NFV is an initiative to transfer the “Network Services” sector through virtualizing the network services by replacing the dedicated hardware with Virtual Machines.
What that means is "NFV is to separate network functions from dedicated hardware devices"; to use Virtual Machines instead of physical routers, physical firewalls and physical load balancers. Once the Hypervisor controls the network functions, the services can be performed on standard x86 servers. The ability to scale up and scale down according to your needs and requirements.
For e.g. We purchase a server which support 1000s of customers, it might also support all the capacity you have but what if you don’t have any customers? You’ve already paid for it and it is just sitting there using power and not doing anything useful. As you grow your business you’ll be able to fill that hardware box to its maximum capacity and then start all over again by purchasing another one. With NFV you can avoid all of that and literally pay for the things you need and when you need them. NFV allows you to instantiate these network services or functions on demand, as many you need, at any given point of time, scaling them up and scaling them down. Ultimately you get a lot of flexibility.
Software-defined networking (SDN) is a function to computer networking that allows network administrators to govern network services through abstraction of lower-level purpose. SDN is meant to respond to the fact that the static formation of conventional networks doesn't support the dynamic, scalable computing and storage needs of more radical computing environments such as data centers. This is done by demerging or disassociating the system that makes decisions about where traffic is sent (the control plane) from the lurking systems that forward traffic to the selected destination (the data plane).
NFV also is flexible, cost-effective, scalable, and secure. With these benefits, NFV addresses several trends shaping service provider networks.
Adaptability: To adapt quickly to users' changing needs and provide new services, operators must be able to scale their network architecture across multiple servers, rather than being limited by what a single box can do.
Virtualization in another service provider network: To meet customers' needs better, service providers want the ability to substantiate their service anywhere in the world using virtualization.
Extensibility: NFV provides operators who are looking to quickly deploy new services with much more flexible and adaptable network.
Security: It has been, and continues to be, a major challenge in networking. Operators want to be able to provision and manage the network while allowing their customers to run their own virtual space and firewall securely within the network
Expenditure: Expenses are the primary consideration for any operator or service provider these days and using virtual machines instead of physical routers, physical firewalls and physical load balancers forgoes a long way in cost/expense cutting.
Shallow and Deep SDN:
In this form of SDN, a virtual overlay network is created between vSwitches. The traffic paths between vSwitches run over a traditional routed/switched network, or perhaps a switched fabric network. Because it relies on vSwitches as the overlay network endpoints, it is primarily a data centre SDN solution.
Deep SDN is a method of controlling packet forwarding behaviour, one that can perform policy routing without complex combinations of protocols, as is required in shallow SDN. The logically centralized controller is able to see the entire network topology and make smarter decisions about the paths to use for each traffic type