SDN-SDWSN Controller Fault Tolerance Framework for Small to Medium Sized Networks

In the OpenFlow-based software defined networking (SDN), a single controller controls the entire network resources. However, it poses a single point of failure and has restricted processing capacity. Multiple controllers emerged as a solution to ensure network reliability, scalability and high availability for large scale networks. Despite the benefits, multiple controllers also brings about increased complexity with several new challenges affecting network management and schedule. Albeit the centralized controller is suitable for small and medium sized networks, the challenge is how to ensure its reliability and resiliency. This means faults have to be detected and failure recover as quickly as possible. Therefore, this paper proposes a fault tolerance framework (FTF) consisting of three controllers and a FT manager (FTM). The FTM has several components that contribute to FT by monitoring and detecting faults using heartbeat messages and recover from failure using checkpointing. The approach is passive replication where only one controller manages the networks and in the event of failure, another controller is elected using a novel voting technique. Additionally, the issue of network state consistency are handled adequately. We theoretically assessed the FTF using several FT design requirements. The evaluation shows our FTF has an acceptable performance operations in ensuring strict consistency and fault tolerant system.