Note: As I finished my PhD (October 2014), this page is no longer updated; however it is kept online to provide easy access to my published research papers.
(This page was originally hosted at http://users.ugent.be/~wvheddeg)
I am working towards a In October 2014 I finished my Ph.D. in Computer Science at IBCN, Ghent University (Belgium). By the way, the IBCN research group is also linked to iMinds (formerly IBBT), a name which might be more familiar to you depending on how you know me. My research focusses on Green ICT, that is, all aspects to make IT and telecom equipment consume less energy. My current focus is on researching ways to make core networks (like the Internet) more energy-efficient.
This tiny page mainly lists a number of research papers and documents which I have (co-)authored as part of my research. I make them available here for download because, while searching for other research papers myself, I am constantly frustrated by not being able to download papers for free.
Tip: If you want to make your own papers available for download online, most publishers (like journals and conferences) allow you to legally put your papers on your homepage/website, usually under the condition that you include a specific note on the first page of the paper. Check the copyright statement of the publication you submit to for exact details. This type of self-archiving is called 'green' open access, by the way.
The official list is available on the ugent biblio website, but the list below should beat the inertia of 'the system'. For already published publications, the publisher [DOI] link at the end leads you to the official publishing website (for example, ieeexplore). The publisher link is doi-based, so it should be future-proof and remain available until a comet strikes the earth; right-click and choose 'copy link location' (or similar) to get the link.
Newer items on top.
Grey boxes indicate first-author publications.
In recent years, rising energy prices and increasing environmental concerns have boosted research in the so called green ICT and green networking research tracks, aimed at improving the energy efficiency of communications while still offering maximal functionality. In this article we explore a future scenario in which low power networking is no longer optional, but instead becomes a necessity due to fluctuating energy availability.
The contribution of this work is twofold. First, we argue why a so called post-peak future scenario, in which we can no longer rely on fossil fuels as our main resource for electricity production, is not unlikely, and what it might entail. Second, we explore the consequences of such a scenario for ICT: How well can current and future infrastructures cope with temporary energy limitations? As an illustration, we present a case study showing the impact of reduced energy availability on a wireless access network.
Energy-efficiency and resiliency are two well-established research topics in optical transport networks. On the other hand, their overall objectives (i.e., power minimization and resource-utilization/availability maximization) are in contrast. In fact, provisioning schemes optimized for best resiliency 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 resiliency are combined in the same networking solution.
The objective of this paper 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 (SLA) requirements. We support the challenges with justifying numbers based on lessons learnt from our previous work. The paper also discusses suitable metrics for energy-efficiency and resiliency 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.
In the last few decades there has been a growing (scientific) consensus that the impact of humanity on our natural ecosystems is increasing beyond the bounds of sustainability. Our ecological footprint is now estimated at 1.5 planets, which means that it now takes the Earth one year and six months to regenerate what we use in a year. Clearly we are tapping into natural resources---such as water, wood, clean air, and energy---that took many hundreds, thousands or even more years to build up. While each of these resources requires our full attention to research how we can drastically reduce their usage, this book focuses on the electricity consumption of ICT. ICT is a broad term to describe electronic goods and technology related to computing, data processing and information transfer.
In the first part of this work we estimate the worldwide electricity consumption of ICT equipment. Subsequently we focus on reducing the electricity consumption in ICT backbone networks, and finally we evaluate the use of solar and wind power to reduce the carbon footprint of data centers.
The power consumption in ICT networks is growing year by year; this growth presents challenges from a technical, economic and environmental point of view. This has lead to a great number of research publications on `green' telecommunication networks. In response, a number of survey works have appeared as well. However, with respect to backbone networks most survey works (a) do not allow for an easy cross-validation of the savings reported in the various works, (b) nor do they provide a clear overview of the individual and combined power saving potential.
Therefore, in this work we survey the reported saving potential in IP-over-WDM backbone telecommunication networks across the existing body of research in that area. We do this by mapping more than 10 different approaches to a concise analytical model, which allows us to estimate the combined power reduction potential.
