On Channel Failures, File Fragmentation Policies, and Heavy-Tailed Completion Times

It has been recently discovered that heavy-tailed completion times can result from protocol interaction even when file sizes are light-tailed. A key to this phenomenon is the use of a restart policy where if the file is interrupted before it is completed, it needs to restart from the beginning. In this paper, we show that fragmenting a file into pieces whose sizes are either bounded or independently chosen after each interruption guarantees light-tailed completion time as long as the file size is light-tailed; i.e., in this case, heavy-tailed completion time can only originate from heavy-tailed file sizes. If the file size is heavy-tailed, then the completion time is necessarily heavy-tailed. For this case, we show that when the file size distribution is regularly varying, then under independent or bounded fragmentation, the completion time tail distribution function is asymptotically bounded above by that of the original file size stretched by a constant factor. We then prove that if the distribution of times between interruptions has nondecreasing failure rate, the expected completion time is minimized by dividing the file into equal-sized fragments; this optimal fragment size is unique but depends on the file size. We also present a simple blind fragmentation policy where the fragment sizes are constant and independent of the file size and prove that it is asymptotically optimal. Both these policies are also shown to have desirable completion time tail behavior. Finally, we bound the error in expected completion time due to error in modeling of the failure process

Heavy Tails and Instabilities in Large-Scale Systems with Failures

Modern engineering systems, e.g., wireless communication networks, distributed computing systems, etc., are characterized by high variability and susceptibility to failures. Failure recovery is required to guarantee the successful operation of these systems. One straight- forward and widely used mechanism is to restart the interrupted jobs from the beginning after a failure occurs. In network design, retransmissions are the primary building blocks of the network architecture that guarantee data delivery in the presence of channel failures. Retransmissions have recently been identified as a new origin of power laws in modern information networks. In particular, it was discovered that retransmissions give rise to long tails (delays) and possibly zero throughput. To this end, we investigate the impact of the ‘retransmission phenomenon’ on the performance of failure prone systems and propose adaptive solutions to address emerging instabilities. The preceding finding of power law phenomena due to retransmissions holds under the assumption that data sizes have infinite support. In practice, however, data sizes are upper bounded 0 ≤ L ≤ b, e.g., WaveLAN’s maximum transfer unit is 1500 bytes, YouTube videos are of limited duration, e-mail attachments cannot exceed 10MB, etc. To this end, we first provide a uniform characterization of the entire body of the distribution of the number of retransmissions, which can be represented as a product of a power law and the Gamma distribution. This rigorous approximation clearly demonstrates the transition from power law distributions in the main body to exponential tails. Furthermore, the results highlight the importance of wisely determining the size of data fragments in order to accommodate the performance needs in these systems as well as provide the appropriate tools for this fragmentation. Second, we extend the analysis to the practically important case of correlated channels using modulated processes, e.g., Markov modulated, to capture the underlying dependencies. Our study shows that the tails of the retransmission and delay distributions are asymptotically insensitive to the channel correlations and are determined by the state that generates the lightest tail in the independent channel case. This insight is beneficial both for capacity planning and channel modeling since the independent model is sufficient and the correlation details do not matter. However, the preceding finding may be overly optimistic when the best state is atypical, since the effects of ‘bad’ states may still downgrade the performance. Third, we examine the effects of scheduling policies in queueing systems with failures and restarts. Fair sharing, e.g., processor sharing (PS), is a widely accepted approach to resource allocation among multiple users. We revisit the well-studied M/G/1 PS queue with a new focus on server failures and restarts. Interestingly, we discover a new phenomenon showing that PS-based scheduling induces complete instability in the presence of retransmissions, regardless of how low the traffic load may be. This novel phenomenon occurs even when the job sizes are bounded/fragmented, e.g., deterministic. This work demonstrates that scheduling one job at a time, such as first-come-first-serve, achieves a larger stability region and should be preferred in these systems. Last, we delve into the area of distributed computing and study the effects of commonly used mechanisms, i.e., restarts, fragmentation, replication, especially in cloud computing services. We evaluate the efficiency of these techniques under different assumptions on the data streams and discuss the corresponding optimization problem. These findings are useful for optimal resource allocation and fault tolerance in rapidly developing computing networks. In addition to networking and distributed computing systems, the aforementioned results improve our understanding of failure recovery management in large manufacturing and service systems, e.g., call centers. Scalable solutions to this problem increase in significance as these systems continuously grow in scale and complexity. The new phenomena and the techniques developed herein provide new insights in the areas of parallel computing, probability and statistics, as well as financial engineering

