No / This paper is not a survey related to generic wireless sensor networks (WSNs), which have been largely treated in a number of survey papers addressing more focused issues; rather, it specifically addresses architectural aspects related to WSNs in some way connected with a satellite link, a topic that presents challenging interworking aspects. The main objective is to provide an overview of the potential role of a satellite segment in future WSNs. In this perspective, requirements of the most meaningful WSN applications have been drawn and matched to characteristics of various satellite/space systems in order to identify suitable integrated configurations. Copyright (c) 2012 John Wiley & Sons, Ltd.

The future quantum Internet (QI) will transform today's communication networks and user experiences by providing unparalleled security levels, superior quantum computational powers, along with enhanced sensing accuracy and data processing capabilities. These features will be enabled through applications like quantum key distribution (QKD) and quantum machine learning (QML). Towards enabling these applications, the QI requires the development of global quantum communication networks (QCNs) that enable the distribution of entangled resources between distant nodes. This dissertation addresses two major challenges facing QCNs, which are the scalability and coverage of their architectures, and the efficiency of their operations. Additionally, the dissertation studies the near-term deployment of QML applications over today's noisy quantum devices, essential for realizing the future QI. In doing so, the scalability and efficiency challenges facing the different QCN elements are explored, and practical noise-aware and physics-informed approaches are developed to optimize the QCN performance given heterogeneous quantum application-specific quality of service (QoS) user requirements on entanglement rate and fidelity. Towards achieving this goal, this dissertation makes a number of key contributions. First, the scaling limits of quantum repeaters is investigated, and a holistic optimization framework is proposed to optimize the geographical coverage of quantum repeater networks (QRNs), including the number of quantum repeaters, their placement and separating distances, quantum memory management, and quantum operations scheduling. Then, a novel framework is proposed to address the scalability challenge of free-space optical (FSO) quantum channels in the presence of blockages and environmental effects. Particularly, the utilization of a reconfigurable intelligent surface (RIS) in QCNs is proposed to maintain a line-of-sight (LoS) connection between quantum nodes separated by blockages, and a novel analytical model of quantum noise and end-to-end (e2e) fidelity in such QCNs is developed. The results show enhanced entangled state fidelity and entanglement distribution rates, improving user fairness by around 40% compared to benchmark approaches. The dissertation then investigates the efficiency challenges in a practical use-case of QCNs with a single quantum switch (QS). Particularly, the average quantum memory noise effects are analytically analyzed and their impacts on the allocation of entanglement generation sources and minimization of entanglement distribution delay while optimizing QS entanglement distillation operations are investigated. The results show an enhanced e2e fidelity and a minimized e2e entanglement distribution delay compared to existing approaches, and a unique capability of satisfying all users QoS requirements. This QCN architecture is scaled up with multiple QSs serving heterogeneous user requests, necessary for scalable quantum applications over the QI. Here, a novel efficient matching theory-based framework for optimizing the request-QS association in such QCNs while managing quantum memories and optimizing QS operations is proposed. Finally, after scaling QCNs and ensuring their efficient operations, the dissertation proposes novel distributed QML frameworks that can leverage both classical networks and QCNs to enable collaborative learning between today's noisy quantum devices. In particular, the first quantum federated learning (QFL) frameworks incorporating different quantum neural networks and leveraging quantum and classical data are developed, and the first publicly available federated quantum dataset is introduced. The results show enhanced performance and reductions in the communication overhead and number of training epochs needed until convergence, compared to classical counterpart frameworks. Overall, this dissertation develops robust frameworks and algorithms that advance the theoretical understanding of QCNs and offers practical insights for the future development of the QI and its applications. The dissertation concludes by analyzing some