# A Survey on Satellite Communication System Security
## 5 Defense in Satellite Communication Systems
### Solutions for Availability
The algorithm shows increased effectiveness in networks with a higher presence of malicious nodes, indicating its robustness and adaptability in challenging environments. **SDN-Based Mitigation:** An SDN is an approach to network virtualization and containerization that optimizes network resources and facilitates rapid adoption of new methods for applications and traffic in changing network environments. The integration of SDNs into SCS networks is a recent transformative development, enhancing the flexibility and functionality of these networks. This is particularly evident in two recent proposals focusing on the application of SDNs in space-based networks, addressing key issues like DDoS attack detection and energy-efficient network designs. First, ref. [88] combines an optimized long short-term memory (LSTM) DL model with a support vector machine (SVM), specifically tailored for the SDN architecture. This approach directly addresses the vulnerability of traditional SDN controllers to network attacks, which can risk network paralysis. By utilizing time series data and flow characteristics, the method aims for accurate detection of DDoS attacks, thereby reducing false alarms and refining the overall detection process. The effectiveness of this method is underscored by experimental results, demonstrating high accuracy and low false alarm rates, thus offering a reliable solution for enhancing the security of space-based networks against such threats. Also, the author of [89] presents an innovative approach that not only mitigates DDoS attacks but also prioritizes energy efficiency. They introduce an energy consumption model and an improved network topology algorithm aimed at minimizing energy usage, a critical consideration given the limited resources and high vulnerability to DDoS attacks in satellite networks. Furthermore, this proposal includes a DDoS mitigation mechanism employing deep reinforcement learning algorithms, adept at managing abnormal traffic and reducing the extra energy consumption that typically results from processing such traffic in satellite nodes. The combination of these approaches in the software-defined satellite network context is proven to effectively decrease energy consumption while simultaneously bolstering network security, thereby making software-defined satellite networks more resilient to DDoS threats and more energy efficient. **Collaborative-Based Mitigation:** Collaborative defense in satellite networks refers to a strategy where multiple terrestrial or satellite nodes or systems work together to enhance network security and resilience. This approach often involves sharing information and resources among satellites or ground stations to identify and mitigate cyber attacks, including DDoS attacks. The collaboration can be based on advanced technologies such as blockchain for secure data sharing or artificial intelligence (AI)-driven algorithms for threat detection. This synergy allows for a more robust and adaptive defense mechanism, crucial for the unique challenges faced by satellite networks in space. [PERSON] et al. [90] present the Distributed Collaborative Entrance Defense (DCED) framework to protect the satellite internet from DDoS attacks, addressing its unique vulnerabilities like the limited computing power and bandwidth. DCED includes a two-stage detection digesting process for traffic feature extraction. First, the entrance traffic digest (ETD) records six items of traffic features using the destination IP addresses as an index. Second, the defense plane digest (DPD) cross-detects different types of DDoS attacks from several perspectives using information theory, enabling the handling of various attacks like UDP, SYN, ACK, and ICMP attacks. Also, smart-contract-based virtual aggregation of digests with blockchain and MapReduce is utilized. [PERSON] et al. [91] introduce a secure, distributed model for cyber threat intelligence (CTI) sharing in SDNs using blockchain technology, specifically Hyperledger Fabric, to provide a secure and tamper-proof environment.