Inter-destination Multimedia Synchronization: A Contemporary Survey

The advent of social networking applications, media streaming technologies, and synchronous communications has created an evolution towards dynamic shared media experiences. In this new model, geographically distributed groups of users can be immersed in a common virtual networked environment in which they can interact and collaborate in real- time within the context of simultaneous media content consumption. In this environment, intra-stream and inter-stream synchronization techniques are used inside the consumers’ playout devices, while synchronization of media streams across multiple separated locations is required. This synchronization is nown as multipoint, group or Inter-Destination Multimedia Synchronization (IDMS) and is needed in many applications such as social TV and synchronous e-learning. This survey paper discusses intraand inter-stream synchronization issues, but it mainly focuses on the most well-known IDMS techniques that can be used in emerging distributed multimedia applications. In addition, it provides some research directions for future work

MediaSync: Handbook on Multimedia Synchronization

This book provides an approachable overview of the most recent advances in the fascinating field of media synchronization (mediasync), gathering contributions from the most representative and influential experts. Understanding the challenges of this field in the current multi-sensory, multi-device, and multi-protocol world is not an easy task. The book revisits the foundations of mediasync, including theoretical frameworks and models, highlights ongoing research efforts, like hybrid broadband broadcast (HBB) delivery and users' perception modeling (i.e., Quality of Experience or QoE), and paves the way for the future (e.g., towards the deployment of multi-sensory and ultra-realistic experiences). Although many advances around mediasync have been devised and deployed, this area of research is getting renewed attention to overcome remaining challenges in the next-generation (heterogeneous and ubiquitous) media ecosystem. Given the significant advances in this research area, its current relevance and the multiple disciplines it involves, the availability of a reference book on mediasync becomes necessary. This book fills the gap in this context. In particular, it addresses key aspects and reviews the most relevant contributions within the mediasync research space, from different perspectives. Mediasync: Handbook on Multimedia Synchronization is the perfect companion for scholars and practitioners that want to acquire strong knowledge about this research area, and also approach the challenges behind ensuring the best mediated experiences, by providing the adequate synchronization between the media elements that constitute these experiences

Supervision de contenus multimédia : adaptation de contenu, politiques optimales de préchargement et coordination causale de flux