Our estimates indicate that the power reduction potential of the once-only approaches is 2.3x in a Moderate Effort scenario and 31x in a Best Effort scenario. Factoring in the historic and projected yearly efficiency improvements ('Moore's law') roughly doubles both values on a 10-year horizon. The large difference between the outcome of the Moderate Effort and Best Effort scenario is explained by the disparity and lack of clarity of the reported saving results, and by our (partly) subjective assessment of the feasibility of the proposed approaches.
The Moderate Effort scenario will not be sufficient to counter the projected traffic growth, although the Best Effort scenario indicates that sufficient potential is likely available. The largest isolated power reduction potential is available in improving the power associated with cooling and power provisioning, and applying sleep modes to overdimensioned equipment.
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 (which have also been referred to as optical bypass and non-bypass, respectively) 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 circuit switching is preferable when the average node-to-node demands are higher than half the transport linerates. However, 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. Our results are consistent for uniform traffic demands and realistic traffic demands.
A key take-away message for other research on power saving solutions in backbone networks is that the ratio between the average demand and the demand bitrate has considerable effect on the overall efficiency, and should be taken into account.
Information and Communication Technology (ICT) devices and services are becoming more and more widespread in all aspects of human life. Following an increased worldwide focus on the environmental impacts of energy consumption in general, there is also a growing attention to the electricity consumption associated with ICT equipment.
In this paper we assess how ICT electricity consumption in the use phase has evolved from 2007 to 2012 based on three main ICT categories: communication networks, personal computers, and data centers. We provide a detailed description of how we calculate the electricity use and evolution in these three categories.
Our estimates show that the yearly growth of all three individual ICT categories (10%, 5%, and 4% respectively) is higher than the growth of worldwide electricity consumption in the same time frame (3%). The relative share of this subset of ICT products and services in the total worldwide electricity consumption has increased from about 3.9% in 2007 to 4.6% in 2012. We find that the absolute electricity consumption of each of the three categories is still roughly equal. This highlights the need for energy-efficiency research across all these domains, rather than focusing on a single one.
Energy saving in telecommunications networks has become a well established topic in the research community. We look at the electrical and optical layers of IP-over-WDM networks, and present a list of evaluation criteria for energy-aware adaptive routing solutions (EA-ARSs) from the perspective of a network operator. Furthermore, we briefly explain the adaptive routing solutions originating from the European Union’s TREND and the FP7 Network of Excellence, show saving of energy consumed by line cards in a reference scenario, and use the evaluation criteria to identify the next steps toward introduction of the EA-ARSs into real operation.
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.
The ICT (Information and Communication Technology) sector has recently been identified as a growing contributor to worldwide greenhouse gases emissions and power consumption. This has triggered interest for more energy efficient ways to design and operate telecommunication networks.
We present an overview of the solutions proposed within the European network of excellence TREND focusing on core and metro networks including data centers. Potential savings are presented and discussed with respect to their impact and applicability within the global picture.
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.
With one third of the world population online in 2013 and an international Internet bandwidth multiplied by more than eight since 2006, the ICT sector is a non-negligible contributor of worldwide greenhouse gases emissions and power consumption. Indeed, power consumption of telecommunication networks has become a major concern for all the actors of the domain, and efforts are made to reduce their impact on the overall figure of ICTs, and to support its foreseen growth in a sustainable way.
In this context, the contributors of the European Network of Excellence TREND have developed innovative solutions to improve the energy efficiency of networks. This paper gives an overview of the solutions related to optical networks.
There is a growing research interest in improving the energy efficiency of communication networks. In order to assess the impact of introducing new energy efficient technologies, an up-to-date estimate for the global electricity consumption in communication networks is needed.
In this paper we consider the use phase electricity consumption of telecom operator networks, office networks and customer premises equipment. Our results show that the network electricity consumption is growing fast, at a rate of 10% per year, and its relative contribution to the total worldwide electricity consumption has increased from 1.3% in 2007 to 1.8% in 2012. We estimate the worldwide electricity consumption of communication networks will exceed 350 TWh in 2012.