open challenges facing QCNs and proposing a vision for physics-informed QCNs, along with important future directions. / Doctor of Philosophy / In today's digital age, we are generating vast amounts of data through videos, live streams, and various online activities. This explosion of data brings not only incredible opportunities for innovation but also heightened security concerns. The current Internet infrastructure struggles to keep up with the demand for speed and security. In this regard, the quantum Internet (QI) emerges as a revolutionary technology poised to make the communication and data sharing processes faster and more secure than ever before. The QI requires the development of quantum communication networks (QCNs) that will be seamlessly integrated with today's existing communication systems that form today's Internet. This way, the QI enables ultra-secure communication and advanced computing applications that can transform various sectors, from finance to healthcare. However, building such global QCNs, requires overcoming significant challenges, including the sensitive nature and limitations of quantum devices. In this regard, the goal of this dissertation is to develop scalable and efficient QCNs that overcome the different challenges facing different QCN elements and enable a wide coverage and robust performance towards realizing the QI at a global scale. Simultaneously, machine learning (ML), which is driving significant advancements and transforming industries in today's world. Here, quantum technologies are anticipated to make a breakthrough in ML through quantum machine learning (QML) models that can handle today's large and complex data. However, quantum computers are still limited in scale and efficiency, often being noisy and unreliable. Throughout this dissertation, these limitations of QML are addressed by developing frameworks that allow multiple quantum computers to work together collaboratively in a distributed manner over classical networks and QCNs. By leveraging distributed QML, it is possible to achieve remarkable advancements in privacy and data utilization. For instance, distributed QML can enhance navigation systems by providing more accurate and secure route planning or revolutionize healthcare by enabling secure and efficient analysis of medical data. In summary, this dissertation addresses the critical challenges of building scalable and efficient QCNs to support the QI and develops distributed QML frameworks to enable near-term utilization of QML in transformative applications. By doing so, it paves the way for a future where quantum technology is integral to our daily lives, enhancing security, efficiency, and innovation across various domains.

Thesis (MScEng)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The perceived quality of Voice over Internet Protocol (IP) (VoIP) communication relies on the network which is used to transport voice packets between the end points. Variable network characteristics such as bandwidth, delay and loss are critical for real-time voice traffic and are not always guaranteed by networks. It is important for network service providers to determine the Quality of Service (QoS) it provides to its customers. The solution proposed here is to predict the perceived quality of a VoIP call, in real-time by using network statistics. The main objective of this thesis is to develop a network analysis tool, which gathers meaningful statistics from network traffic. These statistics will then be used for predicting the perceived quality of a VoIP call. This study includes the investigation and deployment of two main components. Firstly, to determine call quality, it is necessary to extract the voice streams from captured network traffic. The extracted sound files can then be analysed by various VoIP quality models to determine the perceived quality of a VoIP call. The second component is the analysis of network characteristics. Loss, delay and jitter are all known to influence perceived call quality. These characteristics are, therefore, determined from the captured network traffic and compared with the call quality. Using the statistics obtained by the repeated comparison of the call quality and network characteristics, a network specific algorithm is generated. This Non-Intrusive Quality Prediction Algorithm (NIQPA) uses basic characteristics such as time of day, delay, loss and jitter to predict the quality of a real-time VoIP call quickly in a non-intrusive way. The realised algorithm for each network will differ, because every network is different. Prediction results can then be used to adapt either the network (more bandwidth, packet prioritising) or the voice stream (error correction, change VoIP codecs) to assure QoS. / AFRIKAANSE OPSOMMING: Die kwaliteit van spraak oor die internet (VoIP) kommunikasie