Mobile-agent based middleware for mobile users

Abstract

Mobile terminals such as cellular phones and PDAs have rapidly come into widespread use in recent years. Consequently, there is a growing requirement for increased flexibility in applications, especially in overcoming limitations of wireless environments. However, developing distributed applications that make effective use of networked resources from a mobile terminal is difficult for a number of reasons. We focus on two main problems: namely, mobile terminals do not have a permanent connection, and have intermittent connectivity to the fixed network; and the  nature of a mobile terminal is the limiting factor when supporting computation-intensive applications. Such characteristics prevent the large-scale deployment of advanced services to a mobile terminal. Here, we consider an application offering collaborative editing support for mobile users. The coordination model that drives the application keeps track of and coordinates activities performed by mobile collaborators. The application’s architecture is designed so as to allow documents hosted on mobile terminals, to be shared and edited in parallel by mobile collaborators. The collaborative editing application is a complex application requiring communication, memory and computing resources, and does not lend itself to a port to mobile terminals with limited resources and intermittent connectivity. For this reason, we decided to offload the computationally-intensive part of the application to the infrastructure, and to introduce the idea of an intermediary located in the network infrastructure, interacting with applications on behalf of the mobile terminal, thereby hiding away evidence of the intermittent connectivity. Our vision is that of a mobile agent, called a shadow that is always in close vicinity of the mobile terminal. We show that multiple shadows may co-exist, and we propose a protocol capable of coordinating them. We present a middleware application called Mobile-Agent based Middleware for Mobile Users (MAMiMoU), which hides away communication details, and offers a substrate for building the distributed collaborative editing application across mobile terminals and fixed infrastructures. Implementation details of our application are also presented. We undertake a systematic evaluation of our architecture by using a testing environment that simulates different collaborative patterns. Our conclusion is that when a system is supported by MAMiMoU in mobile users’ environments, it performs significantly better than such a system without MaMiMoU.

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