Jean-Christophe Lapayre

Distributed shared memory layer for cooperative work applications

To create cooperative work applications quickly and efficiently, we have developed a cooperative platform called CAliF: Cooperative Application Framework. This system was defined with four layers. We propose a new consistency protocol for the distributed shared memory (DSM) layer where different shared objects are replicated at each site. CAliF uses the DSM to allow programmers to share objects or variables without having to manage the exchange. We present an algorithm which uses the token technique. The token is a data structure which contains the updates of shared data. These data are carried through the ring on the token, named Pilgrim. The Pilgrim protocol provides both reliable consistency and guaranteed performance according to the type of application described. The protocol is discussed and proved, and we demonstrate its qualities.

A new consistency protocol implemented in the CAliF system

We propose a new consistency protocol for distributed shared memory (DSM) where different shared objects are replicated at each site. This protocol was developed for the cooperative platform called CAliF: Cooperative Application Framework. This system uses DSM to transparently handle the data sharing. We present an algorithm which uses the token technique. Updates of shared data are carried through a virtual ring on the token, named Pilgrim. The Pilgrim protocol provides both reliable consistency and guaranteed performance according to the type of application described. The protocol is described, proved and then simulated using the SPIN model checker and we demonstrate its qualities.

Security in Medical Telediagnosis

Telemedicine is the process by which electronic, visual and audio communications are used to support practitioners at remote sites with diagnosis and consultation procedures, such as remote clinical examinations and medical image transfers. Telemedicine is legally regulated by laws and constraints regarding the access of data contained in Personal Medical Files. These requirements are given by international entities such as IHE. They often specify the required functionalities to meet requirements of information exchange in the medical field. These functionalities are presented in this paper and outline some technical examples for their implementation in each level: authentication, communication, data storage, tracking and patient identification.

A co-operative application management platform based on shared virtual memory

Studying the different mechanisms specific to co-operative applications, we think that a co-operative application management platform is needed. Context sharing being one of the main concepts of co-operation, we propose an environment based on shared virtual memory. To clearly identify the various concepts used in every co-operative system, we define our system with four layers: the interprocess communications layers, the shared memory layer, the services layer and the co-operative distributed application layer. We show how these four layers are complementary and allow to optimize the co-operation management in order to allow users transparent access.

Towards an optimistic management of concurrency: a probabilistic study of the pilgrim protocol

In CSCW applications, users modify shared objects in real-time. Thus, concurrency management protocols are required in order to maintain consistency. Such protocols can be classified as optimistic or pessimistic. Our Pilgrim protocol is pessimistic since it is based on ownership. Our new version of this protocol is optimistic and designed to minimize the delay before writing. This paper presents this new version based on atomization and multi-versioning and compares it to the former one through a probabilistic study. Finally, this study allows us to highlight the parameters that make it possible to choose between the two protocols studied.

Medical Image Compression Approach Based on Image Resizing, Digital Watermarking and Lossless Compression

The computerization of images have been important for different medical applications. Nevertheless, the huge volume of medical images can rapidly saturate transmission especially in telemedicine field and may encumber storage systems in case of local saving. Data compression represents the most used solution to deal with this problem. Indeed, it can minimize the data space and may reduce both the time of data transfer and bandwidth consumption. In this context, we have proposed new approaches, which combined image reduction and expansion techniques, digital watermarking and lossless compression standards such as JPEG-LS (JLS) and TIFF formats. We named these compression methods wREPro.TIFF (watermarked Reduction/Expansion Protocol combined with TIFF format) and wREPro.JLS (wREPro combined with JPEG-LS format). The results of comparative experiments show that we have provided significant improvements over the well-known JPEG image compression standard. Indeed, our proposed compression algorithms have ensured a better preservation of the image quality notably for high compression ratios.

WAVA: a new web service for automatic video data flow adaptation in heterogeneous collaborative environments

The progressive needs of video streaming for different applications in varied domains have created a new set of heterogeneous environments especially in Virtual Collaborative Environments. In order to get the best performance of such environments, video streaming has to be adapted to the different parameters that characterize these environments, namely: bandwidth, CPU, GPU, screen resolution, etc. In this paper, we define a new Web Service, named Wava (Web Service for Automatic Video Data Flows Adaptation). Wava allows multimedia platforms and collaborative application servers to adjust the adaptation at two levels: at the static level during initialization and at the dynamic level according to the variation of the environment.

Groups Partitioning Over CORBA for Cooperative Work

Many examples illustrate the usefulness of group partitioning in distributed systems. The process group abstraction is a powerful tool for the development of fault-tolerant distributed applications. This solution is also particularly relevant to group entities sharing similar properties or stakes when applied to the field of cooperative work. When dealing with distributed applications, communication standards have evolved from socket-based interfaces to Remote Procedure Calls and nowadays, towards distributed object platforms like CORBA. This standard from the Object Management Group masks distribution and heterogeneity and provides a good basis for distributed application development. This paper presents a review of group mechanisms found in the literature then focuses on the implementation of groups over CORBA. An implementation of such a service over CORBA illustrates the impact of group auto-organization. Performance we obtain show that our service is efficient and provides good mechanisms to manage operations in a group.

Validation of a protocol for communication management in CSCW systems using a coloured-Petri net modelization

The communication protocol called Chameleon allows users to work over a collaborative platform. This protocol is based on revolutions between active sites of a token which contains the shared objects modified. Indeed, if one site is not active for a certain delay, it becomes inactive, and only token copies are transmitted to this site. To become active again, an inactive site has to send a signal to its tutor. In this protocol, one site can update the shared memory only if it is the owner of the active token. So, there are concurrent treatments (sites becoming active and inactive, updating, active token transmissions, ...) and messages (active token, token copies, activity requests) between the sites. In order to verify our protocol, we modelized it using a coloured Petri Net and made a qualitative study of this protocol verifying the properties of the obtained model. Indeed, we have verified that the state of each site is never lost, the active token also, and the fact that all the signals are treated. Furthermore, we verified that no more than one site can enter in critical section. The exclusive property has been verified. Nevertheless, this study does neither consider the delays nor the frequency of updating using the Chameleon. Our future work will consist on a quantitative study using stochastic Petri Nets.

Modelization of a communication protocol for CSCW systems using coloured petri nets

Concurrency management protocols are implemented over collaborative platforms in order to manage the shared object modifications. We have defined the Chameleon protocol which allows us to obtain a dynamic management of collaborative architecture. Now, we want to use this algorthm over a telemedicine platform within a European project on tele-diagnosis for neurology: TeNeCi. In such a domain, a robust (no errors, no losses...) management of interactions between cooperative members is crucial. Indeed, TeNeCi must provide an efficient and infallible tool to doctors in order to establish a collaborative diagnosis. So, we must validate and prove the Chameleon robustness. Coloured Petri Nets allowed us to correct the Chameleon weaknesses we have discovered during this modeling. Indeed, a time-out and an automatic forwarding mechanisms have been implemented in the first version of our communication protocol. In addition, a timestamp has been added to some messages sent to inactive sites. Finally, a lock mechanism during a particular step has been also implemented in the Chameleon. Due to those results, we have proved that our protocol is robust. Thus, it can be used in medicine applications.