Performance Optimization of VoIP using an Overlay Network

Voice traffic on the Internet (VoIP) is poised to grow rapidly but the Internet is not engineered for such delaysensitive applications. We show how the end-user quality of many VoIP calls can be improved by rerouting them in an intermediate overlay network and thought the use of various path-diversity and error-coding techniques. We present an overlay network (OverPhone) that is tuned to optimize VoIP quality and provide experimental results based on its implementation on the PlanetLab testbed. We show that about a third of the VoIP calls show noticable performance improvement when re-routed through the overlay while using the G.711 codec. We believe that this benefit extends to other well known and proprietary codecs as well. We also investigate the benefits and trade-offs of using techniques such as path-diversity and parity-coding. We find that path-diversity is useful in sustaining throughput at high loads, and that parity-codes can be used to trade-off bandwidth for path-quality.