Power consumption evaluation of circuit-switched versus packet-switched optical backbone networks

While telecommunication networks have historically been dominated by a circuit-switched paradigm, the last decades have seen a clear trend towards packet-switched networks. In this paper we evaluate how both paradigms perform in optical backbone networks from a power consumption point of view, and whether the general agreement of circuit switching being more power-efficient holds. We consider artificially generated topologies of various sizes, mesh degrees and not yet previously explored in this context transport linerates. We cross-validate our findings with a number of realistic topologies. Our results show that, as a generalization, packet switching can become preferable when the traffic demands are lower than half the transport linerate. We find that an increase in the network node count does not consistently increase the energy savings of circuit switching over packet switching, but is heavily influenced by the mesh degree and (to a minor extent) by the average link length

Stochastic Models for Solar Power

International audienceIn this work we develop a stochastic model for the solar power at the surface of the earth. We combine a deterministic model of the clear sky irradiance with a stochastic model for the so-called clear sky index to obtain a stochastic model for the actual irradiance hitting the surface of the earth. Our clear sky index model is a 4-state semi-Markov process where state durations and clear sky index values in each state have phase-type distributions. We use per-minute solar irradiance data to tune the model, hence we are able to capture small time scales fluctuations. We compare our model with the on-off power source model developed by Miozzo et al. (2014) for the power generated by photovoltaic panels, and to a modified version that we propose. In our on-off model the output current is frequently resampled instead of being a constant during the duration of the " on " state. Computing the autocorrelation functions for all proposed models, we find that the irradiance model surpasses the on-off models and it is able to capture the multiscale correlations that are inherently present in the solar irradiance. The power spectrum density of generated trajectories matches closely that of measurements. We believe our irradiance model can be used not only in the mathematical analysis of energy harvesting systems but also in their simulation

Dynamic virtual machine allocation in cloud server facility systems with renewable energy sources

This paper explores the problem of virtual machine (VM) allocation in a network of cloud server facilities which are deployed in different geographical areas. Each cloud server facility is connected to the conventional power grid network and in addition it is supported by an attached renewable energy source (RES). We address the problem of energy-efficient task allocation in the system in the presence of a time-varying grid energy price and the unpredictability and time variation of provisioned power by the RES. The objective is to reduce the total cost of power consumption for the operator. The key idea is to match the VM load with the RES provisioned power. Each request for a task to be executed in the cloud is associated with a VM request with certain resource requirements and a deadline by which it needs to be completed. The cloud provider has to create a VM with the resource requirements of the request and to execute the VM before the deadline. We propose an online algorithm with given look-ahead horizon, in which the grid power prices and patterns of output power of the RESs are known a priori and we compare it with a greedy online algorithm. Numerical results on real traces of cloud traffic and renewable source generation patterns are encouraging in terms of the performance of our techniques and motivate further research on the topic. © 2013 IEEE

Energy-efficient resilient optical networks: Challenges and trade-offs

Energy efficiency and resilience are two well established research topics in optical transport networks. However, their overall objectives (i.e., power minimization and resource utilization/ availability maximization) conflict. In fact, provisioning schemes optimized for best resilience performance are in most cases not energy-efficient in their operations, and vice versa. However, very few works in the literature consider the interesting issues that may arise when energy efficiency and resilience are combined in the same networking solution. The objective of this article is to identify a number of research challenges and trade-offs for the design of energy-efficient and resilient optical transport networks from the perspective of long-term traffic forecasts, short-term traffic dynamics, and service level agreement requirements. We support the challenges with justifying numbers based on lessons learned from our previous work. The article also discusses suitable metrics for energy efficiency and resilience evaluation, in addition to a number of steps that need to be taken at the standardization level to incorporate energy efficiency into already existing and well established protocols