Network Slice Selection Assistance Information

In Release 15, the NSSAI function was introduced to manage network slice selection, including procedures for storing the Configured NSSAI when the PLMN changes and establishing an N1 NAS signalling connection due to changes in network slicing information. It also defined mechanisms for handling S-NSSAI during mobility between EPS and 5GS, including providing S-NSSAI info for PDN connections established over ePDG/EPC and including S-NSSAI received in EPS in the Requested NSSAI upon inter-system change. Furthermore, Release 15 introduced the Allowed NSSAI, which indicates the S-NSSAIs the UE can use in the Serving PLMN, and the Pending NSSAI for scenarios where network slice-specific authorization is ongoing.

• Handling of S-NSSAI and PDU session ID during mobility between EPS and 5GS TS 24.301CR2965
• Mode selection for inter-system change between EPS and 5GS TS 24.301CR2979
• Ciphering keys delivery for broadcast of ciphered assistance data TS 24.301CR3041
• Clarification on usage of ePDG selection procedures TS 24.302CR0662
• S-NSSAI info for PDN connection established over ePDG/EPC TS 24.302CR0666
• Including S-NSSAI received in EPS in Requested NSSAI and in PDU session establishment request upon inter-system change from S1 mode to N1 mode TS 24.501CR0082

+ 233 more changes

In Release 16, the NSSAI function was enhanced to support **Slice-Specific Authentication and Authorisation**, introducing a **Pending NSSAI** to indicate S-NSSAIs awaiting such procedures during registration. It also defined an **Alternative S-NSSAI** for the AMF to use when a requested slice is unavailable or congested, and clarified the use of a **Target NSSAI** to steer the UE to cells supporting specific network slices.

• CIoT Introduction of CN Selection and Steering TS 23.501CR0896
• Description of solution 2 in 23.725 for redundancy as an informational annex TS 23.501CR0754
• ATSSS-SMF and UPF selection TS 23.501CR0761
• Trusted non-3GPP Access Network Selection TS 23.501CR0783
• eSBA communication schemas related to general discovery and selection TS 23.501CR0799
• eSBA communication schemas related to UDM and UDR discovery and selection TS 23.501CR0800

+ 402 more changes

In Release 17, enhancements to NSSAI included the introduction of a Partially Allowed NSSAI, which indicates S-NSSAIs the UE can use only in specific Tracking Areas within its Registration Area. Furthermore, the concept of an Alternative S-NSSAI was defined, allowing the AMF to replace an unavailable or congested S-NSSAI in the Allowed NSSAI with a compatible alternative. The release also expanded network slice support over different Non-3GPP accesses and introduced mechanisms for network slice restriction based on NWDAF analytics.

• Support of different slices over different Non 3GPP access TS 23.501CR2525
• Network Slice restriction based on NWDAF analytics TS 23.501CR2567
• NWDAF discovery and selection TS 23.501CR2575
• NWDAF discovery and selection based on provided ML models TS 23.501CR2585
• UP path selection enhancement based on analytics info provided by NWDAF TS 23.501CR2586
• NWDAF discovery and selection for model sharing TS 23.501CR2614

+ 442 more changes

In Release 18, key enhancements for NSSAI included the introduction of a **Partially Allowed NSSAI**, which indicates S-NSSAIs a UE can use only in specific Tracking Areas within its Registration Area, and an **Alternative S-NSSAI**, determined by the NSSF to replace an unavailable or congested S-NSSAI. Furthermore, the release added support for **network slice replacement** and **graceful termination of PDU sessions** during network slice decommissioning.

• N3IWF selection enhancement for support of S-NSSAI needed by UE TS 23.501CR3707
• Discovery and Selection of the NWDAF Supporting Federated Learning in 5GC TS 23.501CR3772
• KI#4 23.501 AF traffic influence for common EAS, DNAI selection TS 23.501CR3788
• Common EAS/DNAI selection by AF TS 23.501CR3789
• Change of Network Slice instance for PDU sessions TS 23.501CR3867
• Introduction of 5GS Information Exposure TS 23.501CR3887

+ 593 more changes

In Release 19, enhancements for NSSAI include the support of slice change based on an AF request, allowing an Application Function to influence the active network slice for a UE. Furthermore, the concept of a Target NSSAI is utilized to steer the UE to cells supporting specific slices, and the introduction of an Alternative S-NSSAI provides a compatible slice replacement when a requested S-NSSAI is unavailable or congested.

• RVAS with target NF selection enhancement. TS 23.501CR5364
• NF discovery and selection by target PLMN TS 23.501CR5399
• Adding the NAT information exposure and Packet Inspection functionality in the UPF NF profile TS 23.501CR5420
• Support of UPF selection according to the conclusion in FS_UPEAS_Ph2 TS 23.501CR5441
• Introduction of new network function for energy related information, its definition and corresponding Architecture Reference Model TS 23.501CR5636
• I-SMF selection/insertion based on local offloading allowed indication TS 23.501CR5604

+ 257 more changes

In Release 20, the enhancements to NSSAI primarily involved the introduction of the "Alternative S-NSSAI" concept, which allows the AMF to replace an unavailable or congested S-NSSAI in the Allowed NSSAI with a compatible alternative. Furthermore, the specification refined the "Partially Allowed NSSAI" by associating each S-NSSAI within it with a specific list of Tracking Areas where that network slice is supported. These changes improved network slice selection and availability management for UEs.

• N3IWF/TNGF reselection considering energy related information. TS 23.501CR6493
• KI#1: Per UE application ranking related information exposed by EIF TS 23.501CR6501
• Energy Consumption information exposure and policy control TS 23.501CR6508
• Rel-20 CR TS 28.541 Enhancement on PreDefinedPccRule for exposure of information related to XRM service based on QoSMonitoring TS 28.541CR1570
• Rel-20 CR TS 28.541 Enhancement of TrustedAF information to support VFL TS 28.541CR1573
• Rel-20 CR TS 28.541 Enhancement of unTrustedAF information to support VFL TS 28.541CR1574

+ 2 more changes