Cross-layer Peer-to-Peer Computing in Mobile Ad Hoc Networks

The future information society is expected to rely heavily on wireless technology. Mobile access to the Internet is steadily gaining ground, and could easily end up exceeding the number of connections from the fixed infrastructure. Picking just one example, ad hoc networking is a new paradigm of wireless communication for mobile devices. Initially, ad hoc networking targeted at military applications as well as stretching the access to the Internet beyond one wireless hop. As a matter of fact, it is now expected to be employed in a variety of civilian applications. For this reason, the issue of how to make these systems working efficiently keeps the ad hoc research community active on topics ranging from wireless technologies to networking and application systems. In contrast to traditional wire-line and wireless networks, ad hoc networks are expected to operate in an environment in which some or all the nodes are mobile, and might suddenly disappear from, or show up in, the network. The lack of any centralized point, leads to the necessity of distributing application services and responsibilities to all available nodes in the network, making the task of developing and deploying application a hard task, and highlighting the necessity of suitable middleware platforms. This thesis studies the properties and performance of peer-to-peer overlay management algorithms, employing them as communication layers in data sharing oriented middleware platforms. The work primarily develops from the observation that efficient overlays have to be aware of the physical network topology, in order to reduce (or avoid) negative impacts of application layer traffic on the network functioning. We argue that cross-layer cooperation between overlay management algorithms and the underlying layer-3 status and protocols, represents a viable alternative to engineer effective decentralized communication layers, or eventually re-engineer existing ones to foster the interconnection of ad hoc networks with Internet infrastructures. The presented approach is twofold. Firstly, we present an innovative network stack component that supports, at an OS level, the realization of cross-layer protocol interactions. Secondly, we exploit cross-layering to optimize overlay management algorithms in unstructured, structured, and publish/subscribe platforms

Data Storage and Dissemination in Pervasive Edge Computing Environments

Nowadays, smart mobile devices generate huge amounts of data in all sorts of gatherings. Much of that data has localized and ephemeral interest, but can be of great use if shared among co-located devices. However, mobile devices often experience poor connectivity, leading to availability issues if application storage and logic are fully delegated to a remote cloud infrastructure. In turn, the edge computing paradigm pushes computations and storage beyond the data center, closer to end-user devices where data is generated and consumed. Hence, enabling the execution of certain components of edge-enabled systems directly and cooperatively on edge devices. This thesis focuses on the design and evaluation of resilient and efficient data storage and dissemination solutions for pervasive edge computing environments, operating with or without access to the network infrastructure. In line with this dichotomy, our goal can be divided into two specific scenarios. The first one is related to the absence of network infrastructure and the provision of a transient data storage and dissemination system for networks of co-located mobile devices. The second one relates with the existence of network infrastructure access and the corresponding edge computing capabilities. First, the thesis presents time-aware reactive storage (TARS), a reactive data storage and dissemination model with intrinsic time-awareness, that exploits synergies between the storage substrate and the publish/subscribe paradigm, and allows queries within a specific time scope. Next, it describes in more detail: i) Thyme, a data storage and dis- semination system for wireless edge environments, implementing TARS; ii) Parsley, a flexible and resilient group-based distributed hash table with preemptive peer relocation and a dynamic data sharding mechanism; and iii) Thyme GardenBed, a framework for data storage and dissemination across multi-region edge networks, that makes use of both device-to-device and edge interactions. The developed solutions present low overheads, while providing adequate response times for interactive usage and low energy consumption, proving to be practical in a variety of situations. They also display good load balancing and fault tolerance properties.Resumo Hoje em dia, os dispositivos móveis inteligentes geram grandes quantidades de dados em todos os tipos de aglomerações de pessoas. Muitos desses dados têm interesse loca- lizado e efêmero, mas podem ser de grande utilidade se partilhados entre dispositivos co-localizados. No entanto, os dispositivos móveis muitas vezes experienciam fraca co- nectividade, levando a problemas de disponibilidade se o armazenamento e a lógica das aplicações forem totalmente delegados numa infraestrutura remota na nuvem. Por sua vez, o paradigma de computação na periferia da rede leva as computações e o armazena- mento para além dos centros de dados, para mais perto dos dispositivos dos utilizadores finais onde os dados são gerados e consumidos. Assim, permitindo a execução de certos componentes de sistemas direta e cooperativamente em dispositivos na periferia da rede. Esta tese foca-se no desenho e avaliação de soluções resilientes e eficientes para arma- zenamento e disseminação de dados em ambientes pervasivos de computação na periferia da rede, operando com ou sem acesso à infraestrutura de rede. Em linha com esta dico- tomia, o nosso objetivo pode ser dividido em dois cenários específicos. O primeiro está relacionado com a ausência de infraestrutura de rede e o fornecimento de um sistema efêmero de armazenamento e disseminação de dados para redes de dispositivos móveis co-localizados. O segundo diz respeito à existência de acesso à infraestrutura de rede e aos recursos de computação na periferia da rede correspondentes. Primeiramente, a tese apresenta armazenamento reativo ciente do tempo (ARCT), um modelo reativo de armazenamento e disseminação de dados com percepção intrínseca do tempo, que explora sinergias entre o substrato de armazenamento e o paradigma pu- blicação/subscrição, e permite consultas num escopo de tempo específico. De seguida, descreve em mais detalhe: i) Thyme, um sistema de armazenamento e disseminação de dados para ambientes sem fios na periferia da rede, que implementa ARCT; ii) Pars- ley, uma tabela de dispersão distribuída flexível e resiliente baseada em grupos, com realocação preventiva de nós e um mecanismo de particionamento dinâmico de dados; e iii) Thyme GardenBed, um sistema para armazenamento e disseminação de dados em redes multi-regionais na periferia da rede, que faz uso de interações entre dispositivos e com a periferia da rede. As soluções desenvolvidas apresentam baixos custos, proporcionando tempos de res- posta adequados para uso interativo e baixo consumo de energia, demonstrando serem práticas nas mais diversas situações. Estas soluções também exibem boas propriedades de balanceamento de carga e tolerância a faltas

