Mirko Knoll

Rapid Prototyping for Pervasive Applications

VisualRDK is a high-level programming language for prototyping pervasive applications. Context is tightly integrated into the language itself, so developers can attach functionality to locations, persons, or situations instead of the device. Pervasive computing appliances range from consumer devices over embedded sensor boards to PCs and large-scale context servers. Because these devices vary tremendously in their capabilities, application developers must create different programming models for every class of device. This makes rapid prototyping infeasible as soon as more than one class of devices is involved. Rapid prototyping therefore requires a programming model that hides the environments heterogeneity.

A new approach for establishing pairwise keys for securing wireless sensor networks

Wireless sensor networks based on highly resource-constrained devices require symmetric cryptography in order to make them secure. Integral to this is the exchange of unique symmetric keys between two devices. In this paper, we propose a novel decentralized key exchange protocol that guarantees the confidentiality of a key exchange even if an attacker has compromised some of the devices in the network. A central objective of the protocol design was to minimize resource consumption on the individual devices. We evaluate the resource requirements of our protocol in terms of memory requirements, CPU usage and network traffic both through theoretical analysis and through simulations.

Optimizing locality for self-organizing context-based systems

Running context-based systems with a fixed infrastructure involves substantial investments. There have been efforts to replace those systems with self-organizing ones. Therefore, recent systems use peer-to-peer (P2P) technology as a basis. Context-information is bound to a specific location and thus should be stored on a nearby node. Common P2P algorithms use one-dimensional ID spaces. However, locations have at least two coordinates, namely x and y. We use space-filling curves to map the two-dimensional area onto the one-dimensional ID space. In this paper we discuss the suitability of different space-filling curves for the average case and for stochastic scenarios.

Customizable pervasive applications

Human behavior and housing resist every standardization effort. Many aspects such as different technical equipment, furniture, and usage patterns make our surroundings as individual as ourselves. Thus, the personalization of pervasive applications is a fundamental requirement. To enable the development of custom pervasive applications, we propose a software development process. This process is based on the successful process for modern desktop applications. There, developers create extensible applications and components. Customizers use the resulting artifacts to develop custom applications. Finally, users configure applications to their individual needs by adjusting predefined settings. To adopt this process for pervasive computing, we present a component system for developers, a graphical toolkit for customizers, and self-configuration algorithms to ease the deployment

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.

The Internet of Things - Context-based Device Federations

Locating physical devices and accessing their functionality in pervasive environments is strongly restricted by their locality. Since there are more and more devices available, waiting to serve users, a simple way is required to access, connect, and most important to locate them in the real world. In this paper we propose an approach to connect and access arbitrary devices by federating them related to their geographical location. This approach allows us to create context-aware federations of devices - the Internet of things

Scripting your home

Our homes and lives are as individual as ourselves. Many aspects, such as technical equipment, furniture, and usage patterns in these surroundings differ. Thus, personalization of applications that operate in such environments is required. The challenge for tools and programming paradigms is to provide a powerful but yet easy-to-use platform. In this paper we illustrate how our visual scripting language puts these requirements for programming ubiquitous computing environments into action.

Replication in Peer-to-Peer Systems

We present a replication algorithm for peer-to-peer networks that automatically adapts to an increase of requests. If some information is suddenly very popular, the algorithm distributes it in the peer-to-peer system and reduces the replicas when the demand decreases. The algorithm is totally self-organizing, i.e. it does not need any administration and is very resilient to node failures. Furthermore, our algorithm uses the concept of geographical proximity. Data is preferably replicated on peers which are geographically close. This is especially useful for location-based information, such as traffic information, tourist data and weather alerts.

Towards a general purpose user interface for service-oriented context-aware applications

Today context-aware applications are isolated systems designed for a special scenario. There is no way to combine different applications, which is common practice with desktop applications since years. For example, the airline knows when your plane leaves, your PDA knows your GPS position, VirtualEarth knows how long you need to the airport, and another service can order a taxi to your current position. When you manage to combine these services, you will get informed when you must go to the airport and a taxi is ordered to your current position. Thus, in the future we need to federate context-data retrieved from different sources and services on the internet. This imposes several challenges: (1) We need an architecture that allows us to federate these services and to communicate with the users. (2) We need tools that allow programmers to quickly implement and deploy services on the network to generate a grass-roots movement. (3) We need a general purpose user-interface for such applications that allows users to deal with context-data and interact with context-aware services. In this paper we sketch our architecture for service-oriented context-aware applications. Based on this architecture we develop a general purpose user interface which is a collage of instant messenger, roadmap, and web browser. In this paper, we describe the formatting requirements for the CHI Conference and offer a number of suggestions on writing style for the worldwide CHI readership.

Bootstrapping Peer-to-Peer Systems Using IRC

Research in the area of peer-to-peer systems is mainly focused on structuring the overlay network. Little attention is paid to the process of setting up and joining a peer-to-peer overlay network, i.e. the bootstrapping of peer-to-peer networks. The major challenge is to get hold of one peer that is already in the overlay. Otherwise, the first peer must be able to detect that the overlay is currently empty. Successful P2P applications either provide a centralized server for this task (Skype) or they simply put the burden on the user (eMule). We propose an automatic solution which does not require any user intervention and does not exhibit a single point of failure. Such decentralized bootstrapping protocols are especially important for open non-commercial peer-to-peer systems which cannot provide a server infrastructure for bootstrapping. The algorithm we are proposing builds on the Internet Relay Chat (IRC), a highly available, open,and distributed network of chat servers. Our algorithm is designed to put only a very minimal load on the IRC servers.In measurements we show that our bootstrapping protocol scales very well, handles flash crowds, and does only put a constant load on the IRC system disregarding of the peer-to-peer overlay size.