Gregor Schiele

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.

A survey on engineering approaches for self-adaptive systems

The complexity of information systems is increasing in recent years, leading to increased effort for maintenance and configuration. Self-adaptive systems (SASs) address this issue. Due to new computing trends, such as pervasive computing, miniaturization of IT leads to mobile devices with the emerging need for context adaptation. Therefore, it is beneficial that devices are able to adapt context. Hence, we propose to extend the definition of SASs and include context adaptation. This paper presents a taxonomy of self-adaptation and a survey on engineering SASs. Based on the taxonomy and the survey, we motivate a new perspective on SAS including context adaptation.

Energy-efficient cluster-based service discovery for Ubiquitous Computing

Service discovery in Ubiquitous Computing is a task that has to be done frequently due to dynamically changing environments. The limited battery power of mobile devices requires us to optimize frequent and energy costly tasks, especially the ones incurring in communication activities. In this paper we present a novel service discovery algorithm based on node clustering. Nodes within a cluster may sleep to save energy when idle. A cluster head node is always active and answers discovery requests on behalf of other nodes to achieve low discovery latencies. Simulation experiments show energy savings of up to 66% compared to an approach where all nodes are permanently active while the discovery latencies were not increased.

Requirements of Peer-to-Peer-based Massively Multiplayer Online Gaming

Massively multiplayer online games have become increasingly popular. However, their operation is costly, as game servers must be maintained. To reduce these costs, we aim at providing a communication engine to develop massively multiplayer online games based on a peer-to-peer system. In this paper we analyze the requirements of such a system and present an overview of our current work.

A NAT Traversal Mechanism for Peer-To-Peer Networks

In this demo we present our approach for establishing a communication channel between hosts behind a NAT-based router. To do so, we developed a peer-to-peer based variant of the STUN protocol using so-called superpeers. Using this protocol we determine the used NAT types for the hosts and select a suitable NAT traversal technique dynamically.

COMITY: conflict avoidance in pervasive computing environments

Pervasive Computing leads to novel challenges of application coordination. Applications may interfere with each other since they affect and share the same physical environment. A user that executes a navigation application utilizing a loudspeaker as output may annoy a user listening to music. To ensure a conflict-free execution of multiple applications, approaches are needed to avoid conflicts at runtime. In this paper we identify typical conflicts arising in Pervasive Computing. We propose how to detect potential conflicts by requiring applications to communicate their effects on the physical environment. After the detection, a suitable strategy is applied resolving the potential conflict. As a practical validation, we discuss how to model and avoid conflicts using our component-based software system PCOM.

Middleware and application adaptation requirements and their support in pervasive computing

Pervasive computing environments are characterized by an additional heterogeneity compared to existing computing infrastructures. Devices ranging from small embedded systems to full-fledged computers are connected via spontaneously formed networks. In this paper we analyze requirements of applications and system software to cope with the dynamically changing execution environment. Based on our micro-broker-based middleware BASE a component framework for pervasive computing supporting application adaptation is proposed.

Peer-to-peer support for low-latency Massively Multiplayer Online Games in the cloud

Cloud gaming has recently been proposed as an alternative to traditional video game distribution. With this approach, the entire game is stored, run and rendered on a remote server. Player input is forwarded to the server via the Internet and the games output is returned as a video stream. This adds network delay, which can negatively impact the gameplay. The delay is acceptable as long as the user is located geographically close to the cloud servers. However, for Massively Multiplayer Online Games (MMOGs), this delay is added on top of the existing delay between MMOG client and server. As MMOGs are highly delay-sensitive, this can significantly degrade their playability. To deal with this issue, we propose to use peer-to-peer techniques to distribute the MMOG server functionality and place it at the cloud server centers. This allows us to reduce the additional delay introduced by running the MMOG clients in the cloud.

Bootstrapping in Peer-to-Peer Systems

Peer-to-Peer systems have become a substantial element in computer networking. Distributing the load and splitting complex tasks are only some reasons why many developers have come to adopt this technology. However, all of them face a severe problem at the very beginning: setting up an overlay network, such that other clients can easily join it. With an empty peer cache common bootstrapping methods require some manually triggered actions for discovering a peer on the overlay. We therefore introduce an approach for an automated bootstrapping based on DDNS. In this paper we give detailed information about our protocol and document its efficiency and scalability.

ContextCube - providing context information ubiquitously

Sensing the state of the environment is an important source for context-aware applications. Several approaches exist to provide sensor information to mobile application nodes. As the extreme cases we have pure infrastructures and pure ad hoc networks. In order to allow sensor platforms to serve both of these approaches, we have designed a universal sensor platform and integrated it into an infrastructure-based approach as well as into ad hoc networks. In this paper we discuss the requirements on such a platform, the design, and the experiences.