Scalable and Reliable Middlebox Deployment

Middleboxes are pervasive in modern computer networks providing functionalities beyond mere packet forwarding. Load balancers, intrusion detection systems, and network address translators are typical examples of middleboxes. Despite their benefits, middleboxes come with several challenges with respect to their scalability and reliability. The goal of this thesis is to devise middlebox deployment solutions that are cost effective, scalable, and fault tolerant. The thesis includes three main contributions: First, distributed service function chaining with multiple instances of a middlebox deployed on different physical servers to optimize resource usage; Second, Constellation, a geo-distributed middlebox framework enabling a middlebox application to operate with high performance across wide area networks; Third, a fault tolerant service function chaining system

Data Center Energy Retrofits

Within the field of computer science, data centers (DCs) are a major consumer of energy. A large part of that energy is used for cooling down the exhaust heat of the servers contained in the DCs. This thesis describes both the aggregate numbers of DCs and key flagship installations in detail. We then introduce the concept of Data Center Energy Retrofits, a set of low cost, easy to install techniques that may be used by the majority of DCs for reducing their energy consumption. The main contributions are a feasibility study of direct free air cooling, two techniques that explore air stream containment, a wired sensor network for temperature measurements, and a prototype greenhouse that harvests and reuses the exhaust heat of the servers for growing edible plants, including chili peppers. We also project the energy savings attainable by implementing the proposed techniques, and show that global savings are possible even when very conservative installation numbers and payback times are modelled. Using the results obtained, we make a lower bound estimate that direct free air cooling could reduce global greenhouse gas (GHG) emissions by 9.4 MtCO2e already by the year 2005 footprint of the DCs. Air stream containment could reduce the GHG emissions by a further 0.7 MtCO2e, and finally heat harvesting can turn the waste heat into additional profits. Much larger savings are already possible, since the DC footprint has increased considerably since 2005.Nykyaikaisten pilvipalvelujen yleistymisen ovat mahdollistaneet jopa tuhansia tietokoneita sisältävät palvelinsalit. Eräs palvelimiin liittyvä ongelma on niiden yhteenlaskettu sähkönkulutus. Palvelimien käyttämä sähkö muuttuu laskennan sivutuotteena lämmöksi, joka taas voi vaarantaa palvelujen jatkuvuuden mikäli riittävää jäähdytystä ei järjestetä. Jäähdytys on perinteisesti toteutettu koneellisena ilmanvaihtona, joka kuluttaa lisää sähköä. Myös muut palvelimien ylläpitoon liittyvät järjestelmät lisäävät sähkönkulutusta. Varsinaisen laskennan lisäksi kulutettu ylimääräinen sähkö vaikuttaa palvelinsalien energiatehokkuuteen. Pilvipalvelut ovat osoittautuneet taloudellisesti niin merkittäviksi, että ylimääräistä sähköä on pidetty siedettävänä haittana palveluiden arvoon verrattuna. Energiatehokkuuden parantamiseen on kuitenkin viime aikoina kiinnitetty huomiota sekä ympäristön kannalta että myös sähkön hinnasta aiheutuvien säästöjen vuoksi. Palvelujen jatkuvuuden kannalta on toisaalta tärkeää, ettei energiatehokkuuden parantaminen aiheuta toiminnalle käyttökatkoja tai käyttäjille ylimääräisiä viipeitä. Tämä väitöskirja esittelee nykyaikaisten palvelinsalien ominaisuuksia sekä yksittäistapausten että globaalien lukumäärien kautta. Esitellyt yksittäistapaukset ovat suurimpien palvelinsalien omistajien lippulaivoja, joilla pyritään vakuuttamaan käyttäjät yritysten sitoutumisesta ekotehokkuuteen. Globaalit lukumäärät luovat katsauksen palvelinsalien eri suuruusluokkien jakaumalle. Käy ilmi, että valtaosa palvelinsaleista on hyvin pieniä ja huomattavasti kehnompia energiatehokkuudeltaan kuin jättikokoiset lippulaivat. Nämä seikat huomioiden väitöskirja esittelee joukon jälkiasennettavia tekniikoita jotka keskittyvät palvelinsalien jäähdytykseen. Tekniikat esitellään väitöskirjan viidessä osajulkaisussa alkaen korvausilman edullisesta tuottamisesta nk. vapaajäähdytyksen avulla ja päättyen kuuman poistoilman hyötykäyttöön kokeellisessa kasvihuoneessa. Väitöskirja sisältää laskelmat tekniikoiden avulla saavutettavien säästöjen alarajoille. Esimerkiksi pelkästään vapaajäähdytystä käyttämällä säästettäisiin 9,4 Mt hiilidioksidia vastaava määrä päästöjä perustuen jo vuoden 2005 sähkönkulutuslaskelmiin. Sähkönkulutus on ollut jatkuvassa kasvussa vuoteen 2013 asti, joten myös saavutettavat säästöt ovat nykyään huomattavasti suuremmat

