The master’s thesis is focused on the theoretical and practical issues of optical access networks. The first chapter of the thesis deals with the concept of the access networks known as FTTx. The second and third chapters focus on the principles and standardization of the active optical network AON P2P and the passive optical network TDM PON. The fourth chapter of the thesis focuses on the network WDM PON, wavelength multiplexes, solution concept and the LG-Ericsson EA 1100 platform. The fifth chapter of the thesis deals with the infrastructure of the optical paths for optical access networks. The sixth chapter of the thesis presents custom design of the headend for reception, processing and distribution of television broadcasting. Two custom access network solutions (AON P2P and WDM PON) for the town Bystřice nad Pernštejnem are presented in the seventh chapter. Case studies include the design of the optical paths infrastructure, central office infrastructure, end-user infrastructure, CAPEX/OPEX economic analysis and basic simulation in OptSim.

The theses explains the Evolution Packet System (EPS) and subsystem IP Multimedia Subsystem (IMS). It also informs how these systems cooperate and through which interfaces the main data and signals between these two technologies are transfered. The thesis includes practical section, in which installation and configuration of sections of the IMS system including its "core", and application and medial server. For verification of the functionality of the system, two dissimilar clients are installed, and emulator WAN is applied for simulation of Internet. The product of the theses is the design of the laboratory exercise drafted in such a way that it can be solved by students less knowledgeable of the issues.

The diploma thesis Digitization and the Internet - Disruptive Technologies of Television Broadcasting discusses the changes in television forms. Emphasis is placed on the transformation of the market in the form of digitization, which subsequently also led to the intensive distribution of data within the Internet environment. The introductory part of the thesis is arched with theoretical support from the sides of economic and media approaches to the process of change. Their central motif deals with innovation or remediation. A closer description of the technologies themselves and their properties is not omitted either. Thanks to a closer description of the technologies themselves and their properties, it is possible to define the existence of imaginary boundaries of television. The second part of the work focuses specifically on the Czech landscape. It deals with the current state of legislation and the non-linear functions that the Internet has brought to television screens. At the practical level, the thesis focuses on alternative forms of television distribution in the Internet environment. The aim is to present the typical features and innovative elements of the disrupting technology of television broadcasting, which were defined in the theoretical part, on the example of the selected VOD...

[EN] This dissertation addresses the problem of multimedia delivery over multi-hop ad hoc wireless networks, and especially over wireless sensor networks. Due to their characteristics of low power consumption, low processing capacity and low memory capacity, they have major difficulties in achieving optimal quality levels demanded by end users in such communications. In the first part of this work, it has been carried out a study to determine the behavior of a variety of multimedia streams and how they are affected by the network conditions when they are transmitted over topologies formed by devices of different technologies in multi hop wireless ad hoc mode. To achieve this goal, we have performed experimental tests using a test bench, which combine the main codecs used in audio and video streaming over IP networks with different sound and video captures representing the characteristic patterns of multimedia services such as phone calls, video communications, IPTV and video on demand (VOD). With the information gathered in the laboratory, we have been able to establish the correlation between the induced changes in the physical and logical topology and the network parameters that measure the quality of service (QoS) of a multimedia transmission, such as latency, jitter or packet loss. At this stage of the investigation, a study was performed to determine the state of the art of the proposed protocols, algorithms, and practical implementations that have been explicitly developed to optimize the multimedia transmission over wireless ad hoc networks, especially in ad hoc networks using clusters of nodes distributed over a geographic area and wireless sensor networks. Next step of this research was the development of an algorithm focused on the logical organization of clusters formed by nodes capable of adapting to the