ause value to indicate the RAN subsystem the UE tries to access. Based on this, the RAN may perform early admission control, for example, to reject some access request in case of congestion situations. In Message5, the UE may include slice information during the registration procedure for AMF selection. Figure 12.10 gives the PDU session setup/modify procedure, in which the RAN may iden- tify the specific slice requirements based on the S-NSSAI per PDU session and perform the slice-specific RAN part of network slice configurations. The detailed slice level configuration includes the following aspects. Slice-specific network topology: Based on the requested slice type, the RAN may configure and support service-oriented network topologies for different slices. The following gives some examples: - If the requested slice is a V2X slice, the RAN may support both side-link V2X communi- cation and UE-to-UE communication. Also, it can support both unicast and broadcast communication mode for this UE. - If the requested slice is for media delivery, the broadcast/multicast mode communica- tion could be supported. - For wearables and Internet of Things (IoT) slice, the RAN may use multi-hop and relay- ing like integrated access and backhaul (IAB) topology. 12.4 Key Technologies to Enable Service-Oriented RAN Slicing UE RRC connection procedure PDU session setup/modify request (S-NSSAI per PDU session) NG RAN checks the set of slice requirements, and maps to RAN subsystem PDU session setup/modify/release response RRC connection reconfiguration (slice-specific handlings) Figure 12.10 RAN subsystem-aware PDU session setup/modify. (1113) (1(1) Service 1 Service 2 Frequency Service 3 Service 4 Frequency 2 Figure 12.11 Service-oriented RAN topology. - For UEs supporting multiple slices simultaneously, multi-layer connection hierarchy should be supported. Figure 12.11 gives an example in which the UE communicates with one RAN node via fre- quency F1 in RAN sub-system 2 and communicates with another RAN node via frequency F2 in ano