Zhang Liang. / "August 2004." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Computer entertainment is a big business today. Due to the availability of broadband network connections, the Internet is already a platform for many high quality multimedia applications. For example, online theaters and multi-player online games (MOG) are two of the most popular multimedia applications on the Internet. Although the Internet provides us a very convenient channel for data dissemination, its open architecture leads to many security issues. The security problems are especially complicated for computer entertainment applications since we must address both efficiency and security at the same time. In this thesis, we tackle four security issues in different aspects of computer entertainment applications. Specifically, the issues are (1) "to provide secure multimedia streaming while allowing proxy caching by untrusted third parties", (2) "to detect cheating in MOGs other than using conventional labor-intensive methods", (3) "to synchronize game clients in highly-interactive MOGs while resisting cheating in both the application and protocol level", and (4) "to exchange messages in peer-to-peer (P2P) MOGs so that distributed simulation is allowed but information exposure is mitigated". For each of the above issues, we present an effective solution that preserves the architecture of that particular multimedia application and also is feasible and efficient to deploy on the Internet. / Yeung, Siu Fung. / Adviser: John C. S. Lui. / Source: Dissertation Abstracts International, Volume: 70-09, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 137-142). / 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.

Computing consistent global states in a distributed system is a fundamental problem. A large class of distributed system problems can be cast as construction of consistent global states and evaluation of relevant properties over these global states. Examples of such problems include the monitoring and debugging of distributed systems, the detection of stable properties such as deadlock, termination, and loss of tokens, protocol specification and verification, garbage collection, checkpointing and failure recovery, and many others. / Finally, we will present a suit of three new snapshot algorithms for mobile ad hoc network systems: cooperative, localized, and centralized. These new snapshot algorithms have different timing and tailoring components, Compared to existing snapshot algorithms, our snapshot algorithms can be proven to work in the presence of node mobility and dynamic topology changes, i.e., all of them can compute consistent global states in a mobile ad hoc network system. We will also evaluate the effectiveness and efficiency of these newly proposed snapshot algorithms by using extensive simulations. / Firstly, we will develop a system model for a mobile ad hoc network system. In addition to the internal, send and receive events that are considered in a traditional system model for static systems, two novel types of events called on and off are introduced to represent dynamic topology changes in our system model. Based on these on and off events, it is convenient to devise new distributed algorithms that can handle dynamic topology changes for the mobile ad hoc network environment. We will also propose a new relation called the extended-happened-before relation, which is generalized from the well-known happened-before relation defined by Lamport, to fully model the ordering of events in a mobile ad hoc network system. The event orders captured by the extended-happened-before relation playa critical role in solving the snapshot problem at hand. / However, consistent global states are not freely available in distributed systems without shared memory and synchronized clocks. In the literature, the fundamental problem of constructing consistent global states in a distributed system was defined as the snapshot problem. Although many solutions to the snapshot problem have been developed for various types of distributed systems, most of them cannot be applied directly to a mobile ad hoc network system, which has no fixed network infrastructure for operating support and may experience dynamic topology changes due to node mobility. In this thesis, we present a systematic study on the snapshot problem in mobile ad hoc network systems. / Secondly, we will derive a new consistency criterion for constructing a global state in a mobile ad hoc network system. Without a common time base and shared memory, the development of the new consistency criterion sticks to the fundamental principle that if the events for recording the local states are ensured to be concurrent, then the recorded local states are equivalent to those that are recorded simultaneously in real time and the resulting global state is guaranteed to be consistent. Importantly, we will also show a consistency theorem, which gives a necessary and sufficient condition for computing consistent global states in a mobile ad hoc network system. That is, a global state of a mobile ad hoc network system is consistent if and only if its corresponding cut is not only causally consistent but also topologically consistent. / Thirdly, we will propose a simple method called timing-and-tailoring to design and analyze snapshot algorithms in a well structured approach. In this generic method, a snapshot algorithm is decomposed into two basic components. The first component called timing is used to record the ordering of events by using logical time algorithms. The second component called tailoring is used to find a consistent global state based on known event ordering. To demonstrate the proposed timing-and-tailoring method, we will also present several examples of using this method to design and analyze snapshot algorithms. These examples provide helpful insights in designing new snapshot algorithms for mobile ad hoc network systems. / Wu, Dan. / Adviser: Man Hon Wong. / Source: Dissertation Abstracts International, Volume: 73-04, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 135-145). / 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.