circumstances of real-time traffic. The stated goal was to achieve the maximum utilization of the resources offered by the set of nodes that forms the network, allowing simultaneously sending reliably and efficiently all types of content through them, and mixing conventional IP data traffic with multimedia traffic with stringent QoS and QoE requirements. Using the information gathered in the previous phase, we have developed a network architecture that improves overall network performance and multimedia streaming. In parallel, it has been designed and programmed a communication protocol that allows implementing the proposal and testing its operation on real network infrastructures. In the last phase of this thesis we have focused our work on sending multimedia in wireless sensor networks (WSN). Based on the above results, we have adapted both the architecture and the communication protocol for this particular type of network, whose use has been growing hugely in recent years. / [ES] Esta tesis doctoral aborda el problema de la distribución de contenidos multimedia a través de redes inalámbricas ad hoc multisalto, especialmente las redes inalámbricas de sensores que, debido a sus características de bajo consumo energético, baja capacidad de procesamiento y baja capacidad de memoria, plantean grandes dificultades para alcanzar los niveles de calidad óptimos que exigen los usuarios finales en dicho tipo de comunicaciones. En la primera parte de este trabajo se ha llevado a cabo un estudio para determinar el comportamiento de una gran variedad de flujos multimedia y como se ven afectados por las condiciones de la red cuando son transmitidos a través topologías formadas por dispositivos de diferentes tecnologías que se comunican en modo ad hoc multisalto inalámbrico. Para ello, se han realizado pruebas experimentales sobre una maqueta de laboratorio, combinando los principales códecs empleados en la transmisión de audio y video a través de redes IP con diversas capturas de sonido y video que representan patrones característicos de servicios multimedia tales como las llamadas telefónicas, videoconferencias, IPTV o video bajo demanda (VOD). Con la información reunida en el laboratorio se ha podido establecer la correlación entre los cambios inducidos en la topología física y lógica de la red con los parámetros que miden la calidad de servicio (QoS) de una transmisión multimedia, tales como la latencia el jitter o la pérdida de paquetes. En esta fase de la investigación se realiza un estudio para determinar el estado del arte de las propuestas de desarrollo e implementación de protocolos y algoritmos que se han generado de forma explícita para optimizar la transmisión de tráfico multimedia sobre redes ad hoc inalámbricas, especialmente en las redes inalámbricas de sensores y redes ad hoc utilizando clústeres de nodos distribuidos en un espacio geográfico. El siguiente paso en la investigación ha consistido en el desarrollo de un algoritmo propio para la organización lógica de clústeres formados por nodos capaces de adaptarse a las circunstancias del tráfico en tiempo real. El objetivo planteado es conseguir un aprovechamiento máximo de los recursos ofrecidos por el conjunto de nodos que forman la red, permitiendo de forma simultánea el envío de todo tipo de contenidos a través de ellos de forma confiable y eficiente, permitiendo la convivencia de tráfico de datos IP convencional con tráfico multimedia con requisitos exigentes de QoS y QoE. A partir de la información conseguida en la fase anterior, se ha desarrollado una arquitectura de red que mejora el rendimiento general de la red y el de las transmisiones multimedia de audio y video en particular. De forma paralela, se ha diseñado y programado un protocolo de comunicación que permite implementar el modelo y testear su funcionamiento sobre infraestructuras de red reales. En la última fase de esta tesis se ha dirigido la atención hacia la transmisión multimedia en las redes de sensores inalámbricos (WSN). Partiendo de los resultados anteriores, se ha adaptado tanto la arquitectura como el protocolo de comunicaciones para este tipo concreto de red, cuyo uso se ha extendido en los últimos años de forma considerable / [CA] Esta tesi doctoral aborda el problema de la distribució de continguts multimèdia a través de xarxes sense fil ad hoc multi salt, especialment les xarxes sense fil de sensors que, a causa de les seues característiques de baix consum energètic, baixa capacitat de processament i baixa capacitat de memòria, plantegen grans dificultats per a aconseguir els nivells de qualitat òptims que exigixen els usuaris finals en eixos tipus de comunicacions. En la primera part d'este treball s'ha dut a terme un estudi per a determinar el comportament d'una gran varietat de fluxos multimèdia i com es veuen afectats per les condicions de la xarxa quan són transmesos a través topologies formades per dispositius de diferents