On using SDN in 5G: the controller placement problem

To integrate Software Defined Networking (SDN) in the envisioned 5G systems, a separation of the control and user plan at Evolved Packet Core (EPC) is required. This separation will impact mainly the functions available at the Serving GateWay (SGW) and Packet data GateWay (PGW) elements, and will results in two new entities; i.e. the S/PGW-C and S/PGW-U (PGW-C and PGW-U). The S/PGW-C integrates all the control plan functions (such as signaling and tunnel creation), while S/PGW-U contains only forwarding functions. The S/PGW-C will control the S/PGW-U in order to forward the UE traffic to the appropriate destination by enforcing rules using the Openflow protocol. Usually, the S/PGW-C will be run on Virtual Network Function (VNF) and hosted in the federated cloud. In this paper, we focus on the problem of the SGW-C placement, where a tradeoff is needed between reducing the SGW relocation and minimizing the traffic load on each SGW-C. We formulate this problem by using optimisation models, and a fair solution (i.e. Pareto optima) is derived using Nash Bargaining game and the threat point.