Description
Service Area Restriction Information (SARI) is a subscriber-specific or session-specific policy parameter in the 5G System (5GS). It is managed by the Unified Data Management (UDM) function as part of a user's subscription data and is provided to the Access and Mobility Management Function (AMF) during registration and session establishment procedures. The SARI contains two primary lists: an Allowed Area and a Non-Allowed Area, each composed of Tracking Area Identities (TAIs). The AMF uses this information to enforce mobility restrictions by allowing or denying registration, service requests, and handovers based on the UE's current or target location.
Architecturally, SARI is propagated through key 5G interfaces. The UDM includes it in the Nudm_SubscriberDataManagement service responses to the AMF. The AMF then evaluates the UE's current TAI against the SARI. If the UE is in a Non-Allowed Area, the AMF can reject the registration with an appropriate cause code, effectively barring service. For an ongoing session, if a UE moves into a Non-Allowed Area, the AMF can initiate a network-initiated deregistration or modify the PDU session. The policy can also be applied per Network Slice, allowing different service area restrictions for different slices assigned to the same UE.
How it works involves precise coordination between the UE's location update procedures and the AMF's policy enforcement. When a UE performs a Registration Request or a Periodic Registration Update, the AMF receives the UE's current TAI. It fetches the subscriber's SARI (if not already cached) and performs a check. The 'Allowed Area' takes precedence; if a TAI is present in both the Allowed and Non-Allowed lists, it is considered allowed. This granular control allows operators to define complex service footprints, such as permitting service only in a specific city (Allowed Area) or everywhere except a sensitive site (Non-Allowed Area). SARI is a crucial tool for implementing regulatory mandates (e.g., no service in secure government facilities), commercial agreements (geofenced services), and efficient network slice isolation.
Purpose & Motivation
SARI was introduced in 5G to provide a more flexible and powerful mechanism for geographic service control than what was available in previous generations like 4G EPC. Earlier systems used concepts like Forbidden Tracking Areas or equivalent location-based restrictions, but they were often less granular and not as seamlessly integrated with subscriber data management and network slicing policies. The rise of 5G use cases, such as private networks, network slicing for vertical industries, and stringent regulatory requirements, created a need for precise, dynamic, and slice-aware service area management.
The primary problem SARI solves is the need for differentiated access control based on geography. For example, a factory deploying a private 5G network needs to ensure its ultra-reliable low-latency communication (URLLC) slice is only accessible within the factory premises. Similarly, a regulator may require that mobile service be disabled within prisons or military zones. SARI provides the standardized mechanism to enforce these policies at the network core, preventing unauthorized access or service leakage outside defined boundaries.
Its creation was motivated by the 5G architectural shift towards cloud-native, service-based interfaces and the explicit support for network slicing. SARI is a key enabler for slice isolation, allowing different slices to have independent geographic footprints. It also supports dynamic updates; an operator can modify a user's SARI in the UDM, and the change can be pushed to the serving AMF, enabling real-time changes to service areas for security or operational reasons, which was more cumbersome in prior architectures.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (40 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the SARI function was updated through clarifications and the removal of specific data types. The changes included the removal of the "Subscribed-Data-Report" event type and the associated "SARI" data type, as indicated in the relevant Change Request. Furthermore, enhancements were made to procedures involving the transfer of UE context and event subscription information between network functions like the AMF.
- Mobility Restriction TS 29.518CR0040
- Passing NSSF information in N1MessageNotification TS 29.518CR0047
- Clarification on location information in immediate report TS 29.518CR0049
- Correct reference for Event Report Information TS 29.518CR0051
- Information in N1MessageNotify TS 29.518CR62
- Altitude in Provide Positioning Information TS 29.518CR107
+ 1 more changes
In Release 16, the SARI function was enhanced through updates for subscription-based access restriction. This involved refining the procedures for transferring UE context information between AMFs, including access and mobility management policy information received from the PCF. Furthermore, the release specified the inclusion of SNPN Onboarding indication within the UE context for relevant scenarios.
- CreateUEContext – I-SMF and SM Context ID Information TS 29.518CR0