A social network is a structure of individuals and organizations, which are connected by one or more types of interdependency, such as friendship, affinity, common interests or knowledge. Social networks use Web 2.0 technology, which is mostly based on a service-oriented architecture. We are studying patterns for social networks in this environment. A pattern is an encapsulated solution to a software problem in a given context, secure threats are possible in this context. We present a collection of patterns associated with the most important aspects of social networks, with emphasis on controlling the actions of the users of these networks. / by Carolina Marina. / Thesis (M.S.C.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2012. Mode of access: World Wide Web.

Nowadays, broadband applications, such as interactive video and multimedia services, have further increased the demand of bandwidth, and thus make high speed multi-wavelength optical access network highly desirable. Wavelength division multiplexing passive optical network (WDM-PON) is a promising candidate to realize the next generation optical access networks due to its dedicated bandwidth for each subscriber and more flexible bandwidth management. As the network traffic is becoming more data-centric, more networking capabilities are required to provide the data service in a more flexible and reliable way. In this thesis, we have proposed and investigated several interesting optical multicast overlay schemes and network protection architectures for WDM-PONs. Optical multicast overlay technique can support the additional multicast transmission on the existing point-to-point data services, while network protection architectures can assure network availability with short traffic restoration time. We will briefly discuss our work in the following sub-topics. / Optical multicast overlay in WDM-PON: Traditional WDM-PONs support only two-way point-to-point data transmission between the optical line terminal (OLT) and the individual subscribers, via the respective designated set of wavelengths. To enhance the network flexibility, it is more desirable to support various different modes of data or video delivery such as broadcast and multicast, in addition to point-to-point transmissions. In this thesis, we systematically investigate the problems and propose our several feasible schemes to overlay multicast transmission onto the existing point-to-point traffic in a WDM-PON. In the first approach, the control of the multicast transmission is achieved by a simple polarization-assisted scheme at the OLT. By the cross-use of wavelengths, a separate path is provided for the multicast differential phase shift keying (DPSK) data from downstream point-to-point amplitude shift keying (ASK) data without additional light sources, which guarantees the transmission performances in both directions, since the upstream ASK signal is imposed on the multicast DPSK signal. We have also demonstrated its variant, in which an optical switch replaces the polarization-assisted control for multicast transmission. The second approach is based on the optical carrier suppression (OCS) technique at the OLT so as to generate the optical subcarriers or sidebands for multicast ASK data modulation. The downstream unicast data is modulated in DPSK format, which will be re-modulated with the upstream ASK data at the respective optical network unit (ONU). As the downstream unicast signal and the upstream signal are calTied on different fiber feeders, while the upstream signal and the multicast signal are carried on different subcarriers, though on the same fiber feeder, the possible Rayleigh backscattering effect is much alleviated. In the third scheme, by using subcarrier modulation technique, we have first successfully overlaid two independent multicast data streams simultaneously onto a WDM-PON, which is believed to further enhance the network capability for multiple destination traffic and improve the cost effectiveness for the future network. Finally, we will provide a comprehensive comparison on all the proposed schemes in this topic. / Survivable network architectures for WDM-PONs: A survivable WDM-PON architecture which can provide self-protection is attractive to avoid enormous loss in data and business due to fiber cuts. To facilitate the network management, the protection switching is realized at the OLT. In this thesis, a simple centrally controlled survivable WDM-PON architecture employing OCS technique is proposed. Protection switching at the OLT employs electrical switches to control the clock signal for the protection sub-carrier generation, via optical carrier suppression. Both distribution and feeder fibers are protected simultaneously. By employing inverse-RZ (IRZ) format for the downstream transmission and non-retum-to-zero (NRZ) for the upstream re-modulated signal, the optical network units are kept colorless and simple. On the other hand, wavelength division multiplexing/time division multiplexing (WDM/TDM) hybrid network, which combines TDM technology and WDM technology, can further increase the network reach, transmission capacity, and reduces the cost per subscriber. Although the bandwidth per subscriber in a WDM/TDM PON is less than that in a WDM-PON, it is still considered as a smooth migration from TDM-PON to WDM-PON. In this thesis, we have proposed a novel WDM/TDM PON architecture which can provide self-protection using a ring topology to connect the subscribers. Finally, we will provide a comprehensive comparison on all the proposed schemes in this topic. / Qiu, Yang. / Adviser: Chun-Kit Chan. / Source: Dissertation Abstracts International, Volume: 73-06, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 130-140). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

"Resource sharing between applications can significantly improve the resources required for all, which can reduce cost, and improve performance. Isolating resources on the other hand can also be beneficial as the failure or significant load on one application does not affect another. There is a delicate balance between resource sharing and resource isolation. Virtual machines may be a solution to this problem with the added benefit of being able to perform more dynamic load balancing, but this solution may be at a significant cost in performance. This thesis compares three different configurations for machines running application servers. It looks at speed at which a new application server can be started up, resource sharing and resource isolation between applications in an attempt to quantify the tradeoffs for each type of configuration."

