Research On Link Failure Management Mechanism In Software Defined Network

With the rapid development of the Internet,the network has penetrated into all aspects of people's life,traffic on each link is becoming even more important,and link failure problem is increasingly prominent.Software Defined Network(SDN)is a new network paradigm with control plane and data plane separated,which allows operators to easily deploy network applications to deal with link failures.This thesis mainly studies the link failure problem in software defined network.According to the scale of link failure,the problem can be divided into single link failure and multi link failure.In this thesis,the corresponding link recovery algorithm is proposed for these two cases.In the case of single-link failure,this thesis proposes two algorithms: Local Fast Rerouting with traffic aggregation(LFR)and Congestion-AwareLocal Fast Rerouting(CALFR).In the LFR algorithm,thanks to flexibility of flow table in the software defined network,when link fails,all the interrupted traffic will be aggregated into a “big” flow.And the SDN controller dynamically deploys a local recovery path instead of the failed link.The simulation results show that the interrupted traffic can be fast restored with minimizing the total number of flow entries.The CALFR is based on the LFR.Considering the link capacity and traffic bandwidth,the interrupted traffic will be aggregated into multiple “medium” traffics and reassighed to different local recovery paths.CALFR can effectively avoid link congestion after traffic restored.However the failure recovery delay of CALFR is slightly increased.If a link fails,it is necessary to select the appropriate restoration algorihm according to network load.In the case of multi-link failure,considering the large changes in the network topology and most of the network business may be affected,one by one to restore each interrupt service is less efficient.In this thesis,a spanning tree-based fast recovery algorithm is proposed.Once a link fails,all active switches will be connected in the form of a tree.The SDN controller updates the flow entries and all the affected traffic will be automatically restored.Due to the feature of the tree structure,the SDN controller can reduce the number of flow table operation,achieving rapid failure recovery.