Les applications vidéo embarquées sont de plus en plus intégrées dans des systèmes de transport intelligents tels que les véhicules autonomes. De nombreux défis sont rencontrés par les concepteurs de ces applications, parmi lesquels : le développement des algorithmes complexes, la vérification et le test des différentes contraintes fonctionnelles et non-fonctionnelles, la nécessité d’automatiser le processus de conception pour augmenter la productivité, la conception d’une architecture matérielle adéquate pour exploiter le parallélisme inhérent et pour satisfaire la contrainte temps-réel, réduire la puissance consommée pour prolonger la durée de fonctionnement avant de recharger le véhicule, etc. Dans ce travail de thèse, nous avons utilisé les technologies FPGAs pour relever certains de ces défis et proposer des architectures matérielles reconfigurables dédiées pour des applications embarquées de traitement vidéo temps-réel. Premièrement, nous avons implémenté une architecture parallèle flexible avec deux contributions principales : (1) Nous avons proposé un modèle générique de distribution/collecte de pixels pour résoudre le problème de transfert de données à haut débit à travers le système. Les paramètres du modèle requis sont tout d’abord définis puis la génération de l’architecture a été automatisée pour minimiser le temps de développement. (2) Nous avons appliqué une technique d’ajustement de la fréquence pour réduire la consommation d’énergie. Nous avons dérivé les équations nécessaires pour calculer le niveau maximum de parallélisme ainsi que les équations utilisées pour calculer la taille des FIFO pour le passage d’un domaine de l’horloge à un autre. Au fur et à mesure que le nombre de cellules logiques sur une seule puce FPGAaugmente, passer à des niveaux d’abstraction plus élevés devient inévitable pour réduire la contrainte de « time-to-market » et augmenter la productivité des concepteurs. Pendant la phase de conception, l’espace de solutions architecturales présente un grand nombre d’alternatives avec des performances différentes en termes de temps d’exécution, ressources matérielles, consommation d’énergie, etc. Face à ce défi, nous avons développé l’outil ViPar avec deux contributions principales : (1) Un modèle empirique a été introduit pour estimer la consommation d’énergie basé sur l’utilisation du matériel (Slice et BRAM) et la fréquence de fonctionnement ; en plus de cela, nous avons dérivé les équations pour estimer les ressources matérielles et le temps d’exécution pour chaque alternative au cours de l’exploration de l’espace de conception. (2) En définissant les principales caractéristiques de l’architecture parallèle comme le niveau de parallélisme, le nombre de ports d’entrée/sortie, le modèle de distribution des pixels, ..., l’outil ViPar génère automatiquement l’architecture matérielle pour les solutions les plus pertinentes. Dans le cadre d’une collaboration industrielle avec NAVYA, nous avons utilisé l’outil ViPar pour implémenter une solution matérielle parallèle pour l’algorithme de stéréo matching « Multi-window Sum of Absolute Difference ». Dans cette implémentation, nous avons présenté un ensemble d’étapes pour modifier le code de description de haut niveau afin de l’adapter efficacement à l’implémentation matérielle. Nous avons également exploré l’espace de conception pour différentes alternatives en termes de performance, ressources matérielles, fréquence, et consommation d’énergie. Au cours de notre travail, les architectures matérielles ont été implémentées et testées expérimentalement sur la plateforme d’évaluation Xilinx Zynq ZC706. / Embedded video applications are now involved in sophisticated transportation systems like autonomous vehicles. Many challenges faced the designers to build those applications, among them: complex algorithms should be developed, verified and tested under restricted time-to-market constraints, the necessity for design automation tools to increase the design productivity, high computing rates are required to exploit the inherent parallelism to satisfy the real-time constraints, reducing the consumed power to extend the operating duration before recharging the vehicle, etc. In this thesis work, we used FPGA technologies to tackle some of these challenges to design parallel reconfigurable hardware architectures for embedded video streaming applications. First, we implemented a flexible parallel architecture with two main contributions: (1)We proposed a generic model for pixel distribution/collection to tackle the problem of the huge data transferring through the system. The required model parameters were defined then the architecture generation was automated to minimize the development time. (2) We applied frequency scaling as a technique