Abstract

This paper proposes to extend Mobile IP with adaptive individual paging. Paging reduces the signaling cost of Mobile IP making it more adapted to wireless cellular IP networks. By reducing the number of location updates to be sent per mobile host, paging also minimizes power consumption of the mobile devices. In the proposed extension, each mobile host computes dynamically its optimal location area size according to its traffic and mobility parameters. The optimal size is the size that provides the best paging versus location update cost tradeoff and, as a result, minimizes the signaling load in the network. We compare, by simulation, the performance of the proposed scheme with that of Mobile IP \\citeMIP, a paging scheme that uses fixed size location areas and Hierarchical Mobile IP \\citeCas98TR. We show that our extension provides a significant gain compared to Mobile IP and the fixed size paging scheme and performs as well and sometimes better than Hierarchical Mobile IP. We also show that the integration of adaptive individual paging within Hierarchical Mobile IP outperforms all scheme Document type: Report

Abstract

We study the modelling of {\\em mobile hosts} on a network in a simple name-passing process calculus, with the intention of being able to prove properties about a protocol for supporting mobility. Our model may be considered a highly simplified version of proposals for {\\em mobility support} in the version 6 of the Internet Protocols (IP). Being fairly general, the model may also apply to mobile software architectures. We believe that such simplified models help in prototyping mobility protocols and reasoning about them while abstracting away excessive details. We concentrate on the issue of ensuring that messages to and from mobile agents are delivered without loss of connectivity. We provide three models of increasingly complex nature of a network of routers and computing agents that are interconnected via the routers: the first is without mobile agents and is treated as a specification for the next two; the second supports mobile agents, and the third additionally allows correspondent agents to {\\em cache} the current location of a mobile agent. Following a detailed analysis of the three models to extract invariant properties, we show that the three models are related by a suitable notion of equivalence based on {\\em barbed bisimulation}. Document type: Report

Abstract

Today, mobility and persistence are important aspects of distributed computing- . They have many fields of use such as load balancing, fault tolerance and dynamic reconfiguration of applications. In this context, Java provides many useful mechanisms for the mobility of code via dynamic class loading, and the mobility or persistence of data via object serialization. However, Java does not provide any mechanism for the mobility/persistence of computation (i.e., threads). We designed and implemented a new mechanism, called , that is used to build thread mobility or thread persistence. Therefore, a running Java thread can, at an arbitrary state of its execution, migrate to a remote machine where it resumes its execution, or be checkpointed on disk for possible subsequent recovery. With our services, migrating a thread is simply performed by the call of our primitive, and checkpointing/recovering a thread is performed by the call of our and primitives. Several projects have recently addressed the issue of Java thread serialization, e.g., Sumatra, Wasp, JavaGo, Brakes, JavaGoX, Merpati. Some of them have attempted to minimize the overhead incurred by the thread serialization mechanism on thread performance, but none of them has been able to completely avoid this overhead. We propose a generic Java thread serialization mechanism that does not impose any performance overhead on serialized threads. This is achieved thanks to the use of type inference and dynamic de-optimization techniques. In this paper, we describe the design and implementation details of our thread serialization prototype in Sun Microsystems' JDK. We report on experiments conducted with our prototype, present a comparative performance evaluation of the main thread serialization techniques, and confirm the elimination of the performance overhead with our thread serialization mechanism. Document type: Report

Abstract

Projet PRAXITELE; For a large urban area an alternative to public transportation and private cars is considered in the form of a "free" use of electric cars. Such "free" use of electric cars would require periodic redistribution of the cars among different dropoff/pickup stations by a fleet of finite capacity towtrucks stationed at the various depots on the road network. In this study we examine in detail the electric car redistribution problem. The redistribution activity is modelled as that of less than truck load, pickup and delivery with nonsimple paths, allowing for split pickups and deliveries. We propose a Mixed Integer Programming formulation of the problem and we test several solution which include constraint Programming, Lagrangian relaxation methodology applied to the MIP model, and an AI solution approach with a modified A* heuristic. The solution procedures here are designed to solve large practical instances of the car redistribution problem.