In this paper, we discuss the consensus problem for synchronous distributed systems with orderly crash failures. For a synchronous distributed system of n processes with up to t crash failures and f failures actually occur, first, we present a bivalency argument proof to solve the open problem of proving the lower bound, min (t + 1, f + 2) rounds, for early-stopping synchronous consensus with orderly crash failures, where t < n - 1. Then, we extend the system model with orderly crash failures to a new model in which a process is allowed to send multiple messages to the same destination process in a round and the failing processes still respect the order specified by the protocol in sending messages. For this new model, we present a uniform consensus protocol, in which all non-faulty processes always decide and stop immediately by the end of f + 1 rounds. We prove that the lower bound of early stopping protocols for both consensus and uniform consensus are f + 1 rounds under the new model, and our proposed protocol is optimal. / Singapore-MIT Alliance (SMA)

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 53-54). Also available on the World Wide Web.

Due to the advancement of web-based technologies, using LMS to support both asynchronous and synchronous learning has become more and more popular. Another new trend is to combine physical classroom and cyber classroom into a mixture learning environment, that is why blended learning has become an important research topic in e-learning domain. According to the literature survey, blended learning can create a flexible learning environment and improve the learning effects. Besides, blended learning can also reduce the cost, increase the benefit, and extend the outcomes. However, most teachers are not familiar with this kind of blended synchronous learning environment; they have no ideas about how to conduct teaching and learning activities in this kind of environment. The aims of this study are to explore the proper setup of a blended learning environment and to propose some important blended learning models for teachers. We use case study approach for our research. Two online successful courses were chosen as the study cases. These two courses are ¡§E-learning Theory and Practice¡¨ and ¡§Computer Networks and the Internet¡¨ which were instructed by Dr. Nian-Shing Chen at National Sun Yat-Sen University. Observation method and interview method were used to gather the study data. Moreover, the gathered data was analyzed by qualitative methods. The contributions of this study are the setup guideline for blended synchronous classroom and the proposed five blended synchronous learning modes. These results could provide valuable references for administrators to setup appropriate blended learning environments and for instructors to design better blended learning courses.

Following the booming of global e-business, the demand for online negotiations is growing apparently. Recently, instant messaging (IM) software such as Microsoft MSN, Yahoo messenger has become very popular synchronous communication tool. Although the instant messaging tools make people can negotiate or communicate with each other synchronously over the Internet, in terms of the richness of communication media, instant messaging is leaner than that of traditional face-to-face. Previous studies have demonstrated that the media richness of communication has effect on negotiation behavior and result. To improve the richness of the instant messaging, many instant messaging tools have provided a variety of emoticons for user. Due to the popularity of instant messaging and emoticon usage, the purpose of this study is to investigate the effects of emoticons on synchronous e-negotiation environment. In this study, we conducted a lab experiment to simulate synchronous negotiations. The findings reveal that emoticons have effects on negotiation process and negotiators¡¦ communication ability.

Ultra high frequency (UHF) radio frequency identification (RFID) systems suffer from issues that limit their widespread deployment and limit the number of applications where they can be used. These limitations are: lack of a well defined read zone, interference, and environment sensitivity. To overcome these limitations a novel receiver device is introduced into the system. The use of such device or devices mitigates the issues by enabling more "anchor points" in the system. Two such devices exist in industry and academia: the Astraion Sensatag and the Gen2 Listener. The drawbacks of the Sensatag is that it offers poor performance in capturing tag signals. The Gen2 Listener is based on the expensive software defined radio hardware. The purpose of the thesis was to develop a receiver that will enable several new RFID applications that are not available with current RFID systems. The receiver, named ARR (Augmented RFID Receiver), receives tag and reader signals, which are decoded by an FPGA and the results are reported through Ethernet. This device is central to the augmented RFID system. To show the suitability of such an approach, the performance of the implementation was compared to the other two outlined solutions. A comparison of the read rate and range of the implementations were the defining factors. The analysis showed that the ARR is capable of receiving tag signals with a read rate of 50% for passive and 66% for semi-passive tags at a one meter distance and is capable of receiving tag signals at a maximum of 3.25 meters for passive and 5.5 meters for semi- passive tags, with the reader being within 8 meters of the ARR. Two applications were implemented to showcase the ARR: an RFID portal and protocol analyzer.

<p>With the ever increasing demand for data communication methods, power line communication has become an interesting alternative method for data communication. Power line communication falls into two categories: one for data transmission between sites in the power grid and the other for home or office networking. When considering home or office networking, existing methods are either too slow for tasks other than simple automation, or are very fast with a higher cost than necessary for the desired function. The objective in this work is to develop a lower cost communication system with an intermediate data transmission rate.</p><p>At first glance, power line communication looks like a good option because of the availability of power outlets in every room of a building. However, the power conductors were installed solely for the purpose of distributing 60 Hz mains power and, for data signals, they exhibit very high attenuation, variable impedance and there is radio frequency shielding. Furthermore, many of the 60 Hz loads produce radio frequency interference that impedes data communication. Previous research has shown that much of the noise is time synchronous with the 60 Hz mains frequency and that the majority of data errors occur during these periods of high noise.</p><p> This work develops a power line communication protocol that coordinates transmissions and uses only the predictable times of lower noise. Using a central control strategy, the power line 60 Hz mains signal is divided into 16 timeslots and each timeslot is monitored for errors. The central controller periodically polls all stations to learn which timeslots have low noise and it then controls all transmissions to make the best use of these good timeslots. The periodic polling allows the system to adapt to changes in electrical loading and noise. This control strategy has been achieved with modest complexity and laboratory measurements have shown throughput approaching 70% of the modem bit rate.</p>

