CONCLUSION
The need for flexibility, reconfigurability and customization in 5G mobile networks is pushing vendors and operators to exploit novel paradigms for network deployment. In this direction, softwarization and virtualization are two candidates to play a key role in the design of 5G systems, as they allow to decouple network functionalities from the underlying hardware with consequent benefits in terms of easier network management and upgrade. This paper aimed to discuss softwarization and virtualization as enablers of 5G architecture deployment. We presented an overview of the evolution of mobile networks from 2G to 4G, highlighting the design drivers behind each generation of the architecture and the novelties that each generation introduced compared to the previous ones. This allowed to obtain a summary of functionalities and entities currently implemented and deployed in mobile systems. We thus illustrated the 5G ecosystem by providing a detailed discussion of its application scenarios. We highlighted the requirements that 5G use cases push on the network architecture and, accordingly, we analysed the limitations of 4G systems in fulfilling such requirements. This allowed to define a set of features to be considered in the design of 5G system architecture, and to define the role of softwarization and virtualization in implementing such features. We considered the recent advances by 3GPP looking at introducing softwarization and virtualization in the standardization of 5G network architecture. We provide a comprehensive overview of the state of the art by surveying the recent proposals in literature focusing on the exploitation of softwarization and virtualization for the implementation of network entities and functionalities of 5G systems. Moreover, we provided a discussion on the lessons learned according to the surveyed literature. Finally, we highlighted the future steps to be considered by the research community to bring into reality a softwarized and virtualized 5G network architecture.
