ese architectures, a NG-RAN node is typically split into a CU and a DU, with the functionality in each depending on the split option. In some cases, a DU may be further split into a DU and an RU. As a general rule, lower splits (confusingly designated by higher split numbers) have higher centralization of functionality at the cost of increasingly stringent fronthaul bandwidth and latency requirements. All these options are described in detail in Chapter 4. Table 7.2 shows an approximate fronthaul bandwidth (FHBW) required for various protocol splits for low-, mid-, and high-band scenarios assuming 8 antennas per sector, 4 layers, 8 bits per I/Q sample, and an overhead of 25%. This is just an approximate back-of-the-envelope calculation, as in practice it depends on many factors such as quantization, especially for low-level splits. Table 7.2 Fronthaul bandwidth for low-, mid-, and high-band scenarios. Low band Mid-band High band Total bandwidth (MHz) Split type Fronthaul bandwidth (Gbps) Options 2 (Packet Data Convergence Protocol-Radio Link Control [PDCP-RLC]) Options 5 (High Medium Access Control [MAC] - low MAC) Option 7-2 (Intra PHY) Option 7-1 (Intra PHY) 107.5 Option 8 (PHY/RF) 183.5 7 NG-RAN Deployment Considerations The required FHBW is the lowest for Option 2, being very close to actual user traffic with some necessary protocol overheads. The required FHBW increases as we split down the NG-RAN protocol stack with quantized modulation symbols being transported in Options 7 and 8. Low level split Options 7 and 8 provide the ability to carry out coordinated processing across multiple radios at the cost of larger FHBW. The FHBW required for Options 7 and 8 for the high frequency range scenario is espe- cially significant. 2 Therefore, transport network availability and cost becomes an important factor in selecting the right NG-RAN architecture. Large-scale mmWave deployment with lower-layer split would dramatically escalate transport network deployment costs, making it significantly less attractive for opera