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Network Functions Virtualization (NFV) is a network architecture that strongly builds on the top of virtualization concepts [39]. It offers the ability to virtualize network nodes and functions into building blocks which can be connected and chained to create more complex communication services. A virtualized network function (VNF) consists of one or more virtual machines and containers that run specific software to implement networking operations in software. Firewalls, access list controllers, load balancers, intrusions detection systems, VPN terminators, etc. can thus be implemented in software – without buying and installing expensive hardware solutions.

Figure 1.4 Network functions virtualization architecture.

Source: Courteously from Juniper Networks.

NFV consists of three main components as sketched in Figure 1.4: On the top, the VNFs to be implemented, using a software solution; the network functions virtualization infrastructure (NFVI) sits in the middle and offers the hardware components over which deploy the VNFs. It includes the physical servers and the network devices that build the NFV infrastructure; at last, the NFV MANagement and Orchestration (MANO) framework allows to manage the platform offering data repositories and standard interfaces to exchange information. To build a complex function, basic blocks can be chained so that a processing pipeline is built. This is called “service chaining” and allows the reuse of highly specialized and efficient blocks to build complex functionalities.

Considering the management operations, clearly NFV requires the network to instantiate, monitor, repair, and bill for the services it offers. NFV targets indeed the large carrier scenario, being it a data center manager, or an internet service providers. These functionalities are allocated to the orchestration layer, which must manages VNFs irrespective of the actual hardware and software technology sitting below.

NFV is a means to reduce cost and accelerate service development and deployment. Instead of requiring the installation of expensive hardware with dedicated functionalities, service providers rely on inexpensive network devices, storage systems, and servers to run virtual machines that implement the desired network function. When a customer asks for a net functionality, the service provider can simply spin up a new virtual machine to implement that function. This has also the benefit to reduce the dependency on dedicated hardware devices, and improve robustness via migration capabilities that move services in case of failures or maintenance operations.

Clearly, NFV calls for standard to allow interoperability of solutions. Since 2012, over 130 of the world's leading network operators have recently joined together to form a European Telecommunications Standards Institute (ETSI) Industry Specification Group (ISG) for NFV (https://www.etsi.org/technologies/nfv). NFV is also fundamental in the 5G arena, where all the advanced functionalities offered by the network like network slicing, edge computing, or decentralized radio management functions are implemented on the top of NFV.