ations to instantiate and interconnect VMs. It also notifies of link congestion or failure, in order to trigger VM migrations and network reconfiguration. The SDN-based CPE and vSwitch is a lightweight version of legacy CPE with most NFs stripped out. The virtual switch is a software-based OpenFlow switch such as Open vSwitch. The VNFs execute in VMs on top of a hypervisor that is hosted on a server. Multiple virtual services can share the resources of the same server. We assume that one instance of a vSwitch is included in each server for handling the communication between multiple VMs running on the servers within the data center. Both SDN-based CPE and vSwitch are programmable by SDN to support the vCPE applications including service chaining. 5.5 Summary In this chapter, we start with 5G overview. Then, we present the SFC and its several aspects, which is a key use case of SDN and NFV in 5G. We then discuss the SDN and NFV's use cases in the 5G network as two case studies. In particular, we first discuss their usage scenarios and challenges in the packet core network. Next, we discuss their usage in the edge of the telecom network, in the form of customer premise equipment. Both use cases have been widely studied and are going to deployment in the real world. Open Source and Research Activities Network functions virtualization (NFV) has fundamentally changed the way telecom services are invented and deployed today. In the past, network equipment providers (NEPs) used to sell both the hardware and software. With NFV, the two can be sold separately. Network functions run as software on standardized IT servers. Such separation creates a more open environment for new services to be innovated. It allows communications service providers (CSPs) to be more agile and creative in delivering services, while lowering the cost of development and rollout. Given the promising features that NFV can provide, CSPs are eager to try out and deploy NFVs in a faster pace. Given this trend, CSPs, NEPs, and NF vendors come together 