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Amsterdam-Zuidoost, Netherlands

Thorsdottir H.,Science Park 123 | Verloop I.M.,2 Rue C. Camichel | Verloop I.M.,National Polytechnic Institute of Toulouse
Queueing Systems | Year: 2016

This paper deals with a single-server queue with modulated arrivals, service requirements and service capacity. In our first result, we derive the mean of the total workload assuming generally distributed service requirements and any service discipline which does not depend on the modulating environment. We then show that the workload is exponentially distributed under heavy-traffic scaling. In our second result, we focus on the discriminatory processor sharing (DPS) discipline. Assuming exponential, class-dependent service requirements, we show that the joint distribution of the queue lengths of different customer classes under DPS undergoes a state-space collapse when subject to heavy-traffic scaling. That is, the limiting distribution of the queue-length vector is shown to be exponential, times a deterministic vector. The distribution of the scaled workload, as derived for general service disciplines, is a key quantity in the proof of the state-space collapse. © 2016 Springer Science+Business Media New York Source


Vaishnavi I.,Science Park 123 | Cesar P.,Science Park 123 | Bulterman D.,Science Park 123 | Friedrich O.,Kaiserin Augusta Allee 31 | And 2 more authors.
Signal Processing: Image Communication | Year: 2011

Recent developments on Social TV point to an evolution from traditional IPTV services towards more social experiences. Newer applications and services have appeared wherein groups of people in different locations can watch multimedia content while synchronously communicating with each other. We name such applications as synchronous shared experiences. Realization of these shared experiences requires that users feel that they are coherently communicating with each other. This paper identifies and analyzes challenges that need to be tackled to achieve coherence: quality of service, mobility and distributed media synchronization. Furthermore, universal session handling is required to setup these sessions. We then present our solution to one of these challenges: distributed media synchronization. Our design uses the local lag mechanism over a distributed control or masterslave signaling architecture. We validate our implementation via experiments performed with one client located in Amsterdam and the other in Seoul. The experiments demonstrate a bound in play-out skew of 500 ms across these locations. Our results from user tests, presented elsewhere, show that this value is well within tolerance limits. © 2011 Elsevier B.V. All rights reserved. Source


Kokash N.,Science Park 123 | Jaghoori M.M.,Science Park 123 | Arbab F.,Science Park 123
Electronic Notes in Theoretical Computer Science | Year: 2013

The Reo coordination language is an extensible graphical notation for component or service coordination wherein independent autonomous software entities exchange data through a connector or a network imposing synchronization and data constraints on those entities. Each connector is formed from a set of binary connectors, called channels, with precise semantics and, thus, amenable to formal verification. However, the development of verification tools for Reo-specific semantic models, namely, constraint automata with its multiple extensions to represent quality of service, time constraints, context-dependent or probabilistic behavior would require years of research and development. A much more promising approach is to exploit already existing verification tools. In this paper, we present a mapping of timed Reo networks to networks of timed automata used for system specification in Uppaal. Uppaal is a state-of-the-art toolset for modeling, validation and verification of real-time systems used in many large-scale industrial projects. Our work enables its application to the compositional analysis of timed service-based workflow models specified with Reo. © 2013 Elsevier B.V. All rights reserved. Source

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