Design And Implementation Of OSPF Protocol For Space Network

Although successful in Internet,the classical distributed dynamic Open Shortest Path First(OSPF)routing protocol is inefficient in space networks,which is special for the frequent dynamic topology and the fragile inter-satellite links(ISLs).To improve the routing performance,enhanced OSPF routing protocols are proposed and implemented for future in-orbit application.Firstly,the unique characteristics of the space networks are present in detail in this paper.The difficulties and challenges of designing routing protocols in the space network are also explained in this paper.Then the existing applications and improvements of the IP protocol stack in the space network are summarized.The adaptability of OSPF protocol in the space network is analyzed according to core mechanisms of OSPF.Then it is pointed out that the OSPF protocol lacks special measures to speed up route convergence when faced with diversified space topology changes.The space topology changes here are mainly divided into two types:predictable topology changes and unpredictable topology changes.In this paper,the core mechanism and design details of an improved version of OSPF(OSPF+)under predictable topology changes are explained in detail,including topology prediction mechanism and neighbor state machine modification.Then,it analyzes that the OSPF+ protocol has a better convergence performance than the OSPF protocol in the face of spacely predictable link changes.It further points out that neither OSPF/OSPF+ protocol solves the problem of high convergence overhead when unpredictable link changes occur.In view of unpredictable topology changes,this paper proposes to introduce a backup routing mechanism into the OSPF protocol to solve the problem of no available routes within the convergence time of the original OSPF protocol.The implementation scheme of the backup route is elaborated in detail,including the rapid detection mechanism,the failure notification mechanism and the calculation of the backup route.Also the implementation details are explained in detail.Combining the implementation scheme,it analyzes how the backup routing mechanism solves the problem of low routing stability of the OSPF protocol.In this paper,combined with the existing network emulation platform in the laboratory,a quantitative analysis of the performance indicators of the two improved versions of the OSPF protocol is carried out.The failure judgment time and routing stability indicators of the OSPF+ protocol are tested in detail and compared with the original OSPF protocol.It is verified that the OSPF+ protocol has a better convergence performance than the OSPF protocol in the face of spacely predictable link changes.The route switching delay of the OSPF protocol with the introduction of the backup routing mechanism is measured in detail and the time accuracy can reach within seconds.Therefore,it solves the problem that the OSPF protocol has no available routes within the reconvergence time of seconds or even ten seconds.