is afhanklik van die netwerk wat gebruik word om spraakpakkies te vervoer tussen die eindpunte. Netwerk eienskappe soos bandwydte, vertraging en verlies is krities vir intydse spraakverkeer en kan nie altyd gewaarborg word deur netwerkverskaffers nie. Dit is belangrik vir die netwerk diensverskaffers om die vereiste gehalte van diens (QoS) te verskaf aan hul kliënte. Die oplossing wat hier voorgestel word is om die kwaliteit van ’n VoIP oproep intyds te voorspel, deur middel van die netwerkstatistieke. Die belangrikste doel van hierdie projek is om ’n netwerk analise-instrument te ontwikkel. Die instrument versamel betekenisvolle statistiek deur van netwerkverkeer gebruik te maak. Hierdie statistiek sal dan gebruik word om te voorspel wat die gehalte van ’n VoIP oproep sal wees vir sekere netwerk toestande. Hierdie studie berus op die ondersoek en implementering van twee belangrike komponente. In die eerste plek, moet oproep kwaliteit bepaal word. Spraakstrome word uit die netwerkverkeer onttrek. Die onttrekte klanklêers kan dan geanaliseer word deur verskeie spraak kwaliteitmodelle om die kwaliteitdegradasie van ’n spesifieke VoIP oproep vas te stel. Die tweede komponent is die analise van netwerkeienskappe. Pakkieverlies, pakkievertraging en bibbereffek is bekend vir hul invloed op VoIP kwaliteit en is waargeneem. Hierdie netwerk eienskappe word dus bepaal uit die netwerkverkeer en daarna vergelyk met die gemete gesprekskwaliteit. Statistiek word verkry deur die herhaalde vergelyking van gesprekkwaliteit en netwerk eienskappe. Uit die statistiek kan ’n algoritme (vir die spesifieke network) gegenereer word om spraakkwaliteit te voorspel. Hierdie Nie-Indringende Kwaliteit Voorspellings-algoritme (NIKVA), gebruik basiese kenmerke, soos die tyd van die dag, pakkie vertraging, pakkie verlies en bibbereffek om die kwaliteit van ’n huidige VoIP oproep te voorspel. Hierdie metode is vinnig, in ’n nie-indringende manier. Die gerealiseerde algoritme vir die verskillende netwerke sal verskil, want elke netwerk is anders. Die voorspelling van spraakgehalte kan dan gebruik word om òf die netwerk aan te pas (meer bandwydte, pakkie prioriteit) òf die spraakstroom aan te pas (foutkorreksie, verander VoIP kodering) om die goeie kwaliteit van ’n VoIP oproep te verseker.

Security is essential to communication between entities in the internet. Delay tolerant and disconnected Mobile Ad Hoc Networks (MANET) are a class of networks characterized by high end-to-end path latency and frequent end-to-end disconnections and are often termed as challenged networks. In these networks nodes are sparsely populated and without the existence of a central server, acquiring global information is difficult and impractical if not impossible and therefore traditional security schemes proposed for MANETs cannot be applied. This thesis reports trust management schemes for peer to peer (P2P) application in delay tolerant disconnected MANETs. Properties of a profile based file sharing application are analyzed and a framework for structured P2P overlay over delay tolerant disconnected MANETs is proposed. The framework is implemented and tested on J2ME based smart phones using Bluetooth communication protocol. A light weight Content Driven Data Propagation Protocol (CDDPP) for content based data delivery in MANETs is presented. The CDDPP implements a user profile based content driven P2P file sharing application in disconnected MANETs. The CDDPP protocol is further enhanced by proposing an adaptive opportunistic multihop content based routing protocol (ORP). ORP protocol considers the store-carry-forward paradigm for multi-hop packet delivery in delay tolerant MANETs and allows multi-casting to selected number of nodes. Performance of ORP is compared with a similar autonomous gossiping (A/G) protocol using simulations. This work also presents a framework for trust management based on dynamicity aware graph re-labelling system (DA-GRS) for trust management in mobile P2P applications. The DA-GRS uses a distributed algorithm to identify trustworthy nodes and generate trustable groups while isolating misleading or untrustworthy nodes. Several simulations in various environment settings show the effectiveness of the proposed framework in creating trust based communities. This work also extends the FIRE distributed trust model for MANET applications by incorporating witness based interactions for acquiring trust ratings. A witness graph building mechanism in FIRE+ is provided with several trust building policies to identify malicious nodes and detect collusive behaviour in nodes. This technique not only allows trust computation based on witness trust ratings but also provides protection against a collusion attack. Finally, M-trust, a light weight trust management scheme based on FIRE+ trust model is presented.

