Can coexisting overlays inadvertently step on each other?

By allowing end hosts to make routing decisions at the application level, different overlay networks may unintentionally interfere with each other. This paper describes how multiple similar or dissimilar overlay networks making independent routing decisions could experience race conditions, resulting in oscillations in both route selection and network load. We pinpoint the causes for synchronization in terms of partially overlapping routes and periodic path probing processes and derive an analytic formulation for the synchronization probability of two overlays. Our model indicates that the probability of synchronization is non-negligible across a wide range of parameter settings, thus implying that the ill-effects of synchronization should not be ignored. Using the analytical model, we find an upper bound on the duration of traffic oscillations. We validate our model through simulations that are designed to capture the transient routing behavior of both the IP- and overlay-layers. We use our model to study the effects of factors such as path diversity (measured in round trip times) and probing aggressiveness on these race conditions. Finally, we discuss the implications of our study on the design of overlay networks and the choice of their path probing parameters