Energy consumption and network latency are important issues in wireless sensor networks. The mechanism duty cycling is generally used in wireless sensor networks for avoiding energy consumption due to idle listening. Duty cycling, however, also introduces additional latency in communication among sensors. Some protocols have been proposed to work in wireless sensor networks with duty cycling, such as S-MAC and DW-MAC. Those protocols also tried to make efficient channel utilization and to mitigate the chance of packet collision and the network latency increase resulting from collision. DW-MAC was also designed to tolerate bursty and high traffic loads without increasing energy consumption, by spreading packet transmission and node wakeup times during a cycle. Some performance comparison between S-MAC and DW-MAC has been done in previous work; however, this comparison was performed in the ns-2 simulator only. In the real world, there are further issues not considered or discussed in the simulation, and some of those issues contribute significant influences to the MAC protocol performance. In this work, I implemented both S-MAC and DW-MAC physically on MICAz sensor motes and compared their performance through experiments. Through my implementation, experiments, and performance evaluation, hardware properties and issues that were not addressed in the previous work are presented, and their impacts on the performance are shown and discussed. I also simulated S-MAC and DW-MAC on ns-2 to give a mutual validation of the experimental results and my interpretation of the results. The experiences of physical implementations presented in this work can contribute new information and insights for helping in future MAC protocol design and implementation in wireless sensor networks.

<p>With the ever increasing demand for data communication methods, power line communication has become an interesting alternative method for data communication. Power line communication falls into two categories: one for data transmission between sites in the power grid and the other for home or office networking. When considering home or office networking, existing methods are either too slow for tasks other than simple automation, or are very fast with a higher cost than necessary for the desired function. The objective in this work is to develop a lower cost communication system with an intermediate data transmission rate.</p><p>At first glance, power line communication looks like a good option because of the availability of power outlets in every room of a building. However, the power conductors were installed solely for the purpose of distributing 60 Hz mains power and, for data signals, they exhibit very high attenuation, variable impedance and there is radio frequency shielding. Furthermore, many of the 60 Hz loads produce radio frequency interference that impedes data communication. Previous research has shown that much of the noise is time synchronous with the 60 Hz mains frequency and that the majority of data errors occur during these periods of high noise.</p><p> This work develops a power line communication protocol that coordinates transmissions and uses only the predictable times of lower noise. Using a central control strategy, the power line 60 Hz mains signal is divided into 16 timeslots and each timeslot is monitored for errors. The central controller periodically polls all stations to learn which timeslots have low noise and it then controls all transmissions to make the best use of these good timeslots. The periodic polling allows the system to adapt to changes in electrical loading and noise. This control strategy has been achieved with modest complexity and laboratory measurements have shown throughput approaching 70% of the modem bit rate.</p>

Shared objects are a key component in today's large distributed systems. Linearizability is a popular consistency condition for such shared objects which gives the illusion of sequential execution of operations. The time bound of an operation is the worst-case time complexity from the operation invocation to its response. Some time bounds have been proved for certain operations on linearizable shared objects in partially synchronous systems but there are some gaps between time upper bound and lower bound for each operation. In this work, the goal is to narrow or eliminate the gaps and find optimally fast implementations. To reach this goal, we prove larger lower bounds and show smaller upper bounds (compared to 2d for all operations in previous folklore implementations) by proposing an implementation for a shared object with an arbitrary data type in distributed systems of n processes in which every message delay is bounded within [d-u, d] and the maximum skew between processes' clocks is epsilon. Considering any operation for which there exist two instances such that individually, each instance is legal but in sequence they are not, we prove a lower bound of d + min{epsilon, u, d/3}, improving from d, and show this bound is tight when epsilon < d/3 and epsilon < u. Considering any operation for which there exist k instances such that each instance separately is legal and any sequence of them is legal, but the state of the object is different after different sequences, we prove a lower bound of (1-1/k)u, improving from u/2, and show this bound is tight when k = n. A pure mutator only modifies the object but does not return anything about the object. A pure accessor does not modify the object. For a pure mutator OP1 and a pure accessor OP2, if given a set of instances of OP1, the state of the object reflects the order in which the instances occur and an instance of OP2 can detect whether an instance of OP1 occurs, we prove the sum of the time bound for OP1 and OP2 is at least d + min{epsilon, u, d/3}, improving from d. The upper bound is d + 2*epsilon from our implementation.

With the innovation and use of information technology, Blended Learning, which combines traditional face-to-face and e-learning, becomes an emerging trend. Blended Learning has been widely adopted in educational field and enterprises. It is considered as a useful model to transfer knowledge, teaching and learning. What does blended learning mean? What are the impacts on instruction? How many models can blended learning have? What are the related issues and challenges? And what are the future research directions? They are all the vital issues in the future development of e-learning. Many researchers and educators have indicated that interaction is an important factor to influence learning effectiveness. Therefore, our study focus on exploring different interaction modes in blended synchronous learning environment and analyzing what kinds of roles are participated within the interaction procedures. A case study approach is adopted by taking the three blended synchronous learning courses, Negotiation and E-negotiation, Computer network, Database, which are held by the MIS department of National Sun Yat-sen University in the first semester of the 94 academic year as research subjects. We also apply phenomenology view point and qualitative methodology to find out all different phenomenons of interaction existing in the studied blended learning environment. The results found eight different dimensions of interaction including instructor-to-instructor, instructor-to-learner, instructor-to-content, instructor-to-interface, learner-to-instructor, learner-to-learner, learner-to-content and learner-to-interface. We then provide suggestions for instructors, learners and managers how they can improve interaction in blended learning environment according to each interaction dimension.