Patrick Sénac

Modeling logical and temporal synchronization in hypermedia systems

The paper introduces a unified formal model for the complete and accurate specification of both temporal and logical (i.e., link) synchronization within hypermedia distributed and weakly synchronous systems. This new model extends time Petri nets with hierarchical design capabilities and new firing rules. These new firing rules enlighten the notion of hypermedia synchronization through powerful combinations of temporal and logical synchronization. Moreover, the proposed model offers an easy and concise modeling technique of asynchronous events in hypermedia systems.

Time Stream Petri Nets: A Model for Timed Multimedia Information

This paper introduces a model for specifying synchronization constraints in distributed asynchronous multimedia systems and applications. The consistency and semantics of multimedia systems depend on the temporal behaviour of information streams, like audio and video streams, whose synchronization constraints in asynchronous environments need to be enforced. The promoted model, named Time Stream Petri Nets (TStreamPN) allows the timed behaviour of streams to be fully, accurately and formally described using an extension of time Petri nets. This model uses time intervals to label arcs that leave the places of the net. A complete set of firing rules is also proposed to accurately enforce actual synchronization policies between different and related multimedia streams. Therefore, this model allows a formal characterization and verification of time parameters in distributed asynchronous multimedia systems.

Hierarchical Time Stream Petri Net: A Model for Hypermedia Systems

The paper proposes a new class of timed Petri nets for the specification of temporal constraints and description of logical behav- iour in distributed hypermedia systems. In particular, hierarchical design capabilities are added to the Time Stream Petri Net model developed for the specification of multimedia scenarios. The new model is named HTSPN, and its enhanced firing rules give a precise semantic to those synchronization mechanisms usually encountered in hypermedia sys- tems. Both temporal and logical synchronization are considered and can be combined into powerful synchronization schemes. User interactions and other asynchronous events are straightforwardly modeled in HTSPN.

A New UML Profile for Real-Time System Formal Design and Validation

UML solutions in competition on the real-time system market share three common drawbacks: an incomplete formal semantics, temporal operators with limited expression and analysis power, and implementation-oriented tools with limited verification capabilities. To overcome these limitations, the paper proposes a UML profile designed with real-time system validation in mind. Extended class diagrams with associations attributed by composition operators give an explicit semantics to associations between classes. Enhanced activity diagrams with a deterministic delay, a non deterministic delay and a timelimited offering make it possible to work with temporal intervals in lieu of timers with fixed duration. The UML profile is given a precise semantics via its translation into the Formal Description Technique RT-LOTOS. A RT-LOTOS validation tool generates simulation chronograms and reachability graphs for RT-LOTOS specifications derived from UML class and activity diagrams. A coffee machine serves as example. The proposed profile is under evaluation on a satellite-based software reconfiguration system.

Toward a formal specification of multimedia synchronization scenarios

This paper introduces time stream Pétri nets (Ts treamPn), a model for the formal specification of multimedia synchronization scenarios. This new model extends time Pétri nets to formally describe the timed behaviour of multimedia objects and streams in asynchronous distributed systems. The proposed approach uses time intervals to label the arcs exiting from the places of the net, and typed transitions to define different firing rules. This model allows a complete and accurate specification of synchronization constraints between multimedia streams and can be used at different levels of granularity.RésuméCet article introduit un modèle formel pour la spécification de scénarios de synchronisation mettant en jeu des flux d’informations multimédias. Ce nouveau modèle appelé « time stream Pétri net » (TsstreamPn) repose sur un formalisme de type réseau de Pétri et associe des intervalles temporels aux arcs entrant sur les transitions. Différentes règles de tir peuvent être associées aux transitions d’unTstreamPn. Ces règles de tir permettent une spécification complète, précise et à différents niveaux de granularité de la synchronisation intra-et inter-flux multimédias.

FPTP: the XQoS aware and fully programmable transport protocol

Development of new communication services demands the complete understanding of the quality of service (QoS) requirements and efficient interaction with resources and the other services of the communication system. This paper proposes the use of a global QoS framework based on a common semantic namespace for the deployment of QoS oriented communication services offered by the fully programmable transport protocol. Experimental results demonstrate the feasibility and advantages of this proposal.

STEPS - an approach for human mobility modeling

In this paper we introduce Spatio-TEmporal Parametric Stepping (STEPS) - a simple parametric mobility model which can cover a large spectrum of human mobility patterns. STEPS makes abstraction of spatio-temporal preferences in human mobility by using a power law to rule the nodes movement. Nodes in STEPS have preferential attachment to favorite locations where they spend most of their time. Via simulations, we show that STEPS is able, not only to express the peer to peer properties such as inter-contact/contact time and to reflect accurately realistic routing performance, but also to express the structural properties of the underlying interaction graph such as small-world phenomenon. Moreover, STEPS is easy to implement, flexible to configure and also theoretically tractable.

Formal models for the description of timed behaviors of multimedia and hypermedia distributed systems

Abstract This paper presents two modeling approaches that can be used as a formal basis for designing distributed multimedia and hypermedia systems. Using these approaches, users and designers are able to express formally their multimedia and hypermedia synchronization and time requirements. The two different models considered are Hierarchical Time Stream Petri Nets and RT-LOTOS. It will be shown that both models, starting from a different formal basis, are of interest as they possess complementary advantages and can then be used at different stages of the system life cycle. For instance, HTSPN provides an user-friendly graphical specification framework, whereas RT-LOTOS offers an extensive simulation and validation framework applicable to specifications derived from HTSPN.

Enhancing qos through alternate path: an end-to-end framework

In the next generation Internet, the network should not only be considered as a communication medium, but also as an endless source of services available to the end-systems. These services (i.e. Overlay Applications) would be composed of multiple cooperative distributed software elements that dynamically build an ad hoc communication mesh (i.e. an Overlay Association). In this paper we propose and evaluate a collaborative distributed method to provide enhanced QoS between end-points within an overlay association.

PROST: a programmable structured peer-to-peer overlay network

We present the idea of a programmable structured P2P architecture. Our proposed system allows the key-based routing infrastructure, which is common to all structured P2P overlays, to be shared by multiple applications. Furthermore, our architecture allows the dynamic and on-demand deployment of new applications and services on top of the shared routing layer.