Design And Implementation Of Real-Time Message-Oriented System

New challenges are presented for distributed systems because of wide applications of Internet technology and rapid development of mobile computing, grid computing and pervasive computing platforms:The requirements of large-scale distributed control and dynamic changes must be satisfied. This requires that the flexible communication interaction mechanism with dynamic and loosely coupled features should be taken between the various participants in the system. Publish/Subscribe system which is composed of three entities, data publisher, data subscriber and proxy distributing data between them, can adapt to the mechanism. June 2004, the Object Management Group OMG has developed Data Distributed Service specification. Data Distributed Service is a middleware technology which is lightweight and provides real-time data transmission by means of publish/subscribe mechanism. There are a number of mature publish/subscribe models based on OMG DDS specification in the world such as CORBA event service, TIB/Rendezvous, JMS, Gryphon, SIENA, JEDI, etc. However, their common drawback is that there is no effective support of application-level quality of service QoS. While, compared to the other publish/subscribe models, the main feature of DDS specification is rich QoS supprot.More than 20 QoS strategies are defined in DDS specification raised by OMG, but none of them is implemented. By analyzing the QoS strategies in the DDS, a struct for each policy is defined and more than 10 QoS strategies in the specification are implemented at last. Besides, original Real-time Message Oriented System is redesigned and improved. The requirements are analyzed and the architecture and each module are designed; database sheets are redesigned to meet the different data types; the processes of publilsh/subscribe are improved; the terminal view is modified and corresponding interfaces are added so that users can publish/subscribe three different data types like text message, geographic information and video information. Finally, the system response time and information distribution delay are tested and the results show that the system can meet the rapid and real-time requirements.