# Modeling and Performance Analysis of Satellite Network Moving Target Defense System with Petri Nets
###### Abstract
As a result, researchers have begun to explore the application of active defense techniques such as End Hopping (EH) [6; 7], Moving Target Defense (MTD) [8], and Mimic Security Defense (MSD) [9] in satellite networks. These strategies create a new way to achieve a shift from a threat-based reactive defense system to a risk-based proactive defense system, and also provide a new idea for space network security protection. However, network security and performance are often in conflict with each other. Increasing security will lead to degradation of performance metrics (e.g., latency and throughput). Moreover, this situation is even worse in satellite networks, where on-board  
Figure 1: Wide application of satellite networks. resources are severely limited and communication links can be easily blocked. As we all know, \"there is no such thing as a free lunch\". Active network defense can achieve a high level of security in satellite networks through randomization, dynamization, and diversification, but it is also predictable that the dynamicization mechanism will bring a non-negligible additional load, thus reducing availability of the network. It is necessary for us to have a clear understanding of the cost it brings. Currently, researchers mostly focus on how to further improve the security of satellite networks, and rarely analyze the impact of these defense measures on network performance from a theoretical perspective. This motivates us to evaluate the performance of the satellite networks in a quantitative way. Aiming to provide theoretical support for rational configuration of active defense strategies and optimization of satellite networks, in this paper, we propose to use SPN to model and analyze the performance of satellite network moving target defense system from a theoretical perspective. We develop SPN models for the communication process of satellite network in the traditional and active protection states, respectively. Then, we evaluate the performance of the satellite network moving target defense system based on the two corresponding SPN models. Through the analysis of models, performance evaluation indexes such as average time delay, throughput, and bandwidth utilization are obtained, and the impact of relevant parameters of active defense technology on network performance is further discussed. The main contributions of this paper are summarized as follows:  
* We propose two scenarios of traditional satellite network and satellite network based on Moving Target Defense technology, respectively;
* We propose a performance evaluation scheme of satellite network moving target defense system based on Stochastic Petri Nets (SPN). We establish SPN models for these two scenarios and evaluate their performance separately;
* We conduct extensive simulations to validate the correctness of theoretical reasoning results and analyze the influence of various factors on the performance indexes of satellite networks. Finally, the challenges and recommendations for deploying active protection technique are given. The remainder of this paper is organized as follows: in Section 2, we give a brief introduction to Petri Nets and active defense techniques. Then, a literature review of related work is given in Section 3. In Section 4, we establish the SPN models in two scenarios, and then conduct their performance evaluation, respectively. In Section 5, our models are simulated by the PIPE platform, based on which the results of key performance metrics are compared and analyzed, and some specific recommendations are made. In Section 6, we describe the shortcomings of our experiments and the future work. Concluding remarks are given in Section 7.