Contribution to integration and coordination mechanisms for mobile distributed services in publish/subscribe networks

Esta tesis doctoral está enmarcada en dos diferentes pero complementarias áreas de investigación: las redes de Publicación/Subscripción y los servicios móviles distribuidos. Con el paso de los años las redes de Publicación/Subscripción han ido ofreciendo el soporte de comunicaciones desacopladas y ligeras que a su vez, han mejorado la distribución de la información en muchos escenarios de aplicación como lo son la ejecución de servicios distribuidos en entornos fijos. Los servicios móviles distribuidos han de ser desplegados en ambientes inalámbricos en donde los dispositivos móviles deben confiar en las mismas características que las redes de Publicación/Subscripción han estado ofreciendo a sus contrapartes fijos. En este contexto, una de las líneas de investigación pendientes consiste en cómo tomar ventaja de estas características, y cómo avanzar hacia nuevas soluciones no existentes con el fin de mejorar la integración entre los dispositivos fijos y móviles, y la ejecución de los servicios móviles distribuidos. En esta tesis doctoral se pretende avanzar en los mecanismos de integración y coordinación de los servicios móviles distribuidos en el contexto de las redes de Publicación/Subscripción. Los objetivos específicos de esta disertación están enfocados en lograr la integración de los sistemas de Publicación/Suscripción fijos y móviles, y la pro-visión de una versión de red de Publicación/Subscripción específica y uniforme que cuente con mecanismos de coordinación que mejoren la ejecución de los servicios móviles distribuidos. Los resultados de esta tesis doctoral están enmarcados en una versión específica de una red de Publicación/Subscripción que integra brokers fijos y móviles, y permite una coordinación totalmente desacoplada y mejorada entre dispositivos móviles que ejecutan fragmentos de servicios. Las contribuciones específicas son las siguientes: una nueva arquitectura de broker móvil que he llamado Rendezvous Mobile broker, un modelo abstracto de servicios móviles distribuidos coordinados sobre una red de Publicación/Subscripción, mejoras en los mecanismos de enrutamiento epidémicos para diseminar eventos de control producidos por fragmentos de servicios, una solución para soportar servicios altamente fragmentados y geográficamente dispersos, y finalmente una solución de interconexión entre dos dominios de red basados en Publicación/Subscripción: una red basada en el protocolo PubSubHubbub y otro en una red basada en el Publish/Subscribe Internet Routing Paradigm (PSIRP). Los experimentos llevados a cabo confirman que la versión específica de red de Pu-blicación/Subscripción propuesta incrementa el rendimiento de la red en términos de tiempo de espera entre nodos finales, permite una coordinación de los servicios móviles distribuidos más resistente a interrupciones y un mejor uso de los recursos de red, y finalmente logra exitosamente, con variaciones mínimas en el rendimiento de las comunicaciones, la interconexión entre estos dominios de Publicación/Subscripción diferentes. ABSTRACT This dissertation is made up of two different but complementary research areas: Publish/Subscribe networks and mobile distributed services. Over the years, Publish/Subscribe networks have been offering the lightweight and decoupled communication characteristics to improve the information distribution in several application domains such as the execution of distributed services. Mobile distributed services are set to be deployed in wireless environments where mobile devices must rely on the same features Publish/Subscribe networks can offer; so one of the pending research directions consists of how to take advantage of these features and further advance to-wards new un-existing solutions that enhance the integration between mobile and fixed systems and the execution of mobile distributed services. This dissertation seeks to advance the integration and coordination mechanisms of mobile distributed services in the context of Publish/Subscribe networks. The specific objectives aim to enable the integration of mobile and fixed Publish/Subscribe systems and provide a uniform and specific version of a Publish/Subscribe network with new coordination mechanisms that improve the execution of mobile distributed services. The results of this dissertation are enclosed in one specific version of a Publish/Subscribe network that integrates mobile and fixed brokers and coordinates the execution of mobile distributed services. These specific contributions are: a new architecture of a mobile broker I called Rendezvous Mobile Broker, an abstract model for coordinating mobile distributed services executions using a Publish/Subscribe net-work, new gossip routing solutions to disseminate events of services, mechanisms to support highly partitioned and geographically dispersed services and finally, an inter-networking solution between two Publish/Subscribe domains: a PubSubHubbub-based network and the Publish/Subscribe Internet Routing Paradigm (PSIRP)-based network. The experimental efforts confirm that the specific version of the Publish/Subscribe proposed in this dissertation improves the performance of the overall network in terms of end-to-end delay, enables a more resilience execution of mobile distributed services, a better usage of the existing network resources, and finally successfully achieves, with minor variations in the network performance, the internetworking between two different Publish/Subscribe domains.

