ols in 3GPP 5G RAN architecture is shown in Figure 7.23. The DU, as introduced in Chapter 5, covers time critical functionality which includes the retransmission handling (this including besides L1 also the MAC and RLC layers) while the PDCP, SDAP, and RRC are in the Central Unit (CU). As shown in Figure 7.23, the CU can be further divided into the control and user plane parts (CU-CP and CU-UP, respectively). The protocol stacks on different interfaces inside the RAN and between the RAN and the core are covered in Chapter 5. 7.9 Summary The objectives of the 5G radio protocols are to enable on the one hand easy implemen- tation of high rate connectivity and on the other hand to support both power-efficient as well as high-capacity network operation with solutions like the BWP. The introduc- tion of new elements like the flow-based QoS service, RRC_inactive state, and network slicing ensures that 5G can address different needs in line with the service evolution on top 5G networks. 7 5G Radio Protocols CU-CP CU-UP PDCP-C PDCP-U Radio Higher Layer Functional Split Figure 7.23 5G control and UP protocols in 5G architecture. 5G provides inter-working with LTE in Release 15, and will provide eventually in Release 16 inter-working with 3G as well to ensure voice call continuity, as discussed in Chapter 15. The dual connectivity operation is built around using 5G-based PDCP, which helps the UE implementation as then data routing is not visible to the UE. References 1 3GPP Technical Specification TS 38.214 (2019). NR Physical Layer Procedures for Data, Version 15.6.0. June 2019. 2 3GPP Technical Specification TS 38.211 (2019). NR Physical Channel, Version 15.6.0. June 2019. 3 3GPP Technical Specification TS 38.304 (2019). NR User Equipment (UE) Procedures in Idle Mode and in RRC Inactive State, Version 15.4.0. June 2019. 4 3GPP Technical Specification TS 38.213 (2019). NR Physical Layer Procedures for Control, Version 15.6.0. June 2019. Deployment Aspects Harri Holma¹ Riku Luostari² , Jussi Reunanen³, and Puripong Thepcha