Ralf Schumann

Recovery-management in the RelaX distributed transaction layer

Transactions are especially valuable in distributed systems, since they isolate the programmer from the effects of both concurrency and failures. In implementing transactions at the system level, flexibility has to be introduced into the transaction concept. Specifically, the premature release of data objects has to be addressed. To assure recoverability, resulting dependencies between transactions are stored by the system in a distributed data structure called a recovery graph. The storing of redundant information in the recovery graphs at the different sites reduces the complexity of the commit protocol, and a chase protocol used to abort transactions can be derived which excludes infinite chasing. The redundant information can be distributed almost for free because it can be piggybacked on messages. The new commit/abort protocols will be used in the RelaX project (reliable distributed applications support on Unix), which carries on work done at GMD in the PROFEMO project on distributed transaction mechanisms.<<ETX>>

RelaX-an extensible architecture supporting reliable distributed applications

The authors provide a description of RelaX (reliable distributed applications support on UniX), a portable and extensible system software layer on top of UNIX-like operating system kernels that supports reliable distributed applications by a generalized transaction mechanism. The transaction mechanism relieves each programmer of dealing explicitly with error recovery and concurrency control in every distributed application. In order to make transactions applicable as a general programming tool, flexibility has been introduced into the traditional transaction concept. The transaction mechanism is isolated in a server (Transaction Manager) that cooperates with an extensible set of resource managers, which provide different kinds of long-term storage entities accessible by RelaX transactions. Each resource manager provides a standard interface to the transaction kernel, and, if so desired, additional resource managers can be built. In order to ease the construction of new resource managers, RelaX provides generic software components as building blocks for any kind of resource manager. The RelaX architecture is described and the design of an examplary resource manager, the transactional object management system which provides access to persistent shared objects, is outlined.<<ETX>>

Fault-tolerant base station planning of Wireless Mesh Networks in dynamic industrial environments

Wireless Mesh Networks are infrastructure networks with a wireless multi-hop backbone. In this paper we present an innovative algorithm for fault-tolerant base station planning in wireless mesh networks. The algorithm determines a close-to-minimal number and the positions of base stations to be installed such that the radio coverage is correct in the presence of faults (base station crash or link outage). The algorithm considers both the connectivity of the multi-hop backbone and the connectivity of the mobile stations. The presented algorithm produces correct results, in limited number of iterations under realistic network size and in acceptable time. The provided fault-tolerance is sufficient in most practical situations.

Supporting fault-tolerant distributed computations under real-time requirements

Abstract In contrast to conventional (trans)action concepts, the proposed dynamic action model includes the possibility for optimistic recovery to gain high efficiency during normal operation. To minimize time overhead we use a redundant recovery graph to record the necessary recovery information. Based on this graph we provide decentralized protocols that efficiently produce a consistent system state concurrent to normal system activity. Considering real-time applications in distributed systems, error processing time has to be minimized. To achieve this, the proposed concept is extended to the parallel dynamic action scheme where the different versions are executed in parallel. This leads to a recovery concept that combines efficient distributed processing during normal operation and prompt reaction in case of an error.

Integrating fault-tolerant and real-time requirements of distributed systems

The authors propose a distributed dynamic action scheme that allows a recovery concept permitting efficient distributed computing during normal operation to be combined with efficient exception handling in the case of an effective error. They provide a dynamic action model tailored to the dynamic nature of distributed processing. This model offers a recovery concept which allows the recovery region of a recovery line to surmount the size of the corresponding computation in order to gain high efficiency during normal operation. By running the versions of a recovery block as distributed actions, it becomes possible to incorporate a recovery concept that allows efficient distributed processing during normal operation and prompt reaction in the case of error by running the different versions in parallel. To implement the dynamic action model efficiently a redundant recovery graph keeps track of recovery regions. On the basis of this graph the authors provide decentralized protocols that produce a consistent system state that is fast, efficient, and concurrent with normal system activity.<<ETX>>

Efficient Commit/Abort Procedures in the RelaX Distributed Transaction Layer

Transactions are especially valuable in distributed systems, since they isolate the programmer from the effects of both concurrency and failures. In implementing transactions at the system level, flexibility has to be introduced into the transaction concept. Especially, the premature release of objects has to be dealt with. To assure recoverability nevertheless, resulting dependencies between transactions are stored by the system in a distributed data structure called recovery graph. By partially replicating the recovery graph at the different sites, the complexity of the commit procedure is reduced and a chase procedure used to abort transactions can be derived which avoids infinite chasing. The information transfer needed for replication is almost for free because it can be piggybacked on messages sent anyway. The new commit/abort procedures will be used in the RelaX project (Reliable Distributed Applications Support on Unix), which carries on work done at GMD in the PROFEMO project on distributed transaction mechanisms.

Etablierung effektiver Informationssicherheit

International agierende Konzerne haben uber die Jahre hinweg meist ein mehr oder minder umfassendes Regelwerk fur IT-Sicherheit erstellt, grose mittelstandische Unternehmen zumindest eine Reihe einzelner Dokumente fur bestimmte Bereiche der IT-Sicherheit. Diesem Umstand zum Trotz teilten viele IT-Sicherheitsbeauftragten die Einschatzung, dass eine umfassende Umgestaltung, welche teils einer Neuerstellung nahe kommen, oder eine erhebliche Erganzung erforderlich seien.

Steuerung der Informationssicherheit durch Kennzahlen

Die Informationssicherheit ist ein wesentlicher Teil von IT-Governance. Zahlreiche internationale IT-Standards und Best Practices (z.B. COBIT, ITIL, ISO/IEC 27001, ISO/IEC 38500) bestatigen dies. Ziel der Informationssicherheit im Unternehmen ist die Erfullung der internen und externen Anforderungen an den Schutz der Informationen und informationsverarbeitenden Systeme. Schutzziele sind hierbei typischerweise Verfugbarkeit, Vertraulichkeit und Integritat.

Informationssicherheit effektiv Ausrichten durch praktikable Regelwerke

International agierende Konzerne haben uber die Jahre hinweg meist ein mehr oder minder umfassendes Regelwerk fur IT‐Sicherheit erstellt, grose mittelstandische Unternehmen zumindest eine Reihe einzelner Dokumente fur bestimmte Bereiche der IT‐Sicherheit. Diesem Umstandstand zum Trotz teilten viele IT‐Sicherheitsbeauftragten die Einschatzung, dass eine umfassendes Umgestaltung, welche teils einer Neuerstellung nahe kommen, oder eine erhebliche Erganzung erforderlich seien.

Kennzahlenbasierte Steuerung der Informationssicherheit in der Praxis

Dass Informationssicherheit ein wesentlicher Teil von IT‐Governance ist, bestatigen zahlreiche internationale IT‐Standards und Best Practices (z.B. COBIT, ITIL, ISO/IEC 27001, ISO/IEC 38500). Ziel der Informationssicherheit im Unternehmen ist die Erfullung der internen und externen Anforderungen an den Schutz der Informationen und informationsverarbeitenden Systeme. Schutzziele sind hierbei typischerweise Verfugbarkeit, Vertraulichkeit und Integritat.