Using a flexibility measure for network design space analysis of SDN and NFV

Flexibility is often claimed as a competitive advantage when proposing new network designs. However, most proposals provide only qualitative arguments for their improved support of flexibility. Quantitative arguments can quite vary among different proposals. A general understanding of flexibility is not yet clearly defined, leaving it to the reader to draw the right conclusions based on background information. The term flexibility is commonly defined as the ability to adapt to changes. For networks, flexibility would refer to the ability to adapt the available network resources, such as flows or topology, to changes of design requirements, e.g., shorter latency budgets or different traffic distributions. Recent concepts such as Software Defined Networking (SDN) and Network Function Virtualization (NFV) have emerged to provide more flexibility in networks. Nevertheless, a deeper understanding of what flexibility means and how it could be quantified to compare different network designs remains open. In this paper, we propose a flexibility measure for network design space analysis and show its application. As it is quite challenging to formulate a flexibility measure that covers all network characteristics, we propose an initial set of flexibility aspects targeted to SDN and NFV. Moreover, we present the results of a detailed analysis of network function placement following either an SDN-based or an NFV-based approach. Our study reveals that in a logically centralized deployment scenario a mix of SDN and NFV provides the highest flexibility, with respect to our selected flexibility aspect.