Bell Labs Bell Labs Bell Labs Bell Labs Telecom Italia A significant part of the Internet traffic today is generated by peer-to-peer (P2P) applications used traditionally for file-sharing, and more recently for real-time communications and live media streaming. Such applications discover a route to each other through an overlay network with little knowledge of the underlying network topology. As a result, they may choose peers based on information deduced from empirical measurements, which can lead to suboptimal choices. We refer to this as the Application Layer Traffic Optimization (ALTO) problem. In this draft we present a survey of existing literature on discovering topology characteristics.