Due to the rapid spread of botnets, distributed denial of service attacks have become more and more frequent and fatal. In order to detect and defend DDoS attack, many researches have been done, such as using NS2 to simulate such attacks. However, the major bottlenecks in large-scale network simulation are the memory usage and simulation time. In this paper, we present a novel approach to simulate DDoS attack, called Analytical Packet Forwarding Model (APFM), which simplifies the procedure of packet forwarding based on computation. The experimental results show that our model ensures the authenticity of the overall simulation procedure and simulation results, compared to NS2. The most significant contribution of APFM is that it significantly reduced the memory usage and simulation time.

Rolling Rocket/Shell (RR/S) can effectively overcome the impact point error caused by the asymmetry of aerodynamic appearance and mass eccentricity .etc. The spatial attitude of RR/S in the process of flight must be studied for that RR/S realizes the guidance control and improves the falling point precision. This paper introduces a semi physical simulation of RR/S attitude algorithm based on non-holonomic Inertial Measurement Unit (IMU) which is composed of 3 orthogonal import rate gyroscopes. It adopts the 902E-1 two-axis turntable to simulate the spatial attitude of RR/S, and uses the non-holonomic IMU, which is fixed on the turntable by ensuring the axes of them to be aimed, to measure the 3-axis angular rate motion of the turntable. By setting the motion condition of the turntable, we can get the 3-axis angular rate data of the IMU and the 3-axis angular position data of the turntable. The attitude algorithm simulation of IMU adopts the four-sample rotation vector algorithm based on MTLAB/Simulink. The simulation results show that the semi-physical simulation method can model the spatial attitude of RR/S truly and provide exact and real-time attitude information of RR/S which is rolling in the two-axis complex movement condition.