ade cost and increase the innovation flexibility. In addition, with the advent of 5G technology, there is a push toward developing novel real-time ser- vices in the areas of mobile payment, augmented reality, autonomous driving, and Internet of things (IoT) [10]. Typical network functions (e.g., server load balancing (SLB), and firewalling) in large-scale enterprise networks today are generally provided on large vendor-proprietary devices. These are complex to operate and manage, expensive to procure and maintain, and are typically very underutilized. They also do not lend themselves to easy automation since, because they are proprietary appliance based, their application programming interfaces (APIs) are vendor-specific, mak- ing them difficult to integrate into a high-level non-vendor-specific orchestration platform. Efforts to alleviate this complexity through flexible network routing techniques such as SDN have led to only a partial fix, as the physical switch devices controlled via SDN/OF lack Network Function Virtualization: Concepts and Applicability in 5G Networks, First Edition. Ying Zhang. © 2018 John Wiley & Sons, Inc. Published 2018 by John Wiley & Sons, Inc. 3 Network Function Virtualization the intelligence to make decisions based on OSI Layers 5-7 and SO are not able to deliver the higher level services provided by the load balancers and firewalls. In NFV environments, monolithic complex network functions run- ning on specialized hardware are decomposed into smaller functional units and dynamically orchestrated onto a virtualized cloud and edge infrastructure. These network functions include both control plane processing, such as telco equipments for signaling, authentication, and data plane processing, such as normal routing, access control, and quality of service (QoS). These network functions run as software in a virtual machine (VM), which is also called virtualized network function (VNF). Running as VMs among a large number of TOR switches in the data center allows these functions to scale on 