for reducing power consumption. We derived the required equations for calculating the maximum level of parallelism as well as the ones used for calculating the depth of the inserted FIFOs for clock domain crossing. As the number of logic cells on a single FPGA chip increases, moving to higher abstraction design levels becomes inevitable to shorten the time-to-market constraint and to increase the design productivity. During the design phase, it is common to have a space of design alternatives that are different from each other regarding hardware utilization, power consumption and performance. We developed ViPar tool with two main contributions to tackle this problem: (1) An empirical model was introduced to estimate the power consumption based on the hardware utilization (Slice and BRAM) and the operating frequency. In addition to that, we derived the equations for estimating the hardware resources and the execution time for each point during the design space exploration. (2) By defining the main characteristics of the parallel architecture like parallelism level, the number of input/output ports, the pixel distribution pattern, etc. ViPar tool can automatically generate the parallel architecture for the selected designs for implementation. In the context of an industrial collaboration, we used high-level synthesis tools to implement a parallel hardware architecture for Multi-window Sum of Absolute Difference stereo matching algorithm. In this implementation, we presented a set of guiding steps to modify the high-level description code to fit efficiently for hardware implementation as well as we explored the design space for different alternatives in terms of hardware resources, performance, frequency and power consumption. During the thesis work, our designs were implemented and tested experimentally on Xilinx Zynq ZC706 (XC7Z045- FFG900) evaluation board.

This thesis dissertation addresses the problem of providing video streaming services over mobile wireless ad hoc networks. This sort of network represents a hostile environment for this kind of realtime data transmission to the extent that obtaining a good quality of viewer experience is challenging and still under study. Besides the research point of view, providing high-quality multimedia services is decisive for the practical usability and feasibility of wireless ad hoc networks so that service providers can broaden the range of services offered. So far, mobile wireless ad hoc networks have been used to provide network connection among users who could not have connectivity otherwise. However, quality expectations and requirements have been increased notably, fostered by the advent of real-time multimedia applications over mobile devices. Due to the considerable processing and bandwidth constraints underlying these types of devices, coupled with their ability to move freely, it becomes a difficult task to achieve an acceptable quality of service throughout the entire video transmission. Thus, the contribution of this thesis work is twofold. On the one hand, the main problems and limitations that may be encountered and should be faced when deploying real-time services over mobile wireless ad hoc networks are analyzed and discussed. Bandwidth constraints and node mobility are portrayed as the major causes that prevent good quality of service and smooth video playback. On the other hand, following then the aim of improving video streaming quality, this thesis proposes practical solutions that involve diverse routing and cross-layer techniques. One of the proposed approaches focuses on hierarchical routing. Hierarchical arrangement of network nodes may reduce packet interference as well as offer a structured architecture that reduces control traffic overhead. Particularly, the proposed hierarchical routing protocol aims at providing scalability when the number of nodes grows, while maintaining complexity as low as possible. The resulting reduction in packet losses and video playback interruptions finally enhances the quality of received video streams. Furthermore, on the basis that the nodes in an ad hoc network are willing to perform routing tasks, every node could become essential for the proper network operation and routing performance. In tune with this philosophy, a new cross-layer mechanism for recovering lost packets is proposed. By overhearing packets over the wireless shared medium, any node in the surrounding area of the destination endpoint can altruistically retransmit those video packets that have not been correctly received at destination. Moreover, due to the video awareness and frame prioritization algorithm considered in this proposal, it becomes very convenient for real-time video streaming services. The results show that the presented mechanism succeeds in improving video quality and user experience, especially when packet losses are caused due to the mobility of the destination node. / Arce Vila, P. (2014). Hierarchical routing and cross-layer mechanisms for improving video streaming quality of service over mobile wireless ad hoc networks [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/36538 / Alfresco

