As the number of devices in a pervasive environment is increased, the number of components available on the network also grows rapidly. In such cases, it is possible to compose various applications through a combination of different sets of components. Considering the multifaceted problem of having varying device capabilities supporting a different set of protocols, and each device hosting a number of components providing the same functionality, it becomes very difficult to choose a particular device hosting a required component which can be the best-fit for the user. This becomes practically impossible when the required components are distributed across various devices in the networked environment. We propose a solution for dynamic user task composition considering user preferences, device capabilities, and heterogeneity of communication protocols. With our proposed approach, a user task can be instantiated in different environments using a different set of devices and components, depending upon their capabilities and user preferences. We propose mechanisms for modeling device capabilities and user preferences and for modeling the user task as a graph. We then propose algorithms for selection of devices based on user preferences and task requirements. Since the underlying network is also modeled as a graph, we describe an algorithm for mapping of services in the user task on to the components distributed across devices in the pervasive environment. We also give an overview of our initial implementation and some results of our evaluations.

Mobile computing applications are required to operate in environments in which the availability for resources and services may change significantly during system operation. Thus, mobile computing applications need to be capable of adapting to these changes to offer the best possible level of service to their users. However, traditional middleware is limited in its capability of adapting to the environment changes and different users requirements. Aspect Oriented Programming has been used in the design and implementation of adaptive middleware architectures. In this paper, we propose an adaptive middleware architecture which can be used to develop adaptive mobile applications. Such architecture is compared to a component-based architecture from a quantitative perspective. The results suggest that middleware based on this model can be used to build mobile adaptive applications that require only a very small overhead in terms of running time as well as memory footprint while producing code that is more ease to comprehend and modify.

With the development of mobile computing, applications have to be accessible at any time, from any device and in any place in a wide variety of execution contexts. Consequently, applications have to adapt to different terminal capabilities both for efficiency and ergonomics. In this paper, we present a deployment infrastructure, called smart deployment infrastructure (SDI), which aims to ease the installation of large distributed applications for any kind of user terminal. SDI is designed to take into account the execution context (including available resources and the user's terminal capabilities) in order to bring an application to the user and adapt it to the execution context. By considering an application as an assembly of distributed software components, SDI provides the opportunity to decide at installation time which components, among packaged components, will be instantiated on the terminal and which ones will be installed on other hosts. SDI implementation demonstrates that the deployment infrastructure offers acceptable application deployment times and, at the same time, lowers both the application execution times and terminal resource consumption.

As the programming of distributed systems becomes more complex, new programming models have been used for creating applications. Communication between different system components is based on two main communication models: communication by messages and communication by remote method invocations. The choice of synchronous communication via remote method invocation or of message-based asynchronous communication still remains an early decision made at the time of the application design. In this article we propose a mechanism for dynamic and transparent switching of the communication model used between the components of a distributed system. This mechanism, aimed especially at large scale applications and mobile systems, offers the possibility to adapt the communication model to the execution context of an application and changes in its communication environment.

Epsilon is a testbed for monitoring distributed applications involving heterogeneous computers, including microcomputers, interconnected by a local area network. Such a hardware configuration is usual but raises difficulties for the programmer. First, the interprocess communication mechanisms provided by the operating systems are rather cumbersome to use. Second, they are different from one system to another. Third, the programmer of distributed applications should not worry about system and/or network aspects that are not relevant for the application level. The authors present the solution chosen in Epsilon. A set of high-level communication primitives has been designed and implemented to provide the programmer with an interface independent of the operating system and of the underlying interprocess communications facilities. A program participating in a distributed application can be executed on any host without any change in the source code except for host names.>

We study problems of optimization of the topology of interconnected local computer networks using random access to a single channel. An approach to modeling of the system by a queueing network is proposed: the analytical solution of the model allows us to obtain global performance measures, which may be used as evaluation criteria in network topology optimization problems. A heuristic is proposed for the latter aspect for one class of problems. We also derive from the model the time needed, for a new user which joins the network, to transmit its number of messages.