Research On Key Technologies Of High Efficient Software-Defined Vehicular Networks

Vehicular Ad Hoc Networks(VANETs)is an important component of Intelligent Transportation System(ITS).Using vehicle-to-vehicle,vehicle-to-road and vehicle-to-people communication,VENETs can optimize traveling route,improve traveling effi-ciency,reduce gas-waste and improve traveling safety.However,in the distributed ar-chitecture of traditional VANETs,vehicular router chooses the nearest routing path just according to local network information.The distributed routing mechanism may lead to the result that the nearest routing paths have to disseminate most messages,and final-ly causes link-congestion.To solve the unbalanced load upon different routing paths in traditional VANETs,Ian et al.proposed the architecture of software-defined networking based VANETs(SDVN),that implements the idea of software-defined networking(SD-N)to VANETs.SDVN firstly decouples the control plane and data-forwarding plane of vehicular network devices,then collects all the control planes into a central controller.Us-ing the central controller,SDVN can provide network applications with global network topology view and centralized packet-forwarding control,that can be used to optimize routing performance and improve network resources utilization.Currently,the research on software-defined vehicular networks is just in the begin-ning.There are a mount of important technical problems need to solve,such as:the performance bottleneck and single-node false problem of single controller based sys-tem;the huge communication overhead problem of implementing OpenFlow protocol in software-defined vehicular networks;the low utilization of global network topology view in multiple-copy routing protocols;the frequent link-break-down problem in software-defined vehicular network caused by wireless communication links.After deeply study-ing of the above problems,this thesis designed a hierarchical multiple-controller system and a geographical direction based communication protocol named GeoFlow.The thesis also proposed a cooperative multiple-copy routing protocol called Spray-and-Prey and proposed two link recovery mechanisms using mobile communication relay.The major contribution and innovation of this thesis includes the following aspects:Firstly,we propose a hierarchical multiple-controller system for SDVN to solve the performance bottleneck and single-node false problem in single controller based SDVN.The hierarchical multiple-controller system splits the whole network into several subnet-works and deploys a local controller in each subnetwork.Local controllers work together so that the packet processing speed of the whole network can be increased.We have al-so designed controller switching and management mechanisms.The controller switching mechanism is used to reduce the switching time and the controller management mecha-nism is used to reduce the network energy consumption.Secondly,we propose a geographic direction based communication protocol named GeoFlow to solve the problem of high communication overhead when applying OpenFlow protocol in SDVN.GeoFlow protocol uses packet forwarding directions to classify packet flows,that prolongs the available time of flow entries.Thus the frequency of vehicular switches consulting controller can be reduced as well as the communication overhead.Besides,GeoFlow protocol also supports direct route sharing among vehicular switches,that can reduce the among of packet processing in the controller and reduce the packet delivery delay.Thirdly,we propose a cooperative multiple-copy routing protocol called Spray-and-Prey to solve the problem that existing multiple-copy routing protocols can not take ad-vantage of the global network topology view and centralized control in SDVN.Spray-and-Prey protocol evaluates the utility of relay nodes from a global perspective,thus the chosen next relay should be global optimized.We also design cooperative copy-selection mechanism to drop copies may have long delivery delay and duplicate copies that may be delivered with short time.In addition,a copy-clear mechanism is also used to clear other copies of a message when one copy of the message has arrived at the destination so that the cost of network storage and bandwidth can be reduced.Fourthly,we propose two mobile communication relay based mechanism to repair the break-down communication links in SDVN.One is multiple unmanned aerial vehi-cles(UAV)communication chain based control-link repair mechanism,that optimize the control link capacity through motion control of UAVs.The other is multiple UAV net-work based data-link repair mechanism,that optimize the deployment and motion control of UAVs so that a minimum number of new added UAVs are used to maintain the full connectivity of SDVN.