José Coimbra

Fault-Tolerance Planning in Multiradio Hybrid WirelessߝOptical Broadband Access Networks

The wirelessߝoptical broadband-access network (WOBAN) architecture has been proposed as a flexible and cost-effective solution for future access networks. However, for WOBANs to provide geographically continuous wireless coverage it is necessary to integrate fault tolerance in the design of such networks. At the optical back end, multiple failures, having different impact levels, may be addressed (e.g., optical network unit, optical line terminal). At the wireless front end, the disruption of connections, or throughput speed decrease on users devices, can be a consequence of unlicensed spectrum utilization, where the radio band is common to different systems. We address the problem of planning a fault-tolerant multiradio WOBAN while using resources efficiently. The proposed fault model is general and may be applied to any fault-tolerance scenario (e.g., some nodes/links/region only). The adopted approach is revealed to make an efficient reuse of spectrum under different fault-tolerance scenarios.

A game-based algorithm for fair bandwidth allocation in Fibre-Wireless access networks

Abstract Fibre-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.

Load adaptive and fault tolerant framework for energy saving in fiber-wireless access networks

Energy saving (ES) in telecommunication networks is an important criterion when planning access networks. In fiber-wireless (FiWi) access networks the ES potential is high, when compared with other architectures, because different routes and optical access points can be used by routers at the wireless section. Although some proposals to increase energy efficiency in these architectures have been presented, these are not approaches that can adapt to variations in traffic load or distribution of traffic across the network. Here we fill this gap and propose a load adaptive and fault tolerant framework for ES in FiWi access networks. This framework allows optical network units (ONUs) to enter long-standing sleep mode under low traffic conditions, reducing energy waste, permitting fast reaction to ONU or fiber failures, and allowing quality of service (QoS) to be kept at a certain level. Results show that significant ES can be achieved under low to medium traffic loads while maintaining QoS and fault tolerance.

Forwarding Repeated Game for End-to-End QoS Support in Fiber-Wireless Access Networks

Fiber-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.

Energy efficient routing algorithm for fiber-wireless access networks: A network formation game approach

New multimedia services and ubiquitous networking pose great challenges on existing access network infrastructures. To cope with such requirements new access technologies, such as the fiber-wireless (FiWi), are being developed. Together with the emergence of new access networks, efforts are being made to reduce the amount of energy required to provide services. Indeed, this issue plays an increasingly important role. Here we propose an energy efficient routing algorithm for FiWi access networks. The main idea is to exploit the multipath capabilities of the wireless mesh front end of FiWi access networks to create energy efficient routes that optimize the sleeping and active periods of all ONUs and wireless nodes. To achieve this goal, an energy efficient network model based on network formation game theory is used. This model allows several network formation processes to be compared in regard to the energy efficiency of the routes they generate. Our results reveal that the farsighted network formation process establishes the most energy efficient routes, meaning that the choices done by this formation process were the best ones. However, this farsighted process is computationally expensive. For this reason a heuristic algorithm is developed, which explores the most energy efficient choices taken by the network formation processes, and farsighted process in particular. Results show that the proposed heuristic is able to obtain results close to the farsighted process.

Sparse traffic grooming in WDM networks using coarse granularity OXCs

Providing grooming capability to optical crossconnects (OXCs) in wavelength division multiplexing (WDM) networks can allow an effective use of the network bandwidth, however, it increases the node cost that operators must sustain when compared to a non-grooming network. Therefore, operators might consider using sparse grooming instead of full grooming networks. In this article we consider sparse groomed optical networks. Our contribution is 2-fold. First, we address the grooming placement problem that seeks for a set of grooming nodes in the network that leads to the highest overall throughput. This problem is separated into two sub-problems: (i) selection of nodes having grooming capability; (ii) maximization of network throughput assuming the grooming nodes found by the previous step. These two sub-problems are mathematically formulated for different OXC placing strategies considering a static traffic scenario. In the second part, we design a practical heuristic grooming algorithm suitable for dynamic traffic scenarios. The benefit of using sparse grooming nodes, when compared with a non-grooming scenario, is evaluated in terms of throughput and optical port utilization. Our analysis differs of previous ones since it considers grooming at a granularity coarser than the traffic granularity, which is an important aspect since network cost improvement can be obtained at the expense of irrelevant performance impairments. Results show that the insertion of coarse granularity OXCs can be a viable solution for network throughput increase since this can be done at the expense of relatively few or no extra optical ports.

Network game based routing for energy efficient Fibre-Wireless access networks

The 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 proposed 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.

A Manageable and Bandwidth Effective Solution for Traffic Grooming in IP-over-WDM Networks

Traffic grooming can be used in IP-over-WDM networks to efficiently utilize the bandwidth of wavelength channels. In grooming networks, however, the number of lightpaths that need to be managed is high and empty time-slots may be switched together with time-slots taken by traffic. These empty time-slots add an induced connectivity to the network and, to use this induced bandwidth, quite complex induced topologies need to be managed, increasing the computation time. In this paper we present an approach to efficiently use the induced bandwidth while alleviating the management of complex topologies. A network operating dynamically is used to test the effectiveness of such approach.

Distributed Algorithm for Traffic Grooming in IP-over-WDM Network

In this paper we present a distributed algorithm to study the benefits of using sparse grooming in IP-over-WDM networks. The algorithm implements a grooming approach that allows the efficient use of resources while alleviating the management of large and complex topologies.

A Minimization Cost Heuristic Approach for Traffic Grooming in IP-over-WDM Networks

Traffic grooming can be used in IP-over-WDM networks to efficiently utilize the bandwidth of wavelength channels. However, providing grooming capability to network nodes increases the network cost that operators must sustain when compared with a non-grooming network. In this paper a minimization cost heuristic approach is presented that seeks for the cheapest IP-over-WDM grooming network. This approach is manageable, allowing an easy study of large networks, and it is generic since it can be applied to OXCs with different switching granularities and/or number of ports. The proposed approach is able to reduce the network grooming cost by efficiently using the induced bandwidth that results from the OXC grooming granularity being coarser than the bandwidth granularity of IP LSP requests. Adaptive and non-adaptive weight functions, that determine the best grooming operation for an arriving IP LSP request, are also proposed and evaluated.