We present a Markov chain analysis for studying the performance of wireless ad hoc networks. The models presented in this dissertation support an arbitrary backoff strategy. We found that the most important parameter affecting the performance of binary exponential backoff is the initial backoff window size. Our experimental results show that the probability of collision can be reduced when the initial backoff window size equals the number of terminals. Thus, the throughput of the system increases and, at the same time, the delay to transmit the frame is reduced. In our second contribution, we present a new analytical model of a Medium Access Control (MAC) layer for wireless ad hoc networks that takes into account frame retry limits for a four-way handshaking mechanism. This model offers flexibility to address some design issues such as the effects of traffic parameters as well as possible improvements for wireless ad hoc networks. It effectively captures important network performance characteristics such as throughput, channel utilization, delay, and average energy. Under this analytical framework, we evaluate the effect of the Request-to-Send (RTS) state on unsuccessful transmission probability and its effect on performance particularly when the hidden terminal problem is dominant, the traffic is heavy, or the data frame length is very large. By using our proposed model, we show that the probability of collision can be reduced when using a Request-to-Send/Clear- to-Send (RTS/CTS) mechanism. Thus, the throughput increases and, at the same time, the delay and the average energy to transmit the frame decrease. In our third contribution, we present a new analytical model of a MAC layer for wireless ad hoc networks that takes into account channel bit errors and frame retry limits for a two-way handshaking mechanism. This model offers flexibility to address design issues such as the effects of traffic parameters and possible improvements for wireless ad hoc networks. We illustrate that an important parameter affecting the performance of binary exponential backoff is the initial backoff window size. We show that for a low bit error rate (BER) the throughput increases and, at the same time, the delay and the average energy to transmit the frame decrease. Results show also that the negative acknowledgment-based (NAK-based) model proves more useful for a high BER. In our fourth contribution, we present a new analytical model of a MAC layer for wireless ad hoc networks that takes into account Quality of Service (QoS) of the MAC layer for a two-way handshaking mechanism. The model includes a high priority traffic class (class 1) and a low priority traffic class (class 2). Extension of the model to more QoS levels is easily accomplished. We illustrate an important parameter affecting the performance of an Arbitration InterFrame Space (AIFS) and small backoff window size limits. They cause the frame to start contending the channel earlier and to complete the backoff sooner. As a result, the probability of sending the frame increases. Under this analytical framework, we evaluate the effect of QoS on successful transmission probability and its effect on performance, particularly when high priority traffic is dominant. / Graduate

Thesis (M.S.)--Rochester Institute of Technology, 1996. / Typescript. Includes bibliographical references (leaves 76-78).

Made available in DSpace on 2016-08-29T14:10:23Z (GMT). No. of bitstreams: 1 tese_5432_.pdf: 752174 bytes, checksum: 03afdce6fbb1658043bf26e530b8e5b1 (MD5) Previous issue date: 2012-03-23 / As pesquisas no âmbito da adoção vêm chamando cada vez mais a atenção de pesquisadores, propiciando maior visibilidade a esta temática. Apesar dos avanços, permanecem muitas lacunas a serem preenchidas, principalmente com relação às dinâmicas, estratégias de interação e adaptação que podem propiciar um ambiente familiar saudável. Tendo como base a Teoria bioecológica do desenvolvimento, o objetivo geral da dissertação foi estudar os processos proximais e os aspectos macrossistêmicos de famílias adotivas em período de convivência, através de um estudo de casos múltiplos - um caso nacional e outro internacional. Utilizou-se a metodologia da Inserção Ecológica com entrevistas, observações, visitas às famílias (no Brasil e no país de acolhida), escola e instituições de acolhimento, realizados em cerca de quatro meses. A dissertação está dividida em dois estudos. O primeiro estudo investigou os aspectos macrossistêmicos em processos de adoção. Os dados foram organizados em eixos temáticos pré-estabelecidos: significados, motivação, e processo de habilitação na adoção. Nos dois casos a adoção era percebida como uma ação voltada para o bem da criança. A motivação no caso nacional estava ligada ao conhecimento anterior das adotadas e no internacional a problemas de infertilidade. Foi necessário um maior tempo e mais documentos para habilitação na adoção internacional, além de uma maior preparação do que na nacional. Já o segundo estudo investigou os contextos e os processos proximais vivenciados pelas famílias participantes. Os dados foram organizados baseados no modelo PPCT, proposto pela Teoria bioecológica. Na adoção nacional os processos proximais foram facilitados pelo conhecimento anterior da criança/adolescente, e na internacional pela percepção do engajamento das crianças na adoção. Os processos disfuncionais no caso nacional estavam ligados a mudança de comportamento da criança mais nova, enquanto no internacional ao fato do casal italiano estar em um ambiente desconhecido. Conclui-se que os processos de adoção envolvem uma complexa inter-relação entre vários contextos e que as questões tanto macrossistêmicas, como os valores, crenças, leis, etc., quanto dos microssistemas, como a família, comunidade e interações pessoais, têm um papel importante nas crenças e práticas concernentes à adoção, o que torna o período de convivência essencial para a construção dos relacionamentos, bem como para que se propicie a criação de estratégias de interação visando uma boa adaptação familiar.

