@InProceedings{XY07,
  author =	 {Haiyong Xie and Yang Richard Yang},
  title =	 {A Measurement-based Study of the Skype Peer-to-Peer
                  VoIP Performance},
  booktitle =	 {Proceedings of {IPTPS}},
  year =	 2007,
  address =	 {Bellevue, WA},
  month =	 Feb,
  abstract =	 {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-to-end 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 constraints. }
}