A Survey of Green Networking Research
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paper_title: To Slow or Not to Slow: The Economics of The Greenhouse Effect

paper_content:

Over the last decade, scientists have studied extensively the greenhouse effect, which holds that the accumulation of carbon dioxide (CO2) and other greenhouse gases (GHGs) is expected to produce global warming and other significant climatic changes over the next century. Along with the scientific research have come growing alarm and calls for drastic curbs on the emissions of greenhouse gases, as for example the reports of the Intergovernmental Panel on Climate Change (IPCC [I990]) and the Second World Climate Conference (October I990). To date, these call to arms for forceful measures to slow greenhouse warming have been made without any serious attempt to weigh the costs and benefits of climatic change or alternative control strategies. The present study presents a simple approach for analyzing policies to slow climate change. We begin by summarizing the elements of an economic analysis of different approaches to controlling greenhouse warming. We then sketch a mathematical model of economic growth that links the economy, emissions, and climate changes and summarize the empirical evidence on the costs of reducing emissions and concentrations of greenhouse gases and on the damages from greenhouse warming, relying primarily on data for the United States. The different sections are then integrated to provide estimates of the efficient reduction of greenhouse gases, after which the final section summarizes the major results.
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paper_title: Cutting the electric bill for internet-scale systems

paper_content:

Energy expenses are becoming an increasingly important fraction of data center operating costs. At the same time, the energy expense per unit of computation can vary significantly between two different locations. In this paper, we characterize the variation due to fluctuating electricity prices and argue that existing distributed systems should be able to exploit this variation for significant economic gains. Electricity prices exhibit both temporal and geographic variation, due to regional demand differences, transmission inefficiencies, and generation diversity. Starting with historical electricity prices, for twenty nine locations in the US, and network traffic data collected on Akamai's CDN, we use simulation to quantify the possible economic gains for a realistic workload. Our results imply that existing systems may be able to save millions of dollars a year in electricity costs, by being cognizant of locational computation cost differences.
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paper_title: Energy Efficiency in Telecom Optical Networks

paper_content:

Since the energy crisis and environmental protection are gaining increasing concerns in recent years, new research topics to devise technological solutions for energy conservation are being investigated in many scientific disciplines. Specifically, due to the rapid growth of energy consumption in ICT (Information and Communication Technologies), lot of attention is being devoted towards "green" ICT solutions. In this paper, we provide a comprehensive survey of the most relevant research activities for minimizing energy consumption in telecom networks, with a specific emphasis on those employing optical technologies. We investigate the energy-minimization opportunities enabled by optical technologies and classify the existing approaches over different network domains, namely core, metro, and access networks. A section is also devoted to describe energy-efficient solutions for some of today's important applications using optical network technology, e.g., grid computing and data centers. We provide an overview of the ongoing standardization efforts in this area. This work presents a comprehensive and timely survey on a growing field of research, as it covers most aspects of energy consumption in optical telecom networks. We aim at providing a comprehensive reference for the growing base of researchers who will work on energy efficiency of telecom networks in the upcoming years.
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paper_title: The next frontier for communications networks: power management

paper_content:

Storage, memory, processor, and communications bandwidth are all relatively plentiful and inexpensive. However, a growing expense in the operation of computer networks is electricity usage. Estimates place devices connected to the Internet as consuming about 2%, and growing, of the total electricity produced in the USA-much of this power consumption is unnecessary. Power management is needed to reduce this large and growing energy consumption of the Internet. We see power management as the 'next frontier' in research in computer networks. In this paper, we propose methods for reducing energy consumption of networked desktop computers. Using traffic characterization of university dormitory computers, we show that there is significant idle time that can be exploited for power management. However, current Ethernet adapters in desktop computers lack the capabilities needed to allow existing system power management features to be enabled. We address this problem with a proxying Ethernet adapter that handles routine network tasks for a desktop computer when it is in a low-power sleep mode. This proxying adapter can allow existing power management features in desktop computers to remain enabled and have the computer be 'on the network' at all times. The energy that we expect can be saved is in the range of 0.8-2.7 billion US dollars/year.
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paper_title: Enabling an Energy-Efficient Future Internet Through Selectively Connected End Systems

paper_content:

We offer an initial exploration of the architectural constructs required to support selective connectivity, whereby a host can choose the degree to which it maintains a network presence, rather than today's binary notion of "connected" or "disconnected". The driver for our thinking is to allow hosts to go to sleep to Proposed architectural elements
---
paper_title: Cutting the electric bill for internet-scale systems

paper_content:

Energy expenses are becoming an increasingly important fraction of data center operating costs. At the same time, the energy expense per unit of computation can vary significantly between two different locations. In this paper, we characterize the variation due to fluctuating electricity prices and argue that existing distributed systems should be able to exploit this variation for significant economic gains. Electricity prices exhibit both temporal and geographic variation, due to regional demand differences, transmission inefficiencies, and generation diversity. Starting with historical electricity prices, for twenty nine locations in the US, and network traffic data collected on Akamai's CDN, we use simulation to quantify the possible economic gains for a realistic workload. Our results imply that existing systems may be able to save millions of dollars a year in electricity costs, by being cognizant of locational computation cost differences.
---
paper_title: The Case for Energy-Proportional Computing

paper_content:

Energy-proportional designs would enable large energy savings in servers, potentially doubling their efficiency in real-life use. Achieving energy proportionality will require significant improvements in the energy usage profile of every system component, particularly the memory and disk subsystems.
---
paper_title: The next frontier for communications networks: power management

paper_content:

Storage, memory, processor, and communications bandwidth are all relatively plentiful and inexpensive. However, a growing expense in the operation of computer networks is electricity usage. Estimates place devices connected to the Internet as consuming about 2%, and growing, of the total electricity produced in the USA-much of this power consumption is unnecessary. Power management is needed to reduce this large and growing energy consumption of the Internet. We see power management as the 'next frontier' in research in computer networks. In this paper, we propose methods for reducing energy consumption of networked desktop computers. Using traffic characterization of university dormitory computers, we show that there is significant idle time that can be exploited for power management. However, current Ethernet adapters in desktop computers lack the capabilities needed to allow existing system power management features to be enabled. We address this problem with a proxying Ethernet adapter that handles routine network tasks for a desktop computer when it is in a low-power sleep mode. This proxying adapter can allow existing power management features in desktop computers to remain enabled and have the computer be 'on the network' at all times. The energy that we expect can be saved is in the range of 0.8-2.7 billion US dollars/year.
---
paper_title: Power Awareness in Network Design and Routing

paper_content:

Exponential bandwidth scaling has been a fundamental driver of the growth and popularity of the Internet. However, increases in bandwidth have been accompanied by increases in power consumption, and despite sustained system design efforts to address power demand, significant technological challenges remain that threaten to slow future bandwidth growth. In this paper we describe the power and associated heat management challenges in today's routers. We advocate a broad approach to addressing this problem that includes making power-awareness a primary objective in the design and configuration of networks, and in the design and implementation of network protocols. We support our arguments by providing a case study of power demands of two standard router platforms that enables us to create a generic model for router power consumption. We apply this model in a set of target network configurations and use mixed integer optimization techniques to investigate power consumption, performance and robustness in static network design and in dynamic routing. Our results indicate the potential for significant power savings in operational networks by including power-awareness.
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paper_title: Energy Consumption of Residential and Professional Switches

paper_content:

Precise evaluation of network appliance energy consumption is necessary to accurately model or simulate the power consumption of distributed systems. In this paper we evaluate the influence of traffic onto the consumption of electrical power of four switches found in home and professional environments. First we describe our measurement and data analysis approach, and how our results can be used for estimating the power consumption when knowing the average traffic bandwidth.Then we present the measurement results of two residential switches, and two professional switches. For each type we present regression models and parameters describing their quality. Similar to other works we find that for one of the switches the power consumption actually drops for high traffic loads, while for the others the situation is reverse. Measures justify that during most energy consumption evaluation, network appliance energy cost can be approximated as constant. This work gives information on the possible changes of this cost.
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paper_title: A Power Benchmarking Framework for Network Devices

paper_content:

Energy efficiency is becoming increasingly important in the operation of networking infrastructure, especially in enterprise and data center networks. Researchers have proposed several strategies for energy management of networking devices. However, we need a comprehensive characterization of power consumption by a variety of switches and routers to accurately quantify the savings from the various power savings schemes. In this paper, we first describe the hurdles in network power instrumentation and present a power measurement study of a variety of networking gear such as hubs, edge switches, core switches, routers and wireless access points in both stand-alone mode and a production data center. We build and describe a benchmarking suite that will allow users to measure and compare the power consumed for a large set of common configurations at any switch or router of their choice. We also propose a network energy proportionality index, which is an easily measurable metric, to compare power consumption behaviors of multiple devices.
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paper_title: A feasibility study for power management in LAN switches

paper_content:

We examine the feasibility of introducing power management schemes in network devices in the LAN. Specifically, we investigate the possibility of putting various components on LAN switches to sleep during periods of low traffic activity. Traffic collected in our LAN indicates that there are significant periods of inactivity on specific switch interfaces. Using an abstract sleep model devised for LAN switches, we examine the potential energy savings possible for different times of day and different interfaces (e.g., interfaces connecting to hosts to switches, or interfaces connecting switches, or interfaces connecting switches and routers). Algorithms developed for sleeping, based on periodic protocol behavior as well as traffic estimation are shown to be capable of conserving significant amounts of energy. Our results show that sleeping is indeed feasible in the LAN and in some cases, with very little impact on other protocols. However, we note that in order to maximize energy savings while minimizing sleep-related losses, we need hardware that supports sleeping.
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paper_title: Energy-efficient algorithms

paper_content:

Algorithmic solutions can help reduce energy consumption in computing environs.
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paper_title: Using Low-Power Modes for Energy Conservation in Ethernet LANs

paper_content:

Most Ethernet interfaces available for deployment in switches and hosts today can operate in a variety of different low power modes. However, currently these modes have very limited usage models. They do not take advantage of periods of inactivity, when the links remain idle or under-utilized. In this study, we propose methods that allow for detection of such periods to obtain energy savings with little impact on loss or delay. We evaluate our methods on a wide range of real-time traffic traces collected at a high-speed backbone switch within our campus LAN. Our results show that Ethernet interfaces at both ends can be put in extremely low power modes anywhere from 40%-98% of the time observed. In addition, we found that approximately 37% of interfaces studied (on the same switch) can be put in low power modes simultaneously which opens the potential for further energy savings in the switching fabric within the switch.
---
paper_title: Greening the Switch

paper_content:

Active research is being conducted in reducing power consumption of all the components of the Internet. To that end, we propose schemes for power reduction in network switches -- Time Window Prediction, Power Save Mode and Lightweight Alternative. These schemes are adaptive to changing traffic patterns and automatically tune their parameters to guarantee a bounded and specified increase in latency. We propose a novel architecture for buffering ingress packets using shadow ports. ::: ::: We test our schemes on packet traces obtained from an enterprise network, and evaluate them using realistic power models for the switches. Our simple power reduction schemes produce power savings of upto 32% with minimal increase in latency or packet-loss. With appropriate hardware support in the form of Wake-on-Packet, shadow ports and fast transitioning of the ports between its high and low power states, these savings reach 90% of the optimal algorithm's savings.
---
paper_title: Greening of the internet

paper_content:

In this paper we examine the somewhat controversial subject of energy consumption of networking devices in the Internet, motivated by data collected by the U.S. Department of Commerce. We discuss the impact on network protocols of saving energy by putting network interfaces and other router & switch components to sleep. Using sample packet traces, we first show that it is indeed reasonable to do this and then we discuss the changes that may need to be made to current Internet protocols to support a more aggressive strategy for sleeping. Since this is a position paper, we do not present results but rather suggest interesting directions for core networking research. The impact of saving energy is huge, particularly in the developing world where energy is a precious resource whose scarcity hinders widespread Internet deployment.
---
paper_title: NGL02-2: Ethernet Adaptive Link Rate (ALR): Analysis of a Buffer Threshold Policy

paper_content:

Rapidly increasing energy use by computing and communications equipment is a significant problem that needs to be addressed. Ethernet network interface controllers (NICs) consume hundreds of millions of US$ in electricity per year. Most Ethernet links are underutilized and link power consumption can be reduced by operating at lower data rates. An output buffer threshold policy to change link data rate in response to utilization is investigated. Analytical and simulation models are developed to evaluate the performance of Adaptive Link Rate (ALR) with respect to mean packet delay and time spent in low data rate with Poisson traffic and 100 Mb/s network traces as inputs. A Markov model of a state-dependent service rate queue with rate transitions only at service completion is developed. For the traffic traces, it is found that a link can operate at 10 Mb/s for over 99% of the time yielding energy savings with no user-perceivable increase in packet delay.
---
paper_title: Managing energy consumption costs in desktop PCs and LAN switches with proxying, split TCP connections, and scaling of link speed

paper_content:

The IT equipment comprising the Internet in the USA uses about $6 billion of electricity every year. Much of this electricity use is wasted on idle, but fully powered-up, desktop PCs and network links. We show how to recover a large portion of the wasted electricity with improved power management methods that are focused on network issues.
---
paper_title: Reducing the Energy Consumption of Ethernet with Adaptive Link Rate (ALR)

paper_content:

The rapidly increasing energy consumption by computing and communications equipment is a significant economic and environmental problem that needs to be addressed. Ethernet network interface controllers (NICs) in the US alone consume hundreds of millions of US dollars in electricity per year. Most Ethernet links are underutilized and link energy consumption can be reduced by operating at a lower data rate. In this paper, we investigate adaptive link rate (ALR) as a means of reducing the energy consumption of a typical Ethernet link by adaptively varying the link data rate in response to utilization. Policies to determine when to change the link data rate are studied. Simple policies that use output buffer queue length thresholds and fine-grain utilization monitoring are shown to be effective. A Markov model of a state-dependent service rate queue with rate transitions only at service completion is used to evaluate the performance of ALR with respect to the mean packet delay, the time spent in an energy-saving low link data rate, and the oscillation of link data rates. Simulation experiments using actual and synthetic traffic traces show that an Ethernet link with ALR can operate at a lower data rate for over 80 percent of the time, yielding significant energy savings with only a very small increase in packet delay.
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paper_title: On the complexity of time table and multi-commodity flow problems

paper_content:

A very primitive version of Gotlieb's timetable problem is shown to be NP-complete, and therefore all the common timetable problems are NP-complete. A polynomial time algorithm, in case all teachers are binary, is shown. The theorem that a meeting function always exists if all teachers and classes have no time constraints is proved. The multi-commodity integral flow problem is shown to be NP-complete even if the number of commodities is two. This is true both in the directed and undirected cases. Finally, the two commodity real flow problem in undirected graphs is shown to be solvable in polynomial time. The time bound is O(|v|2|E|).
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paper_title: PowerNap: eliminating server idle power

paper_content:

Data center power consumption is growing to unprecedented levels: the EPA estimates U.S. data centers will consume 100 billion kilowatt hours annually by 2011. Much of this energy is wasted in idle systems: in typical deployments, server utilization is below 30%, but idle servers still consume 60% of their peak power draw. Typical idle periods though frequent--last seconds or less, confounding simple energy-conservation approaches. In this paper, we propose PowerNap, an energy-conservation approach where the entire system transitions rapidly between a high-performance active state and a near-zero-power idle state in response to instantaneous load. Rather than requiring fine-grained power-performance states and complex load-proportional operation from each system component, PowerNap instead calls for minimizing idle power and transition time, which are simpler optimization goals. Based on the PowerNap concept, we develop requirements and outline mechanisms to eliminate idle power waste in enterprise blade servers. Because PowerNap operates in low-efficiency regions of current blade center power supplies, we introduce the Redundant Array for Inexpensive Load Sharing (RAILS), a power provisioning approach that provides high conversion efficiency across the entire range of PowerNap's power demands. Using utilization traces collected from enterprise-scale commercial deployments, we demonstrate that, together, PowerNap and RAILS reduce average server power consumption by 74%.
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paper_title: Reducing Network Energy Consumption via Sleeping and Rate-Adaptation

paper_content:

We present the design and evaluation of two forms of power management schemes that reduce the energy consumption of networks. The first is based on putting network components to sleep during idle times, reducing energy consumed in the absence of packets. The second is based on adapting the rate of network operation to the offered workload, reducing the energy consumed when actively processing packets. ::: ::: For real-world traffic workloads and topologies and using power constants drawn from existing network equipment, we show that even simple schemes for sleeping or rate-adaptation can offer substantial savings. For instance, our practical algorithms stand to halve energy consumption for lightly utilized networks (10-20%). We show that these savings approach the maximum achievable by any algorithms using the same power management primitives. Moreover this energy can be saved without noticeably increasing loss and with a small and controlled increase in latency (<10ms). Finally, we show that both sleeping and rate adaptation are valuable depending (primarily) on the power profile of network equipment and the utilization of the network itself.
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paper_title: Power-Aware Speed Scaling in Processor Sharing Systems

paper_content:

Energy use of computer communication systems has quickly become a vital design consideration. One effective method for reducing energy consumption is dynamic speed scaling, which adapts the processing speed to the current load. This paper studies how to optimally scale speed to balance mean response time and mean energy consumption under processor sharing scheduling. Both bounds and asymptotics for the optimal speed scaling scheme are provided. These results show that a simple scheme that halts when the system is idle and uses a static rate while the system is busy provides nearly the same performance as the optimal dynamic speed scaling. However, the results also highlight that dynamic speed scaling provides at least one key benefit - significantly improved robustness to bursty traffic and mis-estimation of workload parameters.
---
paper_title: NGL02-2: Ethernet Adaptive Link Rate (ALR): Analysis of a Buffer Threshold Policy

paper_content:

Rapidly increasing energy use by computing and communications equipment is a significant problem that needs to be addressed. Ethernet network interface controllers (NICs) consume hundreds of millions of US$ in electricity per year. Most Ethernet links are underutilized and link power consumption can be reduced by operating at lower data rates. An output buffer threshold policy to change link data rate in response to utilization is investigated. Analytical and simulation models are developed to evaluate the performance of Adaptive Link Rate (ALR) with respect to mean packet delay and time spent in low data rate with Poisson traffic and 100 Mb/s network traces as inputs. A Markov model of a state-dependent service rate queue with rate transitions only at service completion is developed. For the traffic traces, it is found that a link can operate at 10 Mb/s for over 99% of the time yielding energy savings with no user-perceivable increase in packet delay.
---
paper_title: Managing energy consumption costs in desktop PCs and LAN switches with proxying, split TCP connections, and scaling of link speed

paper_content:

The IT equipment comprising the Internet in the USA uses about $6 billion of electricity every year. Much of this electricity use is wasted on idle, but fully powered-up, desktop PCs and network links. We show how to recover a large portion of the wasted electricity with improved power management methods that are focused on network issues.
---
paper_title: Using Low-Power Modes for Energy Conservation in Ethernet LANs

paper_content:

Most Ethernet interfaces available for deployment in switches and hosts today can operate in a variety of different low power modes. However, currently these modes have very limited usage models. They do not take advantage of periods of inactivity, when the links remain idle or under-utilized. In this study, we propose methods that allow for detection of such periods to obtain energy savings with little impact on loss or delay. We evaluate our methods on a wide range of real-time traffic traces collected at a high-speed backbone switch within our campus LAN. Our results show that Ethernet interfaces at both ends can be put in extremely low power modes anywhere from 40%-98% of the time observed. In addition, we found that approximately 37% of interfaces studied (on the same switch) can be put in low power modes simultaneously which opens the potential for further energy savings in the switching fabric within the switch.
---
paper_title: Greening the Switch

paper_content:

