| With the rapid development of rail transit in China,the train network based on TCN(Train Communication Network)is unable to meet the needs of the train data transmission business,so the train control and service network TCSN(Train Control And Service Network)came into being.The goal of the TCSN is to establish a train network with large bandwidth,high reliability,high trustworthiness,reconfigurability,and intelligent features,integrate train control services and passenger service services into transmission,and improve the quality of service of train data transmission services.Based on the National Science and Technology Support Program 2015BAG14B00,the characteristics of the train business data are analyzed,the application of the weighted fair queuing algorithm and its improved algorithm in TCSN service scheduling are studied and simulation tests are carried out.The main work of the thesis are as follows:First,the main business of the Train Control and Service Network(TCSN)are analyzed.The control services of the traction,braking,air conditioning,doors,displays in the train are analyzed and summarized.Several current passenger service business in trains are analyzed.QoS(Quality of Service)control models in the two networks are analyzed: an integrated service model and a differentiated service model.Secondly,the train communication network based on the comprehensive service model is researched,four types of train business data types based on leaky bucket traffic model are established.The network packet scheduling algorithm WFQ(Weighted Fair Queueing)is studied,and the SCBAWFQ(Service Class and Bandwidth Allocation Based WFQ)based on service classification and bandwidth allocation is designed.Compared with WFQ,the main improvements of SCBAWFQ are as follows: 1)Classification of train services to distinguish between real-time services and non-real-time services;2)An iterative bandwidth allocation method is used to allocate real-time services to their reserved bandwidth and allocate the remaining bandwidth for non-real-time services.Finally,on the network simulation software NS2(Network Simulator version 2)platform,SCBAWFQ algorithm is programmed using C++ language: 1)Add the data packet header file of SCBAWFQ algorithm in the common library;2)Add the SCBAWFQ scheduling algorithm program to the queue;3)Sets up the network topology structure of the train flow model with OTcl scripting language,and calls WFQ and SCBAWFQ to simulate the constant data stream and the burst data stream respectively.The result shows that: SCBAWFQ algorithm can effectively solve the shortcomings of WFQ algorithm can not distinguish between service types on constant traffic data flow.SCBAWFQ algorithm not only can solve the shortcomings of WFQ algorithm can not distinguish between service types,and has certain advantages in bandwidth allocation when dealing with bursts of data traffic on burst traffic data flow.The simulation results show that the performance of the improved algorithm(SCBAWFQ)is better than that of WFQ in view of the large amount of service data and the characteristics of bursty services in the TCSN network.It has certain reference value for real-time scheduling of TCSN research. |