Corporate informatics has undergone a number of changes in past few years. Used devices are becoming more independent from the OS, they rely more on provided services and the level of security. Cloud technologies are increasingly growing in significance and a large number of companies offer their employees BYOD (Bring Your Own Device). This thesis focuses on integration of Apple Mac computers into corporate environments, based on analysis of contemporary approaches and possibilities of dealing with integration. An important part of this thesis is research of chosen implemented solutions in the Czech republic. From both parts of this thesis it then offers recommendations, which are based on practical experience of companies that widely use and deal with integration of Mac computers.

Recently, the wide range of communication applications has greatly increased the number of connected devices, and this trend continues by emerging new technologies such as Internet-of-Things (IoT) and vehicular ad hoc networks (VANETs). The increase in the number of devices may sooner or later cause wireless spectrum shortage. Furthermore, with the limited wireless spectrum, transmission efficiency degrades when the network faces a super-dense situation. In IEEE 802.11ah-based networks whose channel access protocol is basically a contention-based one, the protocol loses its efficiency when the total number of contending users grows. VANETs suffer from the same problem, where broadcasting and receiving safety messages, i.e., beacons, are critical. An inefficient medium access control (MAC) can negatively impact the network's reliability. Effective resource management solutions are needed to improve the network's reliability and scalability considering the features of different types of networks. In this work, we address the resource management problem in dense wireless networks in vehicle-to-everything (V2X) systems and IoT networks. For IoT networks, e.g., sensor networks, in which the network topology is quite stable, the grouping technique is exploited to make the stations (STAs) compete in a group to mitigate the contention and improve the channel access quality. While, in VANETs, devices are mobile and the network topology changes over time. In VANETs, beacons should be broadcast periodically by each vehicle reliably to improve road safety. Therefore, how to share the wireless resources to ensure reliability and scalability for these dense static and mobile wireless networks is still a difficult and open problem. In static IoT networks, we apply the Max-Min fairness criterion to the STAs' throughput to group the STAs to ensure network performance and fairness. Formulation of the problem results in a non-convex integer programming optimization problem which avoids hidden terminals opportunistically. As solving the optimization problem has a high time complexity, the Ant Colony Optimization (ACO) method is applied to the problem to find the sub-optimal solution. To support reliable and efficient broadcasting in VANET, wireless resources are divided into basic resource units in the time and frequency domains, and a distributed and adaptive reservation-based MAC protocol (DARP) is proposed. For decentralized control in VANETs, each vehicle's channel access is coordinated with its neighbors to solve the hidden terminal problem. To ensure the reliability of beacon broadcasting, different kinds of preambles are applied in DARP to support distributed reservation, detect beacon collisions, and resolve the collisions. Once a vehicle reserves a resource unit successfully, it will not release it until a collision occurs due to topology change. Protocol parameters, including transmission power and time slots duration, can be adjusted to reduce collision probability and enhance reliability and scalability. Simulation of urban mobility (SUMO) is used to generated two different city traces to assess the DARP's performance. Then, a distributed network coding-based MAC protocol (NC-MAC) is proposed to support reliable single-hop vehicle-to-vehicle (V2V) beacon broadcasting. We combine the preamble-based feedback mechanism, retransmissions, and network coding together to enhance broadcasting reliability. We deploy the preamble mechanism to facilitate the negative acknowledgment (NACK) and retransmission request procedures. Moreover, linear combinations of missed beacons are generated according to the network coding (NC) principles. We also use SUMO to evaluate the NC-MAC's performance in highway and urban scenarios. Group-casting and applying multi-hop communication can ensure reliability in V2X systems. As an extension of the proposed NC-MAC, a distributed grouping and network coding-assisted MAC protocol (GNC-MAC) is proposed to support reliable group-casting and multi-hop communication, which can address blockchain protocols' requirements. We propose a new grouping protocol by combining preamble-based feedback mechanism, multi-hop communication, and network coding to improve group-casting reliability. The preamble mechanism is responsible for reporting a NACK and requesting retransmission due to beacon missing. The missed beacons are combined according to the NC principles and sent on a resource block. / Graduate