by Lee Chi Man. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 63-65). / Abstracts in English and Chinese. / Chapter CHAPTER 1 --- INTRODUCTION --- p.5 / Chapter 1.1 --- Background --- p.5 / Chapter 1.1.1 --- Backbone network - Long haul mesh network problem --- p.5 / Chapter 1.1.2 --- Access network ´ؤ Last mile problems --- p.8 / Chapter 1.1.3 --- Network integration --- p.9 / Chapter 1.2 --- SUMMARY OF INSIGHTS --- p.10 / Chapter 1.3 --- Contribution of this thesis --- p.11 / Chapter 1.4 --- Structure of the thesis --- p.11 / Chapter CHAPTER 2 --- PREVIOUS PROTECTION ARCHITECTURES --- p.12 / Chapter 2.1 --- Introduction --- p.12 / Chapter 2.2 --- Traditional physical protection architectures in metro area --- p.13 / Chapter 2.2.1 --- Self healing ring --- p.17 / Chapter 2.2.2 --- Some terminology in ring protection --- p.13 / Chapter 2.2.3 --- Unidirectional path-switched rings (UPSR) [17] --- p.13 / Chapter 2.2.4 --- Bidirectional line-switched rings (BLSR) [17] --- p.14 / Chapter 2.2.5 --- Ring interconnection and dual homing [17] --- p.16 / Chapter 2.3 --- Traditional physical protection architectures in access networks --- p.17 / Chapter 2.3.1 --- Basic architecture in passive optical networks --- p.17 / Chapter 2.3.2 --- Fault management issue in access networks --- p.18 / Chapter 2.3.3 --- Some protection architectures --- p.18 / Chapter 2.4 --- Recent protection architectures on a ccess networks --- p.21 / Chapter 2.4.1 --- Star-Ring-Bus architecture --- p.21 / Chapter 2.5 --- Concluding remarks --- p.22 / Chapter CHAPTER 3 --- GROUP PROTECTION ARCHITECTURE (GPA) FOR TRAFFIC RESTORATION IN MULTI- WAVELENGTH PASSIVE OPTICAL NETWORKS --- p.23 / Chapter 3.1 --- Background --- p.23 / Chapter 3.2 --- Organization of Chapter 3 --- p.24 / Chapter 3.3 --- Overview of Group Protection Architecture --- p.24 / Chapter 3.3.1 --- Network architecture --- p.24 / Chapter 3.3.2 --- Wavelength assignment --- p.25 / Chapter 3.3.3 --- Normal operation of the scheme --- p.25 / Chapter 3.3.4 --- Protection mechanism --- p.26 / Chapter 3.4 --- Enhanced GPA architecture --- p.27 / Chapter 3.4.1 --- Network architecture --- p.27 / Chapter 3.4.2 --- Wavelength assignment --- p.28 / Chapter 3.4.3 --- Realization of network elements --- p.28 / Chapter 3.4.3.1 --- Optical line terminal (OLT) --- p.28 / Chapter 3.4.3.2 --- Remote node (RN) --- p.29 / Chapter 3.4.3.3 --- Realization of optical network unit (ONU) --- p.30 / Chapter 3.4.4 --- Protection switching and restoration --- p.31 / Chapter 3.4.5 --- Experimental demonstration --- p.31 / Chapter 3.5 --- Conclusion --- p.33 / Chapter CHAPTER 4 --- A NOVEL CONE PROTECTION ARCHITECTURE (CPA) SCHEME FOR WDM PASSIVE OPTICAL ACCESS NETWORKS --- p.35 / Chapter 4.1 --- Introduction --- p.35 / Chapter 4.2 --- Single-side Cone Protection Architecture (SS-CPA) --- p.36 / Chapter 4.2.1 --- Network topology of SS-CPA --- p.36 / Chapter 4.2.2 --- Wavelength assignment of SS-CPA --- p.36 / Chapter 4.2.3 --- Realization of remote node --- p.37 / Chapter 4.2.4 --- Realization of optical network unit --- p.39 / Chapter 4.2.5 --- Two types of failures --- p.40 / Chapter 4.2.6 --- Protection mechanism against failure --- p.40 / Chapter 4.2.6.1 --- Multi-failures of type I failure --- p.40 / Chapter 4.2.6.2 --- Type II failure --- p.40 / Chapter 4.2.7 --- Experimental demonstration --- p.41 / Chapter 4.2.8 --- Power budget --- p.42 / Chapter 4.2.9 --- Protection capability analysis --- p.42 / Chapter 4.2.10 --- Non-fully-connected case and its extensibility for addition --- p.42 / Chapter 4.2.11 --- Scalability --- p.43 / Chapter 4.2.12 --- Summary --- p.43 / Chapter 4.3 --- Comparison between GPA and SS-CPA scheme --- p.43 / Chapter 4.1 --- Resources comparison --- p.43 / Chapter 4.2 --- Protection capability comparison --- p.44 / Chapter 4.4 --- Concluding remarks --- p.45 / Chapter