Dynamic Spectrum Reservation for CR Networks in the Presence of Channel Failures: Channel Allocation and Reliability Analysis

(c) 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this[EN] Providing channel access opportunities for new service requests and guaranteeing continuous connections for ongoing flows until service completion are two challenges for service provisioning in wireless networks. Channel failures, which are typically caused by hardware and software failures or/and by intrinsic instability in radio transmissions, can easily result in network performance degradation. In cognitive radio networks (CRNs), secondary transmissions are inherently vulnerable to connection breaks due to licensed users' arrivals as well as channel failures. To explore the advantages of channel reservation on performance improvement in error-prone channels, we propose and analyze a dynamic channel reservation (DCR) algorithm and a dynamic spectrum access (DSA) scheme with three access privilege variations. The key idea of the DCR algorithm is to reserve a dynamically adjustable number of channels for the interrupted services to maintain service retainability for ongoing users or to enhance channel availability for new users. Furthermore, the DCR algorithm is embedded in the DSA scheme enabling spectrum access of primary and secondary users with different access privileges based on access flexibility for licensed shared access. The performance of such a CRN in the presence of homogeneous and heterogeneous channel failures is investigated considering different channel failure and repair rates.The work of V. Pla was supported by the Spanish Ministry of Economy, Industry and Competitiveness under Grant TIN2013-47272-C2-1-R.Balapuwaduge, IAM.; Li, F.; Pla, V. (2018). Dynamic Spectrum Reservation for CR Networks in the Presence of Channel Failures: Channel Allocation and Reliability Analysis. IEEE Transactions on Wireless Communications. 17(2):882-898. https://doi.org/10.1109/TWC.2017.2772240S88289817

Modular software architecture for flexible reservation mechanisms on heterogeneous resources

Management, allocation and scheduling of heterogeneous resources for complex distributed real-time applications is a chal- lenging problem. Timing constraints of applications may be fulfilled by a proper use of real-time scheduling policies, admission control and enforcement of timing constraints. However, it is not easy to design basic infrastructure services that allow for an easy access to the allocation of multiple heterogeneous resources in a distributed environment. In this paper, we present a middleware for providing distributed soft real-time applications with a uniform API for reserving heterogeneous resources with real-time scheduling capabilities in a distributed environment. The architecture relies on standard POSIX OS facilities, such as time management and standard TCP/IP networking services, and it is designed around CORBA, in order to facilitate modularity, flexibility and portability of the applications using it. However, real-time scheduling is supported by proper extensions at the kernel-level, plugged within the framework by means of dedicated resource managers. Our current implementation on Linux supports reservation of CPU, disk and network bandwidth. However, additional resource managers supporting alternative real-time schedulers for these resources, as well as additional types of resources, may be easily added. We present experimental results gathered on both synthetic applications and a real multimedia video streaming case study, showing advantages deriving from the use of the proposed middleware. Finally, overhead figures are reported, showing sustainability of the approach for a wide class of complex, distributed, soft real-time applications

Teleoperation of passivity-based model reference robust control over the internet

