Introduction to the special section on dependable network computing

Dependable network computing is becoming a key part of our daily economic and social life. Every day, millions of users and businesses are utilizing the Internet infrastructure for real-time electronic commerce transactions, scheduling important events, and building relationships. While network traffic and the number of users are rapidly growing, the mean-time between failures (MTTF) is surprisingly short; according to recent studies, in the majority of Internet backbone paths, the MTTF is 28 days. This leads to a strong requirement for highly dependable networks, servers, and software systems. The challenge is to build interconnected systems, based on available technology, that are inexpensive, accessible, scalable, and dependable. This special section provides insights into a number of these exciting challenges

OCI-Based Group Communication Support in CORBA

Group communication is a useful mechanism guaranteeing consistency among replicated objects. The existing approaches do not allow transparent plug-in of group communication protocols into CORBA. They either require modification of CORBA or OS, or provide no room for incorporating group communication transport protocols into CORBA. We thus propose a generic group communication framework that allows transparent plug-in of various group communication protocols with no modification of existing CORBA. We extend the open communications interface (OCI) to support interoperability, reusability of existing group communication, and independency on ORB and OS. We also define the group communication inter-ORB protocol (GCIOP) as a group communication instantiation of the general inter-ORB protocol (GIOP) that encapsulates underlying group communication protocols. The proposed scheme can be exploited for fault-tolerant CORBA (FT CORBA)

OCI-Based Group Communication Support in CORBA

Group communication is a useful mechanism guaranteeing consistency among replicated objects. The existing approaches do not allow transparent plug-in of group communication protocols into CORBA. They either require modification of CORBA or OS, or provide no room for incorporating group communication transport protocols into CORBA. We thus propose a generic group communication framework that allows transparent plug-in of various group communication protocols with no modification of existing CORBA. We extend the open communications interface (OCI) to support interoperability, reusability of existing group communication, and independency on ORB and OS. We also define the group communication inter-ORB protocol (GCIOP) as a group communication instantiation of the general inter-ORB protocol (GIOP) that encapsulates underlying group communication protocols. The proposed scheme can be exploited for fault-tolerant CORBA (FT CORBA)

Design and Performance of a Fault-Tolerant Real-Time CORBA Event Service

Developing distributed real-time and embedded (DRE)systems in which multiple quality-of-service (QoS) dimen-sions must be managed is an important and challenging R&D problem. This paper makes three contributions to re-search on multi-dimensional QoS for DRE systems. First, itdescribes the design and implementation of a fault-tolerantreal-time CORBA event service for The ACE ORB (TAO).Second, it describes our enhancements and extensions tofeatures in TAO, to integrate real-time and fault toleranceproperties. Third, it presents an empirical evaluation ofour approach. Our results show that with some refinements,real-time and fault-tolerance features can be integrated ef-fectively and efficiently in a CORBA event service

Middleware services for distributed virtual environments

PhD ThesisDistributed Virtual Environments (DVEs) are virtual environments which allow dispersed users to interact with each other and the virtual world through the underlying network. Scalability is a major challenge in building a successful DVE, which is directly affected by the volume of message exchange. Different techniques have been deployed to reduce the volume of message exchange in order to support large numbers of simultaneous participants in a DVE. Interest management is a popular technique for filtering unnecessary message exchange between users. The rationale behind interest management is to resolve the "interests" of users and decide whether messages should be exchanged between them. There are three basic interest management approaches: region-based, aura-based and hybrid approaches. However, if the time taken for an interest management approach to determine interests is greater than the duration of the interaction, it is not possible to guarantee interactions will occur correctly or at all. This is termed the Missed Interaction Problem, which all existing interest management approaches are susceptible to. This thesis provides a new aura-based interest management approach, termed Predictive Interest management (PIM), to alleviate the missed interaction problem. PIM uses an enlarged aura to detect potential aura-intersections and iii initiate message exchange. It utilises variable message exchange frequencies, proportional to the intersection degree of the objects' expanded auras, to restrict bandwidth usage. This thesis provides an experimental system, the PIM system, which couples predictive interest management with the de-centralised server communication model. It utilises the Common Object Request Broker Architecture (CORBA) middleware standard to provide an interoperable middleware for DVEs. Experimental results are provided to demonstrate that PIM provides a scalable interest management approach which alleviates the missed interaction problem

