Daniele Tafani

Distributed management of energy-efficient lightpaths for computational grids

Information and Communication Technologies (ICTs) are contributing to a large amount of the global electricity consumption. Due to tremendous increase in the bandwidth demands and utilisation of non-renewable energy resources Greenhouse Gas Emissions are increasing proportionally with the increasing demand. Despite their advantages in terms of computing performance, distributed applications such as computational grids are major factors that increase the traffic volume in the Internet. In this paper, we propose a distributed framework to ensure energy savings in the optical WDM backbone which transport the traffic between nodes and several computational grids based on anycast routing. According to the proposed framework, the backbone nodes go to sleep mode and resume active mode in a distributed manner with the objective of maximum energy savings in the backbone. Each node maintains two thresholds which are adaptively adjusted based on the network performance, and these thresholds play the key role in determining the decision of a node whether to sleep or resume. Numerical results confirm that the proposed framework can ensure significant energy savings in the network when compared to the conventional energy-unaware operation mode. We further show that the adoption of the proposed network framework does not degrade significantly the network performance in terms of average blocking probability and end-to-end delay.

Simplified overflow analysis of an optical burst switch with fibre delay lines

We develop an approximate analytic model of an Optical Burst Switch with share-per-node fibre delay lines and tuneable wavelength converters by employing Equivalent Random Theory, an approach from circuit-switching analysis. Our model is formulated in terms of virtual traffic flows within the switch from which we derive expressions for burst blocking probability, fibre delay line occupancy and mean delay, which we then resolve numerically. Emphasis is on simplicity of the model to achieve good numerical efficiency so that the method can be useful for formulating dimensioning problems for large-scale networks. Solution values from the analysis are compared with discrete-event simulation results.

Analysis of a Buffered Optical Switch with General Interarrival Times

We propose an approximate analytic model of an optical switch with fibre delay lines and wavelength converters by employing Equivalent Random Theory. General arrival traffic is modelled by means of Gamma-distributed interarrival times. The analysis is formulated in terms of virtual traffic flows within the optical switch from which we derive expressions for burst blocking probability, fibre delay line occupancy and mean delay. Emphasis is on approximations that give good numerical efficiency so that the method can be useful for formulating dimensioning problems for large-scale networks. Numerical solution values from the proposed analysis method compare well with results from a discrete-event simulation of an optical burst switch.

A two-moment performance analysis of optical burst switched networks with shared fibre delay lines in a feedback configuration

Abstract Fibre delay lines (FDLs) can substantially reduce the burst loss in Optical Burst Switching (OBS) networks and share-per-node FDL configurations can provide a more cost-efficient solution compared to architectures where delay lines are shared per port. Nevertheless, mathematical performance analysis of this configuration is more difficult due to traffic correlations arising from the shared resource. In this paper, an approximate two-moment traffic model is developed for quantifying end-to-end burst blocking probability in networks of OBS switches with share-per-node FDLs. The two-moment approach can improve model accuracy over more usual Poisson network analysis methods and additionally allows the characteristics of offered load to be taken into account. The accuracy of the proposed method is shown to be favourable, when compared to discrete-event simulations of an OBS network.

Energy-efficient lightpaths for computational grids

Optical networks have been pointed out as strong candidates to ensure energy-efficiency in the Internet backbone, as well as the distributed applications such as computational grids. In this paper, we propose a distributed framework to address energy-efficient lightpath establishment problem for computational grids over the optical WDM backbone. Each backbone node maintains two thresholds to determine its sleep/wakeup cycle. A node in the sleep mode saves energy by rejecting transient traffic. Each demand is routed based on anycast routing and with the objective of minimum power consumption. Through numerical results, we show that significant energy savings are attained by the proposed framework without requiring centralized information and control. We further show that coordinated sleep and wakeup management in the optical backbone can address the trade-off between propagation delay and energy savings.

Overflow traffic moments in channel groups with Bernoulli-Poisson-Pascal (BPP) load

An expression is obtained for the variance of overflow traffic from a fully-accessible channel group, when offered Bernoulli-Poisson-Pascal (BPP) traffic. The formula is exact within the context of Delbroucks BPP method and provides an alternative to approximations and numerical-based methods for evaluation of the variance. Applications include two-moment blocking network analysis methods, where switch overflow traffic is not lost but offered on alternative routes, for example in hierarchical cellular networks and optically switched networks with alternative routing schemes.

Analytical model of optical burst switched networks with share-per-node buffers

We propose an approximate modelling method for analysing networks of optical burst switches with shared fibre delay lines (FDLs). To achieve a good accuracy in evaluating burst loss probabilities in the network, and allow a tractable solution method, a two-moment analysis is applied, both to traffic flows within network nodes and on network links. We believe the method is useful for evaluating the performance of share-per-node buffer architectures, which are generally more cost-efficient in terms of switching hardware requirements. Results show good accuracy compared to discrete-event simulations.

A distributed framework for energy-efficient lightpaths in computational grids

Over the past decade, the ever-increasing energy demands of IT infrastructures have posed significant challenges for the research community in terms of reducing their total power consumption and minimizing their environmental impact. Optical communication networks are envisioned to be promising candidates to help preventing this problem affecting the Internet backbone, as well as for distributed applications such as computational grids. In this paper, we propose an adaptive and distributed scheme for the establishment of energy-efficient lightpaths in computational grids. The grid is deployed over an optical circuit-switched backbone network, defining an optical grid network. Each node of the backbone network maintains two different dynamic thresholds values and estimates the changes in network performance by evaluating the moving average of the total wavelength channel occupancy on all its input/output links. The nodes have the ability of reducing the energy consumption by entering into an Energy Saving Mode ESM on the basis of a comparison between their channel occupancy and the thresholds. Furthermore, we extend our framework by allowing the thresholds to be dynamically adapted depending on the network performance in terms of blocking probability. We show that the proposed method achieves considerable energy savings when compared to a normal energy-unaware operational mode and still allows to maintain an acceptable level of network performance in terms of blocking probability and end-to-end delay. Numerical results are obtained with a Java event-driven simulator of two different optical network topologies.

Cost Minimisation for Optical Burst Switched Networks with Share-per-Node Fibre Delay Lines

In this paper, we present a cost minimisation problem for an optical burst switching network with share-per-node fibre delay lines. We solve the problem by means of a genetic algorithm and approximate non-Poisson traffic flows with a two-moment matching method. Emphasis is on the sensitivity of the network hardware cost to the offered traffic characteristics.