es 5-15 ms round-trip latency in Layer 1 and Layer 2 of today's wireless standards and will be more stringent in the next generation (5G) [47]. There are also other concerns such as synchronization, jitter [48], and security [49]. 2.5 Summary Cloud computing has received significant momentum in the past decade and has been widely used in today's IT environment. Virtu- alization is the key technology that enables cloud computing. Host virtualizations such as VMs or containers have been extensively stud- ied and widely deployed. From network virtualization's perspective, the traditional overlay network using encapsulation and tunneling is one type of virtual network. VPN is a form of popular virtual network for security applications. Recently, SDN has become another way to implement network virtualization. For example, one can define the virtual networks in the flow tables of the SDN switches. On the other hand, wireless virtualization has received a lot of momentum lately. The SDN approach brings the ability to do flexible traffic engineering and to gather more intelligence and statistics from the infrastructure. Network Function Virtualization Network function virtualization (NFV) represents a significant trans- formation for telecommunications/service provider networks, driven by the goals of reducing cost, increasing flexibility, and providing per- sonalized services [10]. It is rapidly emerging as the de facto approach operators will use to deploy their networks. The promise of NFV will play out over the next several years, and several challenges need to be addressed to make that happen. Telcos have transitioned most of their communications to standard IP networks and are now starting to migrate most of their computing to industry standard servers. NFV leverages on cloud computing principles to change the way NFs such as gateways and middleboxes are offered. Different from today's tight coupling between the NF software and dedicated hardware, the loosely coupled software and hardware in NFV can reduce the upgr