Várias características da Internet mudaram drasticamente desde que o TCP foi criado, como o maior compartilhamento de recursos devido à maior quantidade de usuários, maior largura de banda disponível, a existência de muitas conexões que podem percorrer longas distâncias e a ubiquidade das redes sem fio. Confrontado com essas novas características, o TCP apresenta diversas limitações. Dentre elas estão a subutilização da rede quando a largura de banda é da ordem de centenas de Gbps, o favorecimento de conexões que possuem pouco atraso (poucas dezenas de milisegundos), a incapacidade de distinção de causas de perdas de pacote e a demora para estabelecimento de conexões seguras (até 3 RTTs). Nesse contexto, com o objetivo de tornar o transporte de dados na Internet mais rápido e eficiente, a Google desenvolveu o protocolo QUIC. O QUIC propõe diversos avanços em relação aos protocolos existentes, como um novo mecanismo para estabelecimento de conexão e controle de congestionamento otimizado. Resultados apresentados pela Google mostraram claro ganho de desempenho em relação ao TCP, justificando o trabalho de tornar o QUIC um padrão IETF da Internet. Porém, esses resultados são impossíveis de serem verificados porque nos relatórios divulgados não há informação suficiente para que os cenários de teste sejam reproduzidos e porque é implausível possuir a mesma infraestrutura para os testes que a Google tem. Neste trabalho, avaliamos o desempenho do protocolo QUIC em diversos cenários de rede, comparando-o com o desempenho de várias implementações do TCP, principalmente o CUBIC. Diferente do realizado na literatura, todos os cenários utilizados são bem descritos, permitindo a reprodutibilidade dos experimentos. Além disso, para a realização dos experimentos foi criado um novo módulo que implementa o QUIC no simulador de redes NS-3. Este módulo está disponível como software livre, permitindo que outros pesquisadores usem o módulo para replicar e verificar nossos experimentos e para criarem novos experimentos de forma reprodutível. Ademais, eles também podem usar o módulo como uma ferramenta para avaliar, de maneira rápida, o comportamento de novas técnicas dentro do protocolo. / Many characteristics of the Internet have drastically changed since TCP was created such as the increase on resource sharing due to a larger number of Internet users, the growth of available bandwidth, the existence of many connections that may travel long distances and the ubiquity of wireless networks. When faced with those new characteristics, TCP showed severe limitations. Among them are network underutilization in high bandwidth environments of hundreds of Gbps, favoring of connections with small delays (few tens of milliseconds), incapacity of distinguishing packet loss causes and high delays for establishing secure connections (up to 3 RTTs). In this context, with the goal of making Internet data transport faster and more efficient, Google has developed the QUIC protocol. QUIC proposes many advances compared to existing protocols, such as a new mechanism for establishing connections and an optimized congestion control algorithm. Google has reported results indicating that QUIC performs better than TCP, justifying the work on making QUIC an IETF Internet standard. However, those results cannot be verified because on the published reports there is not enough information to reproduce the test scenarios and it is implausible to have the same test infrastructure Google has. In this work, we evaluate QUICs performance in a number of network scenarios, comparing it with the performance of different TCP flavours, specially TCP CUBIC. Unlike other works in the literature, all scenarios are well described, enabling experiment replicability. Furthermore, to run experiments we created a new module that implements QUIC on the network simulator NS-3. The module is available as free software, allowing other researchers to use it to reproduce and verify our experiments and to create new ones in a replicable way. Additionally, they can use the module as a tool to quickly assess the behaviour of new techniques in the protocol.

Comprendre les performances d'une application multi-thread est difficile. Les threads interfèrent quand ils accèdent à la même ressource, ce qui ralentit leur exécution. Malheureusement, les outils de profiling existants se focalisent sur l'identification des causes de l'interférence, et non pas sur ses effets.Le développeur ne peut donc pas conclure si l'optimisation d'une interférence identifiée par un outil de profiling peut mener à une meilleure performance. Dans cette thèse, on propose de compléter les outils existants par un outil orienté-effet capable de quantifier l'impact de l'interférence sur la performance, indépendamment de la cause de l'interférence. Avec une évaluation de 27 applications, on montre que notre outil réussit à identifier 12 bottlenecks causés par 6 types d'interférence différents / Understanding the performance of a multi-threaded application is difficult. The threads interfere when they access the same resource, which slows their execution down. Unfortunately, current profiling tools focus on identifying the interference causes, not their effects.The developer can thus not know if optimizing the interference reported by a profiling tool can lead to better performance. In this thesis, we propose to complete the profiling toolbox with an effect-oriented profiling tool able to indicate how much interference impacts performance, regardless of the interference cause. With an evaluation of 27 applications, we show that our tool successfully identifies 12 performance bottlenecks caused by 6 different kinds of interference

