EZCab is a proof-of-concept ubiquitous computing application that allows people to book nearby cabs using their cell phones or PDAs equipped with short-range wireless network interfaces. EZCab discovers and books free cabs using mobile ad hoc networks of vehicles. We have implemented an EZCab prototype on top of smart messages, a middleware architecture based on execution migration, which we had developed to provide a common execution environment for outdoor ubiquitous computing applications. The experimental and simulation results have demonstrated the feasibility of EZCab

Spatial programming (SP) is a space-aware programming model for outdoor distributed embedded systems. Central to SP are the concepts of space and spatial reference, which provide applications with a virtual resource naming in networks of embedded systems. A network resource is referenced using its expected physical location and properties. Together with other SP features, such as reference consistency and access timeout, they help programmers cope with highly dynamic network configurations in a network-transparent fashion. We present the SP design and its implementation using smart messages, a lightweight software architecture similar to mobile agents, that we developed for networks of embedded systems. We also describe the implementation and evaluation of a simple SP application over a testbed consisting of HP iPAQs running Linux and equipped with 802.11 cards for wireless communication. The experimental results indicate that SP is a viable programming model for outdoor distributed computing.

Recent advances in wireless technology allow Java-enabled devices, such as Smart Phones and PDAs, to create mobile ad hoc networks, over which distributed applications can be executed. Although Java shields the programmers from the heterogeneity of the hardware platforms, a common middleware architecture is needed to support a cooperative execution environment in these networks. In this paper, we present a portable runtime system for smart messages (SMs), a middleware architecture based on execution migration, that we designed and implemented on top of an unmodified Java virtual machine. To facilitate portability, we have designed a lightweight migration mechanism based on Java bytecode instrumentation. This mechanism is suitable for mobile ad hoc networks where limited bandwidth and mobility impose constraints on the amount of data transferred. The experimental results for applications executed over wireless networks of HP iPAQs demonstrate the feasibility of our portable runtime system.

In this paper, we present the design and implementation of Smart Messages, a distributed computing platform for networks of embedded systems based on execution migration. A Smart Message (SM) is a user-defined distributed program which executes on nodes of interest, named by their properties, and uses an explicit lightweight migration to reach these nodes. During migrations, an SM carries its code and execution state, and it self-routes at each intermediate node between two nodes of interest. The nodes in the network cooperate to support the SM execution by providing a virtual machine and a shared memory region addressable by names (tag space). To illustrate the flexibility of SMs to program real world applications, we describe EZCab, an application for booking cabs in densely populated urban areas. We also present experimental results to quantify the performance achieved by the SM prototype.

The next generation of computing systems will be embedded, in a virtually unbounded number, and dynamically connected. The current software, network architectures, and their associated programming models are not suitable for this scenario. This paper presents a distributed computing model, Cooperative Computing, and the Smart Messages architecture for programming large networks of embedded systems. In Cooperative Computing, distributed applications are dynamic collections of migratory execution units, called Smart Messages, working to achieve a common goal. Virtually any user-defined distributed application can be implemented using our model. We present preliminary results for our prototype implementation as well as simulation results for two previously proposed applications for sensor networks, Directed Diffusion and SPIN, implemented using Smart Messages.