A large amount of traffic in core networks is highly aggregated and core nodes are interconnected by high-capacity links. Thus, most of the traffic demands in the core area can be accommodated by providing more or less static connections between ingress and egress nodes.
In this paper, we describe and study three particular realizations of static optical core networks and compare them with the dynamic, packet switched architecture based on wavelength-division multiplexing (WDM) transmission and conventional electronic packet routers. We introduce an analytical model for estimating the average number of required switch ports for different network topologies in order to assess both scalability and power consumption of the considered network concepts.
The results show that the concept of a static optically transparent core network promises high energy efficiency, and scalability to several tens of nodes.
Our design rules offers maximally energy efficient Gb/s to Tb/s edge-router upgrade paths. One path assumes 10% average traffic intensity with 68% energy-efficiency gains over 5 upgrades, while 30% traffic load enables 45% energy-efficiency gains over 9 generations.
This presentation will estimate the worldwide power consumption and carbon footprint of communication networks and compare this with other ICT fields such as data centres and personal computers. This paper concentrates on explaining the used methodology.
Reasonably accurate reference power consumption values are required for any work that evaluates power consumption in telecommunication networks. Many existing works provide or use optimal power rating (W/Gbps) values, i.e. the power rating achieved for the maximum capacity of the system, with the shared relative overhead thus being smallest.
In this paper, we evaluate how power rating values are influenced by practical equipment filling levels for core IP-over-WDM equipment. We show that for IP/MPLS routers it is reasonable to almost double the optimal power rating value under real-life equipment filling conditions. For OLAs a correction factor of 1.5 is appropriate, and for WDM terminals the required correction is almost negligible, i.e. 1.1. Furthermore, power measurements on IP routers and OLAs show that their power consumption marginally depends on traffic load.
The evaluation and reduction of energy consumption of backbone telecommunication networks has been a popular subject of academic research for the last decade. A critical parameter in these studies is the power consumption of the individual network devices. It appears that across different studies, a wide range of power values for similar equipment is used. This is a result of the scattered and limited availability of power values for optical multilayer network equipment.
We propose reference power consumption values for Internet protocol/multiprotocol label switching (IP/MPLS), Ethernet, optical transport networking (OTN) and wavelength division multiplexing (WDM) equipment. In addition we present a simplified analytical power consumption model that can be used for large networks where simulation is computationally expensive or unfeasible.
For illustration and evaluation purpose, we apply both calculation approaches to a case study, which includes an optical bypass scenario. Our results show that the analytical model approximates the simulation result to over 90% or higher, and that optical bypass potentially can save up to 50% of power over a non-bypass scenario.
As one of the first worldwide initiatives provisioning ICT (Information and Communication Technologies) services entirely based on renewable energy such as solar, wind and hydroelectricity across Canada and around the world, the GreenStar Network (GSN) is developed to dynamically transport user services to be processed in data centers built in proximity to green energy sources, reducing GHG (Greenhouse Gas) emissions of ICT equipments.
Regarding the current approach, which focuses mainly in reducing energy consumption at the micro-level through energy efficiency improvements, the overall energy consumption will eventually increase due to the growing demand from new services and users, resulting in an increase in GHG emissions.
Based on the cooperation between Mantychore FP7 and the GSN, our approach is, therefore, much broader and more appropriate because it focuses on GHG emission reductions at the macro-level. Whilst energy efficiency techniques are still encouraged at low-end client equipments, the heaviest computing services are dedicated to virtual data centers powered completely by green energy from a large abundant reserve of natural resources, particularly in northern countries.
The environmental footprint of ICT is rising. Data centers are a key contributor to this footprint. In this paper we investigate the influence of the renewal rate of servers on the footprint of the data center. We take into account both the use phase power consumption as well as the contributions of the other life cycle stages. Based on this we construct an analytical model.
From the results, we demonstrate that in a scenario where the data center needs to keep up with the increasing processing capacity of the servers, the footprint increases annually and keeping the servers in operation as long as possible is necessary. However, when the capacity remains constant, the footprint is decreasing and an optimal renewal rate is obtained.
