Clock Hierarchies: An Abstraction for Grouping and controlling Media Systems

Synchronization plays an important role in multimedia systems at various levels of abstraction. In this paper, we propose a set of powerful abstractions for controlling and synchronizing continuous media streams in distributed environments. The proposed abstractions are based on a very general computation model, which allows media streams to be processed (i.e. produced, consumed or transformed) by arbitrarily structured networks of linked components. Further, compound components can be composed of existing ones to provide higher levels of abstractions. The clock abstraction is provided to control individual media streams, i.e. streams can be started, paused or scaled by issuing the appropriate clock operations. Clock hierarchies are used to hierarchically group related streams, where each clock in the hierarchy identifies and controls a certain (sub)group of streams. Control and synchronization requirements can be expressed in a uniform manner by associating group members with control or sync attributes. An important property of the concept of clock hierarchies is that it can be combined in a natural way with component nesting

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

Multimedia-Streaming in Benutzergruppen

At the time being, multimedia services using IP technology like IPTV or video on-demand are a hot topic. Technically, they can be classified under the notion of streaming. A server sends media data in a continuous fashion to one or several clients, which consume and display data portions as soon as they arrive. Using a feedback channel customers may influence the play-back, watching programs time-shifted or pausing the program. An enhancement of such streaming services is to watch those movies with a group of people on several devices in parallel. Similar approaches have been developed using IP multicast. However, users cannot control the presentation: pausing or skipping of more unimportant parts is impossible. Moreover, members cannot be added to the session directly within the application. The costream architecture developed in this works offers a collaborative streaming service without these limitations: People may join others watching a movie or invite others to such a collaborative streaming session. Dependent on the desired course of the session the participants' control operations are executed for all users, or the group is split into subgroups to let watchers follow their own time-lines. A group management controls this by means of user roles. Separate from the group management, the so-called association service provides for streaming session control and synchronization among participants. This separation of duties is advantageous in the sense that standard components can be used: For group management, SIP conferencing servers are suitable, whereas session control can best be handled using RTSP proxies as already used for caching of media data. Eventually, the evaluation of this architecture shows that such a service offers both low latency for clients and an acceptable synchronization of media streams to different client devices. Moreover, the communication overhead compared to usual conferencing or streaming systems is very low.Mit Hilfe der IP-Technologie erbrachte Multimedia-Dienste wie IPTV oder Video-on-Demand sind zur Zeit ein gefragtes Thema. Technisch werden solche Dienste unter dem Begriff "Streaming" eingeordnet. Ein Server sendet Mediendaten kontinuierlich an Empfänger, welche die Daten sofort weiterverarbeiten und anzeigen. Über einen Rückkanal hat der Kunde die Möglichkeit der Einflussnahme auf die Wiedergabe. Eine Weiterentwicklung dieser Streaming-Dienste ist die Möglichkeit, gemeinsam mit anderen denselben Film auf mehreren Geräten anzusehen. Ähnliche Ansätze gibt es im Internet bereits durch IP-Multicast. Allerdings können Benutzer hierbei keinen Einfluss auf die Übertragung nehmen - das Überspringen von Teilen ist zum Beispiel nicht möglich. Andere Benutzer können nicht direkt zur Streaming-Sitzung eingeladen werden. Collaborative Streaming ohne solche Einschränkungen bietet die in dieser Arbeit entwickelte costream-Architektur: Sie erlaubt es, andere zum gemeinsamen Betrachten eines Filmes einzuladen oder sich selbst in eine Benutzergruppe einzuklinken. Abhängig vom gewünschten Ablauf der Sitzung wird die Steuerung für alle Teilnehmer durchgeführt oder die Gruppe aufgeteilt. Eine Gruppenverwaltung regelt dies mit Hilfe von Rollenzuweisungen. Davon getrennt sorgt eine weitere Komponente für die Steuerung der Streaming-Sitzungen und die Synchronisation zwischen Teilnehmern. Diese Aufteilung hat den Vorteil, dass von der IETF entwickelte Standardprotokolle eingesetzt werden können. Für die Gruppenverwaltung sind SIP-Konferenzsysteme geeignet, während für die Sitzungssteuerung ein RTSP-Zwischensystem benutzt wurde. Die Evaluierung dieser Architektur zeigt schließlich, dass ein solcher Dienst nicht nur geringe Wartezeiten aufweist, sondern eine akzeptable Synchronisation der Datenströme auf die verschiedenen Ausgabegeräte der Benutzer erreicht wird. Zudem ist der Zusatzaufwand verglichen mit üblichen Konferenz- oder Streaming-Systemen sehr gering

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

An adaptive stream synchronization protocol

Abstract. Protocols for synchronizing data streams should be highly adaptive with regard to both changing network conditions as well as to individual user needs. The Adaptive Synchronization Protocol we are going to describe in this paper supports any type of distribution of the stream group to be synchronized. It incorporates buffer level control mechanisms allowing an immediate reaction on overflow or underflow situations. Moreover, the proposed mechanism is flexible enough to support a variety of synchronization policies and allows to switch them dynamically during presentation. Since control messages are only exchanged when the network conditions actually change, the message overhead of the protocol is very low.