The highly regulated maturation of the mammary gland is poorly understood. Our studies were designed to further characterize the role of ovarian hormones, growth hormone (GH)/IGF axis proteins and extracellular matrix (ECM) in the growth and development of prepubertal mammary glands. Prepubertal heifers were injected with either exogenous GH or subjected to ovariectomy (OVX). Mammary parenchyma (PAR) and mammary fat pad (MFP) were harvested for DNA, protein, lipid, and western blot analysis. Remaining tissues were preserved for histological staining or snap frozen for quantitative real-time PCR. We examined 13 genes that work in conjunction with the extracellular matrix to regulate mammary proliferation and morphogenesis. Administration of GH, while impacting composition of MFP, had no effect on expression of the selected genes; there was a decrease in expression of fibronectin in PAR. Ovariectomy had no effect on gene expression in MFP but decreased expression of epimorphin, a potent regulator of morphogenesis, in PAR. In both experiments, the presence of a 55 kDa band corresponding to androgen converting enzyme aromatase was detected but its expression was unaffected. In another study, we used in vitro cell culture to evaluate the role of ECM in mammary gland maturation and employed quantitative real-time PCR to evaluate gene expression profiles of select genes involved in proliferation and differentiation. Expression of Rac1 was decreased in response to bovine insulin (BI) but increased on collagen I (Col). Expression of aldehyde dehydrogenase was decreased in BI and serum on plastic and on Col in the presence of BI. Expression of IGF binding proteins (BP) 3, -4, and -6 were decreased in the presence of serum on laminin (LM). Also, IGF-BP2 expression was decreased on Col while IGF-BP6 was increased on LM with BI. Clusterin, a ubiquitous non-adhesive ECM protein was not affected by ECM substrate but did increase over time. In conclusion, we propose that the mammary gland is not able to respond to GH at this age and that while OVX did effect the expression of some genes, the presence of aromatase maintained local estrogen concentrations. Furthermore, ECM alone is insufficient to regulate mammary gland development and growth. / Ph. D.

The use of collection systems for magnetic sorbents such as Magnetic Activated Carbon are discussed in order to gauge their efficacy in marine environments. Two collectors were built and tested, one which utilized a radial orientation of magnets and another with axially placed magnets. The two systems underwent a series of test with differing linear velocities and angular velocities. From the results, the axial system outperformed its radial counterpart, being most effective with a relatively high concentration of discs placed in series. The medium concentration, however, proved increasingly effective with higher velocities, meaning an optimization concentration exists for this design. The radial system was tested with high and low concentrations of small and large magnets, respectively. The larger magnets, although providing less concentration points in the alternating array, proved more effective for the collection of MAC. From these tests several new innovations were suggested, including belt tensioners, add on mechanisms, and a hybridized design in order to fully optimize the collection of MAC.

As wireless sensor platforms become less expensive and more powerful, the promise of their wide-spread use for everything from health monitoring to military sensing continues to increase. Like other networks, sensor networks are vulnerable to malicious attack; however, the hardware simplicity of these devices makes defense mechanisms designed for traditional networks infeasible. This work explores the denial-of-sleep attack, in which a sensor node's power supply is targeted. Attacks of this type can reduce sensor lifetime from years to days and can have a devastating impact on a sensor network. This work identifies vulnerabilities in state-of-the-art sensor network medium access control (MAC) protocols that leave them susceptible to denial-of-sleep attack. It then classifies these attacks in terms of an attacker's knowledge of the MAC layer protocol and ability to bypass authentication and encryption protocols. Attacks from each category in the classification are modeled to show the impacts on four current sensor network MAC protocols: S-MAC, T-MAC, B-MAC and G-MAC. To validate the effectiveness and analyze the efficiency of the attacks, implementations of selected attacks on S-MAC and T-MAC are described and analyzed in detail. This research goes on to introduce a suite of mechanisms designed to detect and mitigate the effects of denial-of-sleep attacks on sensor networks. The Clustered Anti Sleep-Deprivation for Sensor Networks, or Caisson, suite includes a lightweight, platform-independent anti-replay mechanism, an adaptive rate-limiter and a jamming detection and mitigation mechanism. These tools are designed to be applied selectively or in concert to defend against denial-of-sleep attacks depending on the specific vulnerabilities in the MAC protocol used in a particular sensor network deployment. This work makes two major contributions to state-of-the-art wireless sensor network research. First, it fully explores the denial-of-sleep attack, to include the implementation of a subset of these attacks on actual sensor devices and an analysis of the efficiency of these attacks. Second, it provides a set of tools by which these attacks are detected and defeated in a lightweight, platform-independent, and protocol-independent way. If sensor networks are to live up to current expectations, they must be robust in the face of newly emerging network attacks, to include denial-of-sleep. / Ph. D.

