ntage of users. It would still need to procure the hardware at an appropriate size for the original larger capacity, hence greatly increasing the Capital Expenditure (CAPEX) on building and expanding a mobile network. Operators consistently have been under pressure to reduce data rates across the world; hence, it became imperative for them to reduce the operational expenditure and CAPEX. To mitigate this problem, over the last 10 years, a lot of work has been done to find solutions. The most notable one was to build virtualized software for the network elements that could be deployed on Commercial Off-The-Shelf (COTS) hardware. This would free the operator of expensive custom appliances. Hence, the first step toward transformation was to free the mobility (3G/4G) software from purpose-built hardware and virtualize it, SO that the various software for mobility network elements could now run on virtual machines over COTS servers. This was further accelerated by open source projects such as OpenStack, which was adopted by many telecom vendors as their infrastructure of choice. Hence, the first move from appliance-based infrastructure to virtualized infrastructure took place years before discussions on 5G specifications even started. Figure 3.1 describes this transition; to the left of the figure, legacy purpose-built hardware with 3G and 4G packet core application software is shown. To the right, the block depicts a virtualized infrastructure, a Management and Orchestration (MANO) framework, as proposed by the European Telecommunications Standards Institute (ETSI). In the virtualized infrastructure, the telecom software (in this case, the 4G packet core network elements) are hosted on COTS hardware. This is made possible by Virtual Infrastructure Manager (VIM) software, which is responsible for resource allocation and the management of the COTS hardware. The VIM abstracts the hardware from the installed virtual machines and provides compute, storage, and networking capabilities to the virtual machine installed on it