The role of inter-controller traffic in SDN controllers placement

We consider a distributed Software Defined Networking (SDN) architecture adopting a cluster of multiple controllers to improve network performance and reliability. Differently from previous work, we focus on the control traffic exchanged among the controllers, in addition to the Openflow control traffic exchanged between controllers and switches. We develop an analytical model to estimate the reaction time perceived at the switches due to the inter-controller communications, based on the data-ownership model adopted in the cluster. We advocate a careful placement of the controllers, taking into account the two above kinds of control traffic. We evaluate, for some real ISP network topologies, the possible delay tradeoffs for the controllers placement problem.