Research On Optimization Techniques Of The Snapshot Routing In Satellite Networks

Recently,the internet technology is applied more and more widely in the world.Compared to terrestrial networks,the satellite network is more feasible for communication in high mountains,sea and desert for its global real-time coverage and infrastructure independence.However,since satellites are moving around the orbits continuously,the topology of satellite networks changes at the same time,which makes the terrestrial routing protocols not suitable for the satellite network.The snapshot routing algorithm bases on the predictability and periodicity of satellite movements,so it pre-calculates the snapshot routing tables and corresponding topology change time offline and pre-stores them on-board.Through switching the routing tables simultaneously,the snapshot routing algorithm can conceal the impact to network routing caused by the dynamic topology.In this paper,we mainly focus on the optimization techniques for the snapshot routing algorithm,and the main research content of this paper is concluded as follows:(1)We analyze the central control characteristic of satellite networks.Based on the software defined networking technology,we propose the software defined satellite networking architecture(SDSN),and analyze the advantages and challenges of SDSN in design and implementation.Then,we compare the time for one complete update operation between the overhead communication scheme of current satellite network architecture,the inter-satellite links(ISLs)forwarding and GEO broadcasting communication of SDSN by simulations.Finally,simulation results validate the advantages of SDSN architecture.(2)We analyze the predictable topology changes caused by the periodical satellite movement,and firstly discover the rollback traffic caused by the simultaneous snapshot routing table update.The impact of rollback traffic to network routing in the polar-orbit constellation is evaluated and the number of rollback links is quantitatively analyzed as well.Then,we propose the routing table optimization based offline rollback traffic avoidance method,and the simulation results indicate that our method can efficiently decrease and even avoid the rollback paths,reduce extra end-to-end delay and packet drop rate with little increment on the average global delay.Besides,we also propose the update order optimization based online rollback avoidance method – group partitioning synchronous(GPS)update method,which partitions satellites need to update into different groups and determine the snapshot switching sequence for each group.As a result,by using this method,the rollback traffic can be avoided and the original global network delay can be preserved at the same time.(3)We analyze the unpredictable topology change in satellite networks caused by the unpredictable ISL on-off variation,and propose the source routing based multicast(SRM)update method.The multicast update message distribution of SRM is consisting of following three parts:(a)update shortest path tree(USPT)centralized construction,(b)source routing based multicast path quick deployment and(c)update execution and acknowledgement.Simulation results show that our method can not only keep low network convergence time,but also reduce network cost efficiently.Furthermore,for the ordering update condition,we improve the SRM method with pipeline optimization(SRM-PO),and the evaluation results indicate that SRM-PO can reduce more routing convergence time and network overhead.(4)We analyze the topology changing regularity of satellite networks,and propose to control the network topology to improve the performance of snapshot routing algorithm both in polar-orbit and inclined-orbit satellite networks,i.e.regularly reassign the inter-plane ISLs to optimize the distribution quality of the next snapshot at the end of each one.Finally,simulation results indicate that this method can gain fewer snapshot number,longer and constant snapshot duration,higher on-board transceiver utilization and lower average end-to-end delay.