Flow aggregation or time synchronization ensures Low-Rate Denial of Service (LDoS) attack flows form an ideal rectangular pulse at the victim to maximize attack efficiency. The differences of end-to-end delay between each host are critical for aggregation or synchronization. A new approach based on Euclidean distance is proposed to avoid the complexity of direct measuring internet end-to-end delay. Using NS2 experiments, the performances of such coordinated attack are shown and compared with uncoordinated attack. Test results prove that an aggregated or synchronous LDoS attack launched by the approach is even more detrimental.