IEEE has recently finished its ratification of the IEEE Standard 802.3ba in June 2010 which set the target Ethernet speed as 100 Gbps. The studies on the future trends of the ever-increasing demands for higher speed optical fiber communications show that there is no sign of decline in the demand. Constantly increasing internet traffic and the bandwidth-hungry multimedia services like HDTV, YouTube, voice-over-IP, etc. can be shown as the main driving forces. Indeed, the discussions over the future upgrades on the Ethernet speeds have already been initiated. It is predicted that the next upgrade will enable 400 Gbps Ethernet and the one after will be toward enabling the astounding 1 Tbps Ethernet.Although such high and ultra high transmission speeds are unprecedented over any transmission medium, the bottlenecks for achieving them over the optical fiber remains to be fundamental. At such high operating symbol rates, the signal impairments due to inter- and intra-channel fiber nonlinearities and polarization mode dispersion get exacerbated to the levels that cripple the high-fidelity communication over optical fibers. Therefore, efforts should be exerted to provide solutions that not only answer the need for high-speed transmission but also maintain low operating symbol rates.In this dissertation, we contribute to these efforts by proposing nonbinary-LDPC-coded modulation (NB-LDPC-CM) schemes as enabling technologies that can meet both the aforementioned goals. We show that our proposed NB-LDPC-CM schemes can outperform their prior-art, binary counterparts called bit-interleaved coded modulation (BI-LDPC-CM) schemes while attaining the same aggregate bit rates at a lower complexity and latency. We provide comprehensive analysis on the computational complexity of both schemes to justify our claims with solid evidence. We also compare the performances of both schemes by using amplified spontaneous emission (ASE) noise dominated optical fiber transmission and short to medium haul optical fiber transmission scenarios. Both applications show outstanding performances of NB-LDPC-CM schemes over the prior-art BI-LDPC-CM schemes with increasing gaps in coding gain as the transmission speeds increase. Furthermore, we present how a rate-adaptive NB-LDPC-CM can be employed to fully utilize the resources of a long haul optical transport network throughout its service time.

The exponential growth of Internet applications has created new challenges for the control and administration of large-scale networks, which consist of heterogeneous elements under dynamically changing traffic conditions. These emerging applications need guaranteed service levels, beyond those supported by best-effort networks, to deliver the intended services to the end user. Several models have been proposed for a Quality of Service (QoS) framework that can provide the means to transport these services. It is desirable to find efficient routing strategies that can meet the strict routing requirements of these applications. QoS routing is considered as one of the major components of the QoS framework in communication networks. In QoS routing, paths are selected based upon the knowledge of resource availability at network nodes and the QoS requirements of traffic. Several QoS routing schemes have been proposed that differ in the way they gather information about the network state and the way they select paths based on this information. The biggest downside of current QoS routing schemes is the frequent maintenance and distribution of global state information across the network, which imposes huge communication and processing overheads. Consequently, scalability is a major issue in designing efficient QoS routing algorithms, due to the high costs of the associated overheads. Moreover, inaccuracy and staleness of global state information is another problem that is caused by relatively long update intervals, which can significantly deteriorate routing performance. Localized QoS routing, where source nodes take routing decisions based solely on statistics collected locally, was proposed relatively recently as a viable alternative to global QoS routing. It has shown promising results in achieving good routing performance, while at the same time eliminating many scalability related problems. In localized QoS routing each source-destination pair needs to determine a set of candidate paths from which a path will be selected to route incoming flows. The goal of this thesis is to enhance the scalability of QoS routing by investigating and developing new models and algorithms based on the localized QoS routing approach. For this thesis, we have extensively studied the localized QoS routing approach and demonstrated that it can achieve a higher routing performance with lower overheads than global QoS routing schemes. Existing localized routing algorithms, Proportional Sticky Routing (PSR) and Credit-Based Routing (CBR), use the blocking probability of candidate paths as the criterion for selecting routing paths based on either flow proportions or a crediting mechanism, respectively. Routing based on the blocking probability of candidate paths may not always reflect the most accurate state of the network. This has motivated the search for alternative localized routing algorithms and to this end we have made the following contributions. First, three localized bandwidth-constrained QoS routing algorithms have been proposed, two are based on a source routing strategy and the third is based on a distributed routing strategy. All algorithms utilize the quality of links rather than the quality of paths in order to make routing decisions. Second, a dynamic precautionary mechanism was used with the proposed algorithms to prevent candidate paths from reaching critical quality levels. Third, a localized delay-constrained QoS routing algorithm was proposed to provide routing with an end-to-end delay guarantee. We compared the performance of the proposed localized QoS routing algorithms with other localized and global QoS routing algorithms under different network topologies and different traffic conditions. Simulation results show that the proposed algorithms outperform the other algorithms in terms of routing performance, resource balancing and have superior computational complexity and scalability features.