Middleware architectures for the Smart Grid : survey and challenges in the foreseeable future

The traditional power grid is just a one-way supplier that gets no feedback data about the energy delivered, what tariffs could be the most suitable ones for customers, the shifting daily needs of electricity in a facility, etc. Therefore, it is only natural that efforts are being invested in improving power grid behavior and turning it into a Smart Grid. However, to this end, several components have to be either upgraded or created from scratch. Among the new components required, middleware appears as a critical one, for it will abstract all the diversity of the used devices for power transmission (smart meters, embedded systems, etc.) and will provide the application layer with a homogeneous interface involving power production and consumption management data that were not able to be provided before. Additionally, middleware is expected to guarantee that updates to the current metering infrastructure (changes in service or hardware availability) or any added legacy measuring appliance will get acknowledged for any future request. Finally, semantic features are of major importance to tackle scalability and interoperability issues. A survey on the most prominent middleware architectures for Smart Grids is presented in this paper, along with an evaluation of their features and their strong points and weaknesses.

Designing and simulating smart grids

Growing energy demands and the increased use of renewal energies have changed the landscape of power networks leading to new challenges. Smart Grids have emerged to cope with these challenges by facilitating the integration of traditional and renewable energy resources in distributed, open, and self-managed ways. Innovative models are needed to design energy infrastructures that can enable self-management of the power grid. Software architectures smoothly integrate the software that provides self-management to Smart Grids and their hardware infrastructures. We present a framework to design the software architectures of autonomous Smart Grids in an intuitive domain-oriented way and to simulate their execution by automatically generating the code from the designed autonomous smart grid architectures.

Transactional failure recovery for a distributed key-value store

With the advent of cloud computing, many applications have embraced the ensuing paradigm shift towards modern distributed key-value data stores, like HBase, in order to benefit from the elastic scalability on offer. However, many applications still hesitate to make the leap from the traditional relational database model simply because they cannot compromise on the standard transactional guarantees of atomicity, isolation, and durability. To get the best of both worlds, one option is to integrate an independent transaction management component with a distributed key-value store. In this paper, we discuss the implications of this approach for durability. In particular, if the transaction manager provides durability (e.g., through logging), then we can relax durability constraints in the key-value store. However, if a component fails (e.g., a client or a key-value server), then we need a coordinated recovery procedure to ensure that commits are persisted correctly. In our research, we integrate an independent transaction manager with HBase. Our main contribution is a failure recovery middleware for the integrated system, which tracks the progress of each commit as it is flushed down by the client and persisted within HBase, so that we can recover reliably from failures. During recovery, commits that were interrupted by the failure are replayed from the transaction management log. Importantly, the recovery process does not interrupt transaction processing on the available servers. Using a benchmark, we evaluate the impact of component failure, and subsequent recovery, on application performance.

Photonic switching architectures with logic cells

Possible switching architectures, with Optically Programmable Logic Cells - OPLCs - will be reported in this paper. These basic units, previously employed by us for some other applications mainly in optical computing, will be employed as main elements to switch optical communications signals. The main aspect to be considered is that because the nternal components of these cells have nonlinear behaviors, namely either pure bistable or SEED-like properties, several are the possibilities to be obtained. Moreover, because their properties are dependent, under certain condition, of the signal wavelength, they are apt to be employed in WDM systems and the final result will depend on the orresponding optical signal frequency. We will give special emphasis to the case where self-routing is achieved, namely to structures of the Batcher or Banyan type. In these cases, as it will be shown, there is the possibility to route any packet input to a certain direction according to its first bits. The number of possible outputs gives the number of bits needed to route signals. An advantage of this configuration is that a very versatile behavior may be allowed. The main one is the possibility to obtain configurations with different kinds of behavior, namely, Strictly Nonblocking, Wide-Sense Nonblocking or Rearrangeably Nonblocking as well as to eliminate switching conflicts at a certain intermediate stages.

