A Measurement-based Study of the Skype Peer-to-Peer VoIP Performance

It has been increasingly popular to build voice-over-IP (VoIP) applications based on peer-to-peer (P2P) networks in the Internet. However, many such VoIP applications free-ride the network bandwidth of Internet Service Providers (ISPs). Thus their success may come at a cost to ISPs, especially those on the edge of the Internet. In this paper, we study the VoIP quality of Skype, a popular P2P-based VoIP application. Specifically, using large-scale end-toend measurements, we first conduct a systematic analysis of Skype supernode network. We then investigate the impacts of the access capacity constraint and the AS policy constraint on the VoIP quality of Skype. We show that even when free-riding is no longer possible for only 20% of supernodes that are located in stub ISPs, the overall VoIP quality of Skype degrades significantly, and a large percentage of VoIP sessions will have unacceptable quality. This result clearly demonstrates the potential danger of building VoIP applications based on P2P networks without taking into account operational models of the Internet. We also study using time diversity in traffic patterns to reduce the impacts of the preceding