tecnologies que es comuniquen en mode ad hoc multi salt sense fil. Per a això, s'han realitzat proves experimentals sobre una maqueta de laboratori, combinant els principals códecs empleats en la transmissió d'àudio i vídeo a través de xarxes IP amb diverses captures de so i vídeo que representen patrons característics de serveis multimèdia com son les cridades telefòniques, videoconferències, IPTV o vídeo baix demanda (VOD). Amb la informació reunida en el laboratori s'ha pogut establir la correlació entre els canvis induïts en la topologia física i lògica de la xarxa amb els paràmetres que mesuren la qualitat de servei (QoS) d'una transmissió multimèdia, com la latència el jitter o la pèrdua de paquets. En esta fase de la investigació es realitza un estudi per a determinar l'estat de l'art de les propostes de desenvolupament i implementació de protocols i algoritmes que s'han generat de forma explícita per a optimitzar la transmissió de tràfic multimèdia sobre xarxes ad hoc sense fil, especialment en les xarxes sense fil de sensors and xarxes ad hoc utilitzant clusters de nodes distribuïts en un espai geogràfic. El següent pas en la investigació ha consistit en el desenvolupament d'un algoritme propi per a l'organització lògica de clusters formats per nodes capaços d'adaptar-se a les circumstàncies del tràfic en temps real. L'objectiu plantejat és aconseguir un aprofitament màxim dels recursos oferits pel conjunt de nodes que formen la xarxa, permetent de forma simultània l'enviament de qualsevol tipus de continguts a través d'ells de forma confiable i eficient, permetent la convivència de tràfic de dades IP convencional amb tràfic multimèdia amb requisits exigents de QoS i QoE. A partir de la informació aconseguida en la fase anterior, s'ha desenvolupat una arquitectura de xarxa que millora el rendiment general de la xarxa i el de les transmissions multimèdia d'àudio i vídeo en particular. De forma paral¿lela, s'ha dissenyat i programat un protocol de comunicació que permet implementar el model i testejar el seu funcionament sobre infraestructures de xarxa reals. En l'última fase d'esta tesi s'ha dirigit l'atenció cap a la transmissió multimèdia en les xarxes de sensors sense fil (WSN). Partint dels resultats anteriors, s'ha adaptat tant l'arquitectura com el protocol de comunicacions per a aquest tipus concret de xarxa, l'ús del qual s'ha estés en els últims anys de forma considerable. / Díaz Santos, JR. (2016). Design and Implementation of a Communication Protocol to Improve Multimedia QoS and QoE in Wireless Ad Hoc Networks [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/62162

A modalidade de Educação a Distância (EAD) ocupa atualmente um lugar importante no desenvolvimento e expansão da Educação no Brasil. A EAD a partir de novas tecnologias, teve um grande impulso, principalmente aquela que envolve a rede Internet. O uso das tecnologias digitais em espaços educativos permitiu que a comunicação, interação, armazenamento e distribuição de conteúdos para o processo educativo, fossem realizados de maneira mais eficiente. Em meio à diversidade de mídias e tecnologias na atualidade, a IPTV surge como uma nova proposta, um veículo de comunicação interativo que possibilita novas perspectivas para a modalidade de EAD. Neste contexto, a IPTV torna-se fundamental, pois possibilita através de seu alto índice de interatividade e qualidade na entrega de conteúdos síncronos e assíncronos oferecer uma gama cada vez maior de opções para seus usuários. O presente trabalho tem como objetivo apresentar elementos visando o uso da IPTV como modalidade de Educação no sistema a distância, para a entrega de conteúdos no Ensino de Engenharia, buscando reduzir as distâncias no processo de ensino-aprendizagem. Dessa forma, são apresentados os benefícios da integração da IPTV e a Educação em Engenharia, dentro de uma estratégia de Educação a Distância na IPTV. / Distance Education (DE) plays an important role nowadays on the development and expansion of education in Brazil. Due to new technologies, DE had a great propulsion, mainly on those which involve the Internet. The use of digital technologies in educational spaces allowed that communication, interaction, storage and distribution of content became more efficient. In between the diversity of medias and technologies, IPTV arises as a new proposal; an interactive communication tool which enables new perspectives for DE. In this context, IPTV is paramount, since its high rates of interaction and synchronous and asynchronous content delivery quality enables a great range of options for its users. This work aims at presenting elements of IPTV use as a modality of DE in the content delivering for Engineering Teaching and Learning, focusing the reduction of distances in the teaching and learning process. Thus, it is presented benefits of the integration between IPTV and Engineering Education through a strategy of DE in IPTV.

