The Research On Quality Of Service Of Data Service Based On Multi-Rate VBR Service System

Today, new services like data and video spurred by social development have been making the rapid increase of the traffic in the communication network. Because of the traffic and new service growing too fast, the study on performance of the broadband network can not follow the development of the network service, it is hard to optimize the broadband network and find a reasonable programming project. So it is quite important to strengthen the performance research and effectively utilize the existing network condition to support integrated services.The modern communication network can bear various services including best effort services and real time services. The cell loss probability of the multi-rate real time service and the average delay of the best effort service are the most important performance parameters and they can determine the quality of service in broadband integrated networks. So it is significant to study these parameters.Generally, the CBR(Constant Bit Rate) service model has been used to study real time services. However, it is proved that the transmission rate of many real time services like voice and video is variable; the CBR model can not describe them accurately and can not utilize the limited network bandwidth effectively. So the real time service with variable rate should be described as the VBR(Variable Bit Rate) service model. The paper has chosen the typical ON-OFF model to describe the statistical characteristics of real time VBR services, studied the performance on the multiplex system of multi-rate real time VBR services and best effort service. At any moment, real time cells have the advantage over best effort data packets, and these data packets can be buffered and transmitted by utilizing the moment residual capacity. Through comprehensive analysis of the integrated service queuing, this paper has educed computation formulas of the average residual capacity, cell loss probability and average packet delay. By discrete interval simulation, it is proved that the formulas are correct. And through the analysis on the relation between the cell loss probability and the system load, a new conclusion that the cell loss probability is not a monotonic function of the call level load is obtained. These researches have made a new progress in the performance study of broadband integrated service system.As one of typical best effort services, the application of short message service is very extensive. However, the delay problem can not be well solved in GSM. This paper has discussed the transmission mechanism of short message service, analyzed the delay reasons and suggested an improved transmission strategy utilizing GPRS.