RDF Data Indexing and Retrieval: A survey of Peer-to-Peer based solutions

The Semantic Web enables the possibility to model, create and query resources found on the Web. Enabling the full potential of its technologies at the Internet level requires infrastructures that can cope with scalability challenges and support various types of queries. The attractive features of the Peer-to-Peer (P2P) communication model such as decentralization, scalability, fault-tolerance seems to be a natural solution to deal with these challenges. Consequently, the combination of the Semantic Web and the P2P model can be a highly innovative attempt to harness the strengths of both technologies and come up with a scalable infrastructure for RDF data storage and retrieval. In this respect, this survey details the research works that adopt this combination and gives an insight on how to deal with the RDF data at the indexing and querying levels.Le Web Sémantique permet de modéliser, créer et faire des requêtes sur les ressources disponibles sur le Web. Afin de permettre à ses technologies d'exploiter leurs potentiels à l'échelle de l'Internet, il est nécessaire qu'elles reposent sur des infrastructures qui puissent passer à l'échelle ainsi que de répondre aux exigences d'expressivité des types de requêtes qu'elles offrent. Les bonnes propriétés qu'offrent les dernières générations de systèmes pair-à- pair en termes de décentralisation, de tolérance aux pannes ainsi que de passage à l'échelle en font d'eux des candidats prometteurs. La combinaison du modèle pair-à-pair et des technologies du Web Sémantique est une tentative innovante ayant pour but de fournir une infrastructure capable de passer à l'échelle et pouvant stocker et rechercher des données de type RDF. Dans ce contexte, ce rapport présente un état de l'art et discute en détail des travaux autour de systèmes pair-à-pair qui traitent des données de type RDF à large échelle. Nous détaillons leurs mécanismes d'indexation de données ainsi que le traitement des divers types de requêtes offerts

Underlay aware approach to provide reliable and timely dissemination of events in a publish subscribe system

Publish-subscribe is a well-known paradigm for building distributed applications. Events produced by peers, called publishers, are disseminated to interested consumers, called subscribers. Usually publishers and subscribers are arranged in a peer-to-peer overlay network, which helps in dissemination of events in a decentralised manner. Recent research tries to provide Quality-of-Service like delay bounds or reliability in such a system. In order to provide reliability current distributed publish-subscribe systems mostly either rely on overlay level acknowledgement protocols or try to find multiple disjoint paths in the overlay to increase redundancy without taking into account the underlay topology. Acknowledgements induce high delays affecting timeliness of event delivery. Providing multiple paths without looking at the underlay does not take into account correlations between paths within the underlay. We address these drawbacks by designing a content-based publish-subscribe system which provides reliability by taking into account the underlay topology to reduce correlations within the underlay in overlay links. The system consists of three layers: The Topology-Discovery-Overlay (TDO) layer constructs an underlay topology aware overlay which reflects the underlay topology by using a path-matching algorithm. On top of the TDO the Maximum-Reliability-Spanning-Tree (MRST) layer constructs k overlay link disjoint trees which contain the most reliable overlay links. The MRSTs are used by the content-based publish-subscribe layer for subscription flooding and event forwarding. The system has been evaluated by simulations in PeerSim using Internet-like topologies. The results show that the TDO discovers most of the underlay topology and constructs overlay topologies reflecting the underlay topology. Simulations also show that the system converges towards a maximum event delivery probability