A modalidade de Educação a Distância (EAD) ocupa atualmente um lugar importante no desenvolvimento e expansão da Educação no Brasil. A EAD a partir de novas tecnologias, teve um grande impulso, principalmente aquela que envolve a rede Internet. O uso das tecnologias digitais em espaços educativos permitiu que a comunicação, interação, armazenamento e distribuição de conteúdos para o processo educativo, fossem realizados de maneira mais eficiente. Em meio à diversidade de mídias e tecnologias na atualidade, a IPTV surge como uma nova proposta, um veículo de comunicação interativo que possibilita novas perspectivas para a modalidade de EAD. Neste contexto, a IPTV torna-se fundamental, pois possibilita através de seu alto índice de interatividade e qualidade na entrega de conteúdos síncronos e assíncronos oferecer uma gama cada vez maior de opções para seus usuários. O presente trabalho tem como objetivo apresentar elementos visando o uso da IPTV como modalidade de Educação no sistema a distância, para a entrega de conteúdos no Ensino de Engenharia, buscando reduzir as distâncias no processo de ensino-aprendizagem. Dessa forma, são apresentados os benefícios da integração da IPTV e a Educação em Engenharia, dentro de uma estratégia de Educação a Distância na IPTV. / Distance Education (DE) plays an important role nowadays on the development and expansion of education in Brazil. Due to new technologies, DE had a great propulsion, mainly on those which involve the Internet. The use of digital technologies in educational spaces allowed that communication, interaction, storage and distribution of content became more efficient. In between the diversity of medias and technologies, IPTV arises as a new proposal; an interactive communication tool which enables new perspectives for DE. In this context, IPTV is paramount, since its high rates of interaction and synchronous and asynchronous content delivery quality enables a great range of options for its users. This work aims at presenting elements of IPTV use as a modality of DE in the content delivering for Engineering Teaching and Learning, focusing the reduction of distances in the teaching and learning process. Thus, it is presented benefits of the integration between IPTV and Engineering Education through a strategy of DE in IPTV.

中華電信MOD是台灣目前最具規模的互動電視(IPTV)平台，全台已有68萬用戶，除了提供影片隨選（Video on demad）的服務之外，也積極發展其他類型的加值服務，本研究以中華電信MOD之「心靈開運網」算命服務為例，從中探討該服務使用族群的「使用動機」、「服務品質」、「顧客滿意度」、「顧客忠誠度」之間的相互關係，並研究使用動機與服務品質等因子中，何者影響使用族群的滿意度？希望這樣的研究結果日後可提供其他互動電視加值服務開發廠商參考。 本研究經量化研究的統計分析方法與質化研究的深度訪談法，對中華電信MOD加值服務「心靈開運網」算命服務使用族群發放電視問卷，以分析用戶的基本資料與使用行為，同時輔以深度訪談，綜合用戶調查資料、同業建議、MOD平台經營者等各方看法，對本算命服務發現與建議如下： 一.每個年齡層對算命內容的需求有明顯差異，可根據用戶常算的算命分類紀錄，提供客製化的首頁，以方便用戶選擇。 二.從用戶的算命記錄可看出用戶目前的需求，可以針對用戶的需求尋找異業結盟或廣告交換，如理財、婚顧、養生、交友等服務，以提高用戶滿意度。 三.人口統計變項(性別、年齡、教育、職業、收入)對於中華電信MOD加值服務「心靈開運網」之使用動機、服務品質、忠誠度、滿意度，除了學歷之外，並無顯著差異，可能表示不同人口統計變項，對於算命的喜好差異不大。 四.服務品質與滿意度的關連性，較使用動機與滿意度的關連性強，服務品質愈好，滿意度愈高。 五.服務品質對滿意度的影響很大，其中產品可靠度，也就是算命的準確度，將影響整個服務品質構面給用戶的感覺。 六.本算命服務對於個人隱私愈保護，用戶的再度使用意願會愈高，同時算命內容若讓用戶感覺能趨吉避凶，感覺安心，推薦給他人的機會就愈高。 