Massively parallelizable list-mode reconstruction using a Monte Carlo-based elliptical Gaussian model

Purpose: A fully three-dimensional (3D) massively parallelizable list-mode ordered-subsets expectation-maximization (LM-OSEM) reconstruction algorithm has been developed for high-resolution PET cameras. System response probabilities are calculated online from a set of parameters derived from Monte Carlo simulations. The shape of a system response for a given line of response (LOR) has been shown to be asymmetrical around the LOR. This work has been focused on the development of efficient region-search techniques to sample the system response probabilities, which are suitable for asymmetric kernel models, including elliptical Gaussian models that allow for high accuracy and high parallelization efficiency. The novel region-search scheme using variable kernel models is applied in the proposed PET reconstruction algorithm. Methods: A novel region-search technique has been used to sample the probability density function in correspondence with a small dynamic subset of the field of view that constitutes the region of response (ROR). The ROR is identified around the LOR by searching for any voxel within a dynamically calculated contour. The contour condition is currently defined as a fixed threshold over the posterior probability, and arbitrary kernel models can be applied using a numerical approach. The processing of the LORs is distributed in batches among the available computing devices, then, individual LORs are processed within different processing units. In this way, both multicore and multiple many-core processing units can be efficiently exploited. Tests have been conducted with probability models that take into account the noncolinearity, positron range, and crystal penetration effects, that produced tubes of response with varying elliptical sections whose axes were a function of the crystal's thickness and angle of incidence of the given LOR. The algorithm treats the probability model as a 3D scalar field defined within a reference system aligned with the ideal LOR. Results: This new technique provides superior image quality in terms of signal-to-noise ratio as compared with the histogram-mode method based on precomputed system matrices available for a commercial small animal scanner. Reconstruction times can be kept low with the use of multicore, many-core architectures, including multiple graphic processing units. Conclusions: A highly parallelizable LM reconstruction method has been proposed based on Monte Carlo simulations and new parallelization techniques aimed at improving the reconstruction speed and the image signal-to-noise of a given OSEM algorithm. The method has been validated using simulated and real phantoms. A special advantage of the new method is the possibility of defining dynamically the cut-off threshold over the calculated probabilities thus allowing for a direct control on the trade-off between speed and quality during the reconstruction.

Rule Representation in Distributed Environments with Accepting Networks of Splicing Processors.

This paper presents the model named Accepting Networks of Evolutionary Processors as NP-problem solver inspired in the biological DNA operations. A processor has a rules set, splicing rules in this model,an object multiset and a filters set. Rules can be applied in parallel since there exists a large number of copies of objects in the multiset. Processors can form a graph in order to solve a given problem. This paper shows the network configuration in order to solve the SAT problem using linear resources and time. A rule representation arquitecture in distributed environments can be easily implemented using these networks of processors, such as decision support systems, as shown in the paper.

Identifying Potential Risks and Benefits of Using Cloud in Distributed Software Development.

Cloud-based infrastructure has been increasingly adopted by the industry in distributed software development (DSD) environments. Its proponents claim that its several benefits include reduced cost, increased speed and greater productivity in software development. Empirical evaluations, however, are in the nascent stage of examining both the benefits and the risks of cloud-based infrastructure. The objective of this paper is to identify potential benefits and risks of using cloud in a DSD project conducted by teams based in Helsinki and Madrid. A cross-case qualitative analysis is performed based on focus groups conducted at the Helsinki and Madrid sites. Participants observations are used to supplement the analysis. The results of the analysis indicated that the main benefits of using cloud are rapid development, continuous integration, cost savings, code sharing, and faster ramp-up. The key risks determined by the project are dependencies, unavailability of access to the cloud, code commitment and integration, technical debt, and additional support costs. The results revealed that if such environments are not planned and set up carefully, the benefits of using cloud in DSD projects might be overshadowed by the risks associated with it.

