Description
The Single Network Slice Selection Assistance Information (S-NSSAI) is a fundamental construct in the 5G System (5GS) that uniquely identifies a network slice. A network slice is a logical, end-to-end network tailored to meet the specific requirements of a service or customer. The S-NSSAI is used by the User Equipment (UE) and the network to select and associate the UE with the appropriate network slice instance during registration and session establishment procedures. It is a critical parameter carried in Non-Access Stratum (NAS) signaling messages between the UE and the Access and Mobility Management Function (AMF).
An S-NSSAI is composed of two parts: a mandatory Slice/Service Type (SST) and an optional Slice Differentiator (SD). The SST is an 8-bit value that indicates the expected network slice behavior in terms of features and services. Standardized SST values include 1 for enhanced Mobile Broadband (eMBB), 2 for Ultra-Reliable Low Latency Communications (URLLC), and 3 for massive IoT (mIoT). The SD is a 24-bit optional identifier used to differentiate among multiple network slices of the same SST, allowing operators to create further specialized slices within a broad category (e.g., different eMBB slices for enterprise and consumer services). The combination of SST and SD allows for fine-grained slice selection.
During initial registration, the UE provides a Requested NSSAI, which is a list of S-NSSAIs corresponding to the slices it wishes to access. The network validates these requests against the subscriber's Subscribed S-NSSAIs stored in the Unified Data Management (UDM). The AMF, in coordination with the Network Slice Selection Function (NSSF), selects the appropriate network slice instances and returns an Allowed NSSAI to the UE for use in the current registration area. This Allowed NSSAI is then used for subsequent session establishment with the Session Management Function (SMF). The S-NSSAI influences the selection of all other core network functions (SMF, PCF, UPF) and can be used to apply specific network policies, quality of service (QoS) profiles, and charging rules, enabling true end-to-end logical network isolation and customization.
Purpose & Motivation
S-NSSAI was introduced in 3GPP Release 15 as a core enabler of 5G network slicing, a revolutionary concept that allows a single physical network infrastructure to be partitioned into multiple virtual, independent logical networks. Prior to 5G, networks provided largely monolithic services; customizing the network for different service types (e.g., video streaming, autonomous driving, sensor networks) was complex and inefficient. S-NSSAI solves this by providing a simple, standardized identifier that allows both the device and the network to dynamically select a pre-configured slice with specific characteristics.
The creation of S-NSSAI was motivated by the diverse and stringent requirements of 5G use cases, which range from high bandwidth and low latency to massive connection density. It addresses the problem of how to efficiently direct traffic and apply tailored resources without building separate physical networks. By including the S-NSSAI in signaling, the 5G system can instantiate the correct set of network functions and policies on a per-session basis. This enables operators to offer Network-as-a-Service (NaaS), support enterprise private networks, and optimize resource utilization, thereby unlocking new revenue streams and meeting the performance demands of modern applications.
Architecture
Classification
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (298 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the S-NSSAI function was newly introduced to enable network slice selection, with foundational procedures established for its use during inter-system mobility between EPS and 5GS and in PDN connection contexts. The release specified mechanisms for handling S-NSSAI mapping, congestion control based on S-NSSAI, and the inclusion of S-NSSAI in parameters like the Requested NSSAI during handover. Furthermore, it defined the role of the NSCE server in providing S-NSSAI and DNN mapping guidance to influence URSP rules for application traffic.
- S-NSSAI of a PDN connection context vie (e)PCO TS 24.008CR3116
- Handling of S-NSSAI and PDU session ID during mobility between EPS and 5GS TS 24.301CR2965
- 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
- Correction to rejected S-NSSAI TS 23.501CR0007
- Correction to handling of S-NSSAI mapping information TS 23.501CR0020
+ 32 more changes
In Release 16, the S-NSSAI function was enhanced to support non-3GPP access and to enable S-NSSAI-based congestion backoff timers during PDU session establishment. The release also introduced mechanisms for improved PCF selection for multiple PDU Sessions to the same DNN and S-NSSAI, and clarified handling during inter-PLMN mobility and for emergency services. Furthermore, it defined the role of the NSCE server in providing updated S-NSSAI and DNN mappings as guidance for network-based slice re-mapping and URSP determination.
