Space information network is a network system which takes space platform as carrier and has the ability of acquiring,transmitting and processing real-time information.With the development of space technology,status of space information network in political,military and economic field is improving constantly.Meanwhile,it becomes keystone of research around the word.Satellite network,as an important part of space information network,can ensure complete coverage of earth surface regardless of the effect of environment,climate and geographic location.So it undertakes more data services nowadays.Through buildup of satellite network,space information resources are effective integrated,stability of space information network is improved,and more paths are provided for data transmission.Routing technology of network affects reliability and timeliness of data transition and network performance.Although routing problems on the ground network are solved well,it disadvantages are still obvious.Generally,satellite moves in high speed so that its network topology is in dynamic changes.Besides,routing algorithm of traditional ground network is not suitable for satellite network because of the effect of space environment.So routing problem is basic problem of space information network,and it is also a research hotpot in current research field.Software Defined Network(SDN)is a new kind of network architecture which has loosely coupled control plane and data plane.In SDN,controller maintaining centralized control of network,and Switch only need to forward data according to flow table which controller pushes.Network managers could manage network through programming which improve automated management and control ability of network.In this paper,SDN is applied to space information network to solve routing problems.The main work and achievements of this paper include:Firstly,an SDN-based space information network architecture is proposed,which efficiently solve the problems in current network,such as inflexible of network management,big time delay during packet transmission and so on.This architecture adopts the core idea of SDN ’control and forwarding separation’.Three GEO satellites and ground data center compose a controller cluster which makes decision and pushes flows base on global view.Lower satellites are responsible for simple data forwarding and ground data center in charge of data storage regularly and technical support for space information network.Satellites form a network through ISL(Inter-Satellite Link,ISL)so that satellite system become an independent system and reduce reliance on ground station.Secondly,through systematic research of routing algorithms in satellite network,based on overseas and domestic research status and characteristics of network topology,a LEO satellite network topology model is built.It takes advantages of the idea of ’coverage division mechanism’,hiding the movement of satellite,designing logical address for satellites in the network according to satellites’ orbit and the position of satellite in its orbit.In an SDN-based satellite network,logical address is largely used to do routing forwarding and other process.Thirdly,control signal in SDN network is designed according to logical address which contains flow table between controller and switch,multi-controller message synchronization and so on.When design flow table between controller and switch,an important work is to design match field and action command during the controller pushes flow table according to logical address.As to the design of multi-controller message synchronization,the emphasis is on the synchronization of network topology information and task information between multi-controllers.Lastly,a shortest path algorithm in the SDN-based LEO satellite network is proposed according to the topological structure and characteristics of LEO satellite network.Taking advantages of centralized control of SDN,routing results are the best,switch’s computing tasks are reduced and data transmission speed is higher.There are three kinds of forwarding paths according to the position of source satellite and destination satellite.To assure that the path from the source to the destination satellite is the shortest one,congestion control is also used,to avoid that congestion at a point affecting the performance of the whole network.Simulation proved that this algorithm could reduce end to end delay of packets and packet lose rate,rise network throughput,and could be applied to LEO satellite network efficiently. |