Passive inference of path correlation

Overlays have been proposed as a means to improve application performance in many areas, including multimedia streaming and content distribution. Some overlays use parallel transmission to increase aggregate throughput or use backup paths to improve reliability. For such applications, an important consideration is whether the "virtual links" at the overlay level (i.e. paths between overlay nodes) share links in the underlying network. In particular, choosing parallel or backup paths without any information about path correlation can reduce the effectiveness of the overlay. In this paper we show how to use passive measurement of TCP throughput to provide information about path correlation, for use in overlay routing decisions. Our methods have the advantage that they send no probe traffic to collect path information. We present results of experimental evaluation in both controlled testbed (Emulab) and real wide area network (Planetlab). Our results demonstrate that the methods together work well across a wide range of operating conditions.