Wireless communications technology ranging from satellite communications to sensor networks has benefited from the development of flexible, SDR platforms. SDR is used for military applications in radio devices to reconfigure waveforms, frequency, and modulation schemes in both software and hardware to improve communication performance in harsh environments. In the commercial sector, SDRs are present in cellular infrastructure, where base stations can reconfigure operating parameters to meet specific cellular coverage goals. In response to these enhancements, industry leaders in cellular (such as Lucent, Nortel, and Motorola) have embraced the cost advantages of implementing SDRs in their cellular technology. In the future, there will be a need for more capable SDR platforms on inexpensive hardware that are able to balance work loads between several computational processing elements while minimizing power cost to accomplish multiple goals. This thesis will present the development of a random access MAC protocol for the IRIS platform. An assessment of different SDR hardware and software platforms is conducted. From this assessment, we present several SDR technology requirements for networking research and discuss the impact of these requirements on future SDR platforms. As a consequence of these requirements, we choose the USRP family of SDR hardware and the IRIS software platform to develop our two random access MAC implementations: Aloha with Explicit ACK and Aloha with Implicit ACK. A point-to-point link was tested with our protocol and then this link was extended to a 3-hop (4 nodes) network. To improve our protocols' efficiency, we implemented carrier sensing on the FPGA of the USRP E100, an embedded SDR hardware platform. We also present simulations using OMNeT++ software to accompany our experimental data, and moreover, show how our protocol scales as more nodes are added to the network. / Master of Science

Cette thèse a pour objectif de proposer de nouvelles approches d'ordonnancement, de coopération et de gestion de la mobilité dans les réseaux sans fil de type IEEE 802.11. Le maintien de la qualité de service (QoS), au niveau MAC, représente la caractéristique fondamentale de ces approches. L'analyse des mécanismes existants nous a conduits à retenir le protocole EDCF, supportant la QoS, comme une base de travail pour l'ensemble de nos propositions. Dans le but de pallier certaines faiblesses du standard 802.11, une nouvelle architecture à base de multi-ordonnanceurs HCF-T, est proposée. Les performances obtenues sont exprimées en termes de gestion du trafic, de maintien du débit, d'élimination de collisions et de réduction de la charge du réseau. Ensuite, un schéma coopératif est présenté et analysé. Il comporte une étude de deux protocoles de relayage AAF et DAF ainsi qu'une évaluation d'un ensemble de techniques de combinaison au niveau du récepteur. Concernant la problématique de la mobilité, nous avons retenu et analysé un scénario prenant en considération les différentes situations rencontrées dans un modèle réel. Un algorithme de résolution multi-couvertures est proposé afin de traiter l'accès dans les zones de recouvrement. Cette étude a mené à distinguer trois régimes de mobilité : faible, moyen et fort. Les performances sont évaluées en fonction des métriques MAC et pour chaque mode de mobilité, un schéma de synthèse est établi / This thesis proposes a new approach relating to the packets scheduling algorithm, the cooperation scheme and the nodes' mobility for IEEE 802.11 wireless network family. Considering the QoS delivery process at the MAC level consists the main feature of the proposal research study. The analysis of the current mechanisms leads to keep the protocol EDCF as the basic model for our work platform. In order to overcome the weakness of the earlier 802.11 standard, a new model based on multi-scheduler algorithm, called HCF-T, is proposed. The achieved performances are summarized following several criteria: traffic control, throughput improving, collisions avoidance, and network load decreasing. Furthermore, in the way of getting better results according to the PHY layer, we presented and analyzed a model of cooperative diversity scheme. It included a couple of relaying protocols AAF and DAF supported by a set of combining techniques to backup the signal at the receiver. To support node's mobility within EDCF, we built-up a model of WLAN which able to track node motion and control the access as in real condition. In the case of overlapping APs ranges, we developed a Multi-coverage algorithm aiming to carry out the session associations. As a result, three levels (Low, Medium, and High) of node's speed are discerned. Finally, EDCF has been implemented on various static and dynamic scenarios. The performances, based on the main MAC-layer metrics, such as throughput, End-2-End delay, and jitter, have been classified and comprehensively evaluated