<p> In heterogeneous distributed computing system, diversity can be present both in the computational resources and in the types of arriving tasks. In an inconsistently Heterogeneous Computing (HC) system, different task types can have different performance characteristics (<i>i.e.</i>, execution times) on heterogeneous machines. A mapping method is required to match arriving tasks with machines based on both machine availability and performance to maximize the number of tasks meeting their deadlines (known as robustness). In particular, for tasks with hard individual deadlines (<i> e.g.</i>, live video streaming tasks), those that have missed their deadlines are dropped, as there is no value in executing them. The problem investigated in this research is how to maximize robustness of an HC system, specifically, when it is oversubscribed. The proposal is to prune (<i>i.e.</i>, defer or drop) tasks with low probability of meeting their deadlines. Pruning low-chance tasks increases the probability of other tasks meeting their deadlines. To that end, first a model is provided to estimate the probability of meeting deadline for each task in the presence of task dropping. Second, a pruning mechanism is proposed to predictively defer or drop tasks in an effort to maximize the overall robustness of the HC system. Third, a mapping method is proposed that functions based on the pruning mechanism and improves robustness of the HC system. Fourth, to show a broad application, the pruning mechanism is applied to other mapping heuristics. Fifth, further development of the pruning mechanism is made from multiple fronts to improve robustness, engender fairness amongst completed task types, and examine the cost ramifications of using a pruning mechanism. Simulation results, harnessing a selection of mapping heuristics, show the efficacy of the proposed pruning mechanism can improve robustness of some oversubscribed HC system by more than 40%.</p><p>

<p> The global communication infrastructure of the Internet is formed by tens of thousands of Autonomous Systems connecting various organizations and individuals together. Having a global topology map of the Internet allows network researchers to understand the dynamics of the Internet in practice; guides network operators to enhance the reliability and security of their networks; allows network engineers to improve the efficiency of their systems; and helps developers to develop topology aware applications, among others. </p><p> In this dissertation, we study the implications of the Internet&rsquo;s topological structure for its efficiency, security, and reliability. First, we developed a new mapping paradigm for the Internet&rsquo;s topological structure: Cross-AS (X-AS) Internet topology mapping. Second, we developed a metric to identify the criticality of the autonomous systems in the Internet under targeted attacks. Next, we introduced a probabilistic packet marking defense framework against DoS attacks and the variants. Finally, we investigate the geographical properties of Internet routing.</p><p>

<p> The main purpose of this research is to discuss scenarios when some common dynamic changes happen to Wireless Sensor Networks/Autonomous Networked Robots, what the negative effect will be, along with our proposed strategies to keep networks resilient to such influence because communication between sensors/robots is fundamental to cooperation, hence the central role of the network. The first part of this dissertation considers scenarios where dynamic changes happen to static wireless sensor network, causing sensors in some sub-areas to not function anymore. Our work explores two resilient routing strategies to maintain communication links between any two sensors under such situations. Further, the second part of this dissertation brings mobility into wireless sensor networks. Specifically, we consider a more complex scenario where a group of Autonomous Networked Robots are given orders to march from a current field of interest to new one. And our work explores a resilient redeployment strategy that tries to keeps original communication links as many as possible. The dynamic changes and network models in this research are very common in reality; therefore, this research has much practical significance. </p><p>

<p> This paper describes the effect of failures on various video QoS metrics like delay, packet loss, and recovery time. SDN network has been used to guarantee reliability and efficient data transmission. There are many failures that can occur within the SDN mesh network or between the non-SDN and the SDN network. There is a need for both reliable and low-latency transmission of live video streams, especially in situations such as public safety or public gathering events. This is because everyone is trying to use the limited network at the same time. That leads to oversubscription and network outages, and computing devices may fail. Existing mechanisms built into TCP/IP and video streaming protocols, and fault tolerance strategies (such as buffering), are inadequate due to low latency and reliability requirements for live streaming, especially in the presence of limited bandwidth and computational power of mobile or edge devices. The objective of this paper is to develop an efficient fault tolerant strategy at the source-side to produce a high-quality video with low latency and data loss. To recover the lost data during failures, buffering approach is used to store chunks in a buffer and retransmit the lost frames, requested by the receiver.</p><p>

<p> As on-chip interconnection network scales to integrate more processing elements, physical limitations have threatened the scalibility and performance of many-core systems. Currently, Networks-on-Chip have replaced the bus and crossbar methods and been the prevalent many-core architecture because of the flexible scalibility and low cost. In NoCs with ever-growing core count, requests from distant cores generate long range traffic, and the long range traffic has jeopardized the system performance in the format of increasing the end-to-end latency significantly. Though researchers have discovered that almost of the traffic is from nearby nodes, the small portion of the communication between distant nodes consumes most of the network bandwidth. In order to facilitate the NoC communication efficiency, we propose a hierarchical mesh NoC with multiple mesh layers added on a regular 2D mesh base. Deterministic hierarchical routing is implemented to generate shorter routing paths for long range traffic. However, the proposed approaches create a congestion challenge because of uneven traffic distribution among levels. We further introduce a dynamic management scheme to leverage the hierarchy more efficiently. The proposed NoC and management approaches are simulated with Garnet simulator. The results show that our design can produce lower average network latency and higher throughput that translates to faster communication processing. </p><p>

<p> The application of mobile robots has been increased in recent years to include search-and-rescue where a set of robots sweep an area searching for an item of interest, patrolling where a set of robots patrol a fence to protect a region, and pattern formation where the robots form a given pattern. Cooperative mobile robots are autonomous entities that are able to self-coordinate their actions in order to solve a global task, such as emergency response, in distributed systems. In order to achieve the desired cooperation, mobile robots are required to be synchronized. Existing synchronization algorithms need external information from an outside source, depend on a reliable network where messages cannot be lost or corrupted, or require a fixed number of mobile robots during the execution. These are disadvantages in practical applications because messages can simply be lost due to noise or interference in the communication channel. Moreover, the number of mobile robots may vary due to unforeseen incidents such as hardware or software malfunctions. </p><p> In order to address the aforementioned problems, a synchronization algorithm with failure detection has been proposed, implemented, and verified. The proposed algorithm guarantees when all robots start their current assigned task within a bounded time, then the time interval in which they will start the next given task will be bounded as well. The simulation results show that the robots are still able to start the given task in the next round synchronously if the number of consecutive lost messages is less than four. </p><p> The proposed model was developed using the SPIN model checker. The safety and liveness properties were defined using the Linear Time Logic (LTL) in order to verify its functionality under error-prone conditions. It was shown that the proposed algorithm gave the correct results.</p><p>

<p> A CrazyRadio is a 2.4GHZ usb bluetooth dongle and a Crazyflie is a programmable quadrotor used by researchers in the field of distributed computing. A Crazyflie is controlled remotely from a computer or a smartphone through a Crazyradio. However the communication protocol on the CrazyRadio can communicate only with one Crazyflie after pairing, therefore implementing a swarm requires many changes which are prone to failures. This thesis proposes a communication protocol for distributed and highly dynamic systems. The proposed protocol is a combination of two communication protocols: Slotted-Aloha and time division multiple access (TDMA).The implementation of the proposed protocol is done on Crazyradios and Crazyflies. With the proposed protocol a Crazyradio communicates with multiple Crazyradios and Crazyflies. Communication between Crazyradios facilitates realtime data transfer between any type of bots connected to these Crazyradios, adding towards the implementation of swarms of robots. </p><p>

Since 2008, the Android ecosystem has been tremendously popular with consumers, developers, and manufacturers due to the open nature of the operating system and its compatibility and availability on a range of devices. This, however, comes at a cost. The variety of available devices and speed of evolution of the Android system itself adds layers of fragmentation to the ecosystem around which developers must navigate. Yet this phenomenon is not unique to the Android ecosystem, impacting desktop applications like Apache Tomcat and Google Chrome as well. As fragmentation of a system grows, so does the burden on developers to produce software than can execute on a wide variety of potential device, environment, and system combinations, while the reality prevents developers from anticipating every possible scenarios. This study provides the first empirical study characterizing portability bugs in both desktop and Android applications. Specifically, we examined 228 randomly selected bugs from 18 desktop and Android applications for the common root causes, manifestation patterns, and fix strategies used to combat portability bugs. Our study reveals several commonalities among the bugs and platforms, which include: (1) 92.14% of all bugs examined are caused by an interaction with a single dependency, (2) 53.13% of all bugs examined are caused by an interaction with the system, and (3) 33.19% of all bugs examined are fixed by adding a direct or indirect check against the dependency causing the bug. These results provide guidance for techniques and strategies to help developers and researchers identify and fix portability bugs. / A Thesis submitted to the Department of Computer Science in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester 2018. / July 20, 2018. / characteristic study, portability bugs / Includes bibliographical references. / Adrian Nistor, Professor Directing Thesis; Sonia Haiduc, Committee Member; David Whalley, Committee Member.

Conditional branches have traditionally been a performance bottleneck for most processors. The high frequency of branches in code coupled with expensive pipeline flushes on mispredictions make branches expensive instructions worth optimizing. Conditional branches have historically inhibited compilers from applying optimizations across basic block boundaries due to the forks in control flow that they introduce. This thesis describes a systematic way of generating paths (traces) of branch-free code at compile time by decomposing branching and verification operations to eliminate the dependence of a branch on its preceding compare instruction. This explicit decomposition allows us to move comparison instructions past branches and to merge pre and post branch code. These paths generated at compile time can potentially provide additional opportunities for conventional optimizations such as common subexpression elimination, dead assignment elimination and instruction selection. Moreover, this thesis describes a way of coalescing multiple branch instructions within innermost loops to produce longer basic blocks to provide additional optimization opportunities. / A Thesis submitted to the Department of Computer Science in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester 2018. / July 20, 2018. / Includes bibliographical references. / David Whalley, Professor Directing Thesis; Xin Yuan, Committee Member; Weikuan Yu, Committee Member.

DAGDA exposes some of the hidden operations that the hardware uses when performing loads and stores to the compiler to save energy and increase performance. We decouple the micro-operations for loads and stores into two operations: the first, the "prepare to access memory" instruction, or "pam", checks to see if a line is resident in the L1 DC and determines its way in the L1 DC data array, if it exists. The second operations performs the actual data access. This allows us to both save energy using compiler optimization techniques and improve performance because "pam" operations are a natural way of prefetching data into the L1 DC / A Thesis submitted to the Department of Computer Science in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester 2018. / May 4, 2018. / Includes bibliographical references. / David B. Whalley, Professor Directing Thesis; Xiuwen Liu, Committee Member; Gary Tyson, Committee Member.