Tobias Helbig

An Adaptive Stream Synchronization Protocol

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.

An adaptive protocol for synchronizing media streams

Abstract. Stream synchronization is widely regarded as a fundamental problem in the field of multimedia systems. Solutions to this problem can be divided into adaptive and rigid mechanisms. While rigid mechanisms are based on worst case assumptions, adaptive ones monitor the underlying network and are able to adapt themselves to changing network conditions. In this paper, we will present an adaptive stream synchronization protocol. This protocol supports any kind of distribution of the sources and sinks of the streams to be synchronized. It is based on a buffer-level control mechanism, allowing immediate corrections when the danger of a buffer overflow or underflow is recognized. Moreover, the proposed protocol is flexible enough to support a wide variety of synchronization policies, which can be dynamically changed while synchronization is in progress. Finally, the message overhead of this protocol is low, because control messages are only exchanged when network conditions change.

Clock hierarchies: an abstraction for grouping and controlling media streams

Synchronization plays an important role in multimedia systems at various levels of abstraction. 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, that 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 hierarchically group related streams, where each clock in the hierarchy identities and controls a certain group, or subgroup of streams. Control and synchronization requirements can be expressed in a uniform manner by associating group members with control or synchronisation attributes. An important property of the concept of clock hierarchy is that it can be combined in a natural way with component nesting.

Cinema - An architecture for distributed multimedia applications

Distributed multimedia applications combine the advantage of distributed computing with the capability of processing discrete and continuous media in an integrated fashion. The development of multimedia applications in distributed environments requires specific abstractions and services, which are usually not provided by generic operating systems. These services are typically realized by software components, often referred to as middleware.

Efficient engineering in special purpose machinery through automated control code synthesis based on a functional categorisation

Individual customer demands in special purpose machinery shift the focus towards efficient engineering. However, automated engineering approaches fail due to lack of an appropriate description language for the system modelling. Therefore, a categorisation of capabilities and functions is proposed, that can serve as basis for the description of machine parts in model-based approaches. As an example an approach that synthesises control code from a plant model, based on the description language developed in this paper, is presented.

An Architecture for a Distributed Stream Synchronization Service

A stream synchronization service provides the basis for the efficient control and synchronization of continuous, time-dependent data streams in distributed environments. Together with resource management and application configuration, it is one of the core multimedia system services. The stream synchronization service may be realized by a three layer architecture consisting of an interface layer enabling distributed clients to access stream control interfaces, of the control and synchronization layer implementing alternative stream synchronization protocols to coordinate the flow of data units, and of the stream layer where data units of time-dependent streams are transferred and processed.

Implementierung multimedialer Systemdienste in CINEMA

Die Erstellung verteilter Multimedia-Anwendungen setzt leistungsfahige Entwicklungsplattfonnen voraus, innerhalb deren Probleme wie die Ubertragung multimedialer Daten, die Gewahrleistung der Dienstgute durch Reservierung von Ressourcen und die Synchronisation von Datenstromen gelost werden. Cinema (Configurable INtEgrated Multimedia Architecture) bietet als eine solche Entwicklungsplattform Abstraktionen zur Nutzung multimedialer Systemdienste an, womit funktionale Bearbeitungseinheiten erstellt, komplexe Verarbeitungstopologien in verteilten Systemen aufgebaut und unter Einhaltung von Synchronisations- und Dienstgute-Spezifikationen gesteuert werden konnen. In diesem Papier werden nach einem kurzen Uberblick uber die Abstraktionen der Cinema-Dienstschnittstelle die internen Strukturen und Ablaufe vorgestellt, mit denen die Multimedia-Dienste in verteilten Systemen erbracht werden.

Identifying automation components in modular manufacturing systems: A method for modeling dependencies of manufacturing systems

Modularization aims to improve the flexibility and reconfigurability of manufacturing systems. But the effort and complexity required for the coordination of modules increases with the distribution of intelligence. One of the challenges is the identification of subsystems or automation components in modular manufacturing system which is the focus of this paper. The complete identification of a component includes information on the communication channel, the localization of the component and the related process step. As no single identification method is able to gather all aspects of identification, the Manufacturing System Dependency Model (MaSDeM) is introduced which models the dependencies between distributed automation components. This model is based on three layers representing the different perspectives on the system of the involved persons in the development process of a manufacturing system. With the help of this model one single identification fact is sufficient to deduce all the information on the component. This helps to reduce engineering time involved in modular manufacturing systems.