Research And Implementation Of Networking Mechanism For Centralized-routing-based Satellite Networks

Satellite networks have the advantages of wide coverage,large capacity,and little geographical restrictions,which have gradually attracted widespread attention from industry and academia at home and abroad in recent years.Building spatial information networks has become the development trend of the future network.However,the processing power of satellites is weak.The distributed routing of terrestrial networks with long convergence time and weak flexibility is difficult to adapt to satellite networks,which will increase the cost of satellites.The proposal of Software Defined Network(SDN)provides new ideas for the design of satellite routing.SDN separates the data plane from the control plane,which can reduce the workload of satellites and greatly strengthen the management and control capabilities of the networks.The SDN-based satellite networks rely on stable control links to deliver forwarding entries.The topologies of satellite networks present high dynamic changes,there are a large number of forwarding loops,and each satellite can be directly connected to its corresponding ground station for a short period of time during the operation cycle.Therefore,how to build a network between satellites so that they can communicate effectively with other satellites and ground controllers is one of the major challenges facing the construction of SDN-based satellite networks,and further research is needed.To this end,this paper designs a networking mechanism for centralized routing based satellite networks,which aims to establish an effective path between the satellites and controller,and provide the controller with effective global topology detection.Specifically,the proposed mechanism first simplifies the dynamic topologies of the satellite networks with the help of snapshot routing,and transforms it into a series of time slice sets composed of static topology graphs lasting for a period of time.Then,in each time slice,the low-orbit satellites in the same orbit are set as a forwarding group for networking to establish the topological connection within the group,and the nodes directly connected to the ground station or the high-orbit satellite are selected as the access agents of the group.The access agents serve as the default gateway of the forwarding group to the controller,so that the nodes in the group can establish connections with the controller through them.Finally,the access agents periodically summarize and report the topology information in the orbit,which is convenient for the controller to manage the satellite networks.Based on the above mechanism,this paper implements the relevant system to complete the modules of network forwarding,time slice switching,and information reporting in satellite forwarders.Among them,the network forwarding module is the core part,which is responsible for forwarding group division and access agents election.At the same time,the satellites sense topology changes in the group through signaling interaction.When a certain access agent fails,satellites can choose other available access agents to replace it to ensure the smooth flow of the path with the controller.The time slice switching module realizes the pre-configuration of the time slice according to the up-down of the links,and adopts a timer to realize the timely and orderly loading of the configuration.The information reporting module obtains neighbor information through detection,then it integrates and periodically reports the topology information in the group based on the access agent,so as to provide the current actual topology for the controller.Finally,in order to verify the performance of the system,this paper builds a test environment of the system,which performs functional tests on each module,and conducts a performance comparison test with the SDN topology discovery mechanism based on the Link Layer Discovery Protocol(LLDP).The test results show that the networking mechanism designed in this paper can more completely discover the current actual topologies of the satellite networks compared with the SDN topology discovery mechanism.