It's about THYME: On the design and implementation of a time-aware reactive storage system for pervasive edge computing environments

This work was partially supported by Fundacao para a Ciencia e a Tecnologia (FCT-MCTES) through project DeDuCe (PTDC/CCI-COM/32166/2017), NOVA LINCS UIDB/04516/2020, and grant SFRH/BD/99486/2014; and by the European Union through project LightKone (grant agreement n. 732505).Nowadays, smart mobile devices generate huge amounts of data in all sorts of gatherings. Much of that data has localized and ephemeral interest, but can be of great use if shared among co-located devices. However, mobile devices often experience poor connectivity, leading to availability issues if application storage and logic are fully delegated to a remote cloud infrastructure. In turn, the edge computing paradigm pushes computations and storage beyond the data center, closer to end-user devices where data is generated and consumed, enabling the execution of certain components of edge-enabled systems directly and cooperatively on edge devices. In this article, we address the challenge of supporting reliable and efficient data storage and dissemination among co-located wireless mobile devices without resorting to centralized services or network infrastructures. We propose THYME, a novel time-aware reactive data storage system for pervasive edge computing environments, that exploits synergies between the storage substrate and the publish/subscribe paradigm. We present the design of THYME and elaborate a three-fold evaluation, through an analytical study, and both simulation and real world experimentations, characterizing the scenarios best suited for its use. The evaluation shows that THYME allows the notification and retrieval of relevant data with low overhead and latency, and also with low energy consumption, proving to be a practical solution in a variety of situations.publishersversionpublishe

