Christophe Chassot

Partial-order transport service for multimedia and other applications

Investigates a partial-order connection (POC) service/protocol. Unlike classic transport services that deliver objects either in the exact order transmitted or according to no particular order, POC provides a partial-order service, i.e. a service that requires some, but not all objects to be received in the order transmitted. Two versions of POC are proposed: reliable, which requires that all transmitted objects are eventually delivered, and unreliable, which permits the service to lose a subset of the objects. In the unreliable version, objects are more finely categorized into one of three reliability classes depending on their temporal value. Two metrics based on e/sub i/(P), the number of linear extensions of partial-order P in the presence of i lost objects, are proposed as complexity measures of different combinations of partial order and reliability. Formulae for calculating e/sub i/(P) are derived when P is series-parallel. A formal specification of a POC protocol, written in Estelle, is presented and discussed. This specification was designed and validated using formal description tools and provides a basis for future implementations. >

Partial order connections : a new concept for high speed and multimedia services and protocols

This paper presents a new concept that has been developed to define high performance multimedia data transfers between communicating entities. All current protocols use either connectionless (Cl) or connection-oriented (Co) approaches and many mechanisms have been proposed in each case. Both sets of present Cl and co protocols are not conceptually related and there is a design gap between the definition and use of these two families. A new concept, a partial order connection (Poc), is defined here. It will be seen that Cl and Co approaches are two specific cases of the much more general concept presented here. More precisely, a Poc is an end-to-end connection that provides a partial order service where the objects can be delivered to the users in a different order from the transmitted order. It is first shown how this new concept has emerged and what are its interests in terms of resources. Then a formal definition of reliable and unreliable Pocs and a way to measure their complexity will be given. It is shown how such a generalized connection can be used and how time constraints can be handled in an integrated way, leading to the definition of a design space for protocols.RésuméLes protocoles actuels utilisent soit le mode non connecté, soit le mode orienté connexion, et pour chacun de ces modes de nombreux mécanismes ont été développés. Ces deux familles de protocoles présentent une discontinuité conceptuelle, tant pour leur définition que pour leur usage. Avec le nouveau concept de connexion d’ordre partiel, les deux approches apparaissent alors comme deux cas particuliers extrêmes. Une connexion d’ordre partiel est une connexion de bout-en-bout, qui autorise la délivrance d’objets à l’utilisateur dans un ordre éventuellement différent de celui dans lequel ils ont été émis. Ce concept unificateur apparaît à l’analyse des protocoles existants et est intéressant en économie de ressources. Une définition formelle des connexions d’ordre partiel, fiables et non fiables, est ensuite donnée, ainsi qu’un moyen de mesurer leur complexité. On montre enfin comment peut être mise en œuvre une telle connexion généralisée, en intégrant les contraintes temporelles. Cette généralisation conduit à la définition d’un espace de protocoles dans le système (fiabilité, ordre, temps).

A time-efficient architecture for multimedia applications

This paper presents an architecture that enforces time requirements and gives minimal end-to-end delays for multimedia applications. The layers and mechanisms allowing the system to fulfill the selected synchronization, i.e., the logical relationships and timed interval semantics, are presented. The proposed approach relies on the use of a formal model based on extended time Petri nets, i.e., the time stream Petri net model (TStreamPN), that allows the user to completely specify the time requirements of a given application. The architecture implements, in the application layer and on top of asynchronous environments, the requested quality of service (perceived by the user) with respect to time. At the transport layer, the use of a partial order transport service improves the reactive response of the communication transfers. Its principles are presented together with a presynchronization sublayer that makes the partial order transport service match the applicative synchronization requirements. Moreover, measurements on the implementation of a videoconference system show that the requirements of the quality of service are fulfilled.

A rule-driven approach for architectural self adaptation in collaborative activities using graph grammars

Architectural adaptation is important for handling self-configuring properties of autonomic distributed systems. It can be achieved by model-based management of dynamic architectures. Describing dynamic architectures includes defining rules for reconfiguration management. Within this research context, several works have been conducted using formal specification to handle this complexity. Graph and graph rewriting-based approaches showed, through many studies, their appropriateness to tackle architectural adaptation problems. However, scalability of such approaches remains an open issue and has been rarely explored. In this paper, we investigate this issue. We introduce a graph-based general approach for handling of dynamic architectures and we illustrate it within a scenario of collaboration support in crisis management systems. We elaborate the formal models for dynamic architecture management. Using the French Grid GRID5000, we conducted an experimental study to assess the scalability of the elaborated models.

