A Measurement Study of Internet Delay Asymmetry

RTT has been widely used as a metric for peer/server selection. However, many applications involving closest peer/server selection like streaming, tree-based multicast services and other UDP and TCP based services would benefit more from knowing one-way delay (OWD) rather than RTT. In fact, RTT is a compromise solution in most cases and is used to infer forward and reverse delays by many protocols and applications. They assume forward and reverse delay to be equal to half of RTT. In this paper we compare and contrast one way delays and corresponding RTTs using a wide selection of routes in the Internet. We first measure the extent and severeness of asymmetry in forward and reverse OWD in Internet. We then attempt to isolate the causes of OWD asymmetry by correlating OWD asymmetry with the route asymmetry. Finally, we investigate the dynamics of delay asymmetry: There exists a weak correlation between the fluctuation of RTT and OWD and a strong correlation between OWD change and the corresponding route change.