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- A game-based algorithm for fair bandwidth allocation in fibre-wireless access networksPublication . Coimbra, José; Schutz, G.; Correia, NoéliaFibre-Wireless (FiWi) access networks have been proposed as flexible and cost-effective solutions for future access networks. At the wireless mesh section, wireless routers have to forward both local traffic from directly connected users and foreign traffic from neighbour wireless routers. How to allocate resources to local and foreign traffic at each router in a balanced way, while avoiding starvation of routers requiring less resources, is a fundamental issue that must be solved so that new services emerge. Here, we develop a repeated game framework for bandwidth allocation and propose an algorithm that allocates bandwidth in a fair manner. The algorithm is able to detect over claiming routers and avoid possible denial of service that these may cause to others. Moreover, unfruitful use of resource is prevented, avoiding the forwarding of packets that would be dropped at some point later in the path, and queueing delay conditions are kept similar among local and foreign traffic. These fair network conditions open way for QoS support since it is easier to ensure the operationality of services.
- A solution for a real-time stochastic capacitated vehicle routing problem with time windowsPublication . Cardoso, Pedro J. S.; Schütz, Gabriela; Mazayev, Andriy; Ey, Emanuel; Corrêa, TiagoReal-time distribution planning presents major difficulties when applied to large problems. Commonly, this planning is associated to the capacitated vehicle routing problem with time windows (CVRPTW), deeply studied in the literature. In this paper we propose an optimization system developed to be integrated with an existing Enterprise Resource Planning (ERP) without causing major disruption to the current distribution process of a company. The proposed system includes: a route optimization module, a module implementing the communications within and to the outside of the system, a non-relational database to provide local storage of information relevant to the optimization procedure, and a cartographic subsystem. The proposed architecture is able to deal with dynamic problems included in the specification of the project, namely: arrival of new orders while already optimizing as well as locking and closing of routes by the system administrator. A back-office graphical interface was also implemented and some results are presented.
- GACN: Self-clustering genetic algorithm for constrained networksPublication . A. Martins, J.; Mazayev, Andriy; Correia, Noélia; Schutz, G.; Barradas, A.Extending the lifespan of a wireless sensor network is a complex problem that involves several factors, ranging from device hardware capacity (batteries, processing capabilities, and radio efficiency) to the chosen software stack, which is often unaccounted for by the previous approaches. This letter proposes a genetic algorithm-based clustering optimization method for constrained networks that significantly improves the previous state-of-the-art results, while accounting for the specificities of the Internet engineering task force, Constrained RESTful Environment (CoRE), standards for data transmission and specifically relying on CoRE interfaces, which fit this purpose very well.
- Network game based routing for energy efficient fibre-wireless access networksPublication . Coimbra, José; Schutz, G.; Correia, NoéliaThe currently growing demand for information and communication technologies (ICTs), and multimedia services, is generating a fast expansion of digital traffic. To fulfill such demands, new generation access architectures have been pro-posed that try to integrate and optimize available technologies. Besides allowing new services to emerge, such architectures also offer a great opportunity to develop new methods that try to increase energy efficiency by proper equipment management and sharing of resources. Here we focus on energy saving in Fibre-Wireless (FiWi) access networks, which provide high bandwidth and ubiquity to future multimedia services and applications. The goal is to exploit the path diversity of mesh FiWi networks to improve energy efficiency. A model based on network formation game theory is developed, creating ground for energy efficient routing algorithms. To obtain stable and efficient networks, the use of a new stability concept, which avoids unconnected nodes, is proposed and a dynamic network formation process is presented and applied to the model. Our results show that significant energy efficiency gains can be obtained. It is also shown that gateway placement can have a strong impact on energy efficiency.
- Dynamic aggregation and scheduling in CoAP/Observe-based wireless sensor networksPublication . Correia, Noélia; Sacramento, David; Schutz, G.Wireless sensor networks (WSNs) are starting to have a high impact on our societies and, for next generation WSNs to become more integrated with the Internet, researchers recently proposed to embed IPv6 into such very constrained networks. Also, constraint application protocol (CoAP) and Observe have been proposed for RESTful services to be provided. CoAP/Observe supports the use of caches/proxies and, for this reason, an observation request may resort to multiple client/server registration steps in order to get notifications. Here, we propose to plan the multiple registration steps, at proxies, of multiple observation requests in order to make proper aggregation/scheduling of notifications for transmission. This leads to less energy consumption and to an effective use of bandwidth, avoiding energy depletion of nodes, and increasing the network lifetime. Besides, mathematically formalizing the problem, a heuristic approach is developed and a discussion on how to incorporate algorithm's decision into the network is done. The proposed framework can be applied to multiple application domains (e.g., monitoring, machine to machine).
