Joint Backup Controller Placement and Routing for Low Invasive Flow Statistics Collection in SDNs

In Software Defined Networks (SDNs), flow-level fine-grained traffic statistics are essential to support various network functions. Although flow statistics collection (FSC) is convenient in SDNs, it generates significant controller processing overhead and control link bandwidth consumption. Previous research has focused on reducing these costs. However, performing FSC and basic forwarding functions on the same controller can cause an unacceptable flow rule installing delay even if the controller and control link capacity is sufficient. This invasion problem of FSC (FSCIP) can result in the failure of new network connections and a high packet loss rate of the control links. To fully address FSCIP, we offload the FSC function to a selected backup controller and enhance the existing local control plane with a role-based FSC scheme. Then we formulate a joint optimization of backup controller placement and FSC routing problem (JBFR) to minimize the statistic collection cost. Due to its NP-hardness, we propose a randomized rounding-based algorithm as a general solution and a cookie-based FSC routing mechanism as an advanced solution with the help of more programmable devices (e.g., P4-based switches). We implement the proposed solutions on our SDN test bed and perform large-scale investigations with simulations. The extensive experimental and simulation results show that our solutions can reduce the FSC-caused route installing delay by at most 91.3% on the primary controller and minimize the maximum control link bandwidth cost by about 46% compared with ECMP and other benchmark routing schemes.