# On the Rollout of Network Slicing in Carrier Networks: A Technology Radar
## 6 RAN Domain
### Penetration  
In this section, we provide a description of the penetration path we foresee for network slicing in cell sites. For this exercise, it is important to take into account the environment setup. In this regard, we consider three phases: early introduction (phase 1), full adoption on standalone private 5G networks (phase 2) and full adoption in public 5G networks (phase 3).  
The _phase 1_ covers the as-is and deploy rings of the radar. In this phase, it is assumed a baseline RAN slicing solution, consisting of applying 5 QI priority scheduling (see radio resource allocation dimension) over cloud NG-RAN scenarios (see functionality dimensions), with no mobility support. This setup has minimal impact on production networks, without compromising backwards compatibility, and therefore constitutes a good candidate for early introduction in the PLMN. The integration of baseline RAN slicing in first SA networks ensures QoS-based service differentiation on RAN side, which is essential for operators to start commercializing 5 GC Type A2 slices for B2C market (see Figure 11).  
However, for more elaborated setups leveraging open RAN principles, the above rationale is no longer valid. The major changes that these setups bring in RAN planning and configuration patterns prevent their large-scale introduction in today's commercial networks, which account for a large percentage of legacy RAN assets. Instead, operators may initially choose to start testing them RAN slicing on private networks (phase 2) before moving to macro cells (phase 3).  
The _phase 2_ covers the deploy, test and explore rings of the radar. In this phase, the operator may integrate RAN slicing solutions only in greenfield environments, **on-premises**, creating isolated islands of private 5G adoption. This setup constitutes a perfect niche for the operators to start commercializing their innovative RAN slicing solutions towards B2B customers, as the radio resource allocation mechanisms and O-RAN components become available. These solutions can be used either (i) to provide traffic isolation across on-premises customer services, or (ii) to provide the customer with a guaranteed SLA between the device and 5 GC. In the second case, RAN slicing is used in conjunction with the B2B category 5 GC slices to provide PNI-NPN services.  
Figure 15: Radio Resource Partitioning.  
Finally, there is the _phase 3_, spanning across the test and explore rings of the radar. This phase 3 consists of applying the lessons learnt in phase 2 to macro cells. In fact, the trials in phase 2 will serve the operator as a playground before moving to the PLMN, where UE density and traffic patterns are radically different, and where mobility events now need to be taken into account. To facilitate this transition, a three-step journey is foreseen:  
* **PLMN, single-slice TAI**. The operators will start to replicate the trials in specific tracking areas, with their cells configured with one single S-NSSAI.
* **PLMN, multiple-slice TAI**. The same solution as the previous one, but configuring all the cells from the same tracking area with two or more S-NSSAIs.
* **PLMN, large-scale**. The lessons learnt from the small-scale deployments allow improving RAN slicing before massive adoption in the PLMN, where more complex problems on capacity planning and mobility management may appear.