Les réseaux tolérants aux retards (DTN) ont été conçus pour fournir un moyen de communication durable entre terminaux mobiles dans les régions dépourvues d’infrastructure cellulaire. Dans de tels réseaux, l’ensemble des voisins de chaque nœud change au fil du temps en raison de la mobilité des nœuds, ce qui entraîne une connectivité intermittente et des routes instables dans le réseau. Nous analysons la performance d’un système d’incitation pour les DTN à deux sauts dans lequel une source en arriéré offre une récompense fixe aux relais pour délivrer un message. Un seul message à la fois est proposé par la source. Pour un message donné, seul le premier relais à le délivrer reçoit la récompense correspondant à ce message, induisant ainsi une compétition entre les relais. Les relais cherchent à maximiser la récompense attendue pour chaque message alors que l’objectif de la source est de satisfaire une contrainte donnée sur la probabilité de livraison du message. Nous considérons deux réglages différents : l’un dans lequel la source indique aux relais pendant combien de temps un message est en circulation, et l’autre dans lequel la source ne donne pas cette information. Dans le premier paramètre, nous montrons que la politique optimale d’un relais est de type seuil : il accepte un message jusqu’à un premier seuil et le conserve jusqu’à ce qu’il atteigne la destination ou le deuxième seuil. Les formules de calcul des seuils ainsi que de la probabilité de livraison des messages sont dérivées pour une source d’arriérés. Nous étudions ensuite la performance asymptotique de ce réglage dans la limite moyenne du champ. Lorsque le deuxième seuil est infini, nous donnons l’ODE du champ moyen et montrons que tous les messages ont la même probabilité de réussite. Lorsque le deuxième seuil est fini, nous ne donnons qu’une approximation ODE car dans ce cas, la dynamique n’est pas markovienne. Pour le second réglage, nous supposons que la source propose chaque message pour une période de temps fixe et qu’un relais décide d’accepter un message selon une politique randomisée lors d’une rencontre avec la source. S’il accepte le message, un relais le garde jusqu’à ce qu’il atteigne la destina- tion. Nous établissons dans quelle condition la probabilité d’acceptation des relais est strictement positive et montrons que, dans cette condition, il existe un équilibre de Nash symétrique unique, dans lequel aucun relais n’a quelque chose à gagner en changeant unilatéralement sa probabilité d’acceptation. Des expressions explicites pour la probabilité de livraison du message et le temps moyen de livraison d’un message à l’équilibre symétrique de Nash sont dérivées, ainsi qu’une expression de la valeur asymptotique de la livraison du message. Enfin, nous présentons de nombreux résultats de simulations pour com- parer les performances de la stratégie de type seuil et de la stratégie ran- domisée, afin de déterminer dans quelle condition il est rentable pour la source de donner l’information sur l’âge d’un message aux relais. / Delay-Tolerant Networks (DTNs) were designed to provide a sustainable means of communication between mobile terminals in regions without cellular infrastructure. In such networks, the set of neighbors of every node changes over time due to the mobility of nodes, resulting in intermittent connectivity and unstable routes in the network. We analyze the performance of an incentive scheme for two-hop DTNs in which a backlogged source pro- poses a fixed reward to the relays to deliver a message. Only one message at a time is proposed by the source. For a given message, only the first relay to deliver it gets the reward corresponding to this message thereby inducing a competition between the relays. The relays seek to maximize the expected reward for each message whereas the objective of the source is to satisfy a given constraint on the probability of message delivery. We consider two different settings: one in which the source tells the relays for how long a message is in circulation, and one in which the source does not give this