- 23.501 part of PCF selection for PDU sessions with same DNN and S-NSSAI TS 23.501CR1375
- "S-NSSAI not available in the current PLMN" when non NSSAA supported UE requesting the S-NSSAI subjects to NSSAA TS 24.501CR1598
- Support of S-NSSAI for non-3GPP access TS 29.507CR0092
- Same PCF selection for the same UE ID, S-NSSAI and DNN combination TS 29.512CR0383
- include S-NSSAI and DNN in Application Data for xBDT TS 29.519CR0161
- Same PCF selection for the same UE ID, S-NSSAI and DNN combination TS 29.521CR0053
+ 43 more changes
In Release 17, enhancements for S-NSSAI included enabling the support of multiple NSACFs (Network Slice Admission Control Functions) for a single S-NSSAI during UE mobility and clarifying procedures for when an S-NSSAI is rejected due to the maximum number of UEs being reached. The release also introduced mechanisms for reporting the Session S-NSSAI to external DN-AAA servers (both RADIUS and Diameter) and provided clarifications on S-NSSAI usage for SNPN onboarding and within APIs like ChargeableParty and AsSessionWithQoS.
- Support multiple NSACFs for one S-NSSAI during UE mobility TS 23.501CR2909
- 5G DN and S-NSSAI Config TS 24.483CR0149
- DNN/S-NSSAI providing in PDU session establishment for SNPN onboarding TS 24.501CR3322
- S-NSSAI rejected due to maximum number of UEs reached and BO timer value TS 24.501CR3123
- PDU session establishment with the DNN/S-NSSAI for UAS service from the UE whch has valid aerial subscription but UUAA-MM is failed abnormally TS 24.501CR3792
- Update DNN and S-NSSAI in ChargeableParty API TS 29.122CR0347
+ 60 more changes
In Release 18, key enhancements for S-NSSAI introduced the concepts of a "partially Allowed NSSAI" and "partially Rejected S-NSSAI," along with an "Alternative S-NSSAI replacement" determined by the NSSF. The release also added mechanisms for S-NSSAI location availability and validity time information, enabling the AMF to enforce these parameters and handle scenarios where a requested S-NSSAI is unavailable. Furthermore, specific procedures were updated to support Local Area Data Network (LADN) functionality on a per DNN and S-NSSAI basis, including handling for legacy UEs.
- N3IWF selection enhancement for support of S-NSSAI needed by UE TS 23.501CR3707
- TNGF selection enhancement for support of S-NSSAI needed by UE TS 23.501CR3953
- Introduction of partially Allowed NSSAI and Partially Rejected S-NSSAI TS 23.501CR4035
- Introduction of Alternative S-NSSAI replacement determined by NSSF TS 23.501CR4036
- Updates on S-NSSAI Location Availability information TS 23.501CR4487
- Storage of S-NSSAI validity time information TS 23.501CR4488
+ 107 more changes
In Release 19, key enhancements for S-NSSAI included the ability to provision an S-NSSAI via the PDN CONNECTIVITY REQUEST message for EPS interoperability and the introduction of S-NSSAI granularity for energy consumption exposure, supporting the EnergySys feature. The release also clarified and corrected procedures for partially allowed S-NSSAIs, alternative S-NSSAI handling, and interactions with AF-triggered slice replacement, while introducing on-demand NSSAI for alternative S-NSSAI.
- Provisioning an S-NSSAI via the PDN CONNECTIVITY REQUEST message TS 24.301CR3655
- Provisioning an S-NSSAI via the PDN CONNECTIVITY REQUEST message TS 24.526CR0284
- Support S-NSSAI level exposure related to EnergySys feature TS 29.122CR0920
- DNN association for served S-NSSAI in Terminal Response for PLI - list of slices information and Envelope (Event Download slice status) command TS 31.111CR0871
- S-NSSAI selection while in EPS TS 23.501CR5866
- Support for S-NSSAI granularity energy consumption exposure TS 23.501CR5956
+ 26 more changes
Explore further
Broader topics and technologies where S-NSSAI plays a role.
