ystem platforms to support the overall delivery of services to customers. 16 Chapter 1 operator's operating environment. The SDN further extends this concept to streamlining the integration of packet and optical switches into the system, for example, a virtual appliance or NFV orchestration system may control the forwarding behavior of physical switches using SDN. Note that NFV will only scale, if all of the functions can be automated. Security and resilience: Network operators need to be assured that the security, resil- ience, and availability of their networks are not compromised when VNFs are introduced. The NFV improves network resilience and availability by allowing NFs to be recreated on demand after a failure. A virtual appliance should be as secure as a physical appliance if the infrastructure, particularly the hypervisor and its configuration, is secure. Network operators will be seeking tools to control and verify hypervisor configurations. They will also require security-certified hypervisors and virtual appliances. Network stability: It is important to ensure that the stability of the network is not impacted when managing and orchestrating a large number of virtual appliances created by different hardware and hypervisor vendors. This is particularly important when vir- tual functions are relocated or during reconfiguration events (e.g., due to hardware and software failures) or due to a cyber attack. This challenge is not unique to NFV systems and such unsteadiness might also occur in current networks. It should be noted that the occurrence of network instability may have adverse effects on performance parameters or optimized use of resources. Complexity: It must be ensured that virtualized network platforms will be simpler to operate than those that exist today. A significant focus area for network operators is simplification of the plethora of complex network platforms and support systems which have evolved over decades of network technology evolution, while maintaining continu- ity to support impo