Low carbon footprint energy sources such as solar and wind power typically suffer from unpredictable or limited availability. By globally distributing a number of these renewable sources, these effects can largely be compensated for. We look at the feasibility of this approach for powering already distributed data centers in order to operate at a reduced total carbon footprint.
From our study we show that carbon footprint reductions are possible, but that these are highly dependent on the approach and parameters involved. Especially the manufacturing footprint and the geographical region are critical parameters to consider. Deploying additional data centers can help in reducing the total carbon footprint, but substantial reductions can be achieved when data centers with nominal capacity well-below maximum capacity redistribute processing to sites based on renewable energy availability.
One of the main challenges for the future of information and communication technologies is the reduction of the power consumption in telecommunication networks. The key consumers are the home gateways at the customer premises for fixed line access technologies and the base stations for wireless access technologies. However, with increasing bit rates, the share of the core networks could become significant as well. In this paper we characterize the power consumption in the different types of networks and discuss strategies to reduce the power consumption.
Both bandwidth demand and energy consumption of ICT and communication networks is increasing and optical networks are regarded to provide high bandwidth solutions while enabling more energy efficiency. In this article we give an overview of energy consumption in access and core networks with a focus on optical technologies. Also, possible strategies to enable power reductions are discussed.
Green communication technologies currently receive a lot of attention. In this paper we give an overview of the environmental issues related to communication technologies and present an estimation of the overall ICT footprint. Additionally we present some approaches on how to reduce this footprint and how ICT can assist in other sectors reducing their footprint.
The large share of energy consumption in telecommunication networks is expected to shift from access networks to core networks. Estimating the power consumption of core networks is not easy, as they vary a lot in size and topology. Using an exemplary but realistic core network, we estimate its power consumption for both a link-by-link grooming and an optical end-to-end grooming scenario. We show that optical end-to-end grooming consumes about half the power of the alternative scenario.
Power consumption of ICT equipment has a growing impact, both on economic and environmental level. To reduce its energy footprint, drastic actions will be required on four fronts: energy-efficient components, power management techniques, new network paradigms and policy supporting actions. This paper outlines the current trends and research for each category.
= journal paper - = conference paper - = poster
A bunch of documents I've written (mainly assignments), not related to my research above. Definitely not perfect, but of which I think that they are (marginally) more useful here than on my local hard disk.
Newer items on top.
For anybody interested in the subject of green energy (think solar panels, wind turbines, etc.), I can wholeheartedly recommend David MacKay's book "Sunstainable Energy - without the hot air". His motivation for the book, according to the first chapter, was his observation that different smart people talking about the energy issue come to different conclusions: according to one side 'Everything is fine', while the other side predicts gloom and doom. So Mackay, a professor in Physics at Cambridge, decided that the only way to know who's right is to look at the actual numbers of what is physically possible and what is not. This sounds a lot more boring that it actually is!
As an example, and a good starting point: Chapter 19 - Every BIG helps, debunks the myth that 'every little helps', which is a thing commonly heard and said. It does not, at least when it comes to global energy consumption and reduction. Mackay proposes instead the mantra 'if everyone does a little, we’ll achieve only a little'. Check the above linked page to be convinced.
It is a rare, very-readable, humorous, well-balanced book about our energy consumption and the 'green' energy sources we have and have not available. Plus, the book is sprinkled with lots of nice photos and pictures. If that still doesn't convince you, check out boingboing's raving review. You can download it for free, but the book is well-worth the money.
Perhaps you are wondering or looking for tips on what you can do to save on energy used by all the computer-related stuff in your home. If you want to maintain the same level of comfort, there is - unfortunately - not too much you can do that will actually make a difference. Still, if you insist, here's what I would advice (in order of decreasing effectiveness):
This little section is shameless promotion. Below are two rock-solid services I use daily and can recommend without worries. If you think they're useful for you as well, and you decide to sign up using the links below (these are called "referral links"), I'll get some extra credit or space. In the case of Dropbox, you'll get some extra space as well.
An online travelogue (partly in Dutch) about a 3-month trip through the Middle East and Central Asia at the end of 2003.