Multimedia' nature of an application refers to the presence of several media streams in parallel. Whether it is receiving real-time data or retrieving stored data, there exists an end-to-end delay in data transfer from source to destination over the network. This delay experienced can be split into a fixed part and a variable part. Data processing time like coding and decoding at the source and destination are the fixed delays experienced. The variable delay occurs mainly due to queuing at the intermediate nodes during its flow through the network. The variable or unequal delays introduce gaps or discontinuities within a stream. In multi-stream applications where each stream may flow on different routes based on the bandwidth availability experiencing different delays, mismatch between them can also occur. These discontinuities and skews result in poor quality of playout. Clock drift and variations in drift rates between the source/s and destination/s, clock also lead to poor quality of play out. To eliminate these skews and discontinuities, there must be mechanisms, viz., and synchronisation services to convey, reintroduce and maintain the temporal relationship between the media streams for presentation throughout the playout, at the destination. The reintroduction of this lost temporal relationship within a stream and between various media streams for presentation at the destination is the object of multimedia synchronisation and is the subject matter of this thesis. In the presence of synchronised clocks, the main cause of asynchronies between media streams is the difference in delays experienced and the jitter. In this work, to convey the temporal relationship between streams of an application to the playout site, each stream is assigned a priority л, based on its importance to the user. The media streams are then divided into synchronisation units called 'Groups' based on that stream's characteristics which has the highest priority л. A group may therefore consist of one video frame and other data which were generated in that interval. Or may consist of silence and talk-spurt periods of the voice stream with data units of other streams generated in the same interval. Since the quality of playout of temporally related delay-sensitive streams depends upon the delay-experienced, the concept of QoS can be extended to describe the presentation requirements of uch data. Depending on the user perception and the delay experienced, an application can have a range of playout times, giving the best performance. The presentation of many real-time applications can be considered satisfactory even when the delay bound is exceeded by a small amount for a short period of time under varying network conditions. This property can be exploited by defining two sets of QoS parameters, namely QoS optimum and QoSlimit for each real-time application. As the delay and its variations increase, the optimum playout time range decreases. QoS optimum specifies the performance parameters required to perceive 'realtime'. Multimedia data can be played out at its QoSlimit with a deterioration in quality under poor network conditions still maintaining the synchronisation between streams. To control the playout at two levels of QoS, and maintain intra-media and inter-media synchronisation, stream controllers and super stream controllers have been used. The dynamic delay compensation algorithm and synchronisation services were simulated using network delay models and performances studied. It is shown that the proposed algorithm not only synchronised media streams and smoothened jitter but also optimised buffer space and buffer occupancy time while meeting the desired quality of service requirements

Message Sequence Charts are a visual representation of the system specification which shows how all the participating processes are interacting with each other. Message Sequence Graphs provide modularity by easily allowing combination of more than one Message Sequence Charts to show more complicated system behavior. Requirements modeled as Message Sequence Graphs give a global view of the system as interaction across all the participating processes can be viewed. Thus systems modeled as Message Sequence Graphs are like sequential composition of parallel process. This makes it very attractive during the requirements gathering and review phases as it needs inter-working between different stakeholders with varied domain knowledge and expertise – requirements engineers, system designers, end customers, test professionals etc. In this thesis we give a detailed construction of a finite-state transition system for a com-connected Message Sequence Graph. Though this result is fairly well-known in the literature there has been no precise description of such a transition system. Several analysis and verification problems concerning MSG specifications can be solved using this transition system. The transition system can be used to construct correct tools for problems like model-checking and detecting implied scenarios in MSG specifications. There are several contributions of this thesis. Firstly, we have provided a detailed construction of a transition system exactly implementing the message sequence graph. We have provided the detailed correctness arguments for this construction. Secondly, this construction works for general Message Sequence Graphs and not limited to com-connected graphs alone, although, we show that a finite model can be ensured only if the original graph is com-connected. Also, we show that the construction works for both synchronous and asynchronous messaging systems. Thirdly, we show how to find implied scenarios using the transition model we have generated. We also discuss some of the flaws in the existing approaches. Fourthly we provide a proof of undecidability argument for non com-connected MSG with synchronous messaging.

La distribution des génotypes du virus de l’hépatite C (VHC). chez les donneurs de sang Français entre 2008 et 2011 a été analysée afin d’actualiser nos connaissances. Le génotypage des souches a permis d’identifier la diversité des génotypes circulants. Les sous-types 1a, 1b et 3a sont majoritairement retrouvés (80% des souches). L’analyse phylogénétique a démontré une grande variabilité chez les types 2 et 4 représentés par de nombreux sous-types. Les résultats montrent que les comportements à risque tendent à influencer et redessiner la distribution de ces génotypes dans la population générale. Certains sous-types se répandent dans des groupes à risque où ils finissent par adopter un profil épidémique. Enfin, la sélection des donneurs et la mise en place de tests diagnostiques ont permis de rendre la contamination transfusionnelle négligeable. Les données épidémiques obtenues ont été enrichies de nouvelles connaissances sur l'évolution et la classification du VHC. 15 séquences codantes complètes de plusieurs souches appartenant au type 2 ont été caractérisées. L’analyse phylogénétique révèle 2 clusters distincts. Le cluster 1 comprend la plupart des souches tandis que le cluster 2 comprend le sous-type 2l. Les génomes obtenus ont un ORF de 9042 à 9108 bases (3014 à 3036 acides aminés). Les distances moyennes entre sous- types sont égales à 20% dans le cluster 1 et 26% entre les deux clusters. La bifurcation entre clusters a eu lieu tôt lors de l'évolution du virus. L'insertion de 60 bases dans la région NS5A caractéristique du type 2 est absente chez les 2l. Donc, l'apparition et la fixation de celle-ci sont tardives dans l'évolution du virus. / The distribution of genotypes of hepatitis C virus (HCV) infection among blood donors French between 2008 and 2011 was analyzed in order to update our knowledge. Genotyping strains identified the diversity of circulating genotypes. Subtypes 1a, 1b and 3a are found predominantly (80 % of strains). Phylogenetic analysis showed a great variability in types 2 and 4 represented by many subtypes. The results show that risk behaviors tend to influence and reshape the distribution of these genotypes in the general population. Some subtypes are spreading risk groups where they eventually adopt an epidemic profile. Finally, donor selection and implementation of diagnostic tests reduced drastically blood contamination. Epidemic data were enriched of new knowledge about the evolution and classification of HCV. 15 complete coding sequences of several strains of type 2 have been characterized. Phylogenetic analysis reveals two distinct clusters. Cluster 1 includes most strains while cluster 2 includes subtype 2l. Genomes obtained have an ORF of 9042 to 9108 bases (3014-3036 amino acids). The average distances between subtypes are equal to 20% in cluster 1 and 26 % between the two clusters. The bifurcation between clusters occurred early during the evolution of the virus. The insertion of 60 bases in the NS5A region characteristic of Type 2 is absent in 2l. So the appearance and fixing it is late in the evolution of the virus.