On service optimization in community network micro-clouds

Cotutela Universitat Politècnica de Catalunya i KTH Royal Institute of TechnologyInternet coverage in the world is still weak and local communities are required to come together and build their own network infrastructures. People collaborate for the common goal of accessing the Internet and cloud services by building Community networks (CNs). The use of Internet cloud services has grown over the last decade. Community network cloud infrastructures (i.e. micro-clouds) have been introduced to run services inside the network, without the need to consume them from the Internet. CN micro-clouds aims for not only an improved service performance, but also an entry point for an alternative to Internet cloud services in CNs. However, the adaptation of the services to be used in CN micro-clouds have their own challenges since the use of low-capacity devices and wireless connections without a central management is predominant in CNs. Further, large and irregular topology of the network, high software and hardware diversity and different service requirements in CNs, makes the CN micro-clouds a challenging environment to run local services, and to achieve service performance and quality similar to Internet cloud services. In this thesis, our main objective is the optimization of services (performance, quality) in CN micro-clouds, facilitating entrance to other services and motivating members to make use of CN micro-cloud services as an alternative to Internet services. We present an approach to handle services in CN micro-cloud environments in order to improve service performance and quality that can be approximated to Internet services, while also giving to the community motivation to use CN micro-cloud services. Furthermore, we break the problem into different levels (resource, service and middleware), propose a model that provides improvements for each level and contribute with information that helps to support the improvements (in terms of service performance and quality) in the other levels. At the resource level, we facilitate the use of community devices by utilizing virtualization techniques that isolate and manage CN micro-cloud services in order to have a multi-purpose environment that fosters services in the CN micro-cloud environment. At the service level, we build a monitoring tool tailored for CN micro-clouds that helps us to analyze service behavior and performance in CN micro-clouds. Subsequently, the information gathered enables adaptation of the services to the environment in order to improve their quality and performance under CN environments. At the middleware level, we build overlay networks as the main communication system according to the social information in order to improve paths and routes of the nodes, and improve transmission of data across the network by utilizing the relationships already established in the social network or community of practices that are related to the CNs. Therefore, service performance in CN micro-clouds can become more stable with respect to resource usage, performance and user perceived quality.Acceder a Internet sigue siendo un reto en muchas partes del mundo y las comunidades locales se ven en la necesidad de colaborar para construir sus propias infraestructuras de red. Los usuarios colaboran por el objetivo común de acceder a Internet y a los servicios en la nube construyendo redes comunitarias (RC). El uso de servicios de Internet en la nube ha crecido durante la última década. Las infraestructuras de nube en redes comunitarias (i.e., micronubes) han aparecido para albergar servicios dentro de las mismas redes, sin tener que acceder a Internet para usarlos. Las micronubes de las RC no solo tienen por objetivo ofrecer un mejor rendimiento, sino también ser la puerta de entrada en las RC hacia una alternativa a los servicios de Internet en la nube. Sin embargo, la adaptación de los servicios para ser usados en micronubes de RC conlleva sus retos ya que el uso de dispositivos de recursos limitados y de conexiones inalámbricas sin una gestión centralizada predominan en las RC. Más aún, la amplia e irregular topología de la red, la diversidad en el hardware y el software y los diferentes requisitos de los servicios en RC convierten en un desafío albergar servicios locales en micronubes de RC y obtener un rendimiento y una calidad del servicio comparables a los servicios de Internet en la nube. Esta tesis tiene por objetivo la optimización de servicios (rendimiento, calidad) en micronubes de RC, facilitando la entrada a otros servicios y motivando a sus miembros a usar los servicios en la micronube de RC como una alternativa a los servicios en Internet. Presentamos una aproximación para gestionar los servicios en entornos de micronube de RC para mejorar su rendimiento y calidad comparable a los servicios en Internet, a la vez que proporcionamos a la comunidad motivación para usar los servicios de micronube en RC. Además, dividimos el problema en distintos niveles (recursos, servicios y middleware), proponemos un modelo que proporciona mejoras para cada nivel y contribuye con información que apoya las mejoras (en términos de rendimiento y calidad de los servicios) en los otros niveles. En el nivel de los recursos, facilitamos el uso de dispositivos comunitarios al emplear técnicas de virtualización que aíslan y gestionan los servicios en micronubes de RC para obtener un entorno multipropósito que fomenta los servicios en el entorno de micronube de RC. En el nivel de servicio, construimos una herramienta de monitorización a la medida de las micronubes de RC que nos ayuda a analizar el comportamiento de los servicios y su rendimiento en micronubes de RC. Luego, la información recopilada permite adaptar los servicios al entorno para mejorar su calidad y rendimiento bajo las condiciones de una RC. En el nivel de middleware, construimos redes de overlay que actúan como el sistema de comunicación principal de acuerdo a información social para mejorar los caminos y las rutas de los nodos y mejoramos la transmisión de datos a lo largo de la red al utilizar las relaciones preestablecidas en la red social o la comunidad de prácticas que están relacionadas con las RC. De este modo, el rendimiento en las micronubes de RC puede devenir más estable respecto al uso de recursos, el rendimiento y la calidad percibidas por el usuario.Postprint (published version

