Abstract: AQM (Active Queue Management) is based on TCP feedback mechanism,so it fails to control UDP flow when managing hybrid flow of TCP and UDP.At last non-video flow will influence video UDP transmission quality.Ad hoc network TCP/UDP AQM model was deduced based on TCP window principle and hybrid flow queuing mechanism.Then a PI (Proportional Integral) AQM algorithm based on UDP rate-limiting was proposed.The algorithm can mark priority of non-video UDP packet according to the difference between actual rate and committed rate.It will drop these packets from low to high priority order.NS simulation shows that compared with PI control,the new algorithm controls non-video UDP flow and improves video transmission quality to 0.98 dB Peak Signal to Noise Ratio (PSNR).

Key words: Ad hoc network,Congestion control,AQM,Video stream,Quality of service