Hardening digital systems with distributed functionality: robust networks

Collaborative hardening and hardware redundancy are nowadays the most interesting solutions in terms of fault tolerance achieved and low extra cost imposed to the project budget. Thanks to the powerful and cheap digital devices that are available in the market, extra processing capabilities can be used for redundant tasks, not only in early data processing (sensed data) but also in routing and interfacing1

3-Phase Rectifier System with very demanding dynamic load: Architecture analysis and control strategy

A distributed power architecture for aerospace application with very restrictive specifications is analyzed. Parameters as volume, weight and losses are analyzed for the considered power architectures. In order to protect the 3 phase generator against high load steps, an intermediate bus (based in a high capacitance) to provide energy to the loads during the high load steps is included. Prototypes of the selected architecture for the rectifier and EMI filter are built and the energy control is validated.

Performance metrics for small-signal stability assessment of DC-distributed power-system-architecture comparisons

The objective of this paper is to provide performance metrics for small-signal stability assessment of a given system architecture. The stability margins are stated utilizing a concept of maximum peak criteria (MPC) derived from the behavior of an impedance-based sensitivity function. For each minor-loop gain defined at every system interface, a single number to state the robustness of stability is provided based on the computed maximum value of the corresponding sensitivity function. In order to compare various power-architecture solutions in terms of stability, a parameter providing an overall measure of the whole system stability is required. The selected figure of merit is geometric average of each maximum peak value within the system. It provides a meaningful metrics for system comparisons: the best system in terms of robust stability is the one that minimizes this index. In addition, the largest peak value within the system interfaces is given thus detecting the weakest point of the system in terms of robustness.

INDICIa: a new distributed clustering protocol

Many data streaming applications produces massive amounts of data that must be processed in a distributed fashion due to the resource limitation of a single machine. We propose a distributed data stream clustering protocol. Theoretical analysis shows preliminary results about the quality of discovered clustering. In addition, we present results about the ability to reduce the time complexity respect to the centralized approach.

Numerical simulation of the transition from densely distributed to localized cracking.

8th International Conference on Fracture Mechanics of Concrete and Concrete Structures (FraMCoS8).

Advanced characterization of a coffee fermenting tank by multi-distributed wireless sensors: spatial interpolation and phase diagrams.

In coffee processing the fermentation stage is considered one of the critical operations by its impact on the final quality of the product. However, the level of control of the fermentation process on each farm is often not adequate; the use of sensorics for controlling coffee fermentation is not common. The objective of this work is to characterize the fermentation temperature in a fermentation tank by applying spatial interpolation and a new methodology of data analysis based on phase space diagrams of temperature data, collected by means of multi-distributed, low cost and autonomous wireless sensors. A real coffee fermentation was supervised in the Cauca region (Colombia) with a network of 24 semi-passive TurboTag RFID temperature loggers with vacuum plastic cover, submerged directly in the fermenting mass. Temporal evolution and spatial distribution of temperature is described in terms of the phase diagram areas which characterizes the cyclic behaviour of temperature and highlights the significant heterogeneity of thermal conditions at different locations in the tank where the average temperature of the fermentation was 21.2 °C, although there were temperature ranges of 4.6°C, and average spatial standard deviation of ±1.21ºC. In the upper part of the tank we found high heterogeneity of temperatures, the higher temperatures and therefore the higher fermentation rates. While at the bottom, it has been computed an area in the phase diagram practically half of the area occupied by the sensors of the upper tank, therefore this location showed higher temperature homogeneity

Systematic Method to Assess Small-Signal Stability of DC-Distributed Power-System-Architecture

The objective of this paper is to present a simplified method to analyze small-signal stability of a power system and provide performance metrics for stability assessment of a given power-system-architecture. The stability margins are stated utilizing a concept of maximum peak criteria (MPC), derived from the behavior of an impedance-based sensitivity function that provides a single number to state the robustness of the stability of a well-defined minor-loop gain. For each minor-loop gain, defined at every system interface, the robustness of the stability is provided as a maximum value of the corresponding sensitivity function. Typically power systems comprise of various interfaces and, therefore, in order to compare different architecture solutions in terms of stability, a single number providing an overall measure of the whole system stability is required. The selected figure of merit is geometric average of each maximum peak value within the system, combined with the worst case value of system interfaces.