CHAPTER 5 --- MUL 77- WA VELENGTH MUL TICAST NETWORK IN PASSIVE OPTICAL NETWORK --- p.46 / Chapter 5.1 --- Introduction --- p.46 / Chapter 5.2 --- Organization of this chapter --- p.47 / Chapter 5.3 --- Simple Group Multicast Network (SGMN) scheme --- p.47 / Chapter 5.3.1 --- Network design principle --- p.47 / Chapter 5.3.2 --- Wavelength assignment of SGMN --- p.48 / Chapter 5.3.3 --- Realization of remote node --- p.49 / Chapter 5.3.3 --- Realization of optical network unit --- p.50 / Chapter 5.3.4 --- Power budget --- p.51 / Chapter 5.4 --- A mulTI- wa velength a ccess network with reconfigurable multicast …… --- p.51 / Chapter 5.4.1 --- Motivation --- p.51 / Chapter 5.4.2 --- Background --- p.51 / Chapter 5.4.3 --- Network design principle --- p.52 / Chapter 5.4.4 --- Wavelength assignment --- p.52 / Chapter 5.4.5 --- Remote Node design --- p.53 / Chapter 5.4.6 --- Optical network unit design --- p.54 / Chapter 5.4.7 --- Multicast connection pattern --- p.55 / Chapter 5.4.8 --- Multicast group selection in OLT --- p.57 / Chapter 5.4.9 --- Scalability --- p.57 / Chapter 5.4.10 --- Experimental configuration --- p.58 / Chapter 5.4.11 --- Concluding remarks --- p.59 / Chapter CHAPTER 6 --- CONCLUSIONS --- p.60 / LIST OF PUBLICATIONS: --- p.62 / REFERENCES: --- p.63

During the last few years, Service-Oriented Architecture (SOA) has been considered to be the new phase in the evolution of distributed enterprise applications. Even though there is a common acceptance of this concept, a real problem hinders the widespread use of SOA : A methodology to design and build secure service-oriented applications is needed. In this dissertation, we design a novel process to secure service-oriented applications. Our contribution is original not only because it applies the MDA approach to the design of service-oriented applications but also because it allows their securing by dynamically applying security patterns throughout the whole process. Security patterns capture security knowledge and describe security mechanisms. In our process, we present a structured map of security patterns for SOA and web services and its corresponding catalog. At the different steps of a software lifecycle, the architect or designer needs to make some security decisions. / An approach using a decision tree made of security pattern nodes is proposed to help making these choices. We show how to extract a decision tree from our map of security patterns. Model-Driven Architecture (MDA) is an approach which promotes the systematic use of models during a system's development lifecycle. In the dissertation we describe a chain of transformations necessary to obtain secure models of the service-oriented application. A main benefit of this process is that it decouples the application domain expertise from the security expertise that are both needed to build a secure application. Security knowledge is captured by pre-defined security patterns, their selection is rendered easier by using the decision trees and their application can be automated. A consequence is that the inclusion of security during the software development process becomes more convenient for the architects/designers. / A second benefit is that the insertion of security is semi-automated and traceable. Thus, the process is flexible and can easily adapt to changing requirements. Given that SOA was developed in order to provide enterprises with modular, reusable and adaptable architectures, but that security was the principal factor that hindered its use, we believe that our process can act as an enabler for service-oriented applications. / by Nelly A. Delessy. / Thesis (Ph.D.)--Florida Atlantic University, 2008. / Includes bibliography. / Electronic reproduction. Boca Raton, FL : 2008 Mode of access: World Wide Web.

