edundant hardware and proprietary logic. To achieve these benefits, there are several technical challenges that need to be addressed: Achieving high-performance virtualized network functions, which are portable between different hardware vendors, and with different hypervisors. Achieving coexistence with custom hardware-based network platforms while enabling an efficient migration path to fully virtualized network platforms. Similarly, transition- ing from existing business support system (BSS) and operations support system (OSS) to nimbler DevOps and orchestration approaches. Network Functions Virtualization Managing and orchestrating many virtual network appliances while ensuring security from attack and misconfiguration. Ensuring an appropriate level of resilience to hardware and software failures. Integrating multiple virtual appliances from different vendors. Service providers prefer the use of "mix and match" hardware from different vendors, hypervisors from different vendors, and VNFs from different vendors without incurring significant integration costs. NFV AND SOFTWARE-DEFINED NETWORKING Software-defined networking (SDN) is an architectural framework for creating intelligent networks that are programmable, application aware, and open. A key aspect of the architectural framework is the separation of data forwarding from the control plane, and establishment of standard proto- cols and abstractions. However, the term SDN is also applied to a number of other approaches that espouse more open, software-centric methods of developing new abstractions for both the control plane as well as the data plane of networks and the ability to expose network capabilities via APIs. SDN will be discussed in more detail in Chapter 6. Here, we look at the relationship between SDN and NFV. 3.2.1 RELATIONSHIP BETWEEN NFV AND SDN SDN can act as an enabler for NFV, since the separation of control and data planes enables the virtu- alization of the separated control plane software. NFV can also act as an enabler for SDN since the