A Techno-Economic Evaluation of VNF Placement Strategies in Optical Metro Networks

Network Function Virtualization (NFV) has changed the way operators can provision network services. Decoupling network functions from dedicated hardware and running them on software, on top of commodity servers and switches, not only helps operators have more flexible and easy-to-manage networks, but also reduces their capital and operational expenditures. This is especially true for incoming 5G services, characterized by ultra-low latency, high reliability and bandwidth requirements. To satisfy these challenging requirements, multi-layer optical networks based on Optical Transport Network (OTN) over wavelength division multiplexing (WDM) are being deployed in the metro segment to support 5G services. In addition, the possibility to equip metro nodes with computing capabilities, enabled by new paradigms such as CORD (Central Office Re-architected as a Datacenter) is being exploited. In this scenario, an efficient placement of Virtual Network Functions (VNFs) for Service Chain (SC) provisioning within the metro network is needed, and different VNF placement strategies can lead to different costs for network operators. In this paper we analyze the impact of different VNF placement strategies on the optical metro network cost, considering specific Service Level Agreement (SLA) requirements, expressed in terms of service blocking probability. We provide a cost model which takes into consideration both capital and operational expenditures. Through extensive numerical results, we quantify the impact of using a cost-effective VNF placement strategy in decreasing network cost while meeting the desired SLA performance.