Expansion model for the controller placement problem in software defined networks

A key concern in the deployment of Software Defined Networks (SDN) is the location of the controller. One issue network operators will have to face is how to expand their network at minimum cost in order to meet the growing number of users and services. To that end, this letter introduces a new expansion model for the controller placement problem in SDN. More precisely, given a current network design and a list of switches to be added to the network, the model will find how the network should be re-organized such that the update cost is minimized. Since the expansion problem is a generalisation of the planning problem, the model proposed in this letter can be used to plan a new network from scratch or update any existing networks