information. In the first setting, we show that the optimal policy of a relay is of thresh- old type: it accepts a message until a first threshold and then keeps the message until it either meets the destination or reaches the second threshold. Formulas for computing the thresholds as well as probability of message delivery are derived for a backlogged source. We then investigate the asymptotic performance of this setting in the mean field limit. When the second thresh- old in infinite, we give the mean-field ODE and show that all the messages have the same probability of successful delivery. When the second threshold is finite we only give an ODE approximation since in this case the dynamics are not Markovian. For the second setting, we assume that the source proposes each message for a fixed period of time and that a relay decides to accept a message accord- ing to a randomized policy upon encounter with the source. If it accepts the message, a relay keeps it until it reaches the destination. We establish under which condition the acceptance probability of the relays is strictly positive and show that, under this condition, there exists a unique symmetric Nash equilibrium, in which no relay has anything to gain by unilaterally changing its acceptance probability. Explicit expressions for the probability of message delivery and the mean time to deliver a message at the symmetric Nash equilibrium are derived, as well as an expression of the asymptotic value of message delivery. Finally, we present numerous simulations results to compare performances of the threshold-type strategy and the randomized strategy, in order to determine under which condition it is profitable for the source to give the information on the age of a message to the relays

Le principal objectif de la thèse était d'établir un cadre d’étude des communications efficace énergétiquement en définissant et en justifiant de nouvelles mesures d'efficacité énergétique pour divers systèmes sans fils. En général, le rendement énergétique est défini comme le rapport entre le débit total et la puissance totale consommée par l'émetteur. Cette définition implique que, lorsqu’une re-transmission est autorisée (dans le cas d'une erreur sur les paquets), la maximisation de l'efficacité énergétique peut conduire directement à minimiser l'énergie dépensée lors de la transmission d'une unité d'information. Ce travail développe un cadre pour l'efficacité énergétique pour les cas généraux de contrôle de puissance dans la couche physique avec MIMO et inter-couche avec une arrivée de paquets sporadique. Des algorithmes centralisés et décentralisés pour atteindre un point de fonctionnement économe en énergie pour les systèmes à l'étude ont été proposés. Les résultats mettent en évidence le compromis entre la consommation d'énergie et les taux de date en ce qui concerne l'efficacité énergétique des réseaux sans fil. Le principal objectif de la thèse était d'établir un cadre d’étude des communications efficace énergétiquement en définissant et en justifiant de nouvelles mesures d'efficacité énergétique pour divers systèmes sans fil. / The main objective of the thesis was to establish a framework for energy-efficient communication by defining and justifying novel energy-efficiency metrics for various wireless systems and settings. In general, the energy-efficiency is defined as the ratio of the total data rate to the total power consumed at the transmitter. This definition implies that, when re-transmission is allowed (in the case of outage), maximizing energy-efficiency can directly lead to minimizing the energy spent in transmitting a unit of information. This work develops a framework for energy-efficiency for the general cases of power control in the physical layer with MIMO and cross-layer with a sporadic packet arrival. Both centralized and decentralized algorithms for achieving an energy-efficient working point for the systems under consideration were proposed. The results highlight the trade-off between power consumption and date rates in energy efficient wireless networks.

