| With the advancement of wireless mobile communication technology,networks with a large number of wireless terminals such as the mobile Internet and the Internet of Things have also ushered in vigorous development,which has resulted in an explosive growth of the traffic in the network.However,the existing ground network architecture cannot meet this growing demand for communication traffic,nor can it meet the communication needs of places where network coverage is lacking.Increasing the network load capacity and broadening the network coverage are the problems that must be solved in the current ground network.Satellite network has a very wide coverage and can provide instant network communication services,which can make up for the lack of ground network.Among the current research hotspots,it is a trend that ground network and satellite network develop towards Space-Ground Integration Network（SGIN）,and it is a reasonable and feasible solution to introduce Software-Defined Networking（SDN）into the SGIN to build an emerging network architecture.In this SDN-based SGIN,the placement of satellite gateways and controllers will directly affect the network data transmission latency,SDN controller control latency and network reliability.Therefore,this paper mainly studies the joint placement of gateways and controllers in SDN-based SGINFirstly,different from the previous studies that only consider network latency and reliability,this paper introduces the index of load average difference rate to balance the load in the network.In order to minimize the load average difference rate of the network and determine the minimum number of gateways and controllers required for the network,this paper proposes a simulated annealing algorithm based on improved density peak clustering（DBSAA）to solve the joint placement problem of gateways and controllers.Simulation experiments show that the algorithm proposed in this paper is superior to other comparative algorithms in algorithm running time and algorithm effectiveness,and has the advantage of not needing to pre-specify the number of gateways and controllers.Secondly,due to the dynamic nature of the network topology,the static SDN controller placement scheme is not suitable for Low Earth Orbit（LEO）satellite networks.This paper adopts the virtual topology method to deal with the dynamic topology,and proposes a dynamic placement scheme of the controller,which combines the static placement of the controller with the switch migration algorithm based on the shortest path to solve the SDN controller placement problem in the LEO network.The scheme proposed in this paper utilizes the invariable controller placement location and the variable allocation relationship between controllers and switches to complete dynamic placement,which has certain advantages in algorithm validity and migration cost reduction.Finally,this paper uses Py Charm software combined with the relevant Python toolkit to conduct data simulation experiments on the two proposed algorithms.For the DBSAA,this paper not only combines the population density data provided by the 4th edition of the World Grid Population for traffic estimation,but also conducts simulation experiments on the real-world network topology to ensure the authenticity of the data.The simulation results show that the proposed algorithm outperforms the Optimal Enumeration Algorithm（OEA）and the Simulated Annealing Algorithm（SAA）in terms of effectiveness and running time.For the dynamic placement scheme of the controller that combines static placement with the switch migration algorithm based on the shortest path,this paper combines STK software to simulate,the results show that the proposed algorithm is superior to the static placement algorithm and control migration algorithm in both average network latency and maximum network latency. |
