| NGN adopts the method of packet switching, which is based on the technology of VoIP,including SIP, H.323, MGCP and other network communication protocols and various voicecompression technologies, mainly relying on IP bear network.The best effort IP Network has itsinherent data loss, time delay, jitter and other transmission impairments, which would havecomplicated influence on the transmission quality of the voice band signal that based on traditionalcircuit switching. The complexity of the transmission quality control is futher intensified byadopting the method of out of band signal and command.This paper mainly studies the transmissionimpairments of the voice band data in NGN network, and designs a kind of end to end transmissionmethod and control process with certain quality.This thesis describes the common architecture of current fusion network, then a typical end toend communication system is simulated via Simulink. The DTMF signal of an actual system istaken as the example. The experimental environment for its VoIP transmission is setup. Then itsdamage characteristics are analyzed, including selection of coding mode, network load,transmission delay and jitter, and so on. On that basis, a corresponding solution of errortransmission and redundancy coding is designed to reduce the transmission error rate of DTMF.Thesimulation indicates that the stop wait control scheme of3choosing2repeated code and2yardslong frame structure can effectively improve the accuracy of the frame transmission when thetransmission error rate of single DTMF is less than10%.The experiment test bench is setup to validate the proposed solution. This bench is comprisedof Opensips, Partysip and other SIP servers, wireshark tool is also utilized to analyze the SIPcommunication process. A self developed traffic generator is applied to simulate network load. Theproduce mechanism of DTMF transmission damage is analyzed according to different codingmethod and out of band/in band transmission method. The experimental results coincide with thesimulation results. The research shows that all of the data channels after encoding are unavailablewhen the network load is more than70%. The effectiveness of the proposed solution can be ensuredwhen the network is less than20%and the transmission error rate of single DTMF is less than10%.With8%error rate as the target, for double redundancy DTMF signal,G.729encoding data channelcan be applicable when network load is less than30%; and G.711encoding data channel can besuitable when the network load is less than60%. |
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