A Middleware framework for self-adaptive large scale distributed services

Modern service-oriented applications demand the ability to adapt to changing conditions and unexpected situations while maintaining a required QoS. Existing self-adaptation approaches seem inadequate to address this challenge because many of their assumptions are not met on the large-scale, highly dynamic infrastructures where these applications are generally deployed on. The main motivation of our research is to devise principles that guide the construction of large scale self-adaptive distributed services. We aim to provide sound modeling abstractions based on a clear conceptual background, and their realization as a middleware framework that supports the development of such services. Taking the inspiration from the concepts of decentralized markets in economics, we propose a solution based on three principles: emergent self-organization, utility driven behavior and model-less adaptation. Based on these principles, we designed Collectives, a middleware framework which provides a comprehensive solution for the diverse adaptation concerns that rise in the development of distributed systems. We tested the soundness and comprehensiveness of the Collectives framework by implementing eUDON, a middleware for self-adaptive web services, which we then evaluated extensively by means of a simulation model to analyze its adaptation capabilities in diverse settings. We found that eUDON exhibits the intended properties: it adapts to diverse conditions like peaks in the workload and massive failures, maintaining its QoS and using efficiently the available resources; it is highly scalable and robust; can be implemented on existing services in a non-intrusive way; and do not require any performance model of the services, their workload or the resources they use. We can conclude that our work proposes a solution for the requirements of self-adaptation in demanding usage scenarios without introducing additional complexity. In that sense, we believe we make a significant contribution towards the development of future generation service-oriented applications.Las Aplicaciones Orientadas a Servicios modernas demandan la capacidad de adaptarse a condiciones variables y situaciones inesperadas mientras mantienen un cierto nivel de servio esperado (QoS). Los enfoques de auto-adaptación existentes parecen no ser adacuados debido a sus supuestos no se cumplen en infrastructuras compartidas de gran escala. La principal motivación de nuestra investigación es inerir un conjunto de principios para guiar el desarrollo de servicios auto-adaptativos de gran escala. Nuesto objetivo es proveer abstraciones de modelaje apropiadas, basadas en un marco conceptual claro, y su implemetnacion en un middleware que soporte el desarrollo de estos servicios. Tomando como inspiración conceptos económicos de mercados decentralizados, hemos propuesto una solución basada en tres principios: auto-organización emergente, comportamiento guiado por la utilidad y adaptación sin modelos. Basados en estos principios diseñamos Collectives, un middleware que proveer una solución exhaustiva para los diversos aspectos de adaptación que surgen en el desarrollo de sistemas distribuidos. La adecuación y completitud de Collectives ha sido provada por medio de la implementación de eUDON, un middleware para servicios auto-adaptativos, el ha sido evaluado de manera exhaustiva por medio de un modelo de simulación, analizando sus propiedades de adaptación en diversos escenarios de uso. Hemos encontrado que eUDON exhibe las propiedades esperadas: se adapta a diversas condiciones como picos en la carga de trabajo o fallos masivos, mateniendo su calidad de servicio y haciendo un uso eficiente de los recusos disponibles. Es altamente escalable y robusto; puedeoo ser implementado en servicios existentes de manera no intrusiva; y no requiere la obtención de un modelo de desempeño para los servicios. Podemos concluir que nuestro trabajo nos ha permitido desarrollar una solucion que aborda los requerimientos de auto-adaptacion en escenarios de uso exigentes sin introducir complejidad adicional. En este sentido, consideramos que nuestra propuesta hace una contribución significativa hacia el desarrollo de la futura generación de aplicaciones orientadas a servicios.Postprint (published version

Integrating Wireless Sensor Networks and Mobile Ad-hoc NETworks for enhanced value-added services

In some situations where the standard telecommunication infrastructure is not available, Mobile Ad hoc NETworks (MANETs) can be deployed to provide the required communication. These networks are established "on the fly" without a need for prior communication organization and are composed of autonomous mobile devices, such as cell phones, PDAs or laptops. In similar conditions, such as in emergency response operations, integrating MANETs and Wireless Sensor Networks (WSNs) can notably enhance the MANET participant's end-user experience. WSNs sense and aggregate ambient information, such as physiological, environmental or physical data related to a nearby phenomenon. The integration, which provides end-user availability to WSN required information, is feasible via gateways. However, when the ambient information collected by WSNs is intended for applications residing in MANETs, centralized and fixed gateways are not practicably feasible. This is mainly due to ad-hoc nature, lack of centralized control and constraints on the end-user devices that are used in MANETs. These devices are usually limited in power and capacity and cannot host centralized gateways. In this thesis we exploit the integration of WSN and MANET in order to provide novel value-added services which enhance the end-user experience of MANET participants. Motivating scenarios are introduced, background information is presented, requirements are derived and the state of the art regarding the integration of WSN with existing networks, including MANETs, is evaluated. Based on the evaluation, none of the existing solutions satisfies all of our derived requirements. Therefore, we propose an overall two-level overlay architecture to integrate WSNs (with mobile sinks) and MANETs. This architecture is based on the distributed gateway and applications which form the P2P overlays. Overlays are application-layer networks which are created on top of the exiting MANET. To interconnect gateway and application overlays we derive corresponding requirements and evaluate the existing approaches. Since none of these approaches fulfills all of our requirements, we propose protocols, mechanisms and design corresponding modules for the interconnection of overlays. Finally we refine our overall architecture based on the interconnection aspects. As a proof of concept, we implement a prototype for the inter-overlay information exchange. This implementation is based on SIP extensions and uses two existing P2P middlewares. We also simulate our prototype using Oversim simulation tool and collect experimental results. Based on these results, we can see that our architecture is a valid and promising approach for interconnecting different P2P overlays and can be deployed to provide the overall solution for WSN and MANET integrated system