 realize the benefits of NFV-based solutions. There are a number of challenges to implement NFV, which need to be addressed by the industry. Some of the main challenges include the following [43]: Portability/interoperability: This is the ability to load and execute virtual appliances in different but standardized data center environments, which can be provided by different vendors for different operators. The challenge is to define a unified interface which clearly decouples the software instances from the underlying hardware, as represented 5G Network Architecture by VMs and their hypervisors. Portability and interoperability are very important as they create different ecosystems for virtual appliance vendors and data center vendors, while both ecosystems are clearly coupled and depend on each other. Portability also provides the operator with the freedom to optimize the location and required resources of the virtual appliances without constraints. Performance trade-off: Since the NFV approach is based on conventional hardware as opposed to customized hardware, there could be a possible decrease in performance. The challenge is how to limit the performance degradation by using appropriate hyper- visors, hardware accelerators, and advanced software technologies such that the effects on latency, throughput, and processing overhead are minimized. Migration, coexistence, and compatibility with the existing platforms: Implementations of NFV must coexist with network operators' legacy network equipment, and further must be compatible with their existing element management systems (EMSs), network management systems (NMSs), operations support system (OSS), 11 and business support system (BSS), and potentially existing IT orchestration systems, if NFV orchestration and IT orchestration need to converge. The NFV architecture must support a migration path from today's proprietary physical network appliance-based solutions to more open standards-based virtual network appliance solutions. In other words, NFV must work in a 