# On the Rollout of Network Slicing in Carrier Networks: A Technology Radar
## 6 RAN Domain
### Radio Resource Allocation  
In this dimension, we encounter a number of solutions in the gNB scheduler enabling RAN slicing. These solutions are based on two different yet complementary mechanisms: priority scheduling and radio resource partitioning. On the one hand, _priority scheduling_ is a mechanism used for service differentiation between RAN slices when they all compete for the same PRBs. This corresponds to best effort slices, as captured in Table 2. The service differentiation here is achieved with the definition of multiple DRB profiles, each featured with a different scheduling priority, and their allocation to existing RAN slices. This approach allows giving one or more RAN slices a preferential treatment with relative priority to others. The policy for DRB profile allocation is based on QoS criteria, though other business-wise criteria can be applied (e.g., based on platinum/gold/silver subscription). On the other hand, _radio resource partitioning_ is a mechanism based on PRB reservation. Unlike priority scheduling, radio resource partitioning allows segregating cell resources across different RAN slices. Here, resource segregation consists of allocating separate PRB chunks to the DRBs associated to these slices. For this PRB allocation, the gNB scheduler configures the resource quotas per slice. As shown in Figure 6, the operator can configure up to three resource quotas in a slice, namely, maximum slice quota (mandatory), minimum slice quota (mandatory), and dedicated minimum slice quota (optional). For the definition of these per slice quotas, the operator makes use of RRMPolicy class defined in the 5G NRM, by applying the RRMPolicyRatio attributes (i.e., RRMPolicyMaxRatio, RRMPolicyMedicatedRadio) to the [S-NSSAI, PLMN ID] tuple the RAN slice is associated with. For further information on this mapping, see clause 4.3.36 from 3 GPP TS 28.541 [15]. Table 3 provides a comparative analysis between priority scheduling and radio resource partitioning. While it may seem logical to define PRB reservation for each slice supported at the RAN, this is, in practice, suboptimal. There is a trade-off in performance  
Figure 12: AI assisted RAN slice resource control. between the gain from dedicating resources to specific slice services and the overhead in maintaining numerous resource partitions. The balance is to keep sufficient PRB chunks to guarantee resource isolation per RAN slice when needed, while not impacting radio performance due to excessive partitioning. In the following, we describe the solutions that we foresee from these two RAN slicing mechanisms, and that are illustrated in the radar shown in Figure 9.  
In today's dominant NSA scenarios (as-is ring in the radar), the only possible solution for RAN slicing is **QCI Priority Scheduling**, based on giving a preferential treatment to those DRBs associated with top-priority services. The priority of a service depends on the QoS parameters associated with the service flows, with a QCI as key parameter, complemented with other QoS related info (i.e., GBR + MBR values if service flows convey GBR traffic, AMBR values if service flows convey non-GBR traffic). Upon computation on the EPC side, the priorities of different services are sent to the gNB, which uses them to define corresponding DRB profiles. The number of DRB profiles available in current production networks is rather low; the reason is a coarse-grained design of DRBs, and that only few of them convey prioritized traffic. As we move towards the rollout of the first 5G SA networks, new priority scheduling solutions are appearing:  
* **5 QI Priority Scheduling**. This solution is equivalent to the QCI Priority Scheduling, but using 5 GC, which provides much more granular QoS control than the EPC. The fact that (i) the 3 GPP 5G QoS framework allows one slice to convey multiple QoS flows, each featured with a specific 5 QI, and (ii) the DRB profiles are computed based on 5 QI, make it possible to have intra-slice service differentiation. Figure 13 illustrates an example of how this solution works.