Chromatic dispersion (CD) is due to the fact that light with different frequencies travel at different speeds inside fiber. It causes pulse spreading and intersymbol interference (ISI) which would severely degrade the transmission performance. By feeding a signal into a fiber loop which consists of a high-birefringence (Hi-Bi) fiber, we experimentally show that the amount of experienced dispersion can be deduced from the RF power at a specific selected frequency which is determined by the length of the Hi-Bi fiber. Experimental results show that this technique can provide high monitoring resolution and dynamic range. / Polarization mode dispersion (PMD) splits an optical pulse into two orthogonally polarized pulses traveling along the fiber at different speeds, causing crosstalk and ISI. The third part of the thesis demonstrates two different PMD monitoring schemes. The first one is based on the analysis of frequency-resolved state-of-polarization (SOP) rotation, with signal spectrum broadened by self-phase modulation (SPM) effect. Experimental results show that the use of broadened signal spectrum induced by SPM not only relaxes the filter requirement and reduces the computational complexity, but also improves the estimation accuracy, and extends the monitoring range of the pulsewidth. The second one is based on the delay-tap asynchronous waveform sampling technique. By examining the statistical distribution of the measured scatter plot, unambiguous PMD measurement range up to 50% of signal bit-period is demonstrated. / The final part of the thesis focuses on the monitoring of alignment status between the pulse carver and data modulator in an optical system. We again employ the two-tap asynchronous sampling technique to perform such kind of monitoring in RZ-OOK transmission system. Experimental results show that both the misalignment direction and magnitude can be successfully determined. Besides, we propose and experimentally demonstrate the use of off-center optical filtering technique to capture the amount of spectrum broadening induced by the misalignment between the pulse-carver and the data modulator in RZ-DPSK transmission system. The same technique was also applied to monitor the synchronization between the old and the new data in synchronized phase re-modulation (SPRM) system. / The tremendous increase of data traffic in the worldwide Internet has driven the rapid development of optical networks to migrate from numerous point-to-point links towards meshed, transparent optical networks with dynamically routed light paths. This increases the need for appropriate network supervision methods. In view of this, optical performance monitoring (OPM) has emerged as an indispensable element for the quality assurance of an optical network. This thesis is devoted to the proposal of several new and accurate techniques to monitor different optical impairments so as to enhance proper network management. / When the optical signal is carried on fiber links with optical amplifiers, the accumulated amplified spontaneous emission (ASE) noise will result in erroneous detection of the received signals. The first part of the thesis presents a novel, simple, and robust in-band optical signal to noise ratio (OSNR) monitoring technique using phase modulator embedded fiber loop mirror (PM-FLM). This technique measures the in-band OSNR accurately by observing the output power of a fiber loop mirror filter, where the transmittance is adjusted by an embedded phase modulator driven by a low-frequency periodic signal. The robustness against polarization mode dispersion, chromatic dispersion, bit-rate, and partially polarized noise is experimentally demonstrated. / Ku, Yuen Ching. / "August 2007." / Adviser: Chan Chun-Kit. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1208. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (p. 109-120). / 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. / Abstract in English and Chinese. / School code: 1307.

Our study on interdomain traffic engineering focuses on AS Path Prepending (ASPP), a popular way for inbound traffic engineering. In order to improve the current situation that ISPs often practise this approach in a trial-and-error basis, we propose a greedy algorithm to help ISPs perform this approach systematically and efficiently. Then we demonstrate two fundamental issues of decentralized selfish traffic engineering, routing instability and global network performance degradation, based on an abstract model where ISPs perform traffic engineering for their individual load balance. We also present a real-world pathologic case of prepending instability from our measurement study. Some simple guidelines are given for ISPs to avoid such routing instability. / Our work on peering strategy is to help ISPs understand the economic implications of various traffic patterns and make proper decisions to optimize their business. We first conduct an economic analysis for an overlay streaming network to gain some insights on the free ride phenomenon. We further improve the analysis by taking the response of subscribers into consideration and formulate the dynamic market as a multi-leader-follower game to capture the Nash Equilibrium of the routing tussle among the major players of the Internet marketplace. Based on this framework together with a gravity traffic model, we present some important observations on the implications of overlays on ISPs' peering strategy. / Over the past several years, numerous types of "overlay" networks change the interdomain traffic pattern and ISPs lose the routing control of some interdomain traffic flows due to the application layer routing. As a result, some ISPs may provide unintended transit service for other local ISPs. It upsets the traditional business model and makes ISPs' peering strategies more complicated. / The Internet has quickly evolved into a vast global network owned and operated by thousands of interconnected Internet Service Providers. Each of these ISPs, as one autonomous system, has its individual economic interests. ISPs can achieve their objectives through peering strategy and interdomain traffic engineering. These two issues are important for ISPs' business and have significant implications on the Internet architecture. / Wang, Hui. / "September 2007." / Adviser: Dah Ming Chiu. / Source: Dissertation Abstracts International, Volume: 69-08, Section: B, page: 4865. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (p. 163-170). / 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.