[EN] This thesis dissertation tackles the problem concerning provision of video streaming services over mobile wireless ad hoc networks. Such networks are characterized by their versatility and flexibility, features that make them particularly suited to be used in many scenarios. However, some limitations inherited of the wireless channel and the mobility of the nodes make difficult to guarantee certain degree of quality of service, which is a required condition to the multimedia applications. Furthermore, with the massive demand of video content, it has become very necessary for mobile ad hoc networks to have an efficient routing and quality of services mechanisms to support this traffic. This is because video streaming services require network to provide sufficient bandwidth and an upper bound in delay, jitter and loss rate. Consequently, traditional best-effort protocols are not adequate. The main contribution of this thesis is the development of a comprehensive routing protocol that has a feedback scheme in order to provide information to the application about the network conditions. This protocol has a cross-layer architecture and it incorporates three important enhancements. Firstly, a new route recovery strategy, which provides a mechanism to detect the link failures in a route and re-establish the connections taking into account the conditions of quality of service that have been established during the previous route discovery phase. Secondly, an algorithm for the estimation of the available bandwidth along the route, information that is sent to application layer in order to apply an adaptation procedure that adjusts the bit rate of the video source. This rate-adaptive strategy is performed exploiting the layered scheme of the scalable video coding. In particular, the adaptive method removes, from the scalable video stream, those layers that could not be efficiently supported by network since their bitrates exceed the available bandwidth. The third main feature of the proposed routing protocol is a gateway discovery algorithm to improve the interconnectivity between mobile ad hoc networks and infrastructure-based networks. This algorithm incorporates available bandwidth as a metric during the gateway selection and a dynamic adaptation of some operational parameters such as the size of the proactive area and the frequency of the advertisement messages. Additionally, in order to solve the lack of a software tool to simulate rate-adaptive transmission of scalable video, a new simulation framework had be implemented. This simulation tool is an open source software freely available and, thus, it represents other contribution of this thesis. The results reveal performance improvements in terms of packet delay, dropped packets and the number of link failures while a more efficient use of the available bandwidth is obtained. In terms of video transmission, the results prove that the combined use of the proposed protocol and the scalable video coding provides an efficient platform for supporting rate-adaptive video streaming over mobile ad hoc networks. / [ES] Esta tesis aborda los problemas relacionados con los servicios de video en modo streaming sobre las redes móviles ad hoc. Este tipo de redes se caracterizan por su versatilidad y flexibilidad, lo cual las hace especialmente adecuadas para ser utilizadas en diversos escenarios. Sin embargo, algunas limitaciones inherentes a los enlaces inalámbricos y a la movilidad de los nodos, hace difícil garantizar cierto nivel de calidad de servicio, lo cual es una condición necesaria para el transporte de flujos multimedia. Además, con la masiva demanda de videos desde los dispositivos móviles, hace aún más necesario asegurar un encaminamiento eficiente y un cierto nivel de calidad de servicio en las redes móviles ad hoc. Por lo tanto, los tradicionales protocolos que funcionan bajo el modelo del "mejor esfuerzo" no son adecuados. Esto se debe principalmente a que las aplicaciones multimedia necesitan que la red asegure suficiente ancho de banda y unos valores máximos de retardo, jitter, y tasa de pérdidas. La principal contribución de esta tesis es el desarrollo de un protocolo de encaminamiento que contiene un esquema de realimentación que le permite informar a la aplicación sobre las condiciones de la red. Este protocolo tiene una arquitectura cross-layer e incorpora tres importantes