smaller propagation distances. These mmWave deployments are expected to be more appropriate for dense pockets in critical demand areas of an operator's overall COV- erage area. Considering high FHBW as well as tight latency requirements for lower-layer split Options 7/8, it might not be suitable for high-band mmWave deployments, which are typically expected to be used to provide ultra-high throughputs in certain critical areas. The costs of the lower-layer split option for a high frequency range scenario in terms of transport and real estate far outweigh any benefits in terms of cooperative processing and pooling, which are rather minor. High frequency range deployments are thus more suited to single-level centralization using Option 2 as shown in Figure 7.4. In this architecture, the lower layers of the protocol unit (i.e. DU) are co-located with the RU (either integrated or connected via a short cable). The Option 2 split reduces the fronthaul transport network requirements to a reasonable References gNB-DU Central Office PHY + RRH 3GPP F1 gNB-CU Option 2 split Figure 7.4 Single-leve split NG-RAN architecture suitable for mmWave frequencies. level, making it easier to deploy. Furthermore, this architecture only needs a limited num- ber of centralized sites, which can also benefit from virtualization. Conclusions In the present chapter we tried to provide a glimpse into a plethora of complex considera- tions an operator must go through when designing its networks. In relation to the choice of an appropriate NG-RAN architecture, these considerations range from geographical areas where a service needs to be provided, to applications that are expected to be used in the deployed network, to the spectrum frequency range used, and to availability and capabili- ties of the transport network. As one can see, while there are some well-known planning methods that have been used in the past (i.e. 4G), when it comes to 5G deployments there is no established methodology yet, which will have to be developed when 5G networks a