Kurt Rothermel

Mole—concepts of a mobile agent system

Due to its salient properties, mobile agent technology has received a rapidly growing attention over the last few years. Many developments of mobile agent systems are under way in both academic and industrial environments. In addition, there are already various efforts to standardize mobile agent facilities and architectures. Mole is the first mobile agent system that has been developed in the Java language. The first version was finished in 1995, and since then Mole has been constantly improved. Mole provides a stable environment for the development and usage of mobile agents in the area of distributed applications. In this paper we describe the basic concepts of a mobile agent system, i.e., mobility, communication and security, discuss different implementation techniques, present the decisions made in Mole and give an overview of the system services implemented in Mole.

An epidemic model for information diffusion in MANETs

Choosing appropriate information dissemination strategies is crucial in mobile ad hoc networks (MANET) due to the frequent topology changes. Flooding-based approaches like diffusion have a strong similarity with epidemic spreading of diseases. Applying epidemiological models to information diffusion allows the evaluation of such strategies depending on the MANET characteristics, e.g. the node density. In order to choose appropriate strategies at run time, the model should be easily evaluated.In this paper, an epidemic model is developed for a simple information diffusion algorithm based on simulation results. We analytically investigate the impact of node density on information diffusion. The analytical model allows the evaluation at runtime, even on devices with restricted resources, and thus enables mobile nodes to dynamically adapt their diffusion strategies depending on the local node density.

Spatially aware packet routing for mobile ad hoc inter-vehicle radio networks

Inter-vehicle communication can become an important building block for ITS telematics applications like safety and warning functions. Mobile ad hoc networks (MANETs) can serve as a local wireless network for exchanging information between cars for cooperative driver assistance applications. For the routing of data packets in such large-scale MANETs consisting of vehicles on the road, geographic multi-hop packet forwarding is a promising approach. However, a main drawback is that it performs poorly in networks with many topology holes. In this paper, we propose a spatially aware packet routing approach to predict permanent topology holes caused by spatial constraints and avoid them beforehand. This approach is generic and can be used in combination with any existing geographic forwarding protocol as an extension. Our simulations demonstrate that spatial awareness can significantly improve geographic forwarding performance in situations with many permanent topology holes, like in dynamic vehicle networks.

PCOM - a component system for pervasive computing

Applications in the pervasive computing domain are challenged by the dynamism in which their execution environment changes, e.g. due to user mobility. As a result, applications have to adapt to changes regarding their required resources. In this paper we present PCOM, a component system for pervasive computing. PCOM offers application programmers a high-level programming abstraction which captures the dependencies between components using contracts. The resulting application architecture is a tree formed by components and their dependencies. PCOM supports automatic adaptation in cases where the execution environment changes to the better or to the worse. User supplied as well as system provided strategies take users out of the control loop while offering flexible adaptation control.

Dynamic distance maps of the Internet

There is an increasing number of Internet applications that attempt to optimize their network communication by considering the network distance across which data is transferred. Such applications range from replication management to mobile agent applications. One major problem of these applications is to efficiently acquire distance information for large computer networks. This paper presents an approach to creating a global view on the Internet, a so-called network distance map, which realizes a hierarchical decomposition of the network into regions and which allows us to estimate the network distance between any two hosts. This view is not only a single snapshot but is dynamically adapted to the continuously changing network conditions. The main idea is to use a certain set of hosts for performing distance measurements and to use the so-gained information for estimating the distance between arbitrary hosts. A hierarchical clustering provides the notion of regions and allows us to coordinate the measurements in such a way that the resulting network load is minimized. An experimental evaluation on the basis of 119 globally distributed measurement servers shows that already a small number of measurement servers allows us to construct fairly accurate distance maps at low cost.

An Adaptive Stream Synchronization Protocol

Protocols for synchronizing data streams should be highly adaptive with regard to both changing network conditions as well as to individual user needs. The Adaptive Synchronization Protocol we are going to describe in this paper supports any type of distribution of the stream group to be synchronized. It incorporates buffer level control mechanisms allowing an immediate reaction on overflow or underflow situations. Moreover, the proposed mechanism is flexible enough to support a variety of synchronization policies and allows to switch them dynamically during presentation. Since control messages are only exchanged when the network conditions actually change, the message overhead of the protocol is very low.

Next century challenges: Nexus—an open global infrastructure for spatial-aware applications

Due to the lack of a generic platform for locationand spatial-aware systems, many basic services have to be reimplemented in each application that uses spatial-awareness. A cooperation among different applications is also difficult to achieve without a common platform. In this paper we present a platform that solves these problems. It provides an infrastructure that is based on digital models of regions of the physical world, which are augmented by virtual objects. We show how virtual objects make the integration of existing information systems and services in spatial-aware systems easier. Furthermore, our platform supports interactions between the computer models and the real world and integrates single models in a global “Augmented World”.

Architecture and algorithms for a distributed reputation system

Trust is an essential component of successful interactions in social life as well as in business relationships. In this paper we propose a system that closely reflects real-world trust building in an online environment. We describe the models used to represent trust in entities in various categories, algorithms to calculate and update trust based on experiences of entities with each other and the agent interactions necessary for finding and exchanging trust information.

A classification of location privacy attacks and approaches

In recent years, location-based services have become very popular, mainly driven by the availability of modern mobile devices with integrated position sensors. Prominent examples are points of interest finders or geo-social networks such as Facebook Places, Qype, and Loopt. However, providing such services with private user positions may raise serious privacy concerns if these positions are not protected adequately. Therefore, location privacy concepts become mandatory to ensure the user’s acceptance of location-based services. Many different concepts and approaches for the protection of location privacy have been described in the literature. These approaches differ with respect to the protected information and their effectiveness against different attacks. The goal of this paper is to assess the applicability and effectiveness of location privacy approaches systematically. We first identify different protection goals, namely personal information (user identity), spatial information (user position), and temporal information (identity/position + time). Secondly, we give an overview of basic principles and existing approaches to protect these privacy goals. In a third step, we classify possible attacks. Finally, we analyze existing approaches with respect to their protection goals and their ability to resist the introduced attacks.

FlexCup: a flexible and efficient code update mechanism for sensor networks

The ability to update the program code installed on wireless sensor nodes plays an import role in the highly dynamic environments sensor networks are often deployed in. Such code update mechanisms should support flexible reconfiguration and adaptation of the sensor nodes but should also operate in an energy and time efficient manner. In this paper, we present FlexCup, a flexible code update mechanism that minimizes the energy consumed on each sensor node for the installation of arbitrary code changes. We describe two different versions of FlexCup and show, using a precise hardware emulator, that our mechanism is able to perform updates up to 8 times faster than related code update algorithms found in the literature, while consuming only an eighth of the energy.