mejoras. Primero, una nueva estrategia de mantenimiento y recuperación de rutas que provee mecanismos para detectar los fallos de conectividad y el posterior re-establecimiento de las conexiones, teniendo en cuenta las condiciones de calidad de servicio que fueron establecidas durante la etapa inicial del descubrimiento de las rutas. Segundo, un algoritmo para la estimación del ancho de banda disponible a lo largo de la ruta, información que es enviada a la capa de aplicación para aplicar un proceso de adaptación que ajusta la tasa de envío de datos de la fuente. Esta estrategia adaptativa de la tasa aprovecha el esquema por capas de la codificación escalable de video. En particular, el método adaptativo elimina del flujo de video escalable, aquellas capas que no pueden ser transmitidas por la red ya que su tasa de bits supera el ancho de banda disponible. La tercera mejora incluida en el protocolo propuesto es un algoritmo de descubrimiento de gateways para mejorar la interconectividad entre las redes móviles ad hoc y las redes basadas en infraestructura. Dicho algoritmo utiliza el ancho de banda disponible para seleccionar el mejor gateway, así mismo, realiza una adaptación dinámica de algunos parámetros operacionales como el alcance y la frecuencia de los mensajes anuncio. Adicionalmente, ha sido desarrollada una herramienta software para simular la transmisión adaptativa de video escalable sobre redes móviles ad hoc. Esta herramienta de simulación es un software de código abierto y constituye otra contribución más de esta tesis. Los resultados muestran mejoras en el funcionamiento de las redes relacionadas con el retardo, la tasa de pérdidas de paquetes y el número de fallos en la conectividad. Simultáneamente, se obtiene un uso más eficiente del ancho de banda. En relación a la calidad del video transmitido, los resultados demuestran que la utilización del protocolo propuesto junto con la codificación de video escalable, provee un eficiente sistema para la transmisión adaptativa de video escalable sobre redes móviles ad hoc. / [CAT] Aquesta tesi aborda els problemes relacionats amb els serveis de vídeo en mode streaming sobre les xarxes mòbils ad hoc. Aquest tipus de xarxes es caracteritzen per la seva versatilitat i flexibilitat, la qual cosa les fa especialment adequades per a ser utilitzades en diversos escenaris. No obstant això, algunes limitacions inherents als enllaços sense fils i a la mobilitat dels nodes, fa difícil garantir cert nivell de qualitat de servei, cosa que és una condició necessària per al transport de fluxos multimèdia. A més, amb la massiva demanda de vídeos des dels dispositius mòbils, fa encara més necessari assegurar un encaminament eficient i un cert nivell de qualitat de servei en les xarxes mòbils ad hoc. Per tant, els tradicionals protocols que funcionen sota el model del "millor esforç" no són adequats. Això es deu principalment al fet que les aplicacions multimèdia necessiten que la xarxa asseguri suficient ample de banda i uns valors màxims de retard, jitter, i taxa de pèrdues. La principal contribució d'aquesta tesi és el desenvolupament d'un protocol d'encaminament que conté un esquema de realimentació que li permet informar l'aplicació sobre les condicions de la xarxa. Aquest protocol té una arquitectura cross-layer i incorpora tres importants millores. Primer, una nova estratègia de manteniment i recuperació de rutes que proveeix mecanismes per detectar les fallades de connectivitat i el posterior re-establiment de les connexions, tenint en compte les condicions de qualitat de servei que van ser establertes durant l'etapa inicial del descobriment de les rutes. Segon, un algoritme per a l'estimació de l'ample de banda disponible al llarg de la ruta, informació que és enviada a la capa d'aplicació per aplicar un procés d'adaptació que ajusta la taxa d'enviament de dades de la font. Aquesta estratègia adaptativa de la taxa aprofita l'esquema per capes de la codificació escalable de vídeo. En particular, el mètode adaptatiu elimina del flux de vídeo escalable aquelles capes que no poden ser transmeses per la xarxa ja que la seva taxa de bits supera l'ample de banda disponible. La tercera millora inclosa en el protocol proposat és un algoritme de descobriment de gateways per millorar la interconnectivitat entre les xarxes mòbils ad hoc i les xarxes basades en infraestructura. Aquest algoritme utilitza l'ample de banda disponible per seleccionar el millor gateway, així mateix, realitza una adaptació dinàmica d'alguns paràmetres operacionals com l'abast i la freqüència dels missatges anunci. Addicionalment, ha estat desenvolupada una eina programari per a simular la transmissió adaptativa de vídeo escalable sobre xarxes mòbils ad hoc. Aquesta eina de simulació és