La qualité des systèmes d'informations distribués dépend de la pertinence du contenu mis à disposition, de la réactivité du service ainsi que de la cohérence des informations présentées. Nos travaux visent à améliorer ces trois critères de performance et passent par la prise en compte des caractéristiques de l'utilisateur, des ressources disponibles ou plus généralement du contexte d'exécution. Par conséquent, cette thèse comporte trois volets. Le premier volet se place dans le cadre de l'adaptation de systèmes d’information déployés dans des contextes dynamiques et stochastiques. Nous présentons une approche où des agents d’adaptation appliquent des politiques de décision séquentielle dans l'incertain. Nous modélisons ces agents par des Processus Décisionnels de Markov (PDM) selon que le contexte soit observable ou seulement partiellement observable (PDM Partiellement Observables). Dans le cas d’un service mobile de consultation de films, nous montrons en particulier qu’une politique d'adaptation de ce service à des ressources limitées peut être nuancée selon l'intérêt de l'utilisateur, estimé grâce à l’évaluation des signaux de retour implicite. Dans le deuxième volet, nous nous intéressons à l'optimisation de la réactivité d'un système qui propose des contenus hypermédia. Nous nous appuyons sur des techniques de préchargement pour réduire les latences. Comme précédemment, un PDM modélise les habitudes des utilisateurs et les ressources disponibles. La force de ce modèle réside dans sa capacité à fournir des politiques optimales de préchargement. Les premières politiques que nous obtenons sont simples. Nous enrichissons alors le modèle pour dériver des politiques de préchargement plus complexes et plus agressives et montrons leurs performances par simulation. Afin de personnaliser nos stratégies optimales nous proposons finalement un modèle PDMPO dont les politiques s'adaptent aux profils des utilisateurs. Le troisième volet se place dans le contexte des applications multimédia interactives distribuées et concerne le contrôle de la cohérence des flux multimédia répartis. Dans un tel contexte, plusieurs mécanismes de synchronisation sont nécessaires et plusieurs ordres logiques (fifo, causal, total) s'avèrent utiles. Nous proposons une boîte à outils capable de gérer plusieurs protocoles d’ordre partiel et d'assurer une délivrance correcte de chaque message, en respectant tous les ordres qui lui ont été imposés. Nous décrivons ensuite l’intégration des tolérances humaines vis-à-vis des courtes incohérences causales dans notre boîte à outils. Nos simulations montrent que de meilleures performances sont obtenues par cette méthode comparativement à d’autres approches, comme la causalité classique ou la Δ-causalité. ABSTRACT : Distributed systems information quality depends on service responsiveness, data consistency and its relevance according to user interests. The thesis aims to improve these three performance criteria by taking into account user characteristics, available ressources or more generally execution context. Naturally, the document is organized in three main parts. The first part discusses adaptation policies for information systems that are subject to dynamic and stochastic contexts. In our approach adaptation agents apply sequential decisional policies under uncertainty. We focus on the modeling of such decisional processes depending on whether the context is fully or partially observable. We use Markov Decision Processes (MDP) and Partially Observable MDP (POMDP) for modeling a movie browsing service in a mobile environment. Our model derives adaptation policies for this service that take into account the limited (and observable) resources. These policies are further refined according to the (partially observable) users’ interest level estimated from implicit feedback. Our theoretical models are validated through numerous simulations. The second part deals with hypermedia content delivery aiming to reduce navigation latencies by means of prefetching. As previously, we build upon an MDP model able to derive optimal prefetching policies integrating both user behaviour and ressource availability. First, we extend this model and propose more complex and aggressive policies. Second, the extended model is enriched by taking into account user's profile and therefore provides finer prefetching policies. It is worth noting that this model issues personnalized policies without explicily manipulating user profiles. The proposed extensions and the associated policies are validated through comparison with the original model and some heuristic approches. Finally, the third part considers multimedia applications in distributed contexts. In these contexts, highly interactive collaborative applications need to offer each user a consistent view of the interactions represented by the streams exchanged between dispersed groups of users. At the coordination level, strong ordering protocols for capturing and delivering streams' interactions (e.g. CAUSAL, TOTAL order) may be too expensive due to the variability of network conditions. We build upon previous work on expressing streams causality and propose a flexible coordination middleware for integrating different delivery modes (e.g. FIFO, CAUSAL, TOTAL) into a single channel (with respect to each of these protocols). Moreover, the proposed abstract channel can handle the mix of any partial or total order protocols. Integrating perceptual tolerance in our middleware, provides us with a coordination toolkit that performs better than Δ-causality, usually considered the best solutio

Estudio del rendimiento de arquitecturas basadas en grupos para WAHSN

[ES] Existen muchos trabajos relacionados con las redes ad hoc y las redes de sensores donde se presentan nuevos protocolos que encaminamiento que aportan mejores características, otros trabajos donde se comparan para ver cual posee un mejor rendimiento ó incluso presentan nuevas aplicaciones basadas en este tipo de redes, pero este trabajo aporta otro punto de vista. ¿Por que no ver la red como un conjunto que se divide en grupos para aportar un mejor rendimiento a la red independientemente del protocolo de encaminamiento utilizado?. Para ello, en este trabajo, vamos a demostrar a través de simulaciones, que la agrupación de nodos en redes WAHSN (Wireless Ad Hoc & Sensor Networks) aporta mejoras a la red en general, disminuyendo el tráfico de encaminamiento, el retardo, el throughput, etc. Este estudio se ha realizado evaluando los protocolos estándar más utilizados (DSR [1], AODV [2] y OLSR [3]), así podemos observar cual de ellos aporta un mejor rendimiento. Finalmente, se propone una arquitectura de red basada en grupos optimizada para las redes WAHSN[EN] There are many works related with ad hoc networks and sensor networks where the authors present new routing protocols with better or enhanced features, others just compare the performance of them or present an application environment, but this work tries to give another point of view. Why don¿t we see the network as a whole and split it intro groups to give better performance to the network regardless of the used routing protocol?. First, we will demonstrate, through simulations, that grouping nodes in WAHSN (Wireless Ad Hoc & Sensor Networks) improves the whole network by diminishing the routing traffic, the delay, the throughput, etc. This study was conducted to assess the most used standard protocols (DSR [1], AODV [2] and OLSR [3]) that gives better performance to the whole network when there are groups of nodes. Finally, a group-based network architecture optimized for WAHSN is proposedGarcía Pineda, M. (2008). Estudio del rendimiento de arquitecturas basadas en grupos para WAHSN. http://hdl.handle.net/10251/13472Archivo delegad