IMPROVEMENT OF VOIP QUALITY BY PACKET DROPPING IN ADSL ROUTERS

Packet dropping is known as a simple mechanism to control TCP traffic. In this paper, TCP packet dropping is introduced in the egress router of an ADSL downlink. The aim is to improve the quality of VoIP connections that compete with TCP applications in downlink direction. The ADSL downlink buffer is assumed to operate as simple FCFS queue. Different simulations have been conducted that evaluate the mechanism in two scenarios. Firstly, the long-term impact of the mechanism both on VoIP application and TCP applications is investigated. Secondly, with more realistic network settings, the effectiveness of the mechanism for a short-time real speech is evaluated. The speech’s PESQ estimate is used to assess the service quality. The results indicate that in both cases packet dropping can improve the VoIP quality. However, the required high dropping ratio can result in TCP traffic bursts and therefore unstable VoIP quality as well as bad TCP performance.