un programari de codi obert i constitueix una altra contribució més d'aquesta tesi. Els resultats mostren millores en el funcionament de les xarxes relacionades amb el retard, la taxa de pèrdues de paquets i el nombre de fallades en la connectivitat. Simultàniament, se n'obté un ús més eficient de l'ample de banda. En relació a la qualitat del vídeo transmès, els resultats demostren que la utilització del protocol proposat juntament amb la codificació de vídeo escalable, proveeix un eficient sistema per a la transmissió adaptativa de vídeo escalable sobre xarxes mòbils ad hoc. / Castellanos Hernández, WE. (2015). Quality of Service Routing and Mechanisms for Improving Video Streaming over Mobile Wireless Ad hoc Networks [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/53238 / TESIS

Konsumtionen av video på Internet har ökat det senaste decenniet och trenden är förväntad att fortsätta stiga. Strömmande video är en ofta använd lösning för att se video på Internet. Tekniken tillåter användaren att se film medan den laddas ned. Adaptive streaming är en teknik som låter videospelaren ändra bit-raten på videon baserat på användarens tillgängliga bandbredd. En annan lösning för att göra användarens upplevelse mer skräddarsydd är ickelinjära videor. Den här typen av videor kan spelas ur sekvens. Som exempel kan en tittare välja slutet i en film eller välja vägen genom en utställning. Examensarbetet presenterar designen och implementeringen av en ny struktur för ickelinjär video. Denna struktur används av videospelaren för nedladdning och visning av adaptiv video avsedd för ickelinjära filmer, som sparas på en server. Mediaskapare kommer också att ha lättare att både visualisera och skapa filmer på ett enhetligt sätt. Det här examensarbetet presenterar i detalj de modifikationer på Adobes Open Source Media Framework och Strobe Media Playback som tillåter spelning av ickelinjära videor. Ändringarna innefattar ett användargränssnitt för ickelinjär media. Back-end implementeringarna innefattar bufferthantering för parallell nedladdning och tekniker för att hantera den nya strukturen. Slutligen presenterar det här examensarbetet proof-of-concept-tester för att styrka funktionaliteten av designen och implementeringen. Rapporten avslutas med en diskussion om framtida arbete inom fältet. / Video consumption on the Internet has been growing over the last decade and is expected to continue to increase. Video streaming is a widely used approach to viewing video on the Internet, which allows users to watch the video while it is being downloaded. Adaptive streaming is a video streaming technique that allows the player to change the downloading video’s bit rate depending on the user’s available bandwidth. Another approach to a more personal viewing experience is non-linear videos. These videos can be played in a non-sequential order. For example, a viewer can be given the choice of what ending to watch in a movie, or the path through an exhibition. This thesis will present the design and implementation of a novel structure for non-linear video. This structure is used by a video player for downloading and viewing an adaptive video intended for non-linear viewing, stored at some server. Media creators will also have an easier time to both visualize and create uniform video experiences. This thesis presents modifications to Adobe’s Open Source Media Framework and Strobe Media Playback which allow playing non-linear video. Presented in this thesis are the design and implementation details. Changes in the player include a user interface for non-linear media. The changes to the back-end include buffer management for parallel downloading and techniques to handle the new structure. Finally, this thesis presents proof-of-concept validation tests that show the functionality of the design and implementation. The thesis is concluded with a discussion of future work in this area.

This thesis deals with a web-based lecture browser. Its goal is to facilitate the access to information with the use of modern speech and multimedia technologies. Technologies used for this browser are discussed. Video recordings play a very important role in the browser, and therefore the big portion of this work is aimed at the digital video and methods of its delivery using streaming servers. Solutions of similar multimedia browsers are mentioned. The reader is acquainted with the browser design. This includes describing the various components of the browser and how their mutual synchronization is done. The final version of the browser is introduced and the problems that occurred during the development process and deployment into service are mentioned. In the conclusion of this work the future development of the web-based lecture browser is discussed.