關鍵詞：互動電視、IPTV、MOD、加值服務、心靈開運網、使用動機、資訊來源、服務品質、滿意度、忠誠度、電視問卷 / Abstract Chunghwa Telecom MOD is the most popular IPTV provider in Taiwan, which now has around 680,000 subscribers. In addition to providing video on demand services, Chunghwa Telecom MOD is also aggressively expanding other value-added-services (VAS). Using Chunghwa Telecom MOD's "Superfate" service as an example, this study tried to examine the relationships between “usage motivation”, “service quality”, “customer satisfaction”, and “customer loyalty”. Furthermore, we tried to investigate which of the following factors (e.g., usage motivation and service quality) has the greatest impact on “customer satisfaction”. We hope that the research outcome could provide some directions for other VAS developers of IPTV industry. Using both quantitative statistical analysis and qualitative in-depth interviews. We extensively surveyed different consumer groups of Chunghwa Telecom MOD's "Superfate" service in order to understand consumer profile and user behavior. At the same time, we also conducted in-depth interviews Based upon research outcomes from consumer surveys and key industry players interviews, we provide several recommendations to the "Superfate" service as follow: 1.Different age groups have different demands on fortune telling content. To make this service more user-friendly, we should customize the front page according to the record of the customers' most-frequently-visit fortune-telling categories. 2.Based on the usage records of each user, we can easily identify the associated services each customer might need. We can effectively increase customer satisfaction level by forming strategic alliance with other value-added-services, e.g. personal finance, match-making, wedding-planning, and health care related services. 3.Demographic variables (e.g., age, gender, occupation, and income) do not have a significantly different impact on usage motivation, service quality, customer loyalty, and satisfaction. Educational level is the exception. Our results imply that demographic differences do not significantly influence customers' preference on fortune-telling. 4.Service quality has a stronger influence on satisfaction level than usage motivation. The better the service quality, the more satisfied the users are. 5.Service quality has a strong influence on the level of customer satisfaction. Moreover, the reliability of the service, or the accuracy of the fortune-telling result, can greatly impact customers' perception of service quality. 6.Users are more willing to reuse this service when they feel their privacy is protected. Meanwhile, the user is more willing to recommend this service to others when they feel the fortune-telling results could help them approach the positive luck and avoid the negative fate. Keywords：Multimedia On Demand(MOD)、IPTV、value-added-services、Superfate、usage motivation、service quality、customer satisfaction、customer loyalty、TV questionnaire survey

Com o aumento da concorrência sofrido pelas operadoras de telecomunicações frente à entrada de diversas empresas de outros ramos no mercado de comunicação, como, por exemplo, os Provedores de Serviço de Internet (ISPs - Internet Service Providers) através da oferta de serviços de voz sobre IP, tais operadoras viram-se obrigadas a diversificar sua oferta de serviços para gerar novas fontes de receita. Por possuírem ampla infra-estrutura instalada, as operadoras de telecomunicações passaram a oferecer, também, serviço de TV aos usuários, através de suas redes (convergentes) de telefonia e dados já existentes, o chamado IPTV. O objetivo deste trabalho foi possibilitar, neste cenário, que estas empresas consigam oferecer, além dos serviços convencionais de TV (e.g., transmissões lineares dos conteúdos nos canais de TV), serviços diferenciados empregando-se a mesma infra-estrutura. O foco deste trabalho é a oferta do serviço de apresentação deslocada