Defining Specifications
3GPP specifications that define or reference S-NSSAI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.435 vj30 | Network Slice Capability Exposure Procedures | Rel-19 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 23.700 vk00 | XR Services Application Enablement Layer | Rel-20 |
| TR 23.745 vh00 | Study on App Layer Support for Factories of the Future in 5G | Rel-17 |
| TR 23.758 vh00 | Study on Edge Application Architecture | Rel-17 |
| TS 24.008 vj50 | 3GPP TS 24008: Core Network Protocols | Rel-19 |
| TS 24.301 vj60 | NAS protocol for Evolved Packet System | Rel-19 |
| TS 24.302 vj00 | Access to EPC via non-3GPP networks; Stage 3 | Rel-19 |
| TS 24.483 vj20 | Mission Critical Services Management Object | Rel-19 |
| TS 24.484 vj30 | MCS Configuration Management | Rel-19 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TS 24.526 vj30 | UE Policies for 5GS; Stage 3 | Rel-19 |
| TS 24.549 vj10 | SEAL Network Slice Capability Enablement Protocol | Rel-19 |
| TS 24.575 vj00 | UE Pre-configuration for MBS | Rel-19 |
| TS 24.890 vg00 | 5G NAS Protocol for 5GS Stage 3 | Rel-16 |
| TS 28.202 vj00 | 5G Network Slice Management Charging | Rel-19 |
| TS 28.203 vi10 | Charging management | Rel-18 |
| TS 28.204 vi11 | Charging management | Rel-18 |
| TS 28.535 vj00 | Closed Control Loop Assurance Management | Rel-19 |
| TR 28.833 vi01 | Technical Report on 5G LAN-type Service Management | Rel-18 |
| TR 28.836 vi00 | Technical Report on Intent Driven Management | Rel-18 |
| TR 28.843 vi10 | Technical Report on Charging Aspects for Vertical Scenarios | Rel-18 |
| TS 29.122 vj40 | T8 Reference Point for Northbound APIs | Rel-19 |
| TS 29.507 vj40 | 5G Access & Mobility Policy Control Service | Rel-19 |
| TS 29.508 vj40 | 5G Session Management Event Exposure Service | Rel-19 |
| TS 29.512 vj40 | 5G Session Management Policy Control Service | Rel-19 |
| TS 29.513 vj40 | 5G PCC Signalling Flows & QoS Mapping | Rel-19 |
| TS 29.514 vj40 | 5G System; Policy Authorization Service; Stage 3 | Rel-19 |
| TS 29.518 vj50 | AMF Service Based Interface Protocol | Rel-19 |
| TS 29.519 vj40 | UDR Usage for Policy & Exposure Data | Rel-19 |
| TS 29.520 vj40 | 5G Network Data Analytics Services Stage 3 | Rel-19 |
| TS 29.521 vj40 | 5G Binding Support Management Service Stage 3 | Rel-19 |
| TS 29.522 vj40 | 5G NEF Northbound APIs Stage 3 | Rel-19 |
| TS 29.523 vj20 | 5G Policy Control Event Exposure Service | Rel-19 |
| TS 29.532 vj30 | MB-SMF Service Based Interface Protocol | Rel-19 |
| TS 29.543 vj20 | 5G Data Transfer Policy Control Services Stage 3 | Rel-19 |
| TS 29.554 vj10 | 5G Background Data Transfer Policy Control Service | Rel-19 |
| TS 29.561 vj30 | 5G Interworking with External Data Networks | Rel-19 |
| TS 29.581 vj20 | MBSTF Service Based Interface Protocol Specification | Rel-19 |
| TS 29.890 vg00 | CT3 5G System Technical Report | Rel-16 |
| TS 31.105 vj10 | Slice Subscriber Identity Module (SSIM) Application | Rel-19 |
| TS 31.111 vj30 | USIM Application Toolkit (USAT) Specification | Rel-19 |
| TS 31.127 vi40 | UICC-terminal interaction testing specification | Rel-18 |
| TR 31.826 vi00 | Technical Report | Rel-18 |
| TS 32.240 vj40 | Charging Management Architecture & Principles | Rel-19 |
| TR 32.847 vi00 | Technical Report | Rel-18 |
| TS 32.899 vf10 | 5G Charging Architecture Study | Rel-15 |
| TS 33.117 vk00 | Catalogue of General Security Assurance Requirements | Rel-20 |
| TR 33.739 vi10 | Study on security enhancement of support for | Rel-18 |
| TS 33.749 vj00 | Study on security aspects of edge computing enhancement | Rel-19 |
| TS 37.473 vj00 | W1 Application Protocol (W1AP) Specification | Rel-19 |
| TS 37.483 vj10 | E1 Application Protocol (E1AP) | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.413 vj10 | NG Application Protocol (NGAP) | Rel-19 |
| TS 38.423 vj10 | Xn Application Protocol (XnAP) specification | Rel-19 |
| TS 38.463 vj00 | E1 Application Protocol (E1AP) | Rel-19 |
| TS 38.473 vj10 | 5G F1 Application Protocol (F1AP) | Rel-19 |
