f) constitutes a data path through which network traffic traverses, while the NFV to VIM inter- face (Nf-Vi) creates a control path that is used solely for management but not for any net- work traffic. The NFVI consists of three distinct layers: physical infrastructure, virtualization layer, and the virtual infrastructure. The VIM manages the NFVI and acts as a conduit for control path interaction between VNFs and NFVI. In general, the VIM provi- sions, de-provisions, and manages virtual compute, storage, and networking while commu- nicating with the underlying physical resources. The VIM is responsible for operational aspects such as logs, metrics, alerts, analytics, policy enforcement, and service assurance. It is also responsible for interacting with the orchestration layer and SDN controller. Unlike the NFVI which consists of several technologies that can be assembled independently, the VIM comes in the form of complete software stacks. OpenStack13 is the main VIM software stack which is very common in NFV realization. OpenStack software controls large pools of compute, storage, and networking resources throughout a data center, managed through a dashboard or via the OpenStack application programming interface. OpenStack works with popular enterprise and open source technologies, making it ideal for heterogeneous infrastructure (https://www.openstack.org/). 18 Chapter 1 OSS/BSS NFV orchestrator (NFVO) Os-Ma-Nfvo Or-Vnfm catalog catalog instances resources Ve-Vnfm-em VNF manager (VNFM) Ve-Vnfm-vnf Service, VNF, and infrastructure Vn-Nf description Virtual Virtual Virtual Vi-Vnfm computing storage networking Nf-Vi Or-Vi Virtualized infrastructure manager Virtualization layer (VIM) NFV-MANO Computing Storage Networking hardware hardware hardware Figure 1.4 NFV architecture [37,40]. As we mentioned earlier, NFV defines standards for compute, storage, and networking resources that can be used to build VNFs. The NFVI is a key component of the NFV archi- tecture that describes the hardware and software components on