Research On Hybrid Routing Protocol Based SDVN

The traditional VANET(Vehicular Ad-hoc Network)always adopts a distributed architecture.Each OBU(On Board Unit)performs routing independently,so OBUs can only achieve a local optimum,however,the Software Defined Network(SDN)has a global view on routing.Therefore,the SDVN(Software Defined Vehicular Ad-hoc Network),which introduces SDN in VANET,can fundamentally solve its blindness in routing.Because the SDN flow table has a short lifetime in the VANET environment,the flow table may be frequently requested and delivered,which will bring huge communication pressure to the controller.By introducing the clustering algorithm,the stability of the VANET network topology can be enhanced,and the inter-cluster link and its flow table lifetime can be improved.Therefore,the SDVN-based hybrid routing protocol can reduce the times of flow table updating and packet loss ratios.This paper first studies the clustering algorithm in SDVN.Based on the research of current VANET clustering algorithm,this paper proposes a CMCA(Centralized Mobility-based Clustering Algorithm).The vehicle's movement similarity is measured by the vehicle's direction,velocity,acceleration,and position.The SDN controller uniformly divides them into several clusters according to the movement similarity of the vehicle nodes,and selects the cluster heads according to the link's stability between the vehicle nodes at the same time.Nodes with better stability are more likely to be elected as cluster heads,which facilitates stable inter-cluster communication.Through simulation,the reliability of CMCA was verified,and the average lifetime of the clusters was significantly improved.At the same time,the variance of the number of members in the cluster has been significantly reduced.This article also studies the routing protocol in SDVN.The frequent handover of flow tables is caused by the shorter lifetime of the flow table and the longer data transmission time between vehicle and vehicle,this paper proposes a HRP(Hybrid Routing Protocol)combining cluster-based flow table and passive flow table.The protocol can directly use the passive flow table to complete the data packet forwarding for the data with short end-to-end continuous transmission time.For data with long end-to-end persistent transmission time,the controller decides when to send to vehicles and start the passive flow table according to the generation time of the current cluster-based flow table.Simulation results show that HRP can reduce the times of flow table updating and packet loss rate of SDVN,so that SDN technology can better adapt to the high dynamics of routing changes in the VANET.