 and 7, but no agreement on option 7 could be reached. Note that option 8 has already been used in LTE and previous generations, where CPRI was the main fronthaul interface transport scheme. As we move from left to right in Fig. 1.26, the split point moves from layer-3 protocols and functions to the lower layer protocols and functions, that is, layers 1 and 2, and ultimately I/Q samples transmission over the fronthaul. Split option 7 has three variants, as shown in Fig. 1.27, depending on what aspects of physical layer processing are performed in the DU/RRUs. In the following, a detailed description of each functional split and its corresponding advantages and disadvantages are provided [34]: Option 1: This functional split option is similar to the reference architecture for dual connectivity. In this option, the RRC sublayer is located in the CU. The packet data convergence protocol (PDCP), radio link control (RLC), MAC, physical layer, and RF functional processing are located in the DU(s). This option allows separate user-plane connections (split bearers) while providing centralized RRC and management. It may, in some circumstances, provide benefits in handling edge computing or low-latency use cases where the user data must be stored/processed in the proximity of the transmission point. However, due to the separation of RRC and PDCP, securing the interface in prac- tical deployments may affect performance of this option. Furthermore, the RRUs will be more complex and expensive due to the additional hardware for local processing of layer-1 and layer-2 functions. Option 2: This functional split is similar to option 1 except PDCP functions are also co-located with the RRC functions in the CU. This option would allow traffic aggre- gation from NR and LTE transmission points to be centralized. It can further facilitate management of traffic load between NR and LTE links. Note that the PDCP-RLC split was already standardized in LTE under dual-connectivity work item. In addition, this option can be implemented by sep