This dissertation offers a survey of a known theoretical approach and novel experimental results in establishing a live communication medium through the internet to host a virtual communication environment for use in Passivity-Based Model Reference Robust Control systems with delays. The controller which is used as a carrier to support a robust communication between input-to-state stability is designed as a control strategy that passively compensates for position errors that arise during contact tasks and strives to achieve delay-independent stability for controlling of aircrafts or other mobile objects. Furthermore the controller is used for nonlinear systems, coordination of multiple agents, bilateral teleoperation, and collision avoidance thus maintaining a communication link with an upper bound of constant delay is crucial for robustness and stability of the overall system. For utilizing such framework an elucidation can be formulated by preparing site survey for analyzing not only the geographical distances separating the nodes in which the teleoperation will occur but also the communication parameters that define the virtual topography that the data will travel through. This survey will first define the feasibility of the overall operation since the teleoperation will be used to sustain a delay based controller over the internet thus obtaining a hypothetical upper bound for the delay via site survey is crucial not only for the communication system but also the delay is required for the design of the passivity-based model reference robust control. Following delay calculation and measurement via site survey, bandwidth tests for unidirectional and bidirectional communication is inspected to ensure that the speed is viable to maintain a real-time connection. Furthermore from obtaining the results it becomes crucial to measure the consistency of the delay throughout a sampled period to guarantee that the upper bound is not breached at any point within the communication to jeopardize the robustness of the controller. Following delay analysis a geographical and topological overview of the communication is also briefly examined via a trace-route to understand the underlying nodes and their contribution to the delay and round-trip consistency. To accommodate the communication channel for the controller the input and output data from both nodes need to be encapsulated within a transmission control protocol via a multithreaded design of a robust program within the C language. The program will construct a multithreaded client-server relationship in which the control data is transmitted. For added stability and higher level of security the channel is then encapsulated via an internet protocol security by utilizing a protocol suite for protecting the communication by authentication and encrypting each packet of the session using negotiation of cryptographic keys during each session

Flood risk perception near intermediate-sized Kansas dams

Doctor of PhilosophyDepartment of GeographyLisa M HarringtonKansas ranks second in the largest number of dams in the United States, behind Texas (FEMA 2015). In 2020, Kansas dams reached an average age of 52 years, with many exceeding their designed life expectancy or in need of rehabilitation. Climate change and increased urbanization projections suggest more frequent and extreme flooding in the future, requiring greater demands on current infrastructure (O’Neill et al., 2016). Researchers have explored the physical side of flood risk management to a considerable extent. Still, relatively little is known about how flood risk perception varies in areas associated with at-risk dams. Local populations near intermediate-sized dams are less likely to receive attention due to their size and remoteness but are often more susceptible to failures because of dam construction type and design, lack of knowledge or awareness of dam and reservoir conditions, and irregular maintenance. Dam selection was based on the size and age of the structure, primary purpose, and location. Specifically, dams had to be at least 50 years in age, intended mainly for flood control, and likely to experience increased frequency and more intense 24-hour rainfall totals in the future. Understanding risk perceptions now will help prepare decision-makers for communicating with residents and dealing with disaster situations in the near future. A sequential mixed methods design was applied, whereby quantitative and qualitative approaches were used successively to gain in-depth individual perspectives from selected residents and insights from water resource experts on flood risk perception near at-risk dams. The combination of individual risk evaluations and in-depth personal insights provided by this mixed methodology not only provides basic information about the status of thinking about potential dam hazards, but also may be useful for developing strategies that address risk for people living near intermediate-sized dams. Questionnaires were mailed to 1,100 randomly sampled households near ten selected dam sites in eastern Kansas Purposefully selected interviews were conducted with dam safety and water resource experts associated with the selected dams. Closed-ended data provided through questionnaire responses were analyzed through correlation and contingency analyses to explore statistical significance. Qualitative thematic analysis of interviews and open-ended responses provided depth to the close-ended material, in addition to providing another perspective of flood risk perception near aging dams from dam safety and water resource experts. The quantitative results suggested that flood risk perception was higher among residents located within flood zones, but respondents generally were not concerned with the efficacy of aging dams in their locales. The qualitative results identified and explained variations in outcomes for flood experiences, expectations of the dam in its current state and in the event of a dam failure, flood vulnerability, and risk communication. They provide insight on concerns related to dam management, recent flood events, and of how perception relates to physical risk based on location. A significant concern was the lack of accessible and accurate data for intermediate-sized dams that would contribute to local knowledge on flood risk and improved emergency preparedness for high-risk dams. Intensification of education about dams and flood risk awareness near intermediate-sized dams in Kansas appears to be needed, based on this research. It is likely that such needs also are present in other states. Follow-up research should be conducted to determine the statewide perception of aging dams and their potential to exacerbate flood risks in additional areas. Similar studies should be pursued elsewhere

Archaeological Investigations at Four San Antonio Missions: Mission Trails Underground Conversion Project

