Section: 5.15 Network slicing 5.15.1 General
Content: A Network Slice instance is defined within a PLMN or within an SNPN and shall include: - the Core Network Control Plane and User Plane Network Functions, as described in clause 4.2, and, in the serving PLMN, at least one of the following: - the NG-RAN described in TS 38.300[ NR; NR and NG-RAN Overall description; Stage-2 ]  [27]; - the N3IWF or TNGF functions to the non-3GPP Access Network described in clause 4.2.8.2 or the TWIF functions to the trusted WLAN in the case of support of N5CW devices described in clause 4.2.8.5; - the W-AGF function to the Wireline Access Network described in clause 4.2.8.4. The 5G System deployed in a PLMN shall always support the procedures, information and configurations specified to support Network Slice instance selection in the present document, TS 23.502[ Procedures for the 5G System (5GS) ]  [3] and TS 23.503[ Policy and charging control framework for the 5G System (5GS); Stage 2 ]  [45]. NOTE 1: Management of network slices are described in TS 28.530[ Management and orchestration; Concepts, use cases and requirements ]  [175], the procedures for provisioning of networks and network slices are described in TS 28.531[ Management and orchestration; Provisioning ]  [176] and TS 28.541[ Management and orchestration; 5G Network Resource Model (NRM); Stage 2 and stage 3 ]  [149] describes the resource model for managing the resources. Network slicing support for roaming is described in clause 5.15.6. Network slices may differ for supported features and network functions optimisations, in which case such Network Slices may have e.g. different S-NSSAIs with different Slice/Service Types (see clause 5.15.2.1). The operator can deploy multiple Network Slices delivering exactly the same features but for different groups of UEs, e.g. as they deliver a different committed service and/or because they are dedicated to a customer, in which case such Network Slices may have e.g. different S-NSSAIs with the same Slice/Service Type but different Slice Differentiators (see clause 5.15.2.1). The network may serve a single UE with one or more Network Slice instances simultaneously via a 5G-AN regardless of the access type(s) over which the UE is registered (i.e. 3GPP Access and/or N3GPP Access). The AMF instance serving the UE logically belongs to each of the Network Slice instances serving the UE, i.e. this AMF instance is common to the Network Slice instances serving a UE. NOTE 2: Number of simultaneous connection of Network Slice instances per UE is limited by the number of S-NSSAIs in the Requested/Allowed NSSAI as described in clause 5.15.2.1. NOTE 3: In this Release of the specification it is assumed that in any (home or visited) PLMN it is always possible to select an AMF that can serve any combination of S-NSSAIs that will be provided as an Allowed NSSAI. The selection of the set of Network Slice instances for a UE is triggered by the first contacted AMF in a Registration procedure normally by interacting with the NSSF, and can lead to a change of AMF. This is further described in clause 5.15.5. A PDU Session belongs to one and only one specific Network Slice instance per PLMN. Different Network Slice instances do not share a PDU Session, though different Network Slice instances may have slice-specific PDU Sessions using the same DNN. During the Handover procedure the source AMF selects a target AMF by interacting with the NRF as specified in clause 6.3.5. Network Slice-Specific Authentication and Authorization (NSSAA) enables Network Slice specific authentication as described in clause 5.15.10. Network Slice Admission Control (NSAC) controls the number of registered UEs per network slice, the number of UEs with at least one PDU Session/PDN Connection per network slice in the case of EPC interworking and the number of PDU Sessions per network slice as described in clause 5.15.11. Support of subscription-based restrictions to simultaneous registration of network slices uses Network Slice Simultaneous Registration Group (NSSRG) information to enable control of which Network Slices that can be registered simultaneously by a UE as described in clause 5.15.12. Support of data rate limitation per Network Slice for a UE enables enforcement of Maximum Bit Rate per Network Slice for a UE as described in clause 5.15.13. The selection of N3IWF/TNGF supporting a set of slice(s) is described in clause 6.3.6 and clause 6.3.12 respectively. The support of Network Slice usage control is described in clause 5.15.15. Support of Optimized handling of temporarily available network slices is described in clause 5.15.16. It also covers aspects related to graceful release of network slices connectivity during slice decommissioning. The Partial Network Slice support in a Registration Area is described in clause 5.15.17. Support for Network Slices with Network Slice Area of Service not matching deployed Tracking Areas is described in clause 5.15.18. Support of Network Slice Replacement is described in clause 5.15.19.