ry external to the VNFC. Depending on the type of VNF, the instantiation can be more or less complex. For a sim- ple VNF consisting of a single VNFC, the instantiation based on VNF descriptor is straightforward, while for a complex VNF consisting of several VNFCs connected via vir- tual networks, the VNF manager may require support from an internal function that is implemented by VNF to facilitate the process of instantiation. As an example, the VNF manager could boot a predefined number of VNFCs, leaving booting of the remaining VNFCs and the configuration of the VNF to an internal VNF provider-specific process that may also involve an EM. The VNF descriptor is a specification template provided by the VNF developer for describ- ing virtual resource requirements of a VNF. It is used by the NFV-MANO functions to determine how to execute VNF life cycle operations such as instantiation. The NFV-MANO functions consider all VNF descriptor attributes to check the feasibility of instantiating a given VNF. There are several options for how the instances of individual VNFCs can be created, which can be fully or partially loaded virtualization containers; or empty virtualiza- tion containers prepared for booting and loading. It is then the responsibility of the VNF MANO functions to instruct the VIM to create an empty virtualization container with an associated interface that is ready for use. To instantiate a VNF, the VNF manager creates the VNF's set of VNFC instances as defined in the VNF descriptor by executing one or more VNFC instantiation procedures. The VNF descriptor defines which VNFC instances may be created in parallel or sequen- tially as well as the order of instantiation. The set of created VNFC instances may already 24 Chapter 1 correspond to a complete VNF instance. Alternatively, it may contain only a minimal set of VNFC instances needed to boot the VNF instance. The VNF manager requests a new VM and the corresponding network and storage resources for the VNFC instance according to the definition in the V