Performance analysis for an IP Differentiated Services network

Research reported here deals with a communication architecture with guaranteed end-to-end quality of service (QoS) in an IPv6 environment providing differentiated services within a single DiffServ domain. The article successively presents the design principles and services of the proposed architecture, their implementation over a national platform, and experimental measurements evaluating the QoS provided at the user level.

On the definition and representation of the quality of service for multimedia systems

This paper presents a new geometrical view of the concept of Quality of Service (QoS). QoS is of utmost importance and quite often referred to when handling information in distributed communications systems. Nevertheless, no formal definition exists and consequently no evaluation and no comparative analysis of QoS can be done. This paper is considered as a first step towards a well defined approach to access the QoS; such approaches have to be developed to guarantee the quality of high performance multimedia data transfers.

Introducing a cross-layer interpreter for multimedia streams

In the context of multimedia and real-time systems, this article introduces a generic interpreter of QoS properties (xQoS-Interpreter) for the Application Data Units (ADUs) composing standard and proprietary multimedia streams. This approach is intended to make the QoS properties of ADUs publicly available to any mechanism of the underlying communication system. The use of this information allows for cross-layer QoS optimization of the communication services taking the actual per-packet requirements of the applications into account. A case study showing how the xQoS-Interpreter is used at transport layer to seamlessly optimize the perceived QoS of an end-to-end video transmission is presented. In this scenario, the xQoS-Interpreter is used to optimize a TCP-friendly Rate Control mechanism (TFRC) over congested wireless network services in order to demonstrate the feasibility and advantages of our approach.

A user-based approach for the choice of the IP services in the multi domains DiffServ Internet

This paper deals with the design of a distributed architecture and of mechanisms that are able to guarantee quality of service (QoS) in a set of DiffServ domains. The design includes the proposal of a signaling protocol to accept or reject the transmission of flows in a set of adequately controlled domains. More particularly, it provides a proposal for (1) selecting the end-to-end QoS paths resulting from concatenations of the IP services provided by the domains involved in the data path and (2) ensuring that the chosen concatenations fulfil the requested user QoS requirements. With respect to other work, this paper first tries to minimise the use of network resources by discovering the real performance of each domain. Second, the signaling protocol is designed to bring as less constraints as possible on the architecture. It defines the end-to-end concatenations only as a set of transfer bridges, or inter-domain links, and leaves all internal domain paths fully open to any implementation by the domain providers. The architecture, based on the use of bandwidth brokers, provides an answer to the two main problems related to such approaches, i.e. how to identify and build the sequence of the needed bandwidth brokers and how to select the ingress and egress routers of each of these domains to construct the end-to-end paths.

Conception, Implementation, and Evaluation of a QoS-Based Architecture for an IP Environment Supporting Differentiated Services

Research reported in this paper deals with the design of a communication architecture with guaranteed end-to-end quality of service (QoS) in an IPv6 environment providing differentiated services within a single Diff-Serv domain. The paper successively presents the design principles of the proposed architecture, the networking platform on which the architecture has been developed and the experimental measurements validating the IP level mechanisms providing the defined services. Results presented here have been obtained as part of the experiments in the national French project @IRS (Integrated Architecture of Networks and Services).

A framework of models for QoS-oriented adaptive deployment of multi-layer communication services in group cooperative activities

This paper presents a framework of architecture-centric models to support the automated and adaptive deployment of communication services for QoS-enabled end-to-end group communication systems. The Transport level (TCP, UDP level) and the above messaging Middleware level are considered as the two communication levels targeted by the QoS-driven adaptation process. Application to crisis management systems (CMS) is considered as a case study from the more general domain to which our results apply: cooperative activity support systems. The adaptation rules rely on graph matching and graph rewriting. The adaptation enactment is based on the dynamic composition of micro-protocols at the Transport level and on the dynamic binding of software components and services at the Middleware level. The deployment model is used as a central feature of service provisioning. The influence of the cooperation and the communication contexts is expressed and maintained consistent by automated graph-based model refinement and transformation.