no tempo dos conteúdos transmitidos linearmente nos canais de TV, sem a necessidade de configuração prévia por parte do usuário. Desta maneira, dá-se maior flexibilidade ao usuário, possibilitando-o assistir aos conteúdos que lhe interessam, no horário mais conveniente, sem ter que se preocupar com isso antecipadamente (i.e., sem a necessidade de configurar algum equipamento para gravar o conteúdo ou saber antecipadamente quais programas lhe interessam). Para isso foram pesquisadas e analisadas tanto tecnologias de transmissão e distribuição de conteúdos, como também o paradigma peer-to-peer, muito utilizado atualmente no compartilhamento de arquivos na Internet. A partir daí, foi concebida uma arquitetura capaz de oferecer tanto o serviço tradicional de transmissão linear de TV, quanto de apresentar vídeos deslocados no tempo (i.e., vídeos cuja transmissão linear já foi iniciada ou até concluída, a partir de qualquer posição já transmitida), combinando-se técnicas de multidifusão de dados, armazenamento distribuído e protocolos peer-to-peer. Desta maneira, obteve-se uma solução eficiente, utilizando-se os recursos disponíveis em todo o sistema, incluindo recursos ociosos dos usuários finais, para auxiliar no armazenamento e distribuição dos conteúdos deslocados no tempo. Finalmente, um protótipo foi desenvolvido como prova de conceito da arquitetura proposta neste trabalho, e, juntamente com os testes realizados, comprovam a viabilidade de se utilizar redes P2P para a distribuição dos conteúdos para a apresentação deslocada no tempo. / Telecommunication companies are suffering from the increasing offer of cheap and reliable voice over IP services, being forced to diversify their services looking for new revenue possibilities. Since these companies have a vast infrastructure, they are now providing TV services through the same telephony and data infrastructure, using their IP networks to offer IPTV. The goal of the present work is to allow, in this scenario, that such companies offer, additionally to the traditional TV services (e.g., the linear transmissions of the TV channels), differentiated services through the same infrastructure. The focus of the present work is, therefore, the offering of the time-shift service, allowing users to watch linear transmitted contents, time-shifted, without the need for any in-advance configuration. This approach gives more flexibility to the users, allowing them to choose the most appropriate time to watch some content without having to specify their interests in advance (i.e., without configuring some equipment to record the content or knowing in advance which programs will interest themselves). To achieve this goal, technologies for content transmission and distribution, as well as the peer-to-peer paradigm for file sharing were studied, resulting in the development of an architecture capable of offering the traditional linear transmissions service as well as the possibility of time-shift, combining multicast, distributed caching and peer-to-peer technologies. Accordingly, an efficient solution was envisioned, making use of all available resources in the system, including idle resources in the user equipments, to help in the caching and distribution of the time-shifted contents. Finally, a prototype was developed as a proof-of-concept for the designed architecture, which together with the performed tests, shows the viability of utilizing P2P networks in the distribution of time-shifted contents.

