demand. It then helps reduce the operational cost for the telecom operators. It also has the potential to reduce the growth of appliance sprawl, particularly in multitenant data centers (DCs), providing power, space, and cooling savings for a more efficient and greener data center. A highly agile routing instructions that direct network packets through a sequence of VNFs is called service function chaining (SFC), which we will discuss more in later chapters. In this chapter, we focus on the basic building blocks of NFV. NFV Architecture To meet the increasing traffic demands while maintaining or improving average revenue per user (ARPU), network operators are constantly seeking new ways to reduce their OPEX and CAPEX. To this end, the concept of NFV was initiated within the European Telecommunications Standards Institute (ETSI) consortium [50]. NFV allows legacy NFs offered by specialized equipment to run in software on generic hardware. The key driving technologies behind that is cloud computing and virtualization. NFV makes it possible to deploy VNFs in high-performance commodity servers in an operator's data center, with great flexibility to spin on/off the VNFs on demand. The agility has brought NFV increased popularity by network operators because it can achieve high resource utilization. In addition, by decoupling the NF software from the hardware, NFV will facilitate a faster pace for innovations and result in shorter service development cycles. In summary, NFV has great potential in CAPEX/OPEX savings and ARPU increasing. 3.1 NFV Architecture NFV covers a wide spectrum of middleboxes such as firewalls, deep packet inspection (DPI), intrusion detection system (IDS), network address translation (NAT), and wide area network (WAN) accelerators. It also covers a variety of network nodes such as broad- band remote access servers data network gateways (S-GW/P-GW), mobility management entity (MME), home subscriber server (HSS), and virtual IP multimedia subsystem (vIMS) for virtual evolved packet core (vEPC). The