An Adaptive Packet Dropping Algorithm for Improved VoIP Quality at ADSL-Subscribers

Delay is one of the most important parameters of VoIP which can significantly impact the voice quality. When crossing an ADSL downlink, a VoIP application has to contend for the bandwidth with other applications, e.g., TCP. With the assumption that the DSLAM only has a FCFS mechanism employed in the downlink direction, the VoIP packets may suffer from serious queueing delay problem in the DSLAM buffer. This problem can be solved by introducing TCP packet dropping at the receiver. But the drop ratio should be adjusted depending on the network conditions such as network load. In this paper, an adaptive packet dropping algorithm based on the RED mechanism is proposed to guarantee the VoIP quality in ADSL downlink under different network conditions. Simulations are conducted to compare our approach with the fixed drop ratio approach considering different network traffic. The results show that our algorithm can successfully adapt to the network conditions. Moreover, compared with the fixed drop ratio one, our approach can achieve better VoIP quality with fewer TCP packet dropping.