Computing the unmeasured: an algebraic approach to Internet mapping

Distance estimation is important to many Internet applications, most notably for a WWW client that needs to select a server among several potential candidates. Current approaches to distance (i.e., time delay) estimation in the Internet are based on placing Tracer stations in key locations and conducting measurements between them. The Tracers construct an approximated map of the Internet after processing the information obtained from these measurements. This work presents a novel algorithm, based on algebraic tools, that computes additional distances, which are not explicitly measured. As such, the algorithm extracts more information from the same amount of measurement data. Our algorithm has several practical imparts. First, it can reduce the number of Tracers and measurements without sacrificing information. Second, our algorithm is able to compute distance estimates between locations where Tracers cannot be placed. This is especially important when unidirectional measurements are conducted, since such measurements require specialized equipment which cannot be placed everywhere. To evaluate the algorithm's performance, we tested it both on randomly generated topologies and on real Internet measurements. Our results show that the algorithm computes up to 50-200% additional distances beyond the basic Tracer-to-Tracer measurements.