Model-Based Design, Analysis, and Implementations for Power and Energy-Efficient Computing Systems

Modern computing systems are becoming increasingly complex. On one end of the spectrum, personal computers now commonly support multiple processing cores, and, on the other end, Internet services routinely employ thousands of servers in distributed locations to provide the desired service to its users. In such complex systems, concerns about energy usage and power consumption are increasingly important. Moreover, growing awareness of environmental issues has added to the overall complexity by introducing new variables to the problem. In this regard, the ability to abstractly focus on the relevant details allows model-based design to help significantly in the analysis and solution of such problems. In this dissertation, we explore and analyze model-based design for energy and power considerations in computing systems. Although the presented techniques are more generally applicable, we focus their application on large-scale Internet services operating in U.S. electricity markets. Internet services are becoming increasingly popular in the ICT ecosystem of today. The physical infrastructure to support such services is commonly based on a group of cooperative data centers (DCs) operating in tandem. These DCs are geographically distributed to provide security and timing guarantees for their customers. To provide services to millions of customers, DCs employ hundreds of thousands of servers. These servers consume a large amount of energy that is traditionally produced by burning coal and employing other environmentally hazardous methods, such as nuclear and gas power generation plants. This large energy consumption results in significant and fast-growing financial and environmental costs. Consequently, for protection of local and global environments, governing bodies around the globe have begun to introduce legislation to encourage energy consumers, especially corporate entities, to increase the share of renewable energy (green energy) in their total energy consumption. However, in U.S. electricity markets, green energy is usually more expensive than energy generated from traditional sources like coal or petroleum. We model the overall problem in three sub-areas and explore different approaches aimed at reducing the environmental foot print and operating costs of multi-site Internet services, while honoring the Quality of Service (QoS) constraints as contracted in service level agreements (SLAs). Firstly, we model the load distribution among member DCs of a multi-site Internet service. The use of green energy is optimized considering different factors such as (a) geographically and temporally variable electricity prices, (b) the multitude of available energy sources to choose from at each DC, (c) the necessity to support more than one SLA, and, (d) the requirements to offer more than one service at each DC. Various approaches are presented for solving this problem and extensive simulations using Google’s setup in North America are used to evaluate the presented approaches. Secondly, we explore the area of shaving the peaks in the energy demand of large electricity consumers, such as DCs by using a battery-based energy storage system. Electrical demand of DCs is typically peaky based on the usage cycle of their customers. Resultant peaks in the electrical demand require development and maintenance of a costlier energy delivery mechanism, and are often met using expensive gas or diesel generators which often have a higher environmental impact. To shave the peak power demand, a battery can be used which is charged during low load and is discharged during the peak loads. Since the batteries are costly, we present a scheme to estimate the size of battery required for any variable electrical load. The electrical load is modeled using the concept of arrival curves from Network Calculus. Our analysis mechanism can help determine the appropriate battery size for a given load arrival curve to reduce the peak. Thirdly, we present techniques to employ intra-DC scheduling to regulate the peak power usage of each DC. The model we develop is equally applicable to an individual server with multi-/many-core chips as well as a complete DC with an intermix of homogeneous and heterogeneous servers. We evaluate these approaches on single-core and multi-core chip processors and present the results. Overall, our work demonstrates the value of model-based design for intelligent load distribution across DCs, storage integration, and per DC optimizations for efficient energy management to reduce operating costs and environmental footprint for multi-site Internet services

Radio Communications

In the last decades the restless evolution of information and communication technologies (ICT) brought to a deep transformation of our habits. The growth of the Internet and the advances in hardware and software implementations modified our way to communicate and to share information. In this book, an overview of the major issues faced today by researchers in the field of radio communications is given through 35 high quality chapters written by specialists working in universities and research centers all over the world. Various aspects will be deeply discussed: channel modeling, beamforming, multiple antennas, cooperative networks, opportunistic scheduling, advanced admission control, handover management, systems performance assessment, routing issues in mobility conditions, localization, web security. Advanced techniques for the radio resource management will be discussed both in single and multiple radio technologies; either in infrastructure, mesh or ad hoc networks