MobiGATE : a mobile gateway proxy for the active deployment of transport entities

Abstract

Mobile computing environments exhibit operating conditions that differ greatly from their wired counterparts. In particular, the mobile application must be able to tolerate highly dynamic network conditions and the effects of various computing devices. This research aims to develop an adaptive middleware system that adapts data flows over wireless networks to enable overlying applications to operate effectively and optimally in wireless environments. To achieve this goal, an adaptive middleware system, MobiGATE, has been designed to support robust and flexible composition of adaptable services, termed streamlets in this research study. Significantly, the principle of separation-of-concerns is adopted in the system to facilitate clear separation of streamlet coordination from the service computation codes. By this means, the communication codes are completely separated from streamlet objects and modeled as a new type of object channel. An application running in this system is then regarded as a number of streamlet instances connected by channel objects. This has resulted in the formulation of a two-layered MobiGATE execution platform that supports rapid deployment of service streamlets, while facilitating adaptive composition in reaction to changing environmental contexts. To describe application compositions, a coordination language, MCL, is designed. The language adopts the Multipurpose Internet Mail Extensions, MIME, as the underlying type definition to represent messages and streamlet interfaces. With this type system, a fundamental type compatibility check is allowed in the composition activities. In addition, a semantic model in Z language is defined for MCL to analyze composition descriptions and detect possible composition errors, such as feedback loops, open circuit, and mutual exclusions. The applications running in the MobiGATE system can be analyzed based on the derived semantic model to ensure their consistency in the internal structures. A complete design, implementation and evaluation of the system have been fulfilled successfully on a Java platform, in which common runtime operating system elements are abstracted as residing either in the coordination or in the computing sub-layers. Initial experimental results validate the flexibility of the coordination approach in promoting separation-of-concerns in the reconfiguration of services, while achieving low computation and delay overheads. The system has proved to be efficient and robust in adapting to dynamic wireless conditions and can be improved by some recommendation work in future.