【作者】 史恒；

【导师】 黄生叶；

【作者基本信息】 湖南大学 ， 通信与信息系统， 2008， 硕士

【摘要】 当今社会发展所催生的新业务使得通信网络的通信信息量飞速增加。由于通信量和新业务的增长速度太快,网络性能方面的研究跟不上网络业务的发展,导致网络优化工作的艰难及规划的不合理。因此,加强宽带综合业务网络的性能研究,有效利用既定的网络条件为各种业务服务至关重要。随着现代通信网络的发展,宽带网络承载的业务不断丰富,除了尽力而为数据业务之外,还包括各种实时业务。多速率实时业务的丢包率和尽力而为业务的平均延时是体现宽带综合业务网络性能的重要参数,是决定用户服务质量的重要环节,对其进行研究具有重要意义。长期以来研究实时业务采用恒定比特率(CBR,constant bit rate)业务模型。而实践证明,诸如话音、视频等实时业务传输过程中的速率是可变的,传统CBR业务模型不足以精确地表示速率可变的实时业务,不能有效地利用网络有限的带宽资源。因此,速率可变的实时业务应采用可变比特率(VBR,variable bit rate)业务模型。本文采用了流行的ON-OFF模型简单有效地描述实时VBR业务的统计特性,对多速率实时VBR业务与尽力而为业务复用系统的性能进行了研究,在优先处理实时VBR业务分组的基础上,利用系统瞬时剩余容量处理尽力而为业务。通过对该综合业务排队系统的分析,推导出系统平均剩余容量、实时VBR业务丢包率及尽力而为业务平均延时的定量解析式,并利用离散事件的时间步长仿真法进行系统仿真,验证了理论公式的正确性。通过对仿真结果的观察进一步分析了系统负荷的变化对丢包率的影响,得出了丢包率并非随负荷增加而单调增加的新结论。在研究宽带综合业务系统性能上迈出了新的一步。短消息业务作为典型的尽力而为业务之一,其应用非常广泛。而现有的GSM网络不能很好解决其延时问题。本文探讨了短消息的传输机制,分析其延时原因,结合GPRS网络提出短消息传输流程的改善方案。更多还原

【Abstract】 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.更多还原