- Resource design in constrained networks for network lifetime increasePublication . Correia, Noélia; Mazayev, Andriy; Schutz, G.; A. Martins, J.; Barradas, A.As constrained "things" become increasingly integrated with the Internet and accessible for interactive communication, energy efficient ways to collect, aggregate, and share data over such constrained networks are needed. In this paper, we propose the use of constrained RESTful environments interfaces to build resource collections having a network lifetime increase in mind. More specifically, based on existing atomic resources, collections are created/designed to become available as new resources, which can be observed. Such resource design should not only match client's interests, but also increase network lifetime as much as possible. For this to happen, energy consumption should be balanced/fair among nodes so that node depletion is delayed. When compared with previous approaches, results show that energy efficiency and network lifetime can be increased while reducing control/registration messages, which are used to set up or change observations.
- Forwarding Repeated Game for End-to-End QoS Support in Fiber-Wireless Access NetworksPublication . Coimbra, José; Schutz, G.; Correia, NoéliaFiber-wireless (FiWi) access mesh networks have been proposed as flexible and cost-effective solutions for future access networks. However, for FiWi access mesh networks to provide end-to-end QoS guarantees to its customers, efficient QoS routing schemes and scheduling policies become necessary. Here we provide a model, using repeated game theory, that creates ground for scheduling policies to be implemented. That is, our framework provides insights into how much bandwidth a wireless router needs to share, for foreign traffic forwarding, so that services of local users and services of foreign users can all receive bandwidth in a balanced way. Some strategies were tested, under the developed model, to look for equilibrium states. The equilibrium strategies provide the means for QoS guarantees in FiWi access mesh networks, meaning that they can be used as a basis for scheduling policies.
- Planning the reassignment of frequencies in fiber-wireless access networksPublication . Correia, N.; Sabino, S.; Schutz, G.; Barradas, A.FiWi architectures have been proposed as efficient solutions to provide high bandwidth and ubiquity at access network areas. In multi-radio and multi-channel FiWi scenarios an effective frequency assignment should be done to radios so that higher throughput and low delay can be obtained and the best of such architectures is achieved. However, traffic conditions change over time meaning that radio channel reconfigurations can be done to improve network performance. In this article a methodology for FiWi frequency reassignment planning is proposed, together with two algorithms, that avoids service disruption and attempts to increase throughput, reduce delay and increase the overall QoS perceived by users. Results show that the RBR algorithm is the one able to better exploit channel reconfigurations, increasing parallel transmissions and reducing time division required by nodes at the transmission area of each other.
- A problem reduction approach for the design of fault-tolerant wireless-optical access networksPublication . Correia, Noélia; Schutz, G.Wireless-optical approaches, leveraging on the strengths of both wireless and optical technologies, are seen as promising approaches for future access networks. For wireless-optical access networks to provide geographically continuous wireless coverage, fault-tolerance must be integrated in the design of these networks. While at the optical back end different fiber failure impacts must be considered, at the wireless front end the disruption of wireless communication links must be taken into consideration. Here we address the problem of designing a fault-tolerant multi-radio wireless-optical access network, a problem that is hard to solve. Our goal here is to extract guidelines for the reduction of such complex problem, which is done through the analysis of wireless and optical failure impacts on network congestion. Two network scenarios, having different risk groups for gateways, are analysed.
- Design of qos-aware energy-efficient fiber–wireless access networksPublication . Schutz, G.; Correia, NoéliaEnergy-efficient network design has recently become a very important topic because of the energy cost increases in service providers’ infrastructures. This is of particular importance in access networks because of the growing demand for digital traffic by end users. Here we address the challenge of reducing the energy consumption of fiber–wireless (FiWi) access networks, that use both optical and radio frequency technologies to provide high bandwidth and ubiquity for end-user applications, while keeping delay under a threshold. Our goal is to find optimal sleep mode schedulings that allow energy consumption to be reduced while keeping packet delay acceptable. For this purpose a mathematical formalization and an algorithm are developed. The results show that the proposed approach is able to reduce the average packet delay, with negligible energy cost increases, in many scenarios, besides being computationally efficient and scalable. The proposed approach may, therefore, serve as a basis for planning and design of quality of service-aware energy-efficient FiWi access networks.