Forum Session at the First International Conference on Service Oriented Computing (ICSOC03)

The First International Conference on Service Oriented Computing (ICSOC) was held in Trento, December 15-18, 2003. The focus of the conference ---Service Oriented Computing (SOC)--- is the new emerging paradigm for distributed computing and e-business processing that has evolved from object-oriented and component computing to enable building agile networks of collaborating business applications distributed within and across organizational boundaries. Of the 181 papers submitted to the ICSOC conference, 10 were selected for the forum session which took place on December the 16th, 2003. The papers were chosen based on their technical quality, originality, relevance to SOC and for their nature of being best suited for a poster presentation or a demonstration. This technical report contains the 10 papers presented during the forum session at the ICSOC conference. In particular, the last two papers in the report ere submitted as industrial papers

Middleware services for distributed virtual environments

PhD ThesisDistributed Virtual Environments (DVEs) are virtual environments which allow dispersed users to interact with each other and the virtual world through the underlying network. Scalability is a major challenge in building a successful DVE, which is directly affected by the volume of message exchange. Different techniques have been deployed to reduce the volume of message exchange in order to support large numbers of simultaneous participants in a DVE. Interest management is a popular technique for filtering unnecessary message exchange between users. The rationale behind interest management is to resolve the "interests" of users and decide whether messages should be exchanged between them. There are three basic interest management approaches: region-based, aura-based and hybrid approaches. However, if the time taken for an interest management approach to determine interests is greater than the duration of the interaction, it is not possible to guarantee interactions will occur correctly or at all. This is termed the Missed Interaction Problem, which all existing interest management approaches are susceptible to. This thesis provides a new aura-based interest management approach, termed Predictive Interest management (PIM), to alleviate the missed interaction problem. PIM uses an enlarged aura to detect potential aura-intersections and iii initiate message exchange. It utilises variable message exchange frequencies, proportional to the intersection degree of the objects' expanded auras, to restrict bandwidth usage. This thesis provides an experimental system, the PIM system, which couples predictive interest management with the de-centralised server communication model. It utilises the Common Object Request Broker Architecture (CORBA) middleware standard to provide an interoperable middleware for DVEs. Experimental results are provided to demonstrate that PIM provides a scalable interest management approach which alleviates the missed interaction problem

End-To-End Latency of a Fault-Tolerant CORBA Infrastructure

This paper presents an evaluation of the end-to-end latency of a fault-tolerant CORBA infrastructure that we have implemented. The fault-tolerant infrastructure replicates the server applications using active, passive and semi-active replication, and maintains strong replica consistency of the server replicas. By analyses and by measurements of the running fault-tolerant infrastructure, we characterize the end-to-end latency under fault-free conditions. The main determining factor of the run-time performance of the fault-tolerant infrastructure is the Totem group communication protocol, which contributes to the end-to-end latency primarily in two ways: the delay in sending messages and the processing cost of the rotating token. To reduce the delay in sending messages for passive and semi-active replication, the position of the primary server replica on the Totem ring, the token rotation time, the processing time at the client, and the processing time at the server must be considered. For active replication, the presence of duplicate messages adversely affects the performance. However, if an effective sending-side duplicate suppression mechanism is implemented, active replication is more advantageous than both passive and semi-active replication because of the automatic selection of the most favorable position of the server replica that sends the first non-duplicate reply

