# Multi-Topology Routing Algorithms in SDN-Based Space Information Networks
## 1 Introduction
In this paper, we propose a routing algorithm based on snapshot sequence. However, the number of static topologies increases dramatically with the increase of network size. As a complex network, the number of nodes in the SIN is very large, which overburdens the computing and storage capacity of onboard devices. In addition, the traditional satellite network control architecture cannot effectively recalculate the routing when the satellite link fails or the load is too heavy. Therefore, this paper first proposes a SIN management framework based on SDN. The routing calculation, configuration generation and resource management of the whole network are all handled by the SIN resource scheduling and management center and controller on the ground, which cannot only reduce the burden of satellite nodes, but also benefit the overall unified management. The existing routing algorithms based on SDN can be divided into four categories, a routing algorithm based on QoS, a routing algorithm based on energy aware, a routing algorithm based on load balancing, and a routing algorithm based on application/service aware [9]. QoS refers to the ability to provide better services for specific businesses in heterogeneous networks. The goal of QoS is to improve priority services for different businesses. Intuitively speaking, QoS represents meeting some specific needs of users, such as transmission rate, waiting time, error rate, packet loss rate, etc. In order to improve the efficiency of the SIN and satisfy the transmission requirements of different spatial tasks, this paper studies the multi-topology routing algorithm based on QoS routing algorithm. By calculating the link comprehensive weight of SIN, the Warshall-Floyd algorithm is used to select the best transmission path [10]. Based on the selection of transmission links, this paper proposes a TBA algorithm to ensure the priority transmission of special users and important tasks. The main contributions of this paper are as follows. 1. The SIN management architecture based on SDN is established, which realizes the unified management of spatial resources and provides sufficient storage and computing space for the routing algorithm of the SIN based on snapshot sequence. 2. On this basis, according to different space tasks' QoS requirements, a method of calculating integrated link weights of the SIN is designed, so that space tasks with different QoS requirements can get their optimal routing strategy. In view of the transmission of multiple space tasks on the same link, the proposed TBA algorithm can effectively guarantee the timely transmission of important tasks, thereby improving the quality of service of the SIN. The rest chapters of this article are arranged as follows: Section 2 firstly introduces the related concepts of SDN, and analyzes the advantages of the SIN based on SDN. Section 3 establishes SIN management framework based on SDN, and on this basis, designs a snapshot sequence-based SIN routing algorithm process. Section 4 designs the multi-topology routing algorithm, calculates the initial link weight and integrated link weight of the SIN, and proposes a TBA algorithm. Section 5 firstly designs the optimal routing strategy by using Warshall-Floyd algorithm on the basis of Section 4.2, and then simulates the TBA algorithm proposed in Section 4.3. Section 6 discusses and summarizes the full text.