Alvaro L. Barradas

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.

Pre-planned optical burst switched routing strategies considering the streamline effect

Optical burst switching is a promising paradigm for the next IP over optical network backbones. However, due to its bufferless nature, it can be highly affected by burst contention. Several methods have been proposed to address this problem, most of them without considering a phenomenon unique to optical burst switched networks called streamline effect. Most of the reported studies also assume the existence of total wavelength conversion capacity on all nodes, presently a very expensive and somewhat unrealistic configuration, and additionally, the contention resolution schemes adopted increase in the complexity of the core nodes, hampering scalability. In this study, we present a traffic engineering approach for path selection with the objective of minimizing the contention considering the streamline effect and using only topological information. The main idea is to balance the traffic across the network in order to prevent congestion while keeping simple the architecture of the core nodes and without incurring into link state dissemination penalties. We propose and evaluate the path selection strategies in both networks with full wavelength conversion capability and networks with imposed wavelength continuity constraint. Results show that our strategies can outperform the traditionally used shortest path routing.

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.

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).

Correlation-based energy saving approach for smart fiber wireless networks

Energy saving is an important issue that should be taken into consideration when planning telecommunication networks. In fiber-wireless access networks the potential for energy consumption reduction is higher, when compared to other architectures, as many routes toward the optical section are available for nodes at the wireless section, allowing some optical network units (ONUs) to enter long sleep state. However, in a multiradio and multichannel wireless front end, some nodes might not be able to reach all the ONUs. Thus, integrated energy saving mechanisms should be smart and allow for ONU mode adjustments according to wireless node reachability and traffic distribution across the wireless section. In this paper we propose a correlation-aware approach that allows the optical line terminal to infer which ONUs are reachable by wireless nodes. Then, when the network is under low traffic conditions, the appropriate set of ONUs to enter long sleep can be selected. This approach is able, therefore, to integrate knowledge of a wireless front end to promote long-standing sleep periods at the ONUs while avoiding heavy exchange of network state information.

An OMNeT++ model for the evaluation of OBS routing strategies

Optical Burst Switching (OBS) has been proposed as a cost-effective paradigm for supporting, with adequate flexibility, the increasingly high transmission capacity required by the forthcoming next generation of optical internet networks. However, OBS efficiency can be reduced by resource contention of bursts directed to the same transmission links, leading to burst loss. This paper presents a discrete event simulation model and its implementation using OMNeT++ aimed at the evaluation of different routing strategies in terms of link contention. The simulation model is used to compare the performance of novel path selection strategies proposed in [1] with the traditional routing strategy that uses the shortest path. The simulation results confirm that the proposed path selection strategies are effective in reducing the overall network burst drop probability.

Path selection strategy for consumer grid over OBS networks

This paper compares two path selection strategies for optical burst switching networks: a) the path from source to destination is chosen randomly from the set of the k shortest paths; b) the path selection is based on a probabilistic model for the link demands. In the second strategy, the set of shortest paths from source to destination is ranked according to the probability of their overall link demands. The path selection schemes are evaluated for a specific scenario of grid over OBS networks. Our results show that, in general, the probabilistic model outperforms the random k shortest path routing scheme, this improvement is relevant for small job sizes.

GACN: Self-Clustering Genetic Algorithm for Constrained Networks

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.

Path selection strategies for OBS networks using topological network information

Optical Burst Switching (OBS) has been proposed as a cost-effective paradigm for supporting, with adequate flexibility, the increasingly high transmission capacity required by the forthcoming next generation of optical internet networks. However, OBS efficiency can be reduced by resource contention of bursts directed to the same transmission links, leading to burst loss. This paper presents two strategies to minimize this kind of contention on the OBS backbone using only a priori topological network information, thus reducing burst loss probability while avoiding state dissemination protocol penalties. Numerical results, obtained through simulation using a dynamic framework scenario, demonstrate that our approaches are effective in reducing the overall network burst drop probability when compared with the traditionally used shortest path routing.

An Energy-Aware Resource Design Model for Constrained Networks

The Internet of Things is expected to incorporate objects and sensor networks of all kinds, and in particular, constrained sensor networks where energy consumption is a critical issue. In order to increase the lifetime of such networks, intelligent and standard-based solutions should be used. Here, we address this challenge through the use of CoRE interfaces for the resource design. These interfaces allow the server side to compose/organize resources and the client side to discover and determine how to consume such resources, besides allowing decisions to be easily integrated into the operation of the network. An energy-aware resource design model is proposed, based on CoRE interfaces, for the design of resources matching client needs. Based on this model, we develop an algorithm that proved to be energy efficient.