An integrated approach to testing complex systems

Die steigende Komplexität heutiger Testszenarien für komplexe Systeme erfordert einen ganzheitlichen und offenen Ansatz zur Verwaltung des gesamten Testprozesses. Eine Anwendung klassischer modellbasierter Testansätze, in denen eine präzise und vollständige formale Spezifikation des Systems als Referenz zur automatischen Testfallgenerierung dient, ist in der Praxis nicht möglich.Gründe dafür liegen zum einen im Fehlen einer adäquaten formalen Spezifikation. Komplexe Systeme sind aus verschiedenen Komponenten zusammengesetzt, teils Hardware teils Software und oft auch aus Fremdkomponenten. Dadurch ist es inhärent unrealistisch anzunehmen, dass eine solche formale Spezifikation a priori existiert. Andererseits muss eine ausgereifte Testumgebung die Ausführung von verteilten Testfällen unterstützen, denn die Test-Stimuli und -Beobachtungen können an verschiedenen Teilkomponenten des Systems stattfinden.Diese Arbeit präsentiert einen neuartigen Ansatz für das ganzheitliche Testen komplexer Systeme. Der Ansatz stellt eine 'grobgranulare' Testumgebung zur Verfügung, die mittels einer komponentenbasierten Testfallbeschreibung realisiert ist. Die Basis dafür bildet eine Bibliothek von elementaren, aber intuitiv verständlichen Testfallfragmenten. Die Beziehungen zwischen den Testfallfragmenten sind orthogonal. Dies ermöglicht eine Testbeschreibung und -ausführung, die durch formale Verifikationsmethoden ergänzt wird. Hierdurch können die Testfallbeschreibungsaspekte von Experten des Systems und der verwendeten Testwerkzeuge zu Experten der Systemlogik verschoben werden. Der Ansatz wird durch verschiedene, industrielle Fallstudien in zwei verschiedenen Bereichen illustriert: Computer Telephony Integrations Lösungen und Webbasierte Applikationen. Als Erweiterung des ganzheitlichen Testansatzes wird ein Algorithmus zur a posteriori Generierung approximativer Modelle für komplexe Systeme vorgestellt. Dafür wurde ein bekannter Algorithmus aus dem Maschinellen Lernen an applikationsbedingte Charakteristika angepasst, wie Präfix-Abgeschlossenheit,Input-Determinismus, sowie Unabhängigkeit und Symmetrien zwischen Aktionen. Die resultierenden Modelle können zwar nie exakt sein, in dem Sinne, dass sie das vollständige und korrekte Systemverhalten abbilden. Dennoch können sie von hohem praktischen Nutzen sein, da sie das gesammelte Wissen über das System in einer konsistenten Beschreibungsform repräsentieren.The increasing complexity of today's testing scenarios for complex systems demands an integrated, open, and flexible approach to support the managementof the overall test process. ``Classical'' model-based testing approaches, where a complete and precise formal specification serves as a reference for automatic test generation, are often impractical. Reasons are, on the one hand, the absence of a suitable formal specification. As complex systems are composed of several components, either hardware or software, often pre-built and third party, it is unrealistic to assume that a formal specification exists a priori. On the other hand, a sophisticated test execution environment is needed that can handle distributed test cases. This is because the test actions and observations can take place on different subsystems of the overall system. This thesis presents a novel approach to the integrated testing of complex systems. Our approach offers a coarse grained test environment, realized in terms of a component-based test design on top of a library of elementary but intuitively understandable test case fragments. The relations between the fragments are treated orthogonally, delivering a test design and execution environment enhanced by means of light-weight formal verification methods. In this way we are able to shift the test design issues from total experts of the system and the used test tools to experts of the system's logic only. We illustrate the practical usability of our approach by means of industrial case studies in two different application domains: Computer Telephony Integrated solutions and Web-based applications. As an enhancement of our integrated test approach we provide an algorithm for generating approximate models for complex systems a posteriori. This is done by optimizing a standard machine learning algorithm according to domain-specific structural properties, i.e. properties like prefix-closeness, input-determinism, as well as independency and symmetries of events. The resulting models can never be exact, i.e. reflect the complete and correct behaviour of the considered system. Nevertheless they can be useful in practice, to represent the cumulative knowledge of the system in a consistent description