Com o aumento da concorrência sofrido pelas operadoras de telecomunicações frente à entrada de diversas empresas de outros ramos no mercado de comunicação, como, por exemplo, os Provedores de Serviço de Internet (ISPs - Internet Service Providers) através da oferta de serviços de voz sobre IP, tais operadoras viram-se obrigadas a diversificar sua oferta de serviços para gerar novas fontes de receita. Por possuírem ampla infra-estrutura instalada, as operadoras de telecomunicações passaram a oferecer, também, serviço de TV aos usuários, através de suas redes (convergentes) de telefonia e dados já existentes, o chamado IPTV. O objetivo deste trabalho foi possibilitar, neste cenário, que estas empresas consigam oferecer, além dos serviços convencionais de TV (e.g., transmissões lineares dos conteúdos nos canais de TV), serviços diferenciados empregando-se a mesma infra-estrutura. O foco deste trabalho é a oferta do serviço de apresentação deslocada no tempo dos conteúdos transmitidos linearmente nos canais de TV, sem a necessidade de configuração prévia por parte do usuário. Desta maneira, dá-se maior flexibilidade ao usuário, possibilitando-o assistir aos conteúdos que lhe interessam, no horário mais conveniente, sem ter que se preocupar com isso antecipadamente (i.e., sem a necessidade de configurar algum equipamento para gravar o conteúdo ou saber antecipadamente quais programas lhe interessam). Para isso foram pesquisadas e analisadas tanto tecnologias de transmissão e distribuição de conteúdos, como também o paradigma peer-to-peer, muito utilizado atualmente no compartilhamento de arquivos na Internet. A partir daí, foi concebida uma arquitetura capaz de oferecer tanto o serviço tradicional de transmissão linear de TV, quanto de apresentar vídeos deslocados no tempo (i.e., vídeos cuja transmissão linear já foi iniciada ou até concluída, a partir de qualquer posição já transmitida), combinando-se técnicas de multidifusão de dados, armazenamento distribuído e protocolos peer-to-peer. Desta maneira, obteve-se uma solução eficiente, utilizando-se os recursos disponíveis em todo o sistema, incluindo recursos ociosos dos usuários finais, para auxiliar no armazenamento e distribuição dos conteúdos deslocados no tempo. Finalmente, um protótipo foi desenvolvido como prova de conceito da arquitetura proposta neste trabalho, e, juntamente com os testes realizados, comprovam a viabilidade de se utilizar redes P2P para a distribuição dos conteúdos para a apresentação deslocada no tempo. / Telecommunication companies are suffering from the increasing offer of cheap and reliable voice over IP services, being forced to diversify their services looking for new revenue possibilities. Since these companies have a vast infrastructure, they are now providing TV services through the same telephony and data infrastructure, using their IP networks to offer IPTV. The goal of the present work is to allow, in this scenario, that such companies offer, additionally to the traditional TV services (e.g., the linear transmissions of the TV channels), differentiated services through the same infrastructure. The focus of the present work is, therefore, the offering of the time-shift service, allowing users to watch linear transmitted contents, time-shifted, without the need for any in-advance configuration. This approach gives more flexibility to the users, allowing them to choose the most appropriate time to watch some content without having to specify their interests in advance (i.e., without configuring some equipment to record the content or knowing in advance which programs will interest themselves). To achieve this goal, technologies for content transmission and distribution, as well as the peer-to-peer paradigm for file sharing were studied, resulting in the development of an architecture capable of offering the traditional linear transmissions service as well as the possibility of time-shift, combining multicast, distributed caching and peer-to-peer technologies. Accordingly, an efficient solution was envisioned, making use of all available resources in the system, including idle resources in the user equipments, to help in the caching and distribution of the time-shifted contents. Finally, a prototype was developed as a proof-of-concept for the designed architecture, which together with the performed tests, shows the viability of utilizing P2P networks in the distribution of time-shifted contents.

<p>A channel change in digital television is usually conducted at a reference frame, which are sent at certain intervals. A higher compression ratio could however be obtained by sending reference frames at arbitrary long intervals. This would on the other hand increase the average channel change time for the end user. This thesis investigates various approaches for reducing the average channel change time while using arbitrary long intervals between reference frames, and presents an implementation and evaluation of one of these methods, called Baydec.</p><p>The approach of Baydec for solving the channel switch problem is to statistically estimate what the original image looked like, starting with an incoming P-frame and estimate an image between the original and current image. Baydec gathers statistical data from typical video sequences and calculates expected likelihood for estimation. Further on it uses the Simulated Annealing search method to maximise the likelihood function.</p><p>This method is more general than the requirements of this thesis. It is not only applicable to channel switches between video streams, but can also be used for random access in general. Baydec could also be used if an I-frame is dropped in a video stream.</p><p>However, Baydec has so far shown only theoretical result, but very small visual improvements. Baydec produces images with better PSNR than without the method in some cases, but the visual impression is not better than for the motion compensated residual images. Some examples of future work to improve Baydec is also presented.</p>