Made available in DSpace on 2016-04-26T18:11:03Z (GMT). No. of bitstreams: 1 Eduardo Salvino.pdf: 3346937 bytes, checksum: 2b4afa0e92451c0061a01493f495fcd0 (MD5) Previous issue date: 2011-05-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The research in hand analyses political and poetic aspects present in digital communications networks and their extension to the social and public spheres. The research parts from the assumption that these networks- physical, virtual and flexible permit critical reflections as to the configurational complexity of contemporary societies through an informational paradigm. This hypothesis is founded on the reflections of Manuel Castells, Geert Lovink and Lúcia Santaella regarding communications, control and democracy. Through the course of the dissertation, there is a discussion of poetic endeavors that are formed in the flux of information provided by online communications networks. From a base of bibliographic research, theoretical and epstimological reflection, field research based on interviews and an the observation of works by net artists such as Antoni Abad, Denise Agassi, Eduardo Salvino, Fernando Velázquez, Giselle Beiguelman, Lucas Bambozzi e Rafael Marchetti, there is a mapping of different types of authorship that emerge in the relationship between the public and creators, founded on the manipulation and interaction of available content, through the key word indexing of online social networks. Lastly, there is a presentation of the production processes utilized in the experimental net art project ―edo(ar)do‖, executed by the author of the dissertation, focussing on dialogues that provoke questions involving poetic subjectivety and activism. The theoretical background covers references regarding the aesthetics of online databanks and audiovisual features (Geert Lovink, Lev Manovich e Victoria Vesna), technical images and their contexts of diffusion (Vilém Flusser), creative processes and networks (Cecília A. Salles), art, media and discussion (Anne Cauquelin, Herbert Mcluhan and Rosalind Krauss), poetic endeavors and network politics (Gilles Deleuze and Félix Guattari), videoart and artmedia (Arlindo Machado, Christine Mello, Edmond Couchot, Giselle Beiguelman, Lucia Leão and Lúcia Santaella). In this way, the research questions contemporary communication processes, allowing reflection on the ambivalent nature of democratic actions and aesthetic productions involving on and offline networks, concretizing reflections regarding social, political and philosophical aspects in the environment of technology and communicational aesthetics / A presente pesquisa analisa aspectos de práticas políticas e poéticas nas redes digitais de comunicação e seus desdobramentos no espaço social e público. Parte-se do pressuposto que essas redes físicas e virtuais maleáveis e flexíveis permitem reflexões críticas em torno da complexidade da configuração das sociedades contemporâneas sob o paradigma informacional. Essa hipótese está fundada em reflexões de Manuel Castells, Geert Lovink e Lúcia Santaella sobre comunicação, controle e democracia. Ao longo da dissertação, discutem-se os agenciamentos poéticos que se formam nos fluxos informacionais proporcionados pelas redes de comunicação online. Com base em levantamentos bibliográficos, reflexões teóricas e epistemológicas sobre o objeto de estudo, pesquisas de campo baseadas em entrevistas e acompanhamentos dos trabalhos de net artistas como Antoni Abad, Denise Agassi, Eduardo Salvino, Fernando Velázquez, Giselle Beiguelman, Lucas Bambozzi e Rafael Marchetti, é feito um mapeamento dos tipos de autoria que emergem nas relações, entre público e criadores, fundados na manipulação e interação do conteúdo disponível, via indexação por palavras-chave, nas redes sociais online. Por fim, apresenta-se o processo de produção de um projeto experimental em net art ―edo(ar)do‖, executado pelo autor da dissertação tendo em vista diálogos com questões que envolveram subjetividade, poética e ativismo. O quadro teórico abrange referências sobre estética do banco de dados e audiovisuais on-line (Geert Lovink, Lev Manovich e Victoria Vesna), imagens técnicas e seus contextos de difusão (Vilém Flusser), processos criativo e redes (Cecília A. Salles), arte, mídias e discurso (Anne Cauquelin, Herbert Mcluhan e Rosalind Krauss), agenciamentos poéticos e políticos em rede (Gilles Deleuze e Félix Guattari), videoarte e artemídia (Arlindo Machado, Christine Mello, Edmond Couchot, Giselle Beiguelman, Lucia Leão e Lúcia Santaella). Desta forma, a pesquisa questiona os processos comunicacionais atuais e permite refletir a ambivalência em ações democráticas e produções estéticas envolvendo redes on e offline, adensando reflexões sobre o social, o político e o filosófico no âmbito da tecnologia e estética comunicacional