Background:- Artificial Neural networks are motivated from biological nervous system and can be used for classification and forecasting the data. Each neural node contains activation function could be used for solving non-linear problems and optimization function to minimize the loss and give more accurate results. Neural networks are bustling in the field of machine learning, which inspired this study to analyse the performance variation based on the use of different combinations of the activation functions and optimization algorithms in terms of accuracy results and metrics recall and impact of data-set features on the performance of the neural networks. Objectives:- This study deals with an experiment to analyse the performance of the combinations are performing well and giving more results and to see impact of the feature segregation from data-set on the neural networks model performance. Methods:- The process involve the gathering of the data-sets, activation functions and optimization algorithm. Execute the network model using 7X5 different combinations of activation functions and optimization algorithm and analyse the performance of the neural networks. These models are tested upon the same data-set with some of the discarded features to know the effect on the performance of the neural networks. Results:- All the metrics for evaluating the neural networks presented in separate table and graphs are used to show growth and fall down of the activation function when associating with different optimization function. Impact of the individual feature on the performance of the neural network is also represented. Conclusions:- Out of 35 combinations, combinations made from optimizations algorithms Adam,RMSprop and Adagrad and activation functions ReLU,Softplus,Tanh Sigmoid and Hard_Sigmoid are selected based on the performance evaluation and data has impact on the performance of the combinations of the algorithms and activation functions which is also evaluated based on the experimentation. Individual features have their corresponding effect on the neural network.

In-band full-duplex, by which radios may simultaneously transmit and receive over the same channel, has been always considered practically-unfeasible due to the prohibitively strong self-interference. Indeed, a freshly-generated transmit signal power is typically ten orders of magnitude higher than that of a naturally-attenuated received signal. While unable to manage such an overwhelming interference, wireless communications resorted to half-duplex operation, transmitting and receiving over orthogonal channel resources. Recent research has demonstrated the practical feasibility of full-duplexing via successive sophisticated stages of signal suppression/cancellation, bringing this long-held assumption down and reviving the promising full-duplex potentials. Full-duplex relaying (FDR), where intermediate nodes may now support source-destination communication via simultaneous listening/forwarding, represents one of two full-duplex settings currently recommended for deployment in future fifth-generation (5G) systems. Theoretically, it has been widely accepted that FDR potentially doubles the channel capacity when compared to its half-duplex counterpart. Although FDR doubles the multiplexing gain, the effective signal-to-noise ratio (SNR) can be significantly degraded due to the residual self-interference (RSI) if not properly handled. In this work, efficient protocols are devised for different FDR settings. Selective cooperation is proposed for the canonical three-terminal FDR channel with RSI, which exploits the cooperative diversity offered by the independently fading source/relay message replicas arriving at the destination. Closed-form expressions are derived for the end-to-end SNR cumulative distribution function (CDF) under Rayleigh and Nakagami-m fading. Further, the offered diversity gain is presented as a function of the RSI scaling trend with the relay power. We show that the existing diversity problem in simple FDR protocols can be considerably fixed via block transmission with selective cooperation. Beyond the single-relay setting, the outage performance of different opportunistic full-duplex relay selection (FDRS) protocols is also evaluated under Rayleigh and Nakagami-m fading. It is shown that, with state-of-the-art adaptive self-interference cancellation techniques, FDRS can offer the same diversity order of its half-duplex rival while supporting a higher level of spectral efficiency. FDRS is also analyzed when adopted by a spectrum-sharing secondary system while the primary spectrum user imposes an additional interference constraint. Finally, buffer-aided hybrid half-/full-duplex cooperation is addressed. To maximize the end-to-end throughput, joint duplexing mode and link selection is studied where the system leverages the buffer and outage state information at the transmitters. All theoretic findings are corroborated with numerical simulations, with comparisons to existing protocols.