Active research is being conducted in reducing power consumption of all the components of the Internet. To that end, we propose schemes for power reduction in network switches -- Time Window Prediction, Power Save Mode and Lightweight Alternative. These schemes are adaptive to changing traffic patterns and automatically tune their parameters to guarantee a bounded and specified increase in latency. We propose a novel architecture for buffering ingress packets using shadow ports. ::: ::: We test our schemes on packet traces obtained from an enterprise network, and evaluate them using realistic power models for the switches. Our simple power reduction schemes produce power savings of upto 32% with minimal increase in latency or packet-loss. With appropriate hardware support in the form of Wake-on-Packet, shadow ports and fast transitioning of the ports between its high and low power states, these savings reach 90% of the optimal algorithm's savings.
---
paper_title: Skilled in the Art of Being Idle: Reducing Energy Waste in Networked Systems

paper_content:

Networked end-systems such as desktops and set-top boxes are often left powered-on, but idle, leading to wasted energy consumption. An alternative would be for these idle systems to enter low-power sleep modes. Unfortunately, today, a sleeping system sees degraded functionality: first, a sleeping device loses its network "presence" which is problematic to users and applications that expect to maintain access to a remote machine and, second, sleeping can prevent running tasks scheduled during times of low utilization (e.g., network backups). Various solutions to these problems have been proposed over the years including wake-on-lan (WoL) mechanisms that wake hosts when specific packets arrive, and the use of a proxy that handles idle-time traffic on behalf of a sleeping host. As of yet, however, an in-depth evaluation of the potential for energy savings, and the effectiveness of proposed solutions has not been carried out. To remedy this, in this paper, we collect data directly from 250 enterprise users on their end-host machines capturing network traffic patterns and user presence indicators. With this data, we answer several questions: what is the potential value of proxying or using magic packets? which protocols and applications require proxying? how comprehensive does proxying need to be for energy benefits to be compelling? and so on. ::: ::: We find that, although there is indeed much potential for energy savings, trivial approaches are not effective. We also find that achieving substantial savings requires a careful consideration of the tradeoffs between the proxy complexity and the idle-time functionality available to users, and that these tradeoffs vary with user environment. Based on our findings, we propose and evaluate a proxy architecture that exposes a minimal set of APIs to support different forms of idle-time behavior.
---
paper_title: Reducing the Energy Consumption of Ethernet with Adaptive Link Rate (ALR)

paper_content:

The rapidly increasing energy consumption by computing and communications equipment is a significant economic and environmental problem that needs to be addressed. Ethernet network interface controllers (NICs) in the US alone consume hundreds of millions of US dollars in electricity per year. Most Ethernet links are underutilized and link energy consumption can be reduced by operating at a lower data rate. In this paper, we investigate adaptive link rate (ALR) as a means of reducing the energy consumption of a typical Ethernet link by adaptively varying the link data rate in response to utilization. Policies to determine when to change the link data rate are studied. Simple policies that use output buffer queue length thresholds and fine-grain utilization monitoring are shown to be effective. A Markov model of a state-dependent service rate queue with rate transitions only at service completion is used to evaluate the performance of ALR with respect to the mean packet delay, the time spent in an energy-saving low link data rate, and the oscillation of link data rates. Simulation experiments using actual and synthetic traffic traces show that an Ethernet link with ALR can operate at a lower data rate for over 80 percent of the time, yielding significant energy savings with only a very small increase in packet delay.
---
paper_title: Greening of the internet

paper_content:

In this paper we examine the somewhat controversial subject of energy consumption of networking devices in the Internet, motivated by data collected by the U.S. Department of Commerce. We discuss the impact on network protocols of saving energy by putting network interfaces and other router & switch components to sleep. Using sample packet traces, we first show that it is indeed reasonable to do this and then we discuss the changes that may need to be made to current Internet protocols to support a more aggressive strategy for sleeping. Since this is a position paper, we do not present results but rather suggest interesting directions for core networking research. The impact of saving energy is huge, particularly in the developing world where energy is a precious resource whose scarcity hinders widespread Internet deployment.
---
paper_title: Managing energy consumption costs in desktop PCs and LAN switches with proxying, split TCP connections, and scaling of link speed

paper_content:

The IT equipment comprising the Internet in the USA uses about $6 billion of electricity every year. Much of this electricity use is wasted on idle, but fully powered-up, desktop PCs and network links. We show how to recover a large portion of the wasted electricity with improved power management methods that are focused on network issues.
---
paper_title: Skilled in the Art of Being Idle: Reducing Energy Waste in Networked Systems

paper_content:

Networked end-systems such as desktops and set-top boxes are often left powered-on, but idle, leading to wasted energy consumption. An alternative would be for these idle systems to enter low-power sleep modes. Unfortunately, today, a sleeping system sees degraded functionality: first, a sleeping device loses its network "presence" which is problematic to users and applications that expect to maintain access to a remote machine and, second, sleeping can prevent running tasks scheduled during times of low utilization (e.g., network backups). Various solutions to these problems have been proposed over the years including wake-on-lan (WoL) mechanisms that wake hosts when specific packets arrive, and the use of a proxy that handles idle-time traffic on behalf of a sleeping host. As of yet, however, an in-depth evaluation of the potential for energy savings, and the effectiveness of proposed solutions has not been carried out. To remedy this, in this paper, we collect data directly from 250 enterprise users on their end-host machines capturing network traffic patterns and user presence indicators. With this data, we answer several questions: what is the potential value of proxying or using magic packets? which protocols and applications require proxying? how comprehensive does proxying need to be for energy benefits to be compelling? and so on. ::: ::: We find that, although there is indeed much potential for energy savings, trivial approaches are not effective. We also find that achieving substantial savings requires a careful consideration of the tradeoffs between the proxy complexity and the idle-time functionality available to users, and that these tradeoffs vary with user environment. Based on our findings, we propose and evaluate a proxy architecture that exposes a minimal set of APIs to support different forms of idle-time behavior.
---
paper_title: Somniloquy: Augmenting Network Interfaces to Reduce PC Energy Usage

paper_content:

Reducing the energy consumption of PCs is becoming increasingly important with rising energy costs and environmental concerns. Sleep states such as S3 (suspend to RAM) save energy, but are often not appropriate because ongoing networking tasks, such as accepting remote desktop logins or performing background file transfers, must be supported. In this paper we present Somniloquy, an architecture that augments network interfaces to allow PCs in S3 to be responsive to network traffic. We show that many applications, such as remote desktop and VoIP, can be supported without application-specific code in the augmented network interface by using application-level wakeup triggers. A further class of applications, such as instant messaging and peer-to-peer file sharing, can be supported with modest processing and memory resources in the network interface. Experiments using our prototype Somniloquy implementation, a USB-based network interface, demonstrates energy savings of 60% to 80% in most commonly occuring scenarios. This translates to significant cost savings for PC users.
---
paper_title: Managing energy consumption costs in desktop PCs and LAN switches with proxying, split TCP connections, and scaling of link speed

paper_content:

The IT equipment comprising the Internet in the USA uses about $6 billion of electricity every year. Much of this electricity use is wasted on idle, but fully powered-up, desktop PCs and network links. We show how to recover a large portion of the wasted electricity with improved power management methods that are focused on network issues.
---
paper_title: Power-Proxying on the NIC: A Case Study with the Gnutella File-Sharing Protocol

paper_content:

Edge devices such as desktop and laptop computers constitute a majority of the devices connected to the Internet today. Peer-to-Peer (P2P) file-sharing applications generally require edge devices to maintain network presence whenever possible to enhance the robustness of the file-sharing network, which in turn can lead to considerable wastage of energy. We show that energy can be saved by permitting edge devices to enter into standby state and still maintain network connectivity by proxying protocols in the Network Interface Card (NIC).
---
paper_title: A Prototype Power Management Proxy for Gnutella Peer-to-Peer File Sharing

paper_content:

In order to be part of a peer-to-peer (P2P) file sharing network a host must be fully powered-on all of the time. In addition to providing a user interface, a P2P host handles query messages and serves requested files. In this paper, we describe the development of a prototype Gnutella-like P2P power management proxy sub-system that handles query messages. This can allow desktop PCs acting as P2P hosts to enter a low-power sleep state for most of the time and be woken-up by the proxy only when needed to serve files. TCP connections with neighbors are maintained by the host when it is awake and by the proxy when the host is sleeping. Experiments show that a low-cost Freescale ColdFire processor can effectively proxy for a P2P host. This suggests that a controller for a Gnutella P2P proxy could be co-located on an Ethernet NIC at low cost. This could lead to significant energy savings by allowing P2P hosts to power manage into a low-power sleep state when not in active use.
---
paper_title: Managing energy consumption costs in desktop PCs and LAN switches with proxying, split TCP connections, and scaling of link speed

paper_content:

The IT equipment comprising the Internet in the USA uses about $6 billion of electricity every year. Much of this electricity use is wasted on idle, but fully powered-up, desktop PCs and network links. We show how to recover a large portion of the wasted electricity with improved power management methods that are focused on network issues.
---
paper_title: Skilled in the Art of Being Idle: Reducing Energy Waste in Networked Systems

paper_content:

Networked end-systems such as desktops and set-top boxes are often left powered-on, but idle, leading to wasted energy consumption. An alternative would be for these idle systems to enter low-power sleep modes. Unfortunately, today, a sleeping system sees degraded functionality: first, a sleeping device loses its network "presence" which is problematic to users and applications that expect to maintain access to a remote machine and, second, sleeping can prevent running tasks scheduled during times of low utilization (e.g., network backups). Various solutions to these problems have been proposed over the years including wake-on-lan (WoL) mechanisms that wake hosts when specific packets arrive, and the use of a proxy that handles idle-time traffic on behalf of a sleeping host. As of yet, however, an in-depth evaluation of the potential for energy savings, and the effectiveness of proposed solutions has not been carried out. To remedy this, in this paper, we collect data directly from 250 enterprise users on their end-host machines capturing network traffic patterns and user presence indicators. With this data, we answer several questions: what is the potential value of proxying or using magic packets? which protocols and applications require proxying? how comprehensive does proxying need to be for energy benefits to be compelling? and so on. ::: ::: We find that, although there is indeed much potential for energy savings, trivial approaches are not effective. We also find that achieving substantial savings requires a careful consideration of the tradeoffs between the proxy complexity and the idle-time functionality available to users, and that these tradeoffs vary with user environment. Based on our findings, we propose and evaluate a proxy architecture that exposes a minimal set of APIs to support different forms of idle-time behavior.
---
paper_title: Power-Proxying on the NIC: A Case Study with the Gnutella File-Sharing Protocol

paper_content:

Edge devices such as desktop and laptop computers constitute a majority of the devices connected to the Internet today. Peer-to-Peer (P2P) file-sharing applications generally require edge devices to maintain network presence whenever possible to enhance the robustness of the file-sharing network, which in turn can lead to considerable wastage of energy. We show that energy can be saved by permitting edge devices to enter into standby state and still maintain network connectivity by proxying protocols in the Network Interface Card (NIC).
---
paper_title: Power Awareness in Network Design and Routing

paper_content:

Exponential bandwidth scaling has been a fundamental driver of the growth and popularity of the Internet. However, increases in bandwidth have been accompanied by increases in power consumption, and despite sustained system design efforts to address power demand, significant technological challenges remain that threaten to slow future bandwidth growth. In this paper we describe the power and associated heat management challenges in today's routers. We advocate a broad approach to addressing this problem that includes making power-awareness a primary objective in the design and configuration of networks, and in the design and implementation of network protocols. We support our arguments by providing a case study of power demands of two standard router platforms that enables us to create a generic model for router power consumption. We apply this model in a set of target network configurations and use mixed integer optimization techniques to investigate power consumption, performance and robustness in static network design and in dynamic routing. Our results indicate the potential for significant power savings in operational networks by including power-awareness.
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paper_title: Time for a "Greener" Internet

paper_content:

It is anticipated that the Internet traffic will continue to grow exponentially for the foreseeable future, which will require ever-growing energy (electricity). Since a lot of the Internet traffic growth comes from predictable services (such as video) there is a huge potential for decreasing future Internet energy requirements by synchronizing the operation of routers and scheduling traffic in advance, thus reducing complexity (e.g., header processing, buffer size, switching fabric speedup and memory access bandwidth speedup). Today, scheduling and synchronizing large-scale data transfer operations can be easily achieved by utilizing a choice of tens of global time sources, freely available on earth and in space. In a way, this manuscript shows how to "trade" global time for electricity utilized by the global Internet.
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paper_title: Optical Burst Switching ( OBS ) { A New Paradigm for an Optical Internet

paper_content:

To support bursty traffic on the Internet (and especially WWW) efficiently, optical burst switching (OBS) is proposed as a way to streamline both protocols and hardware in building the future generation Optical Internet. By leveraging the attractive properties of optical communications and at the same time, taking into account its limitations, OBS combines the best of optical circuit-switching and packet/cell switching. In this paper, the general concept of OBS protocols and in particular, those based on Just-Enough-Time (JET), is described, along with the applicability of OBS protocols to IP over WDM. Specific issues such as the use of fiber delay-lines (FDLs) for accommodating processing delay and/or resolving conflicts are also discussed. In addition, the performance of JET-based OBS protocols which use an offset time along with delayed reservation to achieve efficient utilization of both bandwidth and FDLs as well as to support priority-based routing is evaluated.
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paper_title: Reducing Network Energy Consumption via Sleeping and Rate-Adaptation

paper_content:

We present the design and evaluation of two forms of power management schemes that reduce the energy consumption of networks. The first is based on putting network components to sleep during idle times, reducing energy consumed in the absence of packets. The second is based on adapting the rate of network operation to the offered workload, reducing the energy consumed when actively processing packets. ::: ::: For real-world traffic workloads and topologies and using power constants drawn from existing network equipment, we show that even simple schemes for sleeping or rate-adaptation can offer substantial savings. For instance, our practical algorithms stand to halve energy consumption for lightly utilized networks (10-20%). We show that these savings approach the maximum achievable by any algorithms using the same power management primitives. Moreover this energy can be saved without noticeably increasing loss and with a small and controlled increase in latency (<10ms). Finally, we show that both sleeping and rate adaptation are valuable depending (primarily) on the power profile of network equipment and the utilization of the network itself.
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paper_title: On reliability, performance and Internet power consumption

paper_content:

With the increasing concern for global warming, the impact of Internet power consumption is gaining interest. In this paper, we explore, for the first time, the relationship between network robustness, performance and Internet power consumption. We first discuss such a relationship based on data collected from Internet sources. Next, we propose a modeling framework to size that relationship. It is shown that when designing networks based on power consumption, careful attention should be paid to the trade-off between energy consumption and network performance since doing otherwise would lead to unreliable networks.
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paper_title: The GREEN-NET framework: Energy efficiency in large scale distributed systems

paper_content:

The question of energy savings has been a matter of concern since a long time in the mobile distributed systems and battery-constrained systems. However, for large-scale non-mobile distributed systems, which nowadays reach impressive sizes, the energy dimension (electrical consumption) just starts to be taken into account. In this paper, we present the GREEN-NET1 framework which is based on 3 main components: an ON/OFF model based on an Energy Aware Resource Infrastructure (EARI), an adapted Resource Management System (OAR) for energy efficiency and a trust delegation component to assume network presence of sleeping nodes.
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paper_title: Reducing Power Consumption in Backbone Networks

paper_content:

According to several studies, the power consumption of the Internet accounts for up to 10% of the worldwide energy consumption, and several initiatives are being put into place to reduce the power consumption of the ICT sector in general. To this goal, we propose a novel approach to switch off network nodes and links while still guaranteeing full connectivity and maximum link utilization. After showing that the problem falls in the class of capacitated multi-commodity flow problems, and therefore it is NP-complete, we propose some heuristic algorithms to solve it. Simulation results in a realistic scenario show that it is possible to reduce the number of links and nodes currently used by up to 30% and 50% respectively during off-peak hours, while offering the same service quality.
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paper_title: Greening backbone networks: reducing energy consumption by shutting off cables in bundled links

paper_content:

In backbone networks, the line cards that drive the links between neighboring routers consume a large amount of energy. Since these networks are typically overprovisioned, selectively shutting down links during periods of low demand seems like a good way to reduce energy consumption. However, removing entire links from the topology often reduces capacity and connectivity too much, and leads to transient disruptions in the routing protocol. In this paper, we exploit the fact that many links in core networks are actually 'bundles' of multiple physical cables and line cards that can be shut down independently. Since identifying the optimal set of cables to shut down is an NP-complete problem, we propose several heuristics based on linear optimization techniques. We evaluate our heuristics on topology and traffic data from the Abilene backbone as well as on two synthetic topologies. The energy savings are significant, our simplest heuristic reduces energy consumption by 79% on Abilene under realistic traffic loads and bundled links consisting of five cables. Our optimization techniques run efficiently using standard optimization tools, such as the AMPL/CPLEX solver, making them a practical approach for network operators to reduce the energy consumption of their backbones.
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paper_title: Energy-aware routing: A reality check

paper_content:

In this work, we analyze the design of green routing algorithms and evaluate the achievable energy savings that such mechanisms could allow in several realistic network scenarios. We formulate the problem as a minimum energy routing optimization, which we numerically solve considering a core-network scenario, which can be seen as a worst-case for energy saving performance (as nodes cannot be switched off). To gather full-relief results, we analyze the energy savings in various conditions (i.e., network topology and traffic matrix) and under different technology assumptions (i.e., the energy profile of the network devices). These results give us insight into the potential benefits of different “green” technologies and their interactions. In particular, we show that depending on the topology and traffic matrices, the optimal energy savings can be modest, partly limiting the interest for green routing approaches for some scenarios. At the same time, we also show that the common belief that there is a trade off between green network optimization and performance does not necessarily hold: in the considered environment, green routing has no effect on the main network performances such as maximum link utilization.
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paper_title: Greening of the internet

paper_content:

In this paper we examine the somewhat controversial subject of energy consumption of networking devices in the Internet, motivated by data collected by the U.S. Department of Commerce. We discuss the impact on network protocols of saving energy by putting network interfaces and other router & switch components to sleep. Using sample packet traces, we first show that it is indeed reasonable to do this and then we discuss the changes that may need to be made to current Internet protocols to support a more aggressive strategy for sleeping. Since this is a position paper, we do not present results but rather suggest interesting directions for core networking research. The impact of saving energy is huge, particularly in the developing world where energy is a precious resource whose scarcity hinders widespread Internet deployment.
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paper_title: A Simulation Study of a New Green BitTorrent

paper_content:

The use of P2P technologies, such as BitTorrent, to distribute legal content to consumers is actively being explored as a means of reducing both file download times and the energy consumption of data centers. This approach pushes the energy use out of the data centers and into the homes of content consumers (who are also then content distributors). The current BitTorrent protocol requires that clients must be fully powered- on to be participating members in a swarm. In this paper, we show that simple changes to the BitTorrent protocol, including long-lived knowledge of sleeping peers and a new wake-up semantic, can enable clients to sleep when not actively downloading or uploading yet still be responsive swarm members. Using ns-2 we simulate a green BitTorrent swarm. We show that significant energy savings are achievable with only a small performance penalty in increased file download time.
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paper_title: Fine-grained energy profiling for power-aware application design

paper_content:

Significant opportunities for power optimization exist at application design stage and are not yet fully exploited by system and application designers. We describe the challenges developers face in optimizing software for energy efficiency by exploiting application-level knowledge. To address these challenges, we propose the development of automated tools that profile the energy usage of various resource components used by an application and guide the design choices accordingly. We use a preliminary version of a tool we have developed to demonstrate how automated energy profiling helps a developer choose between alternative designs in the energy-performance trade-off space.
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paper_title: Green: A System for Supporting Energy-Conscious Programming using Principled Approximation

paper_content:

Energy-efficient computing is important in several systems ranging from embedded devices to large scale data centers. Several application domains offer the opportunity to tradeoff quality of service/solution (QoS) for improvements in performance and reduction in energy consumption. Programmers sometimes take advantage of such opportunities, albeit in an ad-hoc manner and often without providing any QoS guarantees. We propose a system called Green that provides a simple and flexible framework that allows programmers to take advantage of such approximation opportunities in a systematic manner while providing statistical QoS guarantees. Green enables programmers to approximate expensive functions and loops and operates in two phases. In the calibration phase, it builds a model of the QoS loss produced by the approximation. This model is used in the operational phase to make approximation decisions based on the QoS constraints specified by the programmer. The operational phase also includes an adaptation function that occasionally monitors the runtime behavior and changes the approximation decisions and QoS model to provide strong QoS guarantees. To evaluate the effectiveness of Green, we implemented our system and language extensions using the Phoenix compiler framework. Our experiments using benchmarks from domains such as graphics, machine learning, and signal processing, and a real-world web search application, indicate that Green can produce significant improvements in performance and energy consumption with small and statistically guaranteed QoS degradation.
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paper_title: A "Green TCP/IP" to reduce electricity consumed by computers

paper_content:

This new era in engineering calls for a greater understanding of the environmental impacts of modern technology. In the year 2000 it is estimated that personal computers in the USA alone will consume 21.9 TWh of electricity. Most of this electricity will be wasted due to the PCs remaining powered-on, but idle, most of the time. The PCs are often left powered-on so that network connectivity can be maintained even when the PC is not actively used. This paper describes how PCs can be powered-off and network connectivity still be maintained. The design and evaluation of a new connection sleep option in a "Green TCP/IP" is described. The long-term impacts of a Green TCP/IP can be very significant in terms of measured electricity savings.
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paper_title: Computational energy cost of TCP

paper_content:

We present results from a detailed energy measurement study of TCP. We focus on the node-level cost of the TCP protocol and obtain a breakdown of the energy cost of different TCP functions. We analyze the energy consumption of TCP on two platforms (laptop and iPAQ) and three operating systems (FreeBSD 4.2, 5 and Linux 2.4.7). Our results show that 60-70% of the energy cost (for transmission or reception) is accounted for by the kernel NIC (network interface card) copy operation. Of the remainder, /spl sim/15% is accounted for in the copy operation from user space to kernel space with the remaining 15% being accounted for by TCP processing costs. We then further analyze the 15% TCP processing cost and show that the cost of computing checksums accounts for 20-30% of TCP processing cost. Finally, we determine the processing costs of two primary TCP functions - timeouts and triple duplicate ACKs. Pulling all these costs together, we present techniques whereby energy savings of between 20%-30% in the computational cost of TCP can be achieved.
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paper_title: On Delivering Embarrassingly Distributed Cloud Services

paper_content:

Very large data centers are very expensive (servers, power/cooling, networking, physical plant.) Newer, geo-diverse, distributed or containerized designs offer a more economical alternative. We argue that a significant portion of cloud services are embarrassingly distributed – meaning there are high performance realizations that do not require massive internal communication among large server pools. We argue further that these embarrassingly distributed applications are a good match for realization in small distributed data center designs. We consider email delivery as an illustrative example. Geo-diversity in the design not only improves costs, scale and reliability, but also realizes advantages stemming from edge processing; in applications such as spam filtering, unwanted traffic can be blocked near the source to reduce transport costs.
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paper_title: ECHOS: edge capacity hosting overlays of nano data centers

paper_content:

In this paper we propose a radical solution to data hosting and delivery for the Internet of the future. The current data delivery architecture is "network centric", with content stored in data centers connected directly to Internet backbones. This approach has multiple drawbacks among which complexity of deploying data centers, power consumption, and lack of scalability are the most critical. We propose a totally innovative and orthogonal approach to traditional data centers, through what we call "nano" data centers, which are deployed in boxes at the edge of the network (e.g., in home gateways, set-top-boxes, etc.) and accessed using a new peer-to-peer communication infrastructure. Unlike traditional peer-to-peer clients, however, our nano data centers operate under a common management authority, e.g., the ISP who installs and maintains the set-top-boxes, and can thus cooperate more effectively and achieve a higher aggregate performance. Nano data centers are, therefore, better suited for providing guaranteed quality to new emerging applications such as online gaming, interactive IPTV and VoD, and user generated content
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paper_title: Energy-Efficient Dynamic Instruction Scheduling Logic through Instruction Grouping

paper_content:

Dynamic instruction scheduling logic is quite complex and dissipates significant energy in microprocessors that support superscalar and out-of-order execution. We propose a novel microarchitectural technique to reduce the complexity and energy consumption of the dynamic instruction scheduling logic. The proposed method groups several instructions as a single issue unit and reduces the required number of ports and the size of the structure for dispatch, wakeup, select, and issue. The present paper describes the microarchitecture mechanisms and shows evaluation results for energy savings and performance. These results reveal that the proposed technique can greatly reduce energy with almost no performance degradation, compared to the conventional dynamic instruction scheduling logic.
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paper_title: Energy Aware Network Operations

paper_content:

Networking devices today consume a non-trivial amount of energy and it has been shown that this energy consumption is largely independent of the load through the devices. With a strong need to curtail the rising operational costs of IT infrastructure, there is a tremendous opportunity for introducing energy awareness in the design and operation of enterprise and data center networks. We focus on these networks as they are under the control of a single administrative domain in which network-wide control can be consistently applied. In this paper, we describe and analyze three approaches to saving energy in single administrative domain networks, without significantly impacting the networks' ability to provide the expected levels of performance and availability. We also explore the trade-offs between conserving energy and meeting performance and availability requirements. We conduct an extensive case study of our algorithms by simulating a real Web 2.0 workload in a real data center network topology using power characterizations that we obtain from real network hardware. Our results indicate that for our workload and data center scenario, 16% power savings (with no performance penalty and small decrease in availability) can be obtained merely by appropriately adjusting the active network elements (links). Significant additional savings (up to 75%) can be obtained by incorporating network traffic management and server workload consolidation.
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paper_title: Every joule is precious: the case for revisiting operating system design for energy efficiency

paper_content:

By some estimates, there will be close to one billion wirelessdevices capable of Internet connectivity within five years,surpassing the installed base of traditional wired compute devices.These devices will take the form of cellular phones, personaldigital assistants (PDA's), embedded processors, and "Internetappliances". This proliferation of networked computing devices willenable a number of compelling applications, centering aroundubiquitous access to global information services, just in timedelivery of personalized content, and tight synchronization amongcompute devices/appliances in our everyday environment. However,one of the principal challenges of realizing this vision in thepost-PC environment is the need to reduce the energy consumed inusing these next-generation mobile and wireless devices, therebyextending the lifetime of the batteries that power them. While theprocessing power, memory, and network bandwidth of post-PC devicesare increasing exponentially, their battery capacity is improvingat a more modest pace. Thus, to ensure the utility of post-PC applications, it isimportant to develop low-level mechanisms and higher-level policiesto maximize energy efficiency. In this paper, we propose thesystematic re-examination of all aspects of operating system designand implementation from the point of view of energy efficiencyrather than the more traditional OS metric of maximizingperformance. In [7], we made the case for energy as a first-classOS-managed resource. We emphasized the benefits of higher-levelcontrol over energy usage policy and the application/OSinteractions required to achieve them. This paper explores theimplications that this major shift in focus can have upon theservices, policies, mechanisms, and internal structure of the OSitself based on our initial experiences with rethinking systemdesign for energy efficiency. Our ultimate goal is to design an operating system where majorcomponents cooperate to explicitly optimize for energy efficiency.A number of research efforts have recently investigated aspects ofenergy-efficient operating systems (a good overview is available at[16, 20]) and we intend to leverage existing "best practice" in ourown work where such results exist. However, we are not aware of anysystems that systematically revisit system structure with energy inmind. Further, our examination of operating system functionalityreveals a number of opportunities that have received littleattention in the literature. To illustrate this point, Table 1presents major operating system functionality, along with possibletechniques for improving power consumption characteristics. Severalof the techniques are well studied, such as disk spindown policiesor adaptively trading content fidelity for power [8]. For example,to reduce power consumption for MPEG playback, the system couldadapt to a smaller frame rate and window size, consuming lessbandwidth and computation. One of the primary objectives of operating systems is allocatingresources among competing tasks, typically for fairness andperformance. Adding energy efficiency to the equation raises anumber of interesting issues. For example, competingprocesses/users may be scheduled to receive a fair share ofbattery resources rather than CPU resources (e.g., anapplication that makes heavy use of DISK I/O may be given lowerpriority relative to a compute-bound application when energyresources are low). Similarly, for tasks such as ad hoc routing,local battery resources are often consumed on behalf of remoteprocesses. Fair allocation dictates that one battery is not drainedin preference to others. Finally, for the communication subsystem,a number of efforts already investigate adaptively setting thepolling rate for wireless networks (trading latency forenergy). Our efforts to date have focused on the last four areashighlighted in Table 1. For memory allocation, our work exploreshow to exploit the ability of memory chips to transition amongmultiple power states. We also investigate metrics for pickingenergy-efficient routes in ad hoc networks, energy-efficientplacement of distributed computation, and flexible RPC/name bindingthat accounts for power consumption. These last two points of resource allocation and remotecommunication highlight an interesting property for energy-aware OSdesign in the post-PC environment. Many tasks are distributedacross multiple machines, potentially running on machines withwidely varying CPU, memory, and power source characteristics. Thus,energy-aware OS design must closely cooperate with and track thecharacteristics of remote computers to balance the oftenconflicting goals of optimizing for energy and speed. The rest of this paper illustrates our approach with selectedexamples extracted from our recent efforts toward building anintegrated hardware/software infrastructure that incorporatescooperative power management to support mobile and wirelessapplications. The instances we present in subsequent sections coverthe resource management policies and mechanisms necessary toexploit low power modes of various (existing or proposed) hardwarecomponents, as well as power-aware communications and the essentialrole of the wide-area environment. We begin our discussion with theresources of a single machine and then extend it to the distributedcontext.
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paper_title: Scheduling for reduced CPU energy

paper_content:

The energy usage of computer systems is becoming more important, especially for battery operated systems. Displays, disks, and cpus, in that order, use the most energy. Reducing the energy used by displays and disks has been studied elsewhere; this paper considers a new method for reducing the energy used by the cpu. We introduce a new metric for cpu energy performance, millions-of-instructions-per-joule (MIPJ). We examine a class of methods to reduce MIPJ that are characterized by dynamic control of system clock speed by the operating system scheduler. Reducing clock speed alone does not reduce MIPJ, since to do the same work the system must run longer. However, a number of methods are available for reducing energy with reduced clock-speed, such as reducing the voltage [Chandrakasan et al 1992][Horowitz 1993] or using reversible [Younis and Knight 1993] or adiabatic logic [Athas et al 1994]. What are the right scheduling algorithms for taking advantage of reduced clock-speed, especially in the presence of applications demanding ever more instructions-per-second? We consider several methods for varying the clock speed dynamically under control of the operating system, and examine the performance of these methods against workstation traces. The primary result is that by adjusting the clock speed at a fine grain, substantial CPU energy can be saved with a limited impact on performance.
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paper_title: Theoretical and practical limits of dynamic voltage scaling

paper_content:

Dynamic voltage scaling (DVS) is a popular approach for energy reduction of integrated circuits. Current processors that use DVS typically have an operating voltage range from full to half of the maximum Vdd. However, it is possible to construct designs that operate over a much larger voltage range: from full Vdd to subthreshold voltages. This possibility raises the question of whether a larger voltage range improves the energy efficiency of DVS. First, from a theoretical point of view, we show that for subthreshold supply voltages leakage energy becomes dominant, making "just in time completion" energy inefficient. We derive an analytical model for the minimum energy optimal voltage and study its trends with technology scaling. Second, we use the proposed model to study the workload activity of an actual processor and analyze the energy efficiency as a function of the lower limit of voltage scaling. Based on this study, we show that extending the voltage range below 1/2 Vdd will improve the energy efficiency for most processor designs, while extending this range to subthreshold operation is beneficial only for very specific applications. Finally, we show that operation deep in the subthreshold voltage range is never energy-efficient.
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paper_title: A study of thread migration in temperature-constrained multicores

paper_content:

Temperature has become an important constraint in high-performance processors, especially multicores. Thread migration will be essential to exploit the full potential of future thermally constrained multicores. We propose and study a thread migration method that maximizes performance under a temperature constraint, while minimizing the number of migrations and ensuring fairness between threads. We show that thread migration brings important performance gains and that it is most effective during the first tens of seconds following a decrease of the number of running threads.
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paper_title: Power provisioning for a warehouse-sized computer

paper_content:

Large-scale Internet services require a computing infrastructure that can beappropriately described as a warehouse-sized computing system. The cost ofbuilding datacenter facilities capable of delivering a given power capacity tosuch a computer can rival the recurring energy consumption costs themselves.Therefore, there are strong economic incentives to operate facilities as closeas possible to maximum capacity, so that the non-recurring facility costs canbe best amortized. That is difficult to achieve in practice because ofuncertainties in equipment power ratings and because power consumption tends tovary significantly with the actual computing activity. Effective powerprovisioning strategies are needed to determine how much computing equipmentcan be safely and efficiently hosted within a given power budget. In this paper we present the aggregate power usage characteristics of largecollections of servers (up to 15 thousand) for different classes ofapplications over a period of approximately six months. Those observationsallow us to evaluate opportunities for maximizing the use of the deployed powercapacity of datacenters, and assess the risks of over-subscribing it. We findthat even in well-tuned applications there is a noticeable gap (7 - 16%)between achieved and theoretical aggregate peak power usage at the clusterlevel (thousands of servers). The gap grows to almost 40% in wholedatacenters. This headroom can be used to deploy additional compute equipmentwithin the same power budget with minimal risk of exceeding it. We use ourmodeling framework to estimate the potential of power management schemes toreduce peak power and energy usage. We find that the opportunities for powerand energy savings are significant, but greater at the cluster-level (thousandsof servers) than at the rack-level (tens). Finally we argue that systems needto be power efficient across the activity range, and not only at peakperformance levels.
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paper_title: Managing energy and server resources in hosting centers

paper_content:

Internet hosting centers serve multiple service sites from a common hardware base. This paper presents the design and implementation of an architecture for resource management in a hosting center operating system, with an emphasis on energy as a driving resource management issue for large server clusters. The goals are to provision server resources for co-hosted services in a way that automatically adapts to offered load, improve the energy efficiency of server clusters by dynamically resizing the active server set, and respond to power supply disruptions or thermal events by degrading service in accordance with negotiated Service Level Agreements (SLAs).Our system is based on an economic approach to managing shared server resources, in which services "bid" for resources as a function of delivered performance. The system continuously monitors load and plans resource allotments by estimating the value of their effects on service performance. A greedy resource allocation algorithm adjusts resource prices to balance supply and demand, allocating resources to their most efficient use. A reconfigurable server switching infrastructure directs request traffic to the servers assigned to each service. Experimental results from a prototype confirm that the system adapts to offered load and resource availability, and can reduce server energy usage by 29% or more for a typical Web workload.
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paper_title: NOX: towards an operating system for networks

paper_content:

As anyone who has operated a large network can attest, enterprise networks are difficult to manage. That they have remained so despite significant commercial and academic efforts suggests the need for a different network management paradigm. Here we turn to operating systems as an instructive example in taming management complexity. In the early days of computing, programs were written in machine languages that had no common abstractions for the underlying physical resources. This made programs hard to write, port, reason about, and debug. Modern operating systems facilitate program development by providing controlled access to high-level abstractions for resources (e.g., memory, storage, communication) and information (e.g., files, directories). These abstractions enable programs to carry out complicated tasks safely and efficiently on a wide variety of computing hardware. In contrast, networks are managed through low-level configuration of individual components. Moreover, these configurations often depend on the underlying network; for example, blocking a user’s access with an ACL entry requires knowing the user’s current IP address. More complicated tasks require more extensive network knowledge; forcing guest users’ port 80 traffic to traverse an HTTP proxy requires knowing the current network topology and the location of each guest. In this way, an enterprise network resembles a computer without an operating system, with network-dependent component configuration playing the role of hardware-dependent machine-language programming. What we clearly need is an “operating system” for networks, one that provides a uniform and centralized programmatic interface to the entire network. Analogous to the read and write access to various resources provided by computer operating systems, a network operating system provides the ability to observe and control a network. A network operating system does not manage the network itself; it merely provides a programmatic interface. Applications implemented on top of the network operating system perform the actual management tasks. The programmatic interface should be general enough to support a broad spectrum of network management applications. Such a network operating system represents two major conceptual departures from the status quo. First, the network operating system presents programs with a centralized programming model; programs are written as if the entire network were present on a single machine (i.e., one would use Dijkstra to compute shortest paths, not Bellman-Ford). This requires (as in [3, 8, 14] and elsewhere) centralizing network state. Second, programs are written in terms of high-level abstractions (e.g., user and host names), not low-level configuration parameters (e.g., IP and MAC addresses). This allows management directives to be enforced independent of the underlying network topology, but it requires that the network operating system carefully maintain the bindings (i.e., mappings) between these abstractions and the low-level configurations. Thus, a network operating system allows management applications to be written as centralized programs over highlevel names as opposed to the distributed algorithms over low-level addresses we are forced to use today. While clearly a desirable goal, achieving this transformation from distributed algorithms to centralized programming presents significant technical challenges, and the question we pose here is: Can one build a network operating system at significant scale?
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paper_title: A survey of energy efficient network protocols for wireless networks

paper_content:

Wireless networking has witnessed an explosion of interest from consumers in recent years for its applications in mobile and personal communications. As wireless networks become an integral component of the modern communication infrastructure, energy efficiency will be an important design consideration due to the limited battery life of mobile terminals. Power conservation techniques are commonly used in the hardware design of such systems. Since the network interface is a significant consumer of power, considerable research has been devoted to low-power design of the entire network protocol stack of wireless networks in an effort to enhance energy efficiency. This paper presents a comprehensive summary of recent work addressing energy efficient and low-power design within all layers of the wireless network protocol stack.
---
paper_title: Reducing Power Consumption in Backbone Networks

paper_content:

According to several studies, the power consumption of the Internet accounts for up to 10% of the worldwide energy consumption, and several initiatives are being put into place to reduce the power consumption of the ICT sector in general. To this goal, we propose a novel approach to switch off network nodes and links while still guaranteeing full connectivity and maximum link utilization. After showing that the problem falls in the class of capacitated multi-commodity flow problems, and therefore it is NP-complete, we propose some heuristic algorithms to solve it. Simulation results in a realistic scenario show that it is possible to reduce the number of links and nodes currently used by up to 30% and 50% respectively during off-peak hours, while offering the same service quality.
---
paper_title: The Case for Energy-Proportional Computing

paper_content:

Energy-proportional designs would enable large energy savings in servers, potentially doubling their efficiency in real-life use. Achieving energy proportionality will require significant improvements in the energy usage profile of every system component, particularly the memory and disk subsystems.
---
paper_title: Scheduling for reduced CPU energy

paper_content:

The energy usage of computer systems is becoming more important, especially for battery operated systems. Displays, disks, and cpus, in that order, use the most energy. Reducing the energy used by displays and disks has been studied elsewhere; this paper considers a new method for reducing the energy used by the cpu. We introduce a new metric for cpu energy performance, millions-of-instructions-per-joule (MIPJ). We examine a class of methods to reduce MIPJ that are characterized by dynamic control of system clock speed by the operating system scheduler. Reducing clock speed alone does not reduce MIPJ, since to do the same work the system must run longer. However, a number of methods are available for reducing energy with reduced clock-speed, such as reducing the voltage [Chandrakasan et al 1992][Horowitz 1993] or using reversible [Younis and Knight 1993] or adiabatic logic [Athas et al 1994]. What are the right scheduling algorithms for taking advantage of reduced clock-speed, especially in the presence of applications demanding ever more instructions-per-second? We consider several methods for varying the clock speed dynamically under control of the operating system, and examine the performance of these methods against workstation traces. The primary result is that by adjusting the clock speed at a fine grain, substantial CPU energy can be saved with a limited impact on performance.
---
paper_title: Managing energy consumption costs in desktop PCs and LAN switches with proxying, split TCP connections, and scaling of link speed

paper_content:

The IT equipment comprising the Internet in the USA uses about $6 billion of electricity every year. Much of this electricity use is wasted on idle, but fully powered-up, desktop PCs and network links. We show how to recover a large portion of the wasted electricity with improved power management methods that are focused on network issues.
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paper_title: Skilled in the Art of Being Idle: Reducing Energy Waste in Networked Systems

paper_content:

Networked end-systems such as desktops and set-top boxes are often left powered-on, but idle, leading to wasted energy consumption. An alternative would be for these idle systems to enter low-power sleep modes. Unfortunately, today, a sleeping system sees degraded functionality: first, a sleeping device loses its network "presence" which is problematic to users and applications that expect to maintain access to a remote machine and, second, sleeping can prevent running tasks scheduled during times of low utilization (e.g., network backups). Various solutions to these problems have been proposed over the years including wake-on-lan (WoL) mechanisms that wake hosts when specific packets arrive, and the use of a proxy that handles idle-time traffic on behalf of a sleeping host. As of yet, however, an in-depth evaluation of the potential for energy savings, and the effectiveness of proposed solutions has not been carried out. To remedy this, in this paper, we collect data directly from 250 enterprise users on their end-host machines capturing network traffic patterns and user presence indicators. With this data, we answer several questions: what is the potential value of proxying or using magic packets? which protocols and applications require proxying? how comprehensive does proxying need to be for energy benefits to be compelling? and so on. ::: ::: We find that, although there is indeed much potential for energy savings, trivial approaches are not effective. We also find that achieving substantial savings requires a careful consideration of the tradeoffs between the proxy complexity and the idle-time functionality available to users, and that these tradeoffs vary with user environment. Based on our findings, we propose and evaluate a proxy architecture that exposes a minimal set of APIs to support different forms of idle-time behavior.
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paper_title: Greening of the internet

paper_content:

In this paper we examine the somewhat controversial subject of energy consumption of networking devices in the Internet, motivated by data collected by the U.S. Department of Commerce. We discuss the impact on network protocols of saving energy by putting network interfaces and other router & switch components to sleep. Using sample packet traces, we first show that it is indeed reasonable to do this and then we discuss the changes that may need to be made to current Internet protocols to support a more aggressive strategy for sleeping. Since this is a position paper, we do not present results but rather suggest interesting directions for core networking research. The impact of saving energy is huge, particularly in the developing world where energy is a precious resource whose scarcity hinders widespread Internet deployment.
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paper_title: Theoretical and practical limits of dynamic voltage scaling

paper_content:

Dynamic voltage scaling (DVS) is a popular approach for energy reduction of integrated circuits. Current processors that use DVS typically have an operating voltage range from full to half of the maximum Vdd. However, it is possible to construct designs that operate over a much larger voltage range: from full Vdd to subthreshold voltages. This possibility raises the question of whether a larger voltage range improves the energy efficiency of DVS. First, from a theoretical point of view, we show that for subthreshold supply voltages leakage energy becomes dominant, making "just in time completion" energy inefficient. We derive an analytical model for the minimum energy optimal voltage and study its trends with technology scaling. Second, we use the proposed model to study the workload activity of an actual processor and analyze the energy efficiency as a function of the lower limit of voltage scaling. Based on this study, we show that extending the voltage range below 1/2 Vdd will improve the energy efficiency for most processor designs, while extending this range to subthreshold operation is beneficial only for very specific applications. Finally, we show that operation deep in the subthreshold voltage range is never energy-efficient.
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paper_title: Run-time Energy Consumption Estimation Based on Workload in Server Systems

paper_content:

This paper proposes to develop a system-wide energy consumption model for servers by making use of hardware performance counters and experimental measurements. We develop a real-time energy prediction model that relates server energy consumption to its overall thermal envelope. While previous studies have attempted system-wide modeling of server power consumption through subsystem models, our approach is different in that it uses a small set of tightly correlated parameters to create a model relating system energy input to subsystem energy consumption. We develop a linear regression model that relates processor power, bus activity, and system ambient temperatures into real-time predictions of the power consumption of long jobs and as result controlling their thermal impact. Using the HyperTransport bus model as a case study and through electrical measurements on example server subsystems, we develop a statistical model for estimating run-time power consumption. Our model is accurate within an error of four percent(4%) as verified using a set of common processor benchmarks.
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paper_title: A Comparison of High-Level Full-System Power Models

paper_content:

Dynamic power management in enterprise environments requires an understanding of the relationship between resource utilization and system-level power consumption. Power models based on resource utilization have been proposed in the context of enabling specific energy-efficiency optimizations on specific machines, but the accuracy and portability of different approaches to modeling have not been systematically compared. In this work, we use a common infrastructure to fit a family of high-level full-system power models, and we compare these models over a wide variation of workloads and machines, from a laptop to a server. This analysis shows that a model based on OS utilization metrics and CPU performance counters is generally most accurate across the machines and workloads tested. It is particularly useful for machines whose dynamic power consumption is not dominated by the CPU, as well as machines with aggressively power-managed CPUs, two classes of systems that are increasingly prevalent.
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paper_title: Fine-grained energy profiling for power-aware application design

paper_content:

Significant opportunities for power optimization exist at application design stage and are not yet fully exploited by system and application designers. We describe the challenges developers face in optimizing software for energy efficiency by exploiting application-level knowledge. To address these challenges, we propose the development of automated tools that profile the energy usage of various resource components used by an application and guide the design choices accordingly. We use a preliminary version of a tool we have developed to demonstrate how automated energy profiling helps a developer choose between alternative designs in the energy-performance trade-off space.
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paper_title: An Analysis of Hard Drive Energy Consumption

paper_content:

The increasing storage capacity and necessary redundancy of data centers and other large-scale IT facilities has drawn attention to the issue of reducing the power consumption of hard drives. This work comprehensively investigates the power consumption of hard drives to determine typical runtime power profiles. We have instrumented at a fine-grained level and present our findings which show that (i) the energy consumed by the electronics of a drive is just as important as the mechanical energy consumption; (ii) the energy required to access data is affected by physical location on a drive; and (iii) the size of data transfers has measurable effect on power consumption.
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paper_title: Power Awareness in Network Design and Routing

paper_content:

Exponential bandwidth scaling has been a fundamental driver of the growth and popularity of the Internet. However, increases in bandwidth have been accompanied by increases in power consumption, and despite sustained system design efforts to address power demand, significant technological challenges remain that threaten to slow future bandwidth growth. In this paper we describe the power and associated heat management challenges in today's routers. We advocate a broad approach to addressing this problem that includes making power-awareness a primary objective in the design and configuration of networks, and in the design and implementation of network protocols. We support our arguments by providing a case study of power demands of two standard router platforms that enables us to create a generic model for router power consumption. We apply this model in a set of target network configurations and use mixed integer optimization techniques to investigate power consumption, performance and robustness in static network design and in dynamic routing. Our results indicate the potential for significant power savings in operational networks by including power-awareness.
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paper_title: Energy Consumption of Residential and Professional Switches

paper_content:

Precise evaluation of network appliance energy consumption is necessary to accurately model or simulate the power consumption of distributed systems. In this paper we evaluate the influence of traffic onto the consumption of electrical power of four switches found in home and professional environments. First we describe our measurement and data analysis approach, and how our results can be used for estimating the power consumption when knowing the average traffic bandwidth.Then we present the measurement results of two residential switches, and two professional switches. For each type we present regression models and parameters describing their quality. Similar to other works we find that for one of the switches the power consumption actually drops for high traffic loads, while for the others the situation is reverse. Measures justify that during most energy consumption evaluation, network appliance energy cost can be approximated as constant. This work gives information on the possible changes of this cost.
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paper_title: Energy Consumption of the Internet

paper_content:

As concerns about global energy consumption increase, the power consumption of the Internet is a matter of increasing importance. We present a network-based model that estimates Internet power consumption including the core, metro, and access networks.
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paper_title: A feasibility study for power management in LAN switches

paper_content:

We examine the feasibility of introducing power management schemes in network devices in the LAN. Specifically, we investigate the possibility of putting various components on LAN switches to sleep during periods of low traffic activity. Traffic collected in our LAN indicates that there are significant periods of inactivity on specific switch interfaces. Using an abstract sleep model devised for LAN switches, we examine the potential energy savings possible for different times of day and different interfaces (e.g., interfaces connecting to hosts to switches, or interfaces connecting switches, or interfaces connecting switches and routers). Algorithms developed for sleeping, based on periodic protocol behavior as well as traffic estimation are shown to be capable of conserving significant amounts of energy. Our results show that sleeping is indeed feasible in the LAN and in some cases, with very little impact on other protocols. However, we note that in order to maximize energy savings while minimizing sleep-related losses, we need hardware that supports sleeping.
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paper_title: The Case for Energy-Proportional Computing

paper_content:

Energy-proportional designs would enable large energy savings in servers, potentially doubling their efficiency in real-life use. Achieving energy proportionality will require significant improvements in the energy usage profile of every system component, particularly the memory and disk subsystems.
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paper_title: NGL02-2: Ethernet Adaptive Link Rate (ALR): Analysis of a Buffer Threshold Policy

paper_content:

Rapidly increasing energy use by computing and communications equipment is a significant problem that needs to be addressed. Ethernet network interface controllers (NICs) consume hundreds of millions of US$ in electricity per year. Most Ethernet links are underutilized and link power consumption can be reduced by operating at lower data rates. An output buffer threshold policy to change link data rate in response to utilization is investigated. Analytical and simulation models are developed to evaluate the performance of Adaptive Link Rate (ALR) with respect to mean packet delay and time spent in low data rate with Poisson traffic and 100 Mb/s network traces as inputs. A Markov model of a state-dependent service rate queue with rate transitions only at service completion is developed. For the traffic traces, it is found that a link can operate at 10 Mb/s for over 99% of the time yielding energy savings with no user-perceivable increase in packet delay.
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paper_title: Managing energy consumption costs in desktop PCs and LAN switches with proxying, split TCP connections, and scaling of link speed

paper_content:

The IT equipment comprising the Internet in the USA uses about $6 billion of electricity every year. Much of this electricity use is wasted on idle, but fully powered-up, desktop PCs and network links. We show how to recover a large portion of the wasted electricity with improved power management methods that are focused on network issues.
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paper_title: Using Low-Power Modes for Energy Conservation in Ethernet LANs

paper_content:

Most Ethernet interfaces available for deployment in switches and hosts today can operate in a variety of different low power modes. However, currently these modes have very limited usage models. They do not take advantage of periods of inactivity, when the links remain idle or under-utilized. In this study, we propose methods that allow for detection of such periods to obtain energy savings with little impact on loss or delay. We evaluate our methods on a wide range of real-time traffic traces collected at a high-speed backbone switch within our campus LAN. Our results show that Ethernet interfaces at both ends can be put in extremely low power modes anywhere from 40%-98% of the time observed. In addition, we found that approximately 37% of interfaces studied (on the same switch) can be put in low power modes simultaneously which opens the potential for further energy savings in the switching fabric within the switch.
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paper_title: A Power Benchmarking Framework for Network Devices

paper_content:

Energy efficiency is becoming increasingly important in the operation of networking infrastructure, especially in enterprise and data center networks. Researchers have proposed several strategies for energy management of networking devices. However, we need a comprehensive characterization of power consumption by a variety of switches and routers to accurately quantify the savings from the various power savings schemes. In this paper, we first describe the hurdles in network power instrumentation and present a power measurement study of a variety of networking gear such as hubs, edge switches, core switches, routers and wireless access points in both stand-alone mode and a production data center. We build and describe a benchmarking suite that will allow users to measure and compare the power consumed for a large set of common configurations at any switch or router of their choice. We also propose a network energy proportionality index, which is an easily measurable metric, to compare power consumption behaviors of multiple devices.
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paper_title: Reducing Network Energy Consumption via Sleeping and Rate-Adaptation

paper_content:

We present the design and evaluation of two forms of power management schemes that reduce the energy consumption of networks. The first is based on putting network components to sleep during idle times, reducing energy consumed in the absence of packets. The second is based on adapting the rate of network operation to the offered workload, reducing the energy consumed when actively processing packets. ::: ::: For real-world traffic workloads and topologies and using power constants drawn from existing network equipment, we show that even simple schemes for sleeping or rate-adaptation can offer substantial savings. For instance, our practical algorithms stand to halve energy consumption for lightly utilized networks (10-20%). We show that these savings approach the maximum achievable by any algorithms using the same power management primitives. Moreover this energy can be saved without noticeably increasing loss and with a small and controlled increase in latency (<10ms). Finally, we show that both sleeping and rate adaptation are valuable depending (primarily) on the power profile of network equipment and the utilization of the network itself.
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paper_title: Greening the Switch

paper_content:

Active research is being conducted in reducing power consumption of all the components of the Internet. To that end, we propose schemes for power reduction in network switches -- Time Window Prediction, Power Save Mode and Lightweight Alternative. These schemes are adaptive to changing traffic patterns and automatically tune their parameters to guarantee a bounded and specified increase in latency. We propose a novel architecture for buffering ingress packets using shadow ports. ::: ::: We test our schemes on packet traces obtained from an enterprise network, and evaluate them using realistic power models for the switches. Our simple power reduction schemes produce power savings of upto 32% with minimal increase in latency or packet-loss. With appropriate hardware support in the form of Wake-on-Packet, shadow ports and fast transitioning of the ports between its high and low power states, these savings reach 90% of the optimal algorithm's savings.
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paper_title: Power-Proxying on the NIC: A Case Study with the Gnutella File-Sharing Protocol

paper_content:

Edge devices such as desktop and laptop computers constitute a majority of the devices connected to the Internet today. Peer-to-Peer (P2P) file-sharing applications generally require edge devices to maintain network presence whenever possible to enhance the robustness of the file-sharing network, which in turn can lead to considerable wastage of energy. We show that energy can be saved by permitting edge devices to enter into standby state and still maintain network connectivity by proxying protocols in the Network Interface Card (NIC).
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paper_title: Greening of the internet

paper_content:

In this paper we examine the somewhat controversial subject of energy consumption of networking devices in the Internet, motivated by data collected by the U.S. Department of Commerce. We discuss the impact on network protocols of saving energy by putting network interfaces and other router & switch components to sleep. Using sample packet traces, we first show that it is indeed reasonable to do this and then we discuss the changes that may need to be made to current Internet protocols to support a more aggressive strategy for sleeping. Since this is a position paper, we do not present results but rather suggest interesting directions for core networking research. The impact of saving energy is huge, particularly in the developing world where energy is a precious resource whose scarcity hinders widespread Internet deployment.
---
paper_title: JouleSort: a balanced energy-efficiency benchmark

paper_content:

The energy efficiency of computer systems is an important concern in a variety of contexts. In data centers, reducing energy use improves operating cost, scalability, reliability, and other factors. For mobile devices, energy consumption directly affects functionality and usability. We propose and motivate JouleSort, an external sort benchmark, for evaluating the energy efficiency of a wide range of computer systems from clusters to handhelds. We list the criteria, challenges, and pitfalls from our experience in creating a fair energy-efficiency benchmark. Using a commercial sort, we demonstrate a JouleSort system that is over 3.5x as energy-efficient as last year's estimated winner. This system is quite different from those currently used in data centers. It consists of a commodity mobile CPU and 13 laptop drives connected by server-style I/O interfaces.
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paper_title: Energy-Aware Backbone Networks: A Case Study

paper_content:

Power consumption of ICT is becoming more and more a sensible problem, which is of interest for both the research community, for ISPs and for the general public. In this paper we consider a real IP backbone network and a real traffic profile. We evaluate the energy cost of running it, and, speculating on the possibility of selectively turning off spare devices whose capacity is not required to transport off-peak traffic, we show that it is possible to easily achieve more than 23% of energy saving per year, i.e., to save about 3GWh/year considering today's power footprint of real network devices.
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paper_title: On reliability, performance and Internet power consumption

paper_content:

With the increasing concern for global warming, the impact of Internet power consumption is gaining interest. In this paper, we explore, for the first time, the relationship between network robustness, performance and Internet power consumption. We first discuss such a relationship based on data collected from Internet sources. Next, we propose a modeling framework to size that relationship. It is shown that when designing networks based on power consumption, careful attention should be paid to the trade-off between energy consumption and network performance since doing otherwise would lead to unreliable networks.
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paper_title: Energy-aware routing: A reality check

paper_content:

In this work, we analyze the design of green routing algorithms and evaluate the achievable energy savings that such mechanisms could allow in several realistic network scenarios. We formulate the problem as a minimum energy routing optimization, which we numerically solve considering a core-network scenario, which can be seen as a worst-case for energy saving performance (as nodes cannot be switched off). To gather full-relief results, we analyze the energy savings in various conditions (i.e., network topology and traffic matrix) and under different technology assumptions (i.e., the energy profile of the network devices). These results give us insight into the potential benefits of different “green” technologies and their interactions. In particular, we show that depending on the topology and traffic matrices, the optimal energy savings can be modest, partly limiting the interest for green routing approaches for some scenarios. At the same time, we also show that the common belief that there is a trade off between green network optimization and performance does not necessarily hold: in the considered environment, green routing has no effect on the main network performances such as maximum link utilization.
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Title: A Survey of Green Networking Research

Section 1: Why Save Energy
Description 1: Discuss the environmental, economic, and political motivations for reducing energy consumption in networking.

Section 2: Where to Save Energy
Description 2: Identify key areas within networks, such as core and access networks, where significant energy savings can be realized.

Section 3: Definition of Green Networking
Description 3: Define what green networking entails, including using renewable energy and designing energy-efficient components.

Section 4: Green Strategies
Description 4: Overview different paradigms and strategies for reducing energy consumption in networking, such as resource consolidation and proportional computing.

Section 5: Taxonomy of Green Networking Research
Description 5: Introduce a taxonomy to categorize green networking solutions based on criteria such as timescale, architectural layer, and scope.

Section 6: Adaptive Link Rate
Description 6: Explore strategies for adapting link rates to reduce energy consumption, including sleeping mode and rate switching.

Section 7: Interface Proxying
Description 7: Discuss methods for offloading network traffic processing to low-power proxies to extend idle periods of energy-hungry devices.

Section 8: Energy-Aware Infrastructure
Description 8: Examine solutions for designing and managing energy-aware network infrastructures, including clean-slate and incremental approaches.

Section 9: Energy-Aware Applications
Description 9: Detail how software and applications can be redesigned to be more energy-efficient, including protocol modifications and user-level applications.

Section 10: At the Network Edge
Description 10: Briefly overview research trends in related areas such as computer and data-center architectures and wireless networking.

Section 11: Measurement and Models
Description 11: Discuss the importance of power modeling and measurement for evaluating green networking solutions and propose common benchmarks and metrics.

Section 12: Conclusion
Description 12: Summarize the survey findings, highlight the maturity of different research areas, and outline future research directions.