Hui Li. / "May 2000." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (p. 135-144). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web.

by Zhu Jian. / "May 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (p. 162-170). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

by Guo, Xiao-Lei. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (p. 138-[147]). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web.

This thesis focuses on the intersection of human mobility and technology diffusion in Africa. With Ghana as a case study, it looks at how the diffusion of internet access and use are influenced by international mobility. The research is based in the literature on the diffusion of innovations, international knowledge transmission, migration and development, and Information and Communication Technologies for Development (ICT4D). It begins from the hypothesis that international mobility may contribute to lowering barriers to internet penetration in developing countries by facilitating flows of resources, including equipment, finance, skills and knowledge. The research is based on four different datasets: a survey of the internet cafes in the North of Ghana and in Accra; an online survey of users in northern internet cafes; a network study incorporating internet cafe owners and managers in higher-value-added areas of the IT sector, and in-depth interviews with policymakers and donor organisations involved in ICT4D interventions. The data was analysed using a combination of fuzzy-set Qualitative Comparative Analysis (QCA) and network analytic techniques including visualisation, statistical analysis and qualitative analysis. The findings show that international mobility makes an important contribution to the base of adoption capacity for new technologies in poor and remote regions. It enables entrepreneurs and IT workers to address market gaps that restrict access to material and financial resources; by providing access to international circuits of knowledge and ideas which help individuals gain a foothold in the IT sector, and by facilitating local private-sector provision of the internet through internet cafes which serve the hardest-to-reach populations. The thesis concludes by suggesting potential entry points for ICT4D and migration policy in developing countries regarding the efficiency and effectiveness of ICT4D interventions, the role of the private sector in promoting internet usership, and the role of mobility in building adoption capacity in low-income areas.

Leung, Kai Man. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 63-68). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Background --- p.5 / Chapter 2.1 --- Graph Connectivity --- p.5 / Chapter 2.1.1 --- Preliminaries --- p.5 / Chapter 2.1.2 --- Edge Connectivity --- p.7 / Chapter 2.1.3 --- Vertex Connectivity --- p.7 / Chapter 2.1.4 --- Algorithms for Graph Connectivities --- p.9 / Chapter 2.1.5 --- All Pairs Edge Connectivities --- p.10 / Chapter 2.1.6 --- Edge Splitting-off --- p.11 / Chapter 2.1.7 --- Graph Separator --- p.13 / Chapter 2.1.8 --- Expander Graphs --- p.15 / Chapter 2.1.9 --- Superconcentrator --- p.17 / Chapter 2.2 --- Network Coding --- p.19 / Chapter 2.2.1 --- Concept --- p.19 / Chapter 2.2.2 --- Linear Network Coding --- p.21 / Chapter 2.2.3 --- Random Linear Network Coding --- p.25 / Chapter 2.3 --- Algebraic Tools --- p.26 / Chapter 2.3.1 --- Linear Algebraic Algorithms --- p.26 / Chapter 2.3.2 --- Nested Dissection --- p.28 / Chapter 3 --- Algorithms for Graph Connectivities --- p.35 / Chapter 3.1 --- Introduction --- p.35 / Chapter 3.1.1 --- Our Results --- p.36 / Chapter 3.1.2 --- Related Work --- p.39 / Chapter 3.1.3 --- Techniques --- p.40 / Chapter 3.1.4 --- Organization --- p.41 / Chapter 3.2 --- New Algebraic Characterization --- p.41 / Chapter 3.3 --- Connectivities in Acyclic Graph --- p.46 / Chapter 3.3.1 --- Faster Encoding Algorithms --- p.47 / Chapter 3.4 --- Directed Planar Graphs --- p.49 / Chapter 3.5 --- All Pairs Edge Connectivities --- p.53 / Chapter 3.5.1 --- Connections with Previous Work --- p.55 / Chapter 3.6 --- Edge Splitting-off --- p.56 / Chapter 3.6.1 --- Edge Splitting-off in Directed Graphs --- p.57 / Chapter 3.6.2 --- Edge Splitting-off in Undirected Graphs --- p.58 / Concluding Remarks --- p.61 / Bibliography --- p.62