A comunicação de Voz sobre IP (VoIP) vem aumentando com o decorrer do tempo e as redes de comunicação estão se tornando cada vez mais congestionadas, ocasionando perda de pacotes e latência nas redes, prejudicando diretamente a qualidade das comunicações de voz. Neste trabalho, foi estudado em detalhe como a qualidade do sinal de voz transmitido em uma comunicação VoIP é afetada por parâmetros da rede e pelo tipo de codificador utilizado na comunicação. Uma contribuição importante deste trabalho é a apresentação de uma metodologia que serve para predizer o comportamento de um codificador de voz em diferentes cenários de redes. O estabelecimento de um mecanismo de controle que otimize a utilização da rede e ao mesmo tempo garanta a melhor qualidade possível do sinal de voz transmitido vem sendo motivo de pesquisa. O emprego de codificadores multitaxa nas comunicações de voz possibilita a implementação de algoritmos que controlem a comutação destas taxas de codificação baseados em diferentes fatores de decisão como as características do sinal de voz a ser transmitido ou empregando a informação dos parâmetros de rede. Este trabalho apresenta um algoritmo de determinação de taxa de codificação com fator de decisão baseado na qualidade do sinal avaliada no ponto da recepção ou em algum ponto intermediário. Para realização dos testes montou-se um cenário de emulação de rede IP para o estabelecimento de uma chamada VoIP, onde são utilizados codificadores multitaxa (ITU-T G.726 e Speex). Para avaliação da qualidade do sinal de voz foi utilizada a recomendação ITU-T P.563, sendo que o índice MOS obtido no ponto de recepção é transmitido utilizando um laço de transmissão, que forma parte da estrutura do mecanismo de controle apresentado neste trabalho. Este laço de transmissão é implementado via socket sobre uma comunicação UDP. Como as ferramentas utilizadas são todas freeware, o cenário de emulação pode ser facilmente implementado por demais pesquisadores. Os resultados obtidos são confiáveis, já que para cenários onde se mesclam diferentes taxas de codificação, o índice MOS obtido é um valor que está na faixa dos valores obtidos nos cenários onde se utilizou taxa de codificação única. O correto desempenho do mecanismo do RDA também foi verificado, sendo que a qualidade do sinal de voz decresce, o mecanismo de controle no RDA comuta a uma taxa de codificação menor, garantindo o melhor uso do canal de transmissão. Quando os parâmetros da rede passam a melhores condições, o índice MOS do sinal aumenta e o RDA comuta a uma taxa de codificação maior obtendo uma qualidade mais alta na comunicação. / Voice over IP (VoIP) communications are becoming increasingly popular so that data communication networks are ever more prone to degradations like packet losses and rising latency. In this work, it was studied in detail how the quality of the speech signal transmitted in a VoIP communication is affected by parameters of the network and the type of codec used in the communication. An important contribution of this work is to predict the behavior of a speech codec in different network scenarios. The main goal of this research has been the development of an algorithm that constrains rate allocation to a speech communication for best quality according to current network resource availability. The use of multirate codecs in speech communications makes it possible to implement control algorithms for coding rate switching. They are based on speech signal features or network trafic parameters. This work presents an algorithm for the determination of coding rate with decision factor based on speech quality evaluated at the point of reception or intermediate points. For accomplishment of the tests, a scenario of emulation of an IP network for the establishment of a VoIP call was built, where multi-rate codecs are used (ITU-T G.726 and Speex). For evaluation of the quality of the speech signal the Recommendation ITU-T P.563 was used, where the MOS index obtained in the reception is transmitted using a transmission loop, as a part in the control mechanism in the proposed algorithm. This transmission loop consists of a UDP message sent on a socket. As the tools used are all freeware, the simulation scenarios can easily be implemented by other researchers. The results are trustworthy, because for multirate scenarios, the MOS index obtained is a value that is between the ones obtained in the single-rate scenarios. The correct performance of the mechanism of the RDA was also verified, so that when the quality of the signal decreases, the control mechanism in the RDA switches to a lower coding rate, ensuring the best use of the transmission canal. When the parameters of the network drive to best conditions, the MOS index of the signal increases and the RDA decides to switch to a higher coding rate achieving a higher communication quality.