In service networks, discovery plays a crucial role as a layer where providers can be published and enumerated. This work focuses on the responsiveness of the discovery layer, the probability to operate successfully within a deadline, even in the presence of faults. It proposes a hierarchy of stochastic models for decentralized discovery and uses it to describe the discovery of a single service using three popular protocols. A methodology to use the model hierarchy in wireless mesh networks is introduced. Given a pair requester and provider, a discovery protocol and a deadline, it generates specific model instances and calculates responsiveness. Furthermore, this paper introduces a new metric, the expected responsiveness distance der, to estimate the maximum distance from a provider where requesters can still discover it with a required responsiveness. Using monitoring data from the DES testbed at Freie Universität Berlin, it is shown how responsiveness and der of the protocols change depending on the position of nodes and the link qualities in the network.
Today's businesses rely ever more on dependable service provision deployed on information and communications technology (ICT) infrastructures.
Service dependability is highly influenced by the individual infrastructure component properties.
Combining these properties for consistent dependability analysis is challenging as every service requester might use a different set of components during service usage, constituting the user-perceived view on a service.
This paper presents a methodology to evaluate user-perceived instantaneous service availability. It uses three input models: (1) The ICT infrastructure, with failure rates, repair rates and deployment times of all components, (2) an abstract description of complex hierarchical services, (3) a mapping that contains concrete ICT components for the service pair requester and provider, as well as their existing replicas, and a duration of usage. The methodology then automatically generates an availability model from those parts of the ICT infrastructure needed during provision for the specified pair.
To calculate instantaneous availability, the age of the ICT components, the order and time of their usage during service provision are taken into account. The methodology supports generation of different availability models, we demonstrate this by providing reliability block diagrams and fault-trees. We demonstrate the feasibility of the methodology by applying it to parts of the network infrastructure of University of Lugano, Switzerland.
Service-oriented architecture (SOA) has emerged as an approach to master growing system complexity by proposing services as basic building elements of system design. However, it remains difficult to evaluate dependability of such distributed and heterogeneous functionality as it depends highly on the properties of the enabling information and communications technology (ICT) infrastructure. Moreover, every specific pair service client and provider can utilize different ICT components, constituting for the user-perceived view of a service.
We provide a model-driven methodology to automatically create reliability block diagrams of such views. Given a service description, a network topology model and a pair service client and provider, it identifies relevant ICT components and generates a user-perceived service availability model (UPSAM). We then use this UPSAM to calculate the steady-state availability of different views on an exemplary mail service deployed in the network infrastructure of University of Lugano, Switzerland.
An ever-increasing number of both functional and non-functional requirements has resulted in growing system complexity which demands new solutions in system modeling and evaluation.
As a remedy, service-oriented architecture (SOA) offers services as basic building elements of system design.
Service dependability is highly dependent on the properties of the underlying information and communications technology (ICT) infrastructure.
This is especially true for the user-perceived dependability of a specific pair service client and provider as every pair may utilize different ICT components.
We provide a model for the description of ICT components and their non-functional properties based on the Unified Modeling Language (UML). Given a service description, a network topology model and a pair service client and provider, we propose a methodology to automatically identify relevant ICT components and generate a user-perceived service infrastructure model (UPSIM). We demonstrate the feasibility of the methodology by applying it to parts of the service network infrastructure at University of Lugano (USI), Switzerland. We then show how this methodology can be used to facilitate user-perceived service dependability analysis.
Design of complex systems involving a number of experts from various fields necessarily includes modeling at different levels of abstraction. Modeling is particularly important in the initial phase of a joint project when all system requirements and constraints have to be clearly defined and understood by all the partners. Once an unambiguous structural model has been achieved and components interfaces fixed, design of components can be done independently. For the initial phase, a very simplified modeling methodology based on UML that can be easily understood and applied has been proposed. The application of the methodology has been presented through the design of full structural model of the infrastructure for precision farming. Modeled infrastructure is an open ICT hardware-software solution based on ISOBUS specification, that enables partial automation of tractors increasing safety and production efficiency. Model achieved through several steps presents a mutual understanding platform between the partners. Most importantly, a precise model has been achieved without the necessity of in deep study of UML by all the partners.