VORAL: A System for Voice Over IP Routing in Application Layer

There are three key metrics (end-co-ed delay, packet loss rate and delay variation) for determining the quality of Voice over IP (VoIP). The impact of delay variation can be reduced by de-jitter buffering at a receiver side. The impairment caused by the packet delay and loss can be reduced by routing the traJic through an Internet path with a better quality. However, the current Internet infrastructure has not yet supported a complete QoS routing. Consequently, the quality of VoIP today, especially over U wide-area network for international calls, is ofren unbearable. In this paper, we present c1 system VOR4L (Voice Over IP Routing in Applicution Layer) that can signiJcantly improve the QoS of VoIP by routing the voice packets in the upplication layer through various relay servers in the Internet. The routing techniques use R-jiactor, a parameter determined by packet loss rate and packet delay, to select U path with the best VoIP quality for a call. The paths of incoming traflc a d the outgoing traffic can be d@erent and be dynamically changed during a cull. The usefulness of the VORAL system is further validuted by an experimental VoIP service between US and Taiwan.