h and best serve their customers, cellular network operators need to design and manage cellular core network architectures accordingly. There are two main challenges that the cellular network faces. The first challenge is the increasing cost of network operation. While the most advanced cellular technologies today is the 4G technology such as long term evolution (LTE). However, the coexistence of multiple generations of cellular networks is unavoidable today. This is because the subscribers may gradually upgrade their devices over the years. Thus, the operators need to support multiple technologies over a long period of time and manage multiple networks simultaneously. The operational cost may not be covered by the revenue growth. The second challenge is the high demand of network capacity expansion. Many techniques have been proposed to expand the cellular network capacity such as multi- antenna technologies and Wi-Fi offloading architecture. Adding spec- trum and deploying small/femto cells have also been used together to further expand the network capacity, which is, however, expensive and not easy to deploy. Moreover, the changes of infrastructure still cannot keep up with the exponential growth of traffic demand. 1.1 Cloud-Enabled 5G: SDN and NFV The current cellular infrastructure is not capable of addressing the explosive need of data demand. The main reason is that the resource is configured and allocated in a rather static manner. The resources are not utilized in an efficient way. The traffic demand, however, are highly dynamic, exhibiting a time-of-day phenomenon [5, 6]. Flash crowds happen often due to popular events. To fundamentally meet the traffic demand, blindly increasing the network capacity is not enough. We need to find ways to better utilize existing capacity. The traditional business model of cellular carriers was based on revenues for telephony. The Internet was an over-the-top service, priced by online minutes or data volumes during the late 1990s. This has changed completely to a flat-ra