Heiko Kopp

Security architecture for service-based mobile environments

The paper describes an approach for the integration of transparent security mechanisms into de-centralized mobile application scenarios. This becomes necessary as the communication among various devices migrates to wireless technologies at a progressive rate, finally leading to pervasive computing scenarios. Our result is a modular and heterogeneous architecture based on a high-capacity middleware. In this regard, the Web services technology is a guarantor for modularity as well as flexibility. It allows the integration of special tasks applying high security and mobility on different layers. This paper describes basic technologies used in such a system as well as selected aspects of a realized prototype.

Extended Medium Observation (EMO) — A load-aware metric for routing in wireless mesh backbone networks

The main advantage of using specific routing algorithms like AODV-ST or OLSR in wireless mesh backbone networks is their optimized handling of throughput from border nodes to each other. However, currently used metrics tend to ignore load situations and thus result in overloaded clusters within the mesh network. Our work presents a novel approach for load-based routing. We developed load observation methods and proved their practical applicability within fixed IEEE 802.11a structures. The Extended Medium Observation (EMO)-metric is based on a sophisticated concept of an advanced channel observation process, in which topological and load sensitive characteristics become elicited, quantified and composed. A direct comparison of EMO-AODV, a modified version of AODV using EMO with conventional metrics show that EMO-AODV achieves a kind of traffic balancing that tends to smooth load peaks.

Wireless Self-Organizing Backbone Mesh Network (WiSoNet)

Despite significant advances in parts of the physical layer, available WLAN systems still cannot offer wired equivalent bandwidth. In this paper we propose a novel concept, called wireless self-organizing backbone mesh network (WiSoNet), for a wireless network infrastructure as a backbone and describe its long-term potential. WiSoNet combines two major IEEE standards - IEEE 802.11 (WLAN) and IEEE 802.16 (WiMAX) to build a heterogeneous wireless network topology. To aggregate bandwidth of multiple WLAN connections we introduce a hybrid network solution that uses ad-hoc mechanisms. Further, to decrease the amount of administration and resource management, we use specific algorithms for the self-organization of routing and channels assignment. Since the WiMAX-based supply network already supports quality of service, we propose mechanisms to extend the QoS to end users. Accordingly, we present our prototypical system implementation and discuss the issues we will focus on in the future

Evaluation of a Communication Environment for High-Speed Mobile Wireless LAN Clients

The use of networks, especially wireless networks, has been constantly increasing for some years. The use of Wireless LAN was however so far limited to the installation of fixed Hot Spots, especially at airports or train stations. This article exemplifies the accomplished experiments with the use of Wireless LAN IEEE 802.11b Standard in mobile systems, e.g. in driving cars. The most important result is, that slight optimisations of Wireless LAN components can achieve an acceptable communication up to at least 90 km/h.

Environment for I/O performance measurement of distributed and local secondary storage

Whilst the performance gap between main memory and secondary storage of computer systems increased rapidly during the last years, especially the analysis of secondary storage performance becomes very important. For that purpose this paper introduces a plugin-based framework providing an integrated execution environment for new benchmarks and offering analysis tools for the complex result output of particularly I/O measurements. As an example of this environment we describe the PRIOmark, an I/O benchmark that characterizes file system performance of single and distributed systems by means of two different file system interfaces. Additionally, the I/O performance of three file systems, two file system interfaces as well as different I/O workloads are compared to show the flexibility of the presented PRIOmark.

Efficiency of wireless local area networks in clients moving at high speed

Wireless communication structures based on the IEEE 802.11 Standard became an important research area within science and economy during the last years. It forms a basis for an area-wide use of mobile services and personalized information within so called hotspots. However, the common usage is a public available stationary installation like at an airport, office building or university. Besides other wireless technologies like DECT or HiperLAN this paper shows, that Wireless LAN is capable for use in clients moving at high speed. To prove the theory a couple of measurements have been made using components of the IEEE 802.11b standard and clients moving at speeds up to 200 km/h. Beside measuring characteristic parameters like signal- and noise level as well as data throughput for different speeds, measurements on the quality of voice transmission have been made for the first time. In addition to a detailed analysis this article covers perspectives for applications using wireless hotspots.