The exponential increase in the number of mobile users, coupled with the strong demand for high-speed data services results in a significant growth in the required cellular backhaul capacity. Optimizing the cost efficiency while increasing the capacity is becoming a key challenge to the cellular backhaul. It refers to connections between base stations and mobile switching nodes over a variety of transport technologies such as copper, optical fibers, and radio links. These traditional transmission technologies are either expensive, or cannot provide high data rates. This work is focused on the opportunities of free-space-optical (FSO) technology in next generation cellular back- haul. FSO is a cost effective and wide bandwidth solution as compared with the traditional radio-frequency (RF) transmission. Moreover, due to its ease of deployment, license-free operation, high transmission security, and insensitivity to interference, FSO links are becoming an attractive solution for next generation cellular networks. However, the widespread deployment of FSO links is hampered by the atmospheric turbulence-induced fading, weather conditions, and pointing errors. Increasing the reliability of FSO systems, while still exploiting their high data rate communications, is a key requirement in the deployment of an FSO-based backhaul. Therefore, the aim of this work is to provide different approaches to address these technical challenges. In this context, investigation of hybrid automatic repeat request (HARQ) protocols from an information-theoretic perspective is undertaken. Moreover, performance analysis of asymmetric RF/FSO dual-hop systems is studied. In such system models, multiple RF users can be multiplexed and sent over the FSO link. More specifically, the end-to-end performance metrics are presented in closed-form. This also has increased the interest to study the performance of dual-hop mixed FSO/RF systems, where the FSO link is used as a multicast channel that serves different RF users. Having such interesting results motivates further the analysis of dual-hop FSO fixed-gain relaying communication systems, and exact closed-form performance metrics are presented in terms of the bivariate H-Fox function. This model is further enhanced through the deployment of a multihop FSO relaying system as an efficient technique to mitigate the turbulence-induced fading as well as pointing errors.

This paper describes the IBM Power8 system in comparison to the Intel Xeon processors, widely used in today’s solutions. The performance is not evaluated only on the whole system level but also on the level of threads, cores and a memory. Different metrics are demonstrated on typical optimized algorithms. The benchmarked Power8 processor provides extremely fast memory providing sustainable bandwidth up to 145 GB/s between main memory and processor, which Intel is unable to compete. Computation power is comparable (Matrix multiplication) or worse (N-body simulation, division, more complex algorithms) in comparison with current Intel Haswell-EP. The IBM Power8 is able to compete Intel processors these days and it will be interesting to observe the future generation of Power9 and its performance in comparison to current and future Intel processors.

During the last decade, relay networks have attracted a lot of interest due to their numerous benefits. The relaying technique allows extending the coverage zone of wireless networks and offers a higher reliability for communication systems. The performance of relay networks can be improved further by the use of automatic repeat request (ARQ) and hybrid automatic repeat request (HARQ) techniques. ARQ and HARQ are retransmission mechanisms that ensure a good quality of service even in absence of channel state information at the transmitter. We, firstly, study the spectral and energy efficiency of ARQ in Nakagami-m block-fading channels. We maximize both spectral efficiency and energy efficiency with respect to the transmitted power. We derive exact expressions as well as compact and tight approximation for the solutions of these problems. Our analysis shows that the two problems of maximizing spectral efficiency and energy efficiency with respect to the transmitted power are completely different and give different solutions. Additionally, operating with a power that maximizes energy efficiency can lead to a significant drop in the spectral efficiency, and vice versa. Next, we consider a three node relay network comprising a source, a relay, and a destination. The source transmits the message to the destination using HARQ with incremental redundancy (IR). The relay overhears the transmitted message, amplifies it using a variable gain amplifier, and then forwards the message to the destination. This latter combines both the source and the relay message and tries to decode the information. In case of decoding failure, the destination sends a negative acknowledgement. A new replica of the message containing new parity bits is then transmitted in the subsequent HARQ round. This process continues until successful decoding occurs at the destination or a maximum number M of rounds is reached. We study the performance of HARQ-IR over the considered relay channel from an information theoretic perspective. We derive exact expressions and bounds for the information outage probability, the average number of transmissions, and the average transmission rate. Moreover, we evaluate the delay experienced by Poisson arriving packets over the considered relay network. We also provide analytical expressions for the expected waiting time, the sojourn time, and the energy efficiency. The derived exact expressions are validated by Monte Carlo simulations. Finally, we consider a relay network consisting of a source, K relays, and a destination. The source transmits a message to the destination using HARQ-IR. We study the performance of HARQ-IR over dualhop multibranch amplify-and-forward relay channels. We derive exact expression for outage probability of the considered network. We investigate the benefit of relaying and the effect of changing the rate and the maximum number M of rounds on the outage probability.