<p dir="ltr">Ensuring a high quality of experience for Internet applications is challenging owing to the significant variability (e.g., of traffic patterns) inherent to both cloud data-center networks and wide area networks. This thesis focuses on optimizing application performance by both conducting measurements to characterize traffic variability, and designing applications that can perform well in the face of variability. On the data center side, a key aspect that impacts performance is traffic burstiness at fine granular time scales. Yet, little is know about traffic burstiness and how it impacts application loss. On the wide area side, we focus on video applications as a major traffic driver. While optimizing traditional videos traffic remains a challenge, new forms of video such as 360◦ introduce additional challenges such as respon- siveness in addition to the bandwidth uncertainty challenge. In this thesis, we make three contributions.</p><p dir="ltr"><b>First</b>, for data center networks, we present Millisampler, a lightweight network traffic char- acterization tool for continual monitoring which operates at fine configurable time scales, and deployed across all servers in a large real-world data center networks. Millisampler takes a host-centric perspective to characterize traffic across all servers within a data center rack at the same time. Next, we present data-center-scale joint analysis of burstiness, contention, and loss. Our results show (i) bursts are likely to encounter contention; (ii) contention varies significantly over short timescales; and (iii) higher contention need not lead to more loss, and the interplay with workload and burst properties matters.</p><p dir="ltr"><b>Second</b>, we consider challenges with traditional video in wide area networks. We take a step towards understanding the interplay between Content-Delivery-Networks (CDNs), and video performance through end-to-end measurements. Our results show that (i) video traffic in a session can be sourced from multiple CDN layers, and (ii) throughput can vary signifi- cantly based on the traffic source. Next we evaluate the potential benefits of exposing CDN information to the client Adaptive-Bit-Rate (ABR) algorithm. Emulation experiments show the approach has the potential to reduce prediction inaccuracies, and enhance video quality of experience (QoE).</p><p dir="ltr"><b>Third</b>, for 360◦ videos, we argue for a new streaming model which is explicitly designed for continuous, rather than stalling, playback to preserve interactivity. Next, we propose Dragonfly, a new 360° system that leverages the additional degrees of freedom provided by this design point. Dragonfly proactively skips tiles (i.e., spatial segment of the video) using a model that defines an overall utility function that captures factors relevant to user experience. We conduct a user study which shows that majority of interactivity feedback indicating Dragonfly being highly reactive, while the majority of state-of-the-art’s feedback indicates the systems are slow to react. Further, extensive emulations show Dragonfly improves the image quality significantly without stalling playback.</p>

Vad händer när en produkt eller tjänst försämrar konsumentens välmående och förtjänsterna ökar ju mer detta sker? Ett etiskt dilemma har uppstått inom digitala plattformar, däribland videoströmningsplattformar (VSP), på grund av detta. En genomgående trend för VSP:ar men också inom e-handeln och mobilappar har visat sig vara nyttjandet av manipulativ design i användargränssnittet, så kallade mörka mönster (eng. Dark Patterns). Inom VSP:ar har Autouppspelningsfunktionen och Rekommendationer utsetts som stora anledningar till att konsumenterna fortsätter att titta. Etiska riktlinjer för UX-designers (de som formar användargränssnitt) kan vara en möjlig väg från detta, andra åtgärder som diskuterats har varit att lagstifta eller lägga tron i att konsumenterna själva kommer att välja bort de plattformar som använder manipulativ design. I syfte att undersöka respondenters medvetenheten om-, förmåga att hitta- och medveten om den potentiella påverkan- och förmåga att hitta mörka mönster på VSP:ar genomfördes en onlineenkät (n=56). Resultatet för undersökningen visar att även om användare i viss mån är medvetna om- och har förmågan att hitta en del av de givna mönsterna bär dessa skyddsegenskaper ingen signifikant relation till att få användaren att undgå att bli påverkad av manipulationen. / What happens when a product or service impairs the consumer's well-being? And profits increase the more this happens? An ethical dilemma has arisen within digital platforms, including video streaming platforms (VSPs), because of this. A consistent trend for VSPs but also for e-commerce and smartphone apps has proven to be the use of manipulative design in user interfaces, so-called Dark Patterns. Within VSPs, the Autoplay feature and Recommendations have been cited as big reasons for consumers to keep watching. Ethical guidelines for UX designers (the ones who shape user interfaces) could be a possible way out of this, other possible measures are to create a legislation or add to the belief that consumers will opt out of those platforms that contain manipulative design. In order to investigate the awareness of-, ability to find- and influence gained despite awareness of- and ability to find dark patterns on VSPs, an online survey was applied (n=56). The result of the investigation shows that even if users are aware to a certain extent and have the ability to find some of the given patterns, these protective properties do not having a significant relationship with the respondent being able to avoid influence from the patterns.