Currently, optical communications plays an important role in the transmission aspect of backbone fiber networks. However, there still remain two challenges in this field: one is the bottleneck between high-capacity local area networks (LANs) and the backbone network, where the answer is the broadband optical fiber access networks; the other is the bottleneck of low-speed electrical signal processing in high capacity optical networks, where one possible solution is all-optical nonlinear signal processing. This thesis will cover both of the two topics. In the first topic, the emphasis will be put on the novel optical access network infrastructure design to improve the access network reliability and functionality as well as the reduction of system complexity. In the second topic, the focus is how to utilize the newly-emerging photonic devices or newly-designed configurations to improve the performance of current optical signal processing subsystems for applications in lightwave transmission systems. / In summary, this thesis introduces a series of novel optical access network architecture designs and transmission system technologies for optical fiber communications and discusses their feasibilities in practice from the research perspective. We hope that these proposed technologies can contribute to the further developments in this field. / In the area of broadband optical fiber access networks, two aspects are considered: survivability and monitoring function. For the first part, several new network protection schemes among various access network topologies (i.e. tree and ring) are proposed and experimentally demonstrated, which could reduce the access network cost and simplifying the operation of the access network. For the second part, an interesting in-service fault surveillance scheme in the current TDM-PON is proposed via analyzing the composite radio-frequency (RF) spectrum of the common supervisory channel at the central office (CO). Experiment proves its effectiveness with negligible influence on the signal channels. In addition, a system demonstration of the WDM-based optical broadband access network with automatic optical protection function is presented, showing the potential of WDM technologies in the broadband optical access networks. / In the area of nonlinear optical signal processing, the technology innovation is in two areas: new architecture design and the new photonic devices. For the issue of architecture design, the focus is on the Nonlinear Optical Loop Mirror (NOLM) structure. A new polarization-independent OTDM demultiplexing scheme is proposed and demonstrated by incorporating a polarization-diversity loop into a conventional NOLM, which offers stable operation using the conventional components without sacrificing the operation speed or structural simplicity. In another study the design of a novel OFSK transmitter based on phase-modulator-embedded NOLM is conceived and implemented, which features data-rate transparent, continuous tuning of the wavelength spacing and stable operation. For the aspect of new photonic devices, this thesis focuses on the applications of photonic crystal fibers (PCF). In one work, a relatively short-length of dispersion-flattened high-nonlinearity PCF (gamma=11.2 (W-km)-1, D<-1 ps/nm/km 1500-1600 nm, S<1 x 10-3 ps/km/nm2) is integrated into a dispersion-imbalanced loop mirror (DILM) to form a nonlinear intensity discriminator and its application in the nonlinear suppression of the incoherent interferometric crosstalk has been successfully demonstrated. The special characteristics of the PCF ensure a broadband signal quality improvement and make the DILM more compact and stable. In the other work, the small birefringence of this PCF helps to simply achieve the polarization-insensitive wide-band wavelength converter based on four-wave-mixing in PCF. / Wang Zhaoxin. / "September 2006." / Advisers: Chinlon Lin; Chun-Kit Chan. / Source: Dissertation Abstracts International, Volume: 68-03, Section: B, page: 1846. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (p. 93-101). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Ho Ho-ching. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 104-107). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgment --- p.vi / Chapter 1. --- Introduction --- p.1 / Chapter 1.1. --- Introduction to PBX based Call Center --- p.1 / Chapter 1.2. --- The Scenarios --- p.2 / Chapter 1.3. --- Thesis Overview --- p.5 / Chapter 2. --- Features of Collaborative Browsing --- p.8 / Chapter 2.1. --- Feature Synchronization vs Bitmap Screen Transfer --- p.8 / Chapter 2.2. --- Basic Collaborative Features of the Collaborative Browser --- p.9 / Chapter 2.2.1. --- Web Page Pushing --- p.10 / Chapter 2.2.2. --- Screen Widget Synchronization --- p.11 / Chapter 2.2.3. --- Tele-pointing and Shared Whiteboard --- p.12 / Chapter 2.3. --- Collaborative Form Manipulation --- p.13 / Chapter 2.3.1. --- Importance of Electronic Form Collaboration --- p.13 / Chapter 2.3.2. --- Basic Support for Form Collaboration ´ؤ´ؤData Synchronization --- p.14 / Chapter 2.3.3. --- Existence of Form Complexity ´ؤForm Data Dependency --- p.75 / Chapter 2.3.4. --- Hinting --- p.17 / Chapter 2.4. --- Collaborative IVR --- p.23 / Chapter 2.4.1. --- Traditional Interactive Voice Response (IVR) Service --- p.23 / Chapter 2.4.2. --- Abstraction ´ؤCorrelating Form Interaction Mechansim with IVR --- p.25 / Chapter 2.4.3 --- Collaborative IVR by Form Interaction Mechanism --- p.27 / Chapter 3. --- Software Architecture --- p.33 / Chapter 3.1. --- The Three-Tier Architecture --- p.33 / Chapter 3.2. --- The Collaboration Mechanism for Collaborative Browser --- p.37 / Chapter 3.2.1. --- Session Initialization/Termination --- p.37 / Chapter 3.2.2. --- Data Flow of the Basic Collaboration Features --- p.39 / Chapter 3.2.3. --- Control Mechanism --- p.40 / Chapter 3.2.4. --- The Hinting Mechanism for Collaborative Form Manipulation --- p.43 / Chapter 3.3. --- The Collaboration Mechanism for Collaborative IVR --- p.45 / Chapter 4. --- Implementation --- p.51 / Chapter 4.1. --- Shareable Document Object Architecture for Collaboration --- p.51 / Chapter 4.1.1. --- Document Object Architecture --- p.51 / Chapter 4.1.2. --- Generalizing to Shareable Document Object Architecture --- p.53 / Chapter 4.2. --- Whiteboard Mechanism --- p.55 / Chapter 4.3. --- Packet Data Unit for Communication --- p.57 / Chapter 4.4. --- Bridging Different Software Components --- p.60 / Chapter 4.5. --- Hinting Mechanism for Collaborative Form Manipulation --- p.63 / Chapter 4.5.1. --- Relating Form Fields to Table Fields --- p.63 / Chapter 4.5.2. --- Hinting by the Hinting Tables --- p.69 / Chapter 4.6. --- Collaborative IVR --- p.73 / Chapter 4.6.1. --- Using Mediator for Collaborative IVR --- p.73 / Chapter 4.6.2. --- Concept of Telephone Form --- p.74 / Chapter 4.6.3. --- Hinting for Collaborative IVR --- p.78 / Chapter 4.7. --- System Integration --- p.81 / Chapter 5. --- Performance Evaluation and Experiment Results --- p.84 / Chapter 5.1. --- Optimizing the Transmission Methodology --- p.84 / Chapter 5.2. --- Browser Responsiveness Study --- p.86 / Chapter 5.2.1. --- Experiment Details --- p.86 / Chapter 5.2.2. --- The Assumptions --- p.89 / Chapter 5.2.3. --- Experiment Results and Analysis --- p.90 / Chapter 5.3. --- Bandwidth Consumption --- p.94 / Chapter 6. --- Conclusions --- p.97 / Appendix A 一 Government Profit Tax Return Form --- p.101 / Appendix B ´ؤ A Phone Banking IVR Service Tree --- p.103 / Bibliography --- p.104