Generalized fading has been an imminent part and parcel of wireless communications. It not only characterizes the wireless channel appropriately but also allows its utilization for further performance analysis of various types of wireless communication systems. Under the umbrella of generalized fading channels, a unified performance analysis of a free-space optical (FSO) link over the Malaga (M) atmospheric turbulence channel that accounts for pointing errors and both types of detection techniques (i.e. indirect modulation/direct detection (IM/DD) as well as heterodyne detection) is presented. Specifically, unified exact closed-form expressions for the probability density function (PDF), the cumulative distribution function (CDF), the moment generating function (MGF), and the moments of the end-to-end signal-to-noise ratio (SNR) of a single link FSO transmission system are presented, all in terms of the Meijer's G function except for the moments that is in terms of simple elementary functions. Then capitalizing on these unified results, unified exact closed-form expressions for various performance metrics of FSO link transmission systems are offered, such as, the outage probability (OP), the higher-order amount of fading (AF), the average error rate for binary and M-ary modulation schemes, and the ergodic capacity (except for IM/DD technique, where closed-form lower bound results are presented), all in terms of Meijer's G functions except for the higher-order AF that is in terms of simple elementary functions. Additionally, the asymptotic results are derived for all the expressions derived earlier in terms of the Meijer's G function in the high SNR regime in terms of simple elementary functions via an asymptotic expansion of the Meijer's G function. Furthermore, new asymptotic expressions for the ergodic capacity in the low as well as high SNR regimes are derived in terms of simple elementary functions via utilizing moments. All the presented results are verified via computer-based Monte-Carlo simulations. Besides addressing the pointing errors with zero boresight effects as has been addressed above, a unified capacity analysis of a FSO link that accounts for nonzero boresight pointing errors and both types of detection techniques (i.e. heterodyne detection as well as IM/DD) is also addressed. Specifically, an exact closed-form expression for the moments of the end-to-end SNR of a single link FSO transmission system is presented in terms of well-known elementary functions. Capitalizing on these new moments expressions, approximate and simple closed-form results for the ergodic capacity at high and low SNR regimes are derived for lognormal (LN), Rician-LN (RLN), and M atmospheric turbulences. All the presented results are verified via computer-based Monte-Carlo simulations. Based on the fact that FSO links are cost-effective, license-free, and can provide even higher bandwidths compared to the traditional radio-frequency (RF) links, the performance analysis of a dual-hop relay system composed of asymmetric RF and FSO links is presented. This is complemented by the performance analysis of a dual-branch transmission system composed of a direct RF link and a dual-hop relay composed of asymmetric RF and FSO links. The performance of the later scenario is evaluated under the assumption of the selection combining (SC) diversity and the maximal ratio combining (MRC) schemes. RF links are modeled by Rayleigh fading distribution whereas the FSO link is modeled by a unified GG fading distribution. More specifically, in this work, new exact closed-form expressions for the PDF, the CDF, the MGF, and the moments of the end-to-end SNR are derived. Capitalizing on these results, new exact closed-form expressions for the OP, the higher-order AF, the average error rate for binary and M-ary modulation schemes, and the ergodic capacity are offered. Cognitive radio networks (CRN) have also proved to improve the performance of wireless communication systems and hence based on this, the hybrid system analyzed above is extended with CRN technology wherein the outage and error performance analysis of a dual-hop transmission system composed of asymmetric RF channel cascaded with a FSO link is presented. For the RF link, an underlay cognitive network is considered where the secondary users share the spectrum with licensed primary users. Indoor femtocells act as a practical example for such networks. Specifically, it is assumed that the RF link applies power control to maintain the interference at the primary network below a predetermined threshold. While the RF channel is modeled by the Rayleigh fading distribution, the FSO link is modeled by a unified Gamma-Gamma turbulence distribution. The FSO link accounts for pointing errors and both types of detection techniques (i.e. heterodyne detection as well as IM/DD). With this model, a new exact closed-form expression is derived for the OP and the error rate of the end-to-end SNR of these systems in terms of the Meijer's G function and the Fox's H functions under amplify-and-forward relay schemes. All new analytical results are verified via computer-based Monte-Carlo simulations and are illustrated by some selected numerical results.

Shared Disk database systems offer a high flexibility for parallel transaction and query processing. This is because each node can process any transaction, query or subquery because it has access to the entire database. Compared to Shared Nothing database systems, this is particularly advantageous for scan queries for which the degree of intra-query parallelism as well as the scan processors themselves can dynamically be chosen. On the other hand, there is the danger of disk contention between subqueries, in particular for index scans. We present a detailed simulation study to analyze the effectiveness of parallel scan processing in Shared Disk database systems. In particular, we investigate the relationship between the degree of declustering and the degree of scan parallelism for relation scans, clustered index scans, and non-clustered index scans. Furthermore, we study the usefulness of disk caches and prefetching for limiting disk contention. Finally, we show that disk contention in multi-user mode can be limited for Shared Disk database systems by dynamically choosing the degree of scan parallelism.

This study addresses on facet of Joseph Turrin's compositional oeuvre: his published works for solo trumpet. Complete histories if all six trumpet compositions are chronicles. A discussion of formal organization and significant style features including harmonic language, melodic style and rhythmic features is included. A detailed performance analysis follows. The degree of difficulty of each work is assessed through an investigation of tessitura, range, melodic contour, endurance factors, fingerings, and technical features of the accompaniment. Analysis of tempi and dynamics, articulation and phrasing, and timbral considerations provides additional points of focus to the study. Finally, the importance of Turrin's works for trumpet and his impact on trumpet literature is assessed. Idiomatic aspects of composition that make Turrin's music attractive to performers are investigated and discussed.