This report contains the results of archaeological work performed by the Center for Archaeological Research (CAR) at The University of Texas San Antonio (UTSA) for City Public Service (CPS). The archaeological investigation and monitoring for the Mission Trails Underground Conversion Project was carried out under Texas Historical Commission (THC) Permit Number: 2020, and the work was conducted at each of the four historical San Antonio missions which make up San Antonio Missions National Historical Park. The Mission Trails Underground Conversion Project was created to enhance and upgrade electrical and utility connections by replacing aboveground connections with underground connections at each ofthe four missions. Mission San Juan (41BX5)-In October of 1998, personnel from CAR began archaeological investigations at Mission San Juan Capistrano in advance of the proposed installation of underground utility lines for the Mission Trails Underground Conversion Project. The purpose of the investigation was to test for intact, buried cultural features in advance of trenching activities involved in the relocation of utility lines and connections. CAR archaeologists developed a plan regarding the area to be impacted which included ten 1 x 1-m excavations units and a series of twelve shovel tests along the proposed path of the utility trench. Excavation units uncovered evidence of existing buildings, wall foundations and Colonial-period flooring episodes, revealing new data west of the known structures and not previously accounted for. Further excavations are warranted to determine the nature of features such as a Colonial-period wall revealed near one of the excavation units. This material discovered by the archaeological investigations resulted in the altering of the projected utility trench alignment to avoid disturbing deposits. Further archaeological investigations are recommended for the newly revealed features. Mission San Jose (41BX3)- In January of 1999, personnel from CAR began archaeological investigations at Mission San Jose y San Miguel de Aguayo in advance of the proposed installation of underground utility lines for the Mission Trails Underground Conversion Project. The purpose of the investigation was to test for intact, buried cultural features in advance of trenching activities involved in the relocation of utility lines and connections. CAR archaeologists conducted a series of shovel tests along the center-lines of the proposed utility trenches to identifY areas of possible impact to intact Spanish Colonial cultural materials. In addition to shovel testing, monitoring of the trenching was conducted in areas where the possibility of impacting cultural material was high. An early-twentieth century trash midden was encountered during monitoring of the trench where it paralleled the Service Drive in the northwest comer of the Mission compound. This material did not warrant altering the course of the trench, and no further archaeological work is recommended at this time. Mission Concepcion (41BX12)- In January of 1999, personnel from CAR began archaeological investigations at Mission Nuestra Senora de la Purisima Concepcion as part of the Mission Trails Underground Conversion Project. A construction crew, while excavating a manhole designed to provide access to underground electrical utilities, had unearthed a large number of animal bones. After concluding a large feature had been unexpectedly impacted, CAR conducted test excavations to ascertain the nature of this feature. It was determined to be a section of an acequia which had been refilled during the Colonial period with construction debris and trash, including a large number of animal bones. Test units and the original manhole excavations allowed for a profile of the acequia to be constructed. This information combined with previous archaeological work and historical research, allowed a tentative proposal on the sequence of acequia construction and re-routing for the Concepcion mission. Monitoring of other underground work conducted in the area resulted in the discovery of a location of a Colonial-period wall, southeast of the Visitors\u27 Center, which may be a portion of the original south wall of the mission. It is recommended that if any further work is required, consideration should be given to testing and/or monitoring to reduce the risk of negative impact to historic remains. Mission Espada (41BX4)- In July of 1999, personnel from CAR began archaeological investigations at Mission San Francisco de la Espada in advance of the proposed installation of underground utility lines for the Mission Trails Underground Conversion Project. From initial discussions, it was noted that the proximity of the proposed route of the underground utility trench could have an impact on the old compound walls of the mission and the path was altered to avoid any possible impact. A series of thirteen shovel tests were conducted in advance along the altered path of the proposed utility trench as it progressed from the southwest comer of the mission compound across the dry irrigation ditch or acequia to the northwest. Monitoring of the trenching activities followed with no significant deposits being exposed. No further work is recommended within the project area, but if future construction is to occur in the area between the utility trench and the Church at Mission Espada, monitoring should then be considered

Great Plains Research, Volume 22, Number 2, Fall 2012 (complete issue)

