How does the recursive undns algorithm affect the accuracy of an IP geolocation system?

IP geolocation services are playing an increasingly important role in Web applications. Landmark-based IP geolocation can gain better IP geolocation performance. However, the accuracy of landmarks is still an urgent issue to address. The paper proposes a filtering landmark mechanism to guarantee the accuracy of landmarks. First, a Ping-Delay Coarse Filtering Landmark algorithm (PCFL) is proposed to coarsely filter landmarks. Second, a recursive undns model is presented to make full use of undns. Third, a Recursive Undns Evaluating Landmark algorithm (RUEL) is proposed to accurately evaluate the accuracy of landmarks. The experimental results and analyses show that using the filtering landmark mechanism proposed in this paper, the accuracy of landmarks can be increased, which in turn makes the median error distance of the IP geolocation system reduced to a certain extent.