Choy Man Ting. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 66-69). / Abstracts in English and Chinese. / Acknowledgments --- p.ii / Abstract --- p.v / Table of Contents --- p.vii / List of figures --- p.viii / Chapter Chapter 1 --- p.12 / Chapter 1.1 --- OBS Network Architecture --- p.3 / Chapter 1.2 --- Offset Time and Reservation Schemes --- p.5 / Chapter 1.3 --- Research Objectives --- p.7 / Chapter 1.4 --- Overview --- p.8 / Chapter Chapter 2 --- p.9 / Chapter 2.1 --- WDM crossbar architectures --- p.9 / Chapter 2.2 --- Switch Based on Optical Crossbars --- p.10 / Chapter 2.3 --- Switch Based on Wavelength Grating Routers --- p.11 / Chapter Chapter 3 --- p.14 / Chapter 3.1 --- Basics of Dual Shuffle Exchange Network --- p.14 / Chapter 3.2 --- Dual Shuffle-exchange Network --- p.16 / Chapter 3.3 --- Proposed Architecture based on DSN --- p.19 / Chapter 3.4 --- Analysis on blocking due to output contention --- p.20 / Chapter 3.5 --- Implementation issues on the 4x4 switching module --- p.23 / Chapter 3.6 --- Analysis: Non-blocking versus banyan --- p.25 / Chapter Chapter 4 --- p.30 / Chapter 4.1 --- First Scheme --- p.30 / Chapter 4.2 --- Simulation on the first scheme --- p.33 / Chapter 4.3 --- Second Scheme: Tunable wavelength converter --- p.37 / Chapter 4.4 --- Third Scheme: Route to specific wavelength port --- p.42 / Chapter 4.5 --- Analysis on blocking due to insufficient stages --- p.46 / Chapter Chapter 5 --- p.49 / Chapter 5.1 --- Delay analysis of DSN --- p.49 / Chapter 5.2 --- Vertical Expansion --- p.51 / Chapter 5.3 --- Simulation results on vertical expansion --- p.52 / Chapter 5.4 --- Building DSN with 8x8 MEMS switches --- p.54 / Chapter 5.5 --- Prove of the proposed Quarter shuffle network --- p.56 / Chapter 5.6 --- Comparison between Quarter shuffle and doubled links approaches --- p.58 / Chapter Chapter 6 --- p.64 / Conclusion --- p.64 / Bibliography --- p.66

Present-day datacenter networks (DCNs) are designed to achieve full bisection bandwidth in order to provide high network throughput and server agility. However, the average utilization of typical DCN infrastructure is below 10% for significant time intervals. As a result, energy is wasted during these periods. In this thesis we analyze traffic behavior of datacenter networks using traces as well as simulated models. Based on the insight developed, we present techniques to reduce energy waste by making energy use scale linearly with load. The solutions developed are analyzed via simulations, formal analysis, and prototyping. The impact of our work is significant because the energy savings we obtain for networking infrastructure of DCNs are near optimal. A key finding of our traffic analysis is that network switch ports within the DCN are grossly under-utilized. Therefore, the first solution we study is to modify the routing within the network to force most traffic to the smallest of switches. This increases the hop count for the traffic but enables the powering off of many switch ports. The exact extent of energy savings is derived and validated using simulations. An alternative strategy we explore in this context is to replace about half the switches with fewer switches that have higher port density. This has the effect of enabling even greater traffic consolidation, thus enabling even more ports to sleep. Finally, we explore a third approach in which we begin with end-to-end traffic models and incrementally build a DCN topology that is optimized for that model. In other words, the network topology is optimized for the potential use of the datacenter. This approach makes sense because, as other researchers have observed, the traffic in a datacenter is heavily dependent on the primary use of the datacenter. A second line of research we undertake is to merge traffic in the analog domain prior to feeding it to switches. This is accomplished by use of a passive device we call a merge network. Using a merge network enables us to attain linear scaling of energy use with load regardless of datacenter traffic models. The challenge in using such a device is that layer 2 and layer 3 