sponsible for VNF life cycle management (e.g., instantiation, update, query, scaling, and termination). Multiple VNF managers may be deployed where a VNF manager may be deployed for each VNF or multiple VNFs. Service, VNF and infrastructure description is a data set which provides information regarding the VNF deployment template, VNF forwarding graph, service-related infor- mation, and NFVI information models. These templates/descriptors are used internally within NFV-MANO. The NFV-MANO functional blocks handle information contained in the templates/descriptors and may expose (subsets of) such information to applicable functional blocks. Operations and Business Support Systems (OSS/BSS) The management and organization working group of the ETSI¹ has defined the NFV- MANO architecture. According to ETSI specification, NFV-MANO comprises three major functional blocks: VIM, VNF manager, and NFVO [37,40]. The VIM is a key component of the NFV-MANO architectural framework. It is responsible for controlling and managing the NFVI compute, storage, and network resources, usually within one operator's infrastruc- ture domain (see Fig. 1.4). These functional blocks help standardize the functions of virtual European Telecommunications Standards Institute, http://www.etsi.org/.ETSI, network function virtualization specifications are listed and can be found at http://www.etsi.org/technologies-clusters/technologies/nfv. 5G Network Architecture 21 networking to increase interoperability of SDN elements. The VIMs can also handle hard- ware in a multi-domain environment or may be optimized for a specific NFVI environment. The VIM is responsible for managing the virtualized infrastructure of an NFV-based solu- tion. The VIM operations include the following: It maintains an inventory of the allocation of virtual resources to physical resources. This allows the VIM to orchestrate the allocations, upgrade, release, and retrieval of NFVI resources and optimize their use. It supports the management of VNF forwarding graphs by organizin