Design And Implementation Of VoIP System Based On 4G Converged Network

As mobile Internet develops in leaps and bounds,a vast application space has been laid for VoIP communication technology based on mobile Internet.Traditional VoIP wireless terminal equipment usually employs a single SIM card to access the Internet,in real life,however,the communication environment is far more complex with factors such as poor coverage of base station signals,blind coverage area,aging equipment,too many connected terminals under a single base station and others that will lead to the deterioration of the communication link between terminal equipment and base station,thus hindering the stability of the VoIP communication system based on mobile Internet.Meanwhile,in order to alleviate the problem of increasing deficiency of IPv4 public network address space,NAT technology which can make a public network IP address shared by multiple intranet hosts is applied in the industry.But it also brings NAT traversal problem to VoIP systems based on SIP signaling protocol.In the case of communication data transmission based on mobile Internet,how to utilize the base station resources of three major operators to improve the VoIP communication quality and assist SIP signaling in traversing NAT has become an outstanding problem to be solved.This thesis studies specific to the above problems,analyzes the main factors affecting the communication quality of VoIP system.Through case study,it deeply investigates the internal causes of SIP traversing NAT,analyzes the shortcomings of existing solutions combining application scenarios,and proposes an improvement scheme of VoIP system based on 4G converged network.Compared with the traditional VoIP system,this scheme adds two intermediate subsystems of converged gateway and converged server.SIP terminal accesses the Internet through the converged gateway and sends the communication data to the converged server.After the original communication data are processed by the converged server in a way of redundancy and SIP message adaptation,the converged server will relay it to the original destination server.The converged gateway designed in this scheme supports three 4G modules.The data transmission between the converged gateway and the converged server uses the 4G network of three major operators.While the communication data are transmitted through three communication links at the same time,the converged server cooperates to process the redundant data to achieve the convergence of 4G network.Transmitting data through the converged network aims to reduce the packet loss probability and delay in the communication process so as to improve the overall performance of the VoIP system.An application layer protocol is designed between the converged gateway and the converged server.In the transmission process between the converged gateway and the converged server,the address information of the original SIP client and the destination server will be carried,and the converged service software will complete the mapping among the intranet address of original SIP client,the public network address of converged server and the public network address of destination server so as to solve the NAT traversal problem.According to the proposed scheme,this thesis has completed the system software architecture design and code implementation of the converged server and the converged gateway,followed with the simulation experiment and result analysis of the system.The experimental results show that the system can effectively solve the NAT traversal problem of SIP signaling;in times of the differences in the delay of various communication links,the minimum link delay transmission can be realized;in the case of packet loss in each communication link,the packet loss probability after convergence is smaller than that of each communication link.