An optimal median calculation algorithm for estimating Internet link delays from active measurements

Delay estimation in the Internet can improve performance of many applications, e.g., web browsing, peer-to-peer applications, and distributed games. For this purpose, researchers suggested building an Internet distance service that can efficiently supply applications with delay information based on an Internet delay map. This can be achieved by deploying a large scale measurement infrastructure such as the DIMES project where internal delay information is extracted from end-to-end measurements. We suggest estimating internal Internet link delays by the median of the differences between the measurements to its end points. For this purpose we introduce an efficient median calculation algorithm, which works in linear time and constant space; prove its correctness; and compare its performance to the much slower intuitive algorithms on real Internet data.