No description available.

Video-on-demand streaming從90年代就在適當的科技下成為網際網路流量的龍頭，故宮教育頻道在技術上採用TCP-based video streaming，但Video streaming使得負載較一般的伺服器繁重。透過負載平衡來分散負載是可行的方式之一，但在TCP-based video streaming的技術下，還是可能遭遇服務品質之相關議題。而服務品質要求 (Quality of Service, QoS)是用來對使用者適配的服務品質表現，做具體之等級劃分的管理工具，本研究以故宮教育頻道 (iPalace Video Channel; iPalace)為標的，針對其DNS Load Balancing搭配Round Robin的運作背景，提出VM Side QoS及Client Side QoS，在VM Side設定Load rate作為指標、在Client Side則以撥放器的表現為主，設定Initial Buffering Time、Mean Rebuffering Duration以及Rebuffering Frequency共三個指標，並搭配流量的實驗操作，劃分Regular及Class情境來蒐集資料。 在分析後發現，在環境較為一致的Class情境中，Mean Rebuffering Duration與Load Rate及Rebuffering Frequency與Load Rate具有低度正相關。未來，若能在環境及客戶端的變異性有較多的控制及掌握，則可讓資料在蒐集上更為正確，讓後續的分析及探討與實際狀況更為相符。

近十年來，由於無線網路的普及與人們對於影像串流服務的需求愈高，導致人們迫切需要更好的服務品質。但在IEEE 802.11無線網路中，本身的設計並非針對影像串流來設計，為讓影像串流能在無線網路更有效率，我們必須重新設計適合影像串流的無線網路。本研究首先探討IEEE 802.11 MAC層DCF (Distributed Coordination Function)與802.11e EDCA (Enhanced Distributed Channel Access)機制的潛在問題。由於DCF與EDCA並未特別對影像串流做設計，會導致具有時延(delay time)限制的影像封包等待過久造成失效，卻仍繼續傳送。本研究提出幾個有效方法，改善原本IEEE 802.11無線網路對影像串流傳輸效能不彰的現象。我們將利用跨層設計使MAC層能取得影像串流封包資訊，並改善DCF與EDCA的重傳(retransmission)機制，使用time limit與retry limit混和設計節省不必要的等待時間，並使用single-video multi-level queue改善傳輸效能。最後本研究將利用網路模擬器NS-2 (Network Simulater ver. 2)與影像串流測試實驗架構myEvalvid-NT作不同效能的驗證比較並評估我們所提出方法的有效性。 / Over the past decade, wireless network access and video streaming services have become more popular than ever. People are eager to have better quality of video streaming services over wireless network. However, IEEE 802.11 DCF and IEEE 802.11e EDCA are not specifically designed for video streaming. This leads to the problem of transmitting overdue video packets and thus degrades both the network performance and video quality. In this paper, we propose a hybrid design framework to improve the quality of video streaming. This framework consists of a MAC-centric cross-layer architecture to allow MAC-layer to retrieve video streaming packet information (slice type and transmission deadline), a retransmission mechanism of hybrid retransmission deadline and retry limit to save unnecessary packet waiting time, and a single-video multi-level queue to prioritize I/P/B slice delivery. Simulations show that the proposed methodology outperforms IEEE 802.11e, IEEE 802.11e Timebase and IEEE 802.11e MultiQ in packet loss rate, invalid packet ratio, lost and invalid packet ratio, delay time, jitter, and PSNR.