pp. 297-314 297 Patrick SI~NAC *,** Michel DIAZ * Pierre de SAQUI-SANNES *'** Toward a formal specification of multimedia synchronization scenarios Abstract This paper introduces time stream Pdtri nets (TS treamPN), a model for the formal specification of multi- media synchronization scenarios. This new model extends time Pdtri nets to formally describe the timed behaviour of multimedia objects and streams in asyn- chronous distributed systems. The proposed approach uses time intervals to label the arcs exiting from the places of the net, and typed transitions to define diffe- rent firing rules. This model allows a complete and accu- rate specification of synchronization constraints between multimedia streams and can be used at different levels of granularity. Key words 9 Multimedia service, Transport layer, Synchronization, Formal description technique, Multipoint point communication, Prtri net, Jitter. CONTRIBUTION A LA SPI~CIFICATION FORMELLE DE SCI~NARIOS DE SYNCHRONISATION MULTIMI~DIAS R6sum6 Cet article introduit un moddle formel pour la speci- fication de scenarios de synchronisation mettant en jeu des flux d' informations multimddias. Ce nouveau moddle appel~ << time stream P~tri net >> (TsstreameN) repose sur un formalisme de type rOseau de P~tri et associe des intervalles temporels aux arcs entrant sur les transitions. Diff~rentes rdgles de tir peuvent Otre associ~es aux tran- sitions d' un TstreameN. Ces rdgles de tir permettent une specification compldte, precise et ~ diff~rents niveaux de granularit~ de la synchronisation intra- et inter-flux multim~dias. Mots cirs: Service multimrdia, Couche transport, Synchronisa- tion, Technique description formelle, Communication point multipoint, Rrseau Prtri, Gigue. Contents I. Introduction. II. Modeling issues. III. Modeling with P~tri nets. IV. An overview of time in P~tri nets. V. Multimedia synchronization. VI. Time stream P~tri nets. VII. Formal semantics TStreamPN. VIII. Conclusion. References (25 ref.). I. INTRODUCTION Multimedia applications need to handle new types of data such as audio, video or synthetic animations. One of the main new characteristics of these data is their dynamic aspect. Dynamic multimedia data are structu- red as series of temporaly ordered information units (ru) or segments; they can be defined as streams or conti- nuous multimedia objects. For instance a video stream is structured as a temporaly ordered serie of video frames. * LAAS du CNRS, 7, avenue du Colonel-Roche, F-31077 Toulouse Cedex, France. ** ENSICA, 49, avenue L~on-Blum, F-31056 Toulouse Cedex, France. 1/18 ANN. TI~LI~COMMUN., 49, n ~ 5-6, 1994