protocols require a one-to-one mapping of hardware addresses to IP (Internet Protocol) addresses. We overcome this problem by building a software shim layer that hides the fact that traffic is being merged. In order to validate the idea of a merge network, we build a simple mere network for gigabit optical interfaces and demonstrate correct operation at line speeds of layer 2 and layer 3 protocols. We also conducted measurements to study how traffic gets mixed in the merge network prior to being fed to the switch. We also show that the merge network uses only a fraction of a watt of power, which makes this a very attractive solution for energy efficiency. In this research we have developed solutions that enable linear scaling of energy with load in datacenter networks. The different techniques developed have been analyzed via modeling and simulations as well as prototyping. We believe that these solutions can be easily incorporated into future DCNs with little effort.

Application-layer overlay networks have recently emerged as a promising platform to deploy additional services over the Internet. A virtual network of overlay nodes can be used to regulate traffic flows of an underlay network, without modifying the underlay network infrastructure. As a result, an opportunity to redeem the inefficiency of IP routing and to improve end-to-end performance of the Internet has arisen, by routing traffic over multiple overlay paths. However, to achieve high end-to-end performance over the Internet by means of overlay networks, a number of challenging issues, including limited knowledge of the underlay network characteristics, fluctuations of overlay path performance, and interactions between overlay and the underlay traffic must be addressed. This thesis provides solutions to some of these issues, by proposing a framework to construct a multi-path overlay architecture for improving Internet end-to-end performance and availability. The framework is formed by posing a series of questions, including i) how to model and forecast overlay path performance characteristics; ii) how to route traffic optimally over multiple overlay paths; and iii) how to place overlay nodes to maximally leverage the Internet resource redundancy, while minimizing the deployment cost. To answer those research questions, analytical and experimental studies have been conducted. As a result, i) a loss model and a hybrid forecasting technique are proposed to capture, and subsequently predict end-to-end loss/delay behaviors; with this predictive capability, overlay agents can, for example, select overlay paths that potentially offer good performance and reliability; ii) to take full advantage of the predictive capability and the availability of multiple paths, a Markov Decision Process based multi-path traffic controller is developed, which can route traffic simultaneously over multiple overlay paths to optimize some performance measures, e.g. average loss rate and latency. As there can be multiple overlay controllers, competing for common resources by making selfish decisions, which could jeopardize performance of the networks, game theory is applied here to turn the competition into cooperation; as a consequence, the network performance is improved; iii) furthermore, to facilitate the deployment of the multi-path overlay architecture, a multi-objective genetic-based algorithm is introduced to place overlay nodes to attain a high level of overlay path diversity, while minimizing the number of overlay nodes to be deployed, and thus reducing the deployment cost. The findings of this thesis indicate that the use of multiple overlay paths can substantially improve end-to-end performance. They uncover the potential of multi-path application-layer overlay networks as an architecture for achieving high end-to-end performance and availability over the Internet.