IEEE Internet Computing
Guest Editors' Introduction S teadily rising energy costs and the need to reduce global greenhouse gas emissions to protect our environment have turned energy into one of the primary technological challenges of our time. Without direct action, a temperature increase of more than 5°C is predicted by the end of this century. 1 In this context, information and communications technology (ICT) is expected to play a major role in reducing worldwide energy requirements by optimizing energy generation,
... transportation, and consumption. Recent research, however, also reveals staggering facts about how ICT is becoming a major component of the energy consumption budget. Detailed surveys show that ICT is responsible for roughly 4 percent of world energy consumption, 2 and this percentage is expected to double in the next decade, if things don't drastically change. Other parallel studies worldwide reached similar results. One determined that "the CO2 emission of the ICT industry alone exceeds the carbon output of the entire aviation industry" (see http://greenict. or g .u k /s ite s/de f au lt /f i le s/A n%20 Inefficient%20Truth%20-%20Full%20 Repor t.pdf ). A revea ling case st udy in t he telecommunications sector comes from Italy, where the incumbent telecommunications operator consumes more than 2 terawatts a year, or roughly 1 percent of the total national electricity demand, second only to the Italian railway system. 3 Similar considerations, and even more pessimistic ones (as in Japan 4 ), also hold for other developed countries. Challenges in ICT Energy Reduction So, which ICT sectors most impact global energy consumption? Should improvement efforts be focused on a specific field? Some studies show that no sector dominates ICT consumption, 2,5 so we need energy-efficient solutions in all of them, from data centers to network devices and infrastructures to user devices. Consider data centers: estimates are that in the US, data center electricity consumption reached 1.5 percent of national consumption; the growing demand for the services data centers offer translates into a yearly 12 percent increase in their energy needs. 6 These needs are continuously and exponentially increasing with the advent and generalization of cloud applications (for example, email or photo storage and editing) and virtualization approaches (such as the virtualization of network elements). Current estimates about the carbon footprint of network elements indicate that on average, each server produces eight tons of CO 2 per year, each PC or laptop produces four tons per year, each router 20 tons, and each Ethernet switch five tons. Studies on the full ICT device life cycle, including manufacturing, the use phase, and disposal, show that the use phase has the largest overall energy costs, accounting for up to 85 percent. 7 In today's telecommunications networks, most power consumption comes from wireless and fixed access networks, whose equipment, while consuming less than that of core networks, exists in much larger numbers. For example, in cellular access networks, one Node B consumes only about 1,500 W per hour, but altogether these devices contribute 80 percent of all mobile network energy consumption. 8,9 In fixed access networks, the current trend is to replace copper-based technologies (used in the majority of current ADSL and VDSL accesses) with optical fibers, due to the latter's significantly higher bandwidth, lower power consumption, and reduced sensitivity to increased bit rates. This could suggest that, in the long run, the percentage of energy used in the network bone might become predominant because of router power consumption. Indeed, routers have shown a large augmentation of power consumption as bit rates increase. If the present trend of increasing data rates continues, the energy share of core and aggregation networks will largely increase compared to that of access networks. As a result of these trends, some projections indicate that next-generation Internet applications will require electricity in amounts that can't be generated or transported to major metropolitan areas. We must thus find our way to a sustainable future Internet. The current situation has generated a keen interest in energy-saving approaches by all the actors in ICT, who view reducing their networks' energy consumption as an opportunity for cost reduction and an important aspect for promoting their image in the media. Different solutions are under investigation for data centers, including algorithms to distribute the load so as to free up servers and put them in sleep mode, sensors that can identify which servers to shut down given environmental conditions, and specific physical layouts that reduce the need for cooling. Some ingenious approaches include moving data centers and service farms to colder areas (for example, mountain resorts) -where cooling is less of a problem than it is in large cities, which are normally located in warmer climates -or placing generators where energy is needed, so that no loss is incurred between producer and consumer. On the network side, operators and providers are pushing their suppliers to produce more energy-parsimonious equipment. One of the most promising techniques for reducing energy consumption in wireless and fixed networks is dynamic stand-by of network equipment. This approach exploits the fact that during low-load periods, a fraction of the deployed equipment (such as cellular base stations) becomes unnecessary and can enter some low-consumption mode. 10 In addition, energy awareness is having a greater impact on how equipment works, and new protocols and algorithms are under study that would reduce energy consumption while jointly satisf ying users' qualit y-of-ser vice expectations. Naturally, all these techniques can improve the current situation that has resulted from limited attention to the energy issue in network design, planning, and management phases in the past. However, new, comprehensive, energyaware approaches to networking are necessary for a systematic evolution toward sustainable networks. We must consider the network as a whole, including core networks, wired and wireless access networks, and customer premises network equipment, data centers, and server farms. Advanced approaches must also consider the entire network's energy consumption in the design, planning, and management phases to achieve a comprehensive and sustainable approach to energy-efficient networking. In this special issue, we aim to provide a snapshot of ongoing efforts toward a global solution to these urgent challenges that will lead, in the end, to a new energy-efficient and sustainable Internet.