentralized voting protocol together with incentives and security mechanisms, for use in a fully decentralized P2P network. In order to fuse the concepts of peer-to-peer networks and voting, elements from several intersecting domains, such as for instance, network security and incentives for cooperation, were closely examined and exploited in this thesis. The design of the decentralized voting mechanism was implemented and integrated in a prototype P2P application. Preliminary experiments with the prototype show that the proposed scheme could be used for decentralized voting in a fully decentralized P2P network.

The usage of biometric data for authentication purposes increases. The possibility of reliable identification of humans by biometric characteristics and authentication for access control offers a simplification of key management functions. The BioLANCC software project is a solution for biometric access control management. It provides functionality for the administration of user groups and access schedules, and controls biometric devices used for access control over a TCP/IP network. The integration of BioLANCC in the application landscape of an enterprise is a necessity to enable the administration and realization of access control on enterprise levels. This thesis focuses on the integration of the existing BioLANCC application in an enterprise application landscape. It designs an API for the integration of external data sources like user data, and analyzes the possibilities of data exchange with other applications of the landscape. Furthermore, management flexibility is extended by enhancing distributed access to the BioLANCC application over a network. For this purpose, a Web application for BioLANCC based on Java EE is designed and further services for external applications are provided.

The need for mobile network services such as Voice over IP (VoIP) increases steadily. Users will access these services from everywhere with their mobile devices. They will even access the services while moving. Mobile IPv6 was developed to bring mobility to the Internet. The access networks have to authenticate and authorize the users. This thesis develops architectures to integrate the mobility signaling with the authentication/authorization signaling in order to enhance handover performance. One of these architectures is implemented and evaluated. Depending on the network delay, it shows a better handover performance than if no integration of the mobility signaling with the authentication/authorization signaling is done.

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Competition in the economic world has turned harder. New ways of communication enable global access to markets. This phenomenon yields product markets which were impossible to reach. In order to prevail in this challenging environment, enterprises need to adapt established organizational structures. Consequently, a shift in focus towards core competen¬cies can observed. The virtual organization is a possible organizational structure to meet these new requirements. In an environment with mobile or nomadic users, the virtual orga¬nization concept is extended by mobility and increased dynamics, which results in the notion of Mobile Dynamic Virtual Organizations (MDVO). From a technical point of view, MDVOs are best implemented applying mobile grid technology. Accordingly, the main objective of this thesis is to identify the economic potential of MDVOs and mobile grids. Norway's aquaculture domain is the favored application field for this evaluation. The thesis gives an outline on the relevant set of related topics. Three sce¬narios for exemplary implementation of a mobile grid are introduced. The key technical and economic requirements are determined to assess the scenarios from a conceptual viewpoint. For further assessment, the applicable scenario is chosen based on a qualitative require¬ments evaluation. This scenario is modeled with the help of an established business model¬ing tool which leads to an in-depth quantitative assessment by means of corporate finance methods. This allows a detailed economic inspection of a mobile grid implementation applied in Norwegian aquaculture.

Biometrics has experienced its growth in the last years and is used more frequently in the field of identity verification within passport and access control systems, such as BioLANCC. The target of evaluation for this thesis is the BioLANCC access control system. BioLANCC is a software system that centrally administers the data and biometric hardware and transfers biometric traits to the biometric hardware over a TCP/IP network. New security-relevant questions arise when attaching a software system to a network and exchanging information over it. Also, general concerns about capturing and storing biometric data need consideration. With an overall security protection concept the drawbacks can be avoided and the advantages of biometric access control systems strengthened. This thesis deals with the security-relevant aspects in biometric management software and how security is improved and sustained in BioLANCC.

Obtaining information about the usage of network ressources by individual users forms the basis for establishing network billing systems or network management operations. While there are already widely used accounting techniques available for measuring IP Network traffic on a per-host basis, there is no adequate solution for charging users on a multi-user operating system. This thesis provides a survey on existing aproaches to this problem and identifies the requirements for a user-based IP accounting module. It develops a suitable software architecture and proposes a prototypical implementation for the Linux 2.6 operating system which is capable of providing per-user accounting for both the IPv4 and the IPv6 protocols. The thesis ends with the evaluation of the prototype, the discussion of problems that have turned up and deals with possible future extensions.

Usually, users interact with software by graphical user interfaces. The graphical user interface has to be user-friendly to perform tasks with effectiveness, efficiency and satisfaction. This goal can be reached by a consistent and intuitively comprehensible user interface, which also facilitates the usage of the software for beginners. The software BioLANCC (Biometric Local Area Network Control Center) manages biometric access control devices, which are distributed in a TCP/IP network. BioLANCC shows large deficiencies concerning the usability of the user interface. Design guidelines are being developed to eliminate these deficits. These guidelines are built on existent and established design principles of interactive systems. The usability of the user interface of BioLANCC should be improved by applying these design guidelines. In addition, a new user interface for the user group management and the attendance overview are being developed by applying these design guidelines. Finally, a usability test evaluates the developed design guidelines and the improved user interface of BioLANCC. The two versions of BioLANCC, one without and one including the improvements concerning the usability, are compared. The results show an evident improvement in the satisfaction of the new version of BioLANCC. In the re-designed user group management, the test subjects solved the given tasks with a superior effectiveness and efficiency.

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Dienstleistungen basierend auf IP werden im Internet mit zunehmender Vielfalt angeboten. Das wachsende Dienstangebot wird durch die verstärkte Verbreitung von IP getragen und in einigen Jahren zu All-IP führen. Aus dieser All-IP-Perspektive ergeben sich an Verrechnungssysteme von IP-Dienstleistungen zusätzliche Anforderungen. Eine dieser ist die Unterstützung der in den mobilen Telekommunikationsnetzen weit verbreiteten Prepaid-Verrechnung.

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