Noélia S. C. Correia

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.

Radio over fiber access network architecture employing reflective semiconductor optical amplifiers

This paper introduces the RoFnet-Reconfigurable Radio over Fiber network, which is a project supported by the Portuguese Foundation for Science and Technology. This project proposes an innovative radio over fiber optical access network architecture, which combines a low cost Base Station (BS) design, incorporating reflective semiconductor optical amplifiers, with fiber dispersion mitigation provided by optical single sideband modulation techniques. Optical wavelength division multiplexing (WDM) techniques are used to simplify the access network architecture allowing for different Base Stations to be fed by a common fiber. Different wavelength channels can be allocated to different BSs depending on user requirements. Additionally, in order to improve radio coverage within a cell, it is considered a sectorized antenna interface. The combination of subcarrier multiplexing (SCM) with WDM, further simplifies the network architecture, by using a specific wavelength channel to feed an individual BS and different subcarriers to drive the individual antenna sectors within the BS.

Aggregation and scheduling in CoAP/Observe based wireless sensor networks

Wireless sensor networks (WSNs) gained worldwide attention and already have a high impact on our societies. For next generation WSNs one of the challenges was to integrate IPv6 over such very constrained networks, a standardization process already in progress. Together with this, the constraint application protocol (CoAP), and then the Observe extension, were proposed for RESTful services to be provided. The observing capabilities of CoAP/Observe, together with the possibility of using proxies, raise optimization issues when there are multiple notification requests in a network. These issues involve deciding which registration steps to be done, while keeping consistency of data, so that energy is saved. In this article a framework is proposed for the planning of such registration steps, together with the aggregation and scheduling of notification deliveries at proxies, so that energy saving is maximized, bandwidth is used efficiently and the overall delay is reduced.

Dynamic Aggregation and Scheduling in CoAP/Observe-Based Wireless Sensor Networks

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 algorithms decision into the network is done. The proposed framework can be applied to multiple application domains (e.g., monitoring, machine to machine).

Protection Schemes for IP-over-WDM Networks: Throughput and Recovery Time Comparison

This article presents a novel protection approach using Generalized Multi-Protocol Label Switching (GMPLS). This strategy provides protection at the Wavelength Division Multiplexing (WDM) layer, meaning that all Internet Protocol Label-Switched Path (IP LSPs) nested inside a lightpath are protected in an aggregated way. It uses resources efficiently since spare capacity of working primary lightpaths can be used for backup purposes whenever necessary. The IP and WDM layers are treated together as a single integrated network from a control plane point of view, so that network state information from both layers can be used. Besides discussing the strategy proposed and the key features of GMPLS that will allow its implementation, we mathematically formulate the maximum throughput problem. Thereafter, we propose and compare heuristic algorithms for IP-over-WDM networks using three protection approaches: WDM lightpath protection, IP LSP protection, and the proposed protection scheme. Their throughputs and recovery times are analyzed and compared. Our results show that, for a representative mesh network, the proposed aggregated protection scheme presents better protection efficiency and good scalability properties when compared with the other two schemes.

Frequency assignment in multi-channel and multi-radio FiWi access networks

FiWi architectures have been proposed as cost effective solutions to provide high bandwidth and ubiquity at access network areas. In multi-radio and multi-channel scenarios an effective frequency assignment must be done to radios so that higher throughput and low delay can be obtained and the best of such architectures is achieved. Here we propose an approach for frequency assignment in multi-radio and multi-channel FiWi access networks. A simulation model is built to evaluate the effectiveness of our approach. Results show that our scheme is able to increase throughput and reduce delay, when compared with a fixed assignment strategy, by carefully planning frequency assignments which makes it possible to increase network parallel transmissions (reduce time division).

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.