Research And Implementation Of Anti-packet-loss Strategy For Video Conference System

With the rapid development of Internet technology,the transmission capacity of the network has been improved rapidly.In addition,the audio and video coding technology is becoming more and more mature,multimedia communication has become a hot research direction of modem communication.Video conference has been widely used in many fields,such as distance education,remote medical treatment,business negotiation,communication field,government affairs,etc.,for its convenience,real-time and stability.However,the IP network can only provide the "best-effort" service,which cannot ensure the transmission's reliability,and packet loss can not be avoided.Video communication has the characteristics of large data volume and high real-time requirement,and has high requirements for network delay and jitter.In addition,video data use the GOP encoding format in the transmission,and the frame data has a strong correlation,which is sensitive to packet loss that a single data frame decoding failure may cause decoding failure of the subsequent series of data frame.Therefore,how to protect the QoS(Quality of Service)of video communication in packet loss environment has become an important direction of video conference research.This thesis studies the video communication technology of QoS security and the main direction of current research begin with the reason and effects of packet loss in video communication.Combining with the architecture of the video conference system,this thesis puts forward a packet loss recovery architecture based on forward error correction.The main work of this thesis is as follows:1)This thesis proposed a Tornado coding algorithm based on the comparison and analysis of the principle and performance of the RS code and the Tornado code.This algorithm breaks the isolation of packet recovery within one packet group and improves the packet loss recovery capability and the ability to cope with the burst packet loss by the convolution association between different groups.2)In order to avoid more packet loss due to the bandwidth occupation of FEC processing,this thesis proposes a network transmission control mechanism based on bandwidth and frame rate adaptive adjustment,which reducing the transmission pressure effectively.3)This thesis studies the generation of delayed jitter and the effect of FEC processing on it,and adopts a control mechanism based on Jitter Buffer technology to ensure the smooth output of data stream and avoid the adverse effects of jitter on video images.At last,a video conference system adopt this packet loss recovery architecture is implemented.It is proved in the experiments in the actual environment that this scheme can significantly recover the lost data and reduce the adverse effects such as flower screen and stutters caused.Users can not aware of the existence of packet loss under the condition of lower packet loss(below 10%packet loss)and the video image is basically normal under the condition of large packet loss(10%to 15%packet loss),which improves the quality of service of video communication effectively.