Author: Andreas Dittrich Proceedings of the Joint Workshop of the German Research Training Groups in Computer Science, Algorithmic synthesis of reactive and discrete-continuous systems (AlgoSyn), Dagstuhl, Germany, May 31 – June 2, 2010 Download: extended abstract

Disasters striking in inhabited areas pose a significant risk to the development and growth of modern societies. The impact of any disaster would be severe. In case a disaster strikes, fast and safe mitigation of damages is important. Information and communication technology (ICT) plays a crucial role in helping reconnaissance and first response teams on disaster sites.

Most rescue teams bring their own network equipment to use several IT services. Many of these services (e.g., infrastructure, location, communication) could be shared among teams but most of the time they are not. Coordination of teams is partly done by pen and paper-based methods. A single network for all participating teams with the possibility to reliably publish, discover and use services would be of great benefit.

Despite the participating teams and course of action being different on every site, described service networks display certain common properties: They arise spontaneously,
the number of nodes and their capabilities are subject to high fluctuation, the number and types of services are also fluctuating strongly and there is no global administrative configuration.

Because of these properties all network layers involved would need to be configured automatically. Based on the Internet Protocol (IP) — the only well-established global networking standard — a number of mechanisms promise to automatically configure service networks. In disaster management scenarios, where various services are critical for operation, mission control could benefit from these mechanisms by getting a live view of all active services and their states. It needs to be investigated if and how they are applicable.

Given an ad-hoc, auto-configuring service network, how and to what extent can we guarantee dependability properties such as availability, the ability to perform in the presence of faults (performability) and ultimately the ability to sustain certain levels of availability or performability (survivability) for critical services at run-time?

The goal of this dissertation is to provide a comprehensive dependability evaluation for such heterogenous and dynamic service networks. A run-time dependability cycle is being embedded into the network. In this cycle, the network is constantly monitored.
A distributed service discovery layer provides network-wide service presence monitoring. This will be extended to provide monitoring for availability and performability assessment. Based on monitoring data, dependability properties are evaluated at run-time. The survivability of critical services can be estimated by calculating the expected availability or performability with a given fault model. If necessary, adaptation measures are triggered which in turn can cause the monitoring to be reconfigured. Even if no adaptation is possible, run-time awareness of critical states is already a huge benefit. This cycle is the base of a self-aware adaptive service network.

	Authors: Andreas Dittrich Felix Salfner 24th IEEE International Symposium on Parallel Distributed Processing, Workshops and PhD Forum (IPDPSW), Atlanta, GA, USA, April 19-23, 2010 Download: final published version, IEEEXplore

Service discovery is a fundamental concept in service networks. It provides networks with the capability to publish, browse and locate service instances. Service discovery is thus the precondition for a service network to operate correctly and for the services to be available. In the last decade, decentralized service discovery mechanisms have become increasingly popular. Especially in ad-hoc scenarios – such as ad-hoc wireless networks – they are an integral part of auto-configuring service networks. Albeit the fact that auto-configuring networks are increasingly used in application domains where dependability is a major issue, these environments are inherently unreliable. In this paper, we examine the dependability of decentralized service discovery. We simulate service networks that are automatically configured by Zeroconf technologies. Since discovery is a time-critical operation, we evaluate responsiveness – the probability to perform some action on time even in the presence of faults – of domain name system (DNS) based service discovery under influence of packet loss. We show that responsiveness decreases significantly already with moderate packet loss and becomes practicably unacceptable with higher packet loss.

	Authors: Tobias Goldschmidt Andreas Dittrich Miroslaw Malek 15th IEEE Pacific Rim International Symposium on Dependable Computing (PRDC), Shanghai, China, November 16-18, 2009 Download: final published version, IEEEXplore

With ever-growing complexity of computer and communication systems analytical methods do not scale, especially with respect to dependability assessment of information technology (IT) organization. Generic reference models can be used as an alternative to analytical approaches by focusing on transforming qualitative assessment into quantitative evaluation of IT organization. In this paper, we examine the reference models IT Infrastructure Library (ITIL) and the Control Objectives for Information and Related Technology (CobiT) to derive a quantifiable concept for estimating the criticality of dependability-related IT organization processes in CobiT. After systematically analyzing ITIL processes and deriving properties that are relevant to dependability, those processes are mapped onto CobiT processes. Furthermore, we propose a process criticality index (PCI) which reflects the significance of each dependability-related process within a particular reference model. The PCI is based on the graph theory concept of betweenness centrality and uses a directed graph where nodes represent dependability-related processes and edges relations among them. Finally, using cycle and sequence analysis we are able to identify for every process which processes have to be implemented a priori. This provides an efficient strategy for implementing most significant processes first, according to the ranking based on the PCI.

	Authors: Andreas Dittrich Jon Kowal Miroslaw Malek International Workshop on Dependable Network Computing and Mobile Systems, DNCMS 2008, in conjunction with IEEE SRDS 2008, Naples, Italy, October 2012 Download full paper

Service-oriented architectures focus mainly on the automatic configuration of the attributes that describe the different layers involved in service communication and treat service instances monolithically – they either exist in the network which means that they are fully usable or they do not. This approach does not work well in environments where services are insufficiently dependable and the types of services used are not well known or standardized. This paper proposes a model to compose complex services from independent components with basic functionality that are organized as minimal services in the same service-oriented architecture. The approach promises to better handle run-time diagnostics and on-the-fly (re-)composition of service functionality in networks with highly dynamic capabilities.

	Autor: Andreas Dittrich Exposé zur Dissertation HU Berlin Paper: (mail)

Herkömmliche, dienstbasierte Architekturen gehen von idealisierten Bedingungen aus, innerhalb derer sie die Konfiguration der verschiedenen Schichten der Dienstnutzung zuverlässig automatisieren. In diesem Exposé wird das Konzept der Survivability eines serviceorientierten Systems diskutiert, damit es in Umgebungen überlebensfähig und vorhersagbar bleibt, in denen Ressourcen nicht nur stark begrenzt sind, sondern auch unzuverlässig zur Verfügung stehen. Dies ist besonders in Katastrophenszenarien der Fall. Der hier beschriebene Ansatz basiert darauf, dass ein System durch die permanente Überwachung des eigenes Zustands Self-Awareness erreicht, aufgrund dieser Erkenntnis intelligente Anpassungen vornehmen und mittels definierter Szenarios vorausschauend handeln kann. Die geeigneten Modelle, Metriken und Simulationen für die vollständige Erforschung der Problemstellung sollen innerhalb des interdisziplinären Graduiertenkollegs METRIK im Rahmen einer Dissertation erfolgen.