## 8 RAN Decomposition Scheme
### Virtualized RAN  
It is highly imperative to consider RAN architecture in which functionalities can be virtualized into software modules for easy customization and modification. A vRAN is one of the viable and scalable evolutions from the traditional C-RAN architecture. The vRAN functions can be implemented in virtual machines (VMs) that are running on a general-purpose hardware platform rather than on dedicated hardware. Regarding the use cases, several categories of VMs can be specified and different RAN FSOns between the CU and the DUs can be defined to encourage deployment flexibility. Moreover, this architectural evolution offers cost-effective solutions through the implementations of flexible hardware [424; 425; 426; 429]. When the vRAN is incorporated with PTN capable of supporting various transport technologies and services, the scalable architecture can flexibly attend to the dynamic nature of different use cases like URLLC, mMTC, and eMBB. The architecture should enable different elements of the RAN signal processing block to be partitioned into modules with PTNI that should be open enough to enable multi-vendor interoperability and integration with third-party PS software. Besides, the interface should support effective synchronization, real-time control, and management. Consequently, the architecture will not only enable appropriate and flexible assignment of modularized elements to either the CU or the DU based on the radio configuration, deployment scenarios, and use cases but will also facilitate the adaptation of the PTNI to any specified PS [424; 426; 429]. Moreover, it might not be cost-effective for the MNOs to deploy various dedicated transport networks for the envisaged massive services with diversified requirements. Accordingly, this demands support for various services on a shared infrastructure. This could be achieved with the aids of Netsli that is capable of partitioning the physical network into several slices. Then, a slice can be dedicated for delivering the demanded KPIs for a group of applications/services and yet being isolated entirely from other slices [434]. With PTN and Netsli, transport resources can be appropriately assigned for an on-demand resource provisioning with optimal utilization. The 5G use cases demands can be ideally achieved by SDN aided Netsli with effective preemption. This can ensure that the traffic and bandwidth are preempted appropriately to realize a high-QoS with near-zero jitter and efficient bandwidth demand differentiation. Additionally, as shown in Figure 30(a mode A), with efficient scalability and flexibility offered by SDN/NFV, dynamic split options can be realized in the 5G architecture with efficient load management and real-time performance optimization resulting in an information-centric network [47]. This will help in handling the dynamic nature of the user traffic to facilitate on-demand resource provisioning and optimal utilization based on context-aware service delivery. Moreover, various deployment scenarios/use cases can be effectively adapted to the reconfigurable FSOns offered by the architecture. As there can be a flexible and efficient adaptation of FSOn in time, this will not only help the MNOs in the innovative technologies adoption but also aids in adapting to the incessant and demanding network requirements. However, it is noteworthy that, the architecture may negate the advantages offered by Option 8 regarding the low footprint and cost of the DUs. As flexible split that varies over time demands the processing blocks be deployed at the DUs [427]. This issue can be addressed by locating a virtualized DU (vDU) closer to the DUs where MAC and higher-layer processing functions are centralized leaving the PHY and RF functions to the DUs as depicted in Figure 30(b) (mode B). This presents a relatively simplified DU architecture. The architecture can be simplified further, as illustrated in Figure 30(c) (mode C) by shifting the high-PHY to the vDU.