Reconsidering National Park Interpretation of the Great Plains and TransMississippi West • Robert Pahre Evaluating the Role of Latinidad and the Latino Threat in the State of Missouri • Joel Jennings and J.S. Onesimo Sandoval The Right Call: Baseball Coaches\u27 Attempts to Influence Umpires • Kevin Warneke and Dave Ogden Documenting Change at Upper Hamburg Bend: Nebraska\u27s First SideChannel Restoration • Brandon L. Eder and Gerald E. Mestl Initial Changes in Species Cover Following Savanna Restoration Treatments in Western Iowa • David A. McKenzie, Thomas B. Bragg, and David M. Sutherland Monitoring Standing Herbage of the Sands and Choppy Sands Ecological Vegetation Types in the Nebraska Sandhills • Daniel W. Uresk Review of Conspecific Attraction and Area Sensitivity of Grassland Birds • David R. W. Bruinsma and Nicola Koper New Distributional Records of Great Plains Pseudoscorpions (Arachnida: Pseudoscorpiones) • Paul O. Cooney and James A. Kalisch REVIEW ESSAY: An Atlas to Be Read from Cover to Cover • A review of Atlas of the Great Plains • Harm J. de Blij BOOK REVIEWS Hockensmith, John S. • Spanish Mustangs in the Great American West: Return of the Horse • Reviewed by Karen Dalke Brown, Mary Bomberger, Stephen J. Dinsmore, and Charles R. Brown • Birds of Southwestern Nebraska: An Annotated Check-List of Species in the North and South Platte River Valleys and at Lake McConaughy • Reviewed by Wayne J. Mollhoff Adelman, Charlotte, and Bernard L. Schwartz • The Midwestern Native Garden: Native Alternatives to Nonnative Flowers and Plants, An Illustrated Guide • Reviewed by Stephen L. Young Marchildon, Gregory P., ed. • Agricultural History: History of the Prairie West Series, Volume 3 • Reviewed by Bradford Rennie Freeman, David M.; Foreword by Robert Ward • Implementing the Endangered Species Act on the Platte Basin Water Commons • Reviewed by Mary Bomberger Brown Bower, Shannon Stunden; Foreword by Graeme Wynn • Wet Prairie: People, Land, and Water in Agricultural Manitoba • Reviewed by Sterling Evans Waters, Michael R., Charlotte D. Pevny, David L. Carlson, et al.; Foreword by Michael B. Collins • Clovis Lithic Technology: Investigation of a Stratified Workshop at the Gault Site, Texas • Reviewed by Heather M. Rockwell. Arnn, John Wesley, III; Foreword by Tom D. Dillehay • Land of the Tejas: Native American Identity and Interaction in Texas, A.D. 1300 to 1700 • Reviewed by Robert Cast Clark, Bonnie J. • On the Edge of Purgatory: An Archaeology of Place in Hispanic Colorado • Reviewed by Jason M. LaBelle Barker, Joanne • Native Acts: Law, Recognition, and Cultural Authenticity • Reviewed by Jo Carrillo Regan, Paulette • Unsettling the Settler Within: Indian Residential Schools, Truth Telling, and Reconciliation in Canada • Reviewed by Robyn Green Prussing, Erica • White Man\u27s Water: The Politics of Sobriety in a Native American Community • Reviewed by Paul Spicer Lehr, John, and David McDowell • Trailblazers: The Lives and Times of Michael Ewanchuk and Muriel (Smith) Ewanchuk • Reviewed by Denis Hlynka Pachirat, Timothy • Every Twelve Seconds: Industrialized Slaughter and the Politics of Sight •Reviewed by Donald D. Stull. Pawley, Howard; Foreword by Paul Moist • Keep True: A Life in Politics • Reviewed by Kelly Saunders Sinner, George A Bud, and Bob Jansen; Foreword by Clay S. Jenkinson • Turning Points: A Memoir • Reviewed by Stephen W. King Daum, Courtenay W., Robert J. Duffy, and John A Straayer, eds. • State of Change: Colorado Politics in the Twenty-First Century • Reviewed by Robert R. Preuhs Hiler, Edward A, and Steven L. Bosserman • Together We Can: Pathways to Collective Leadership in Agriculture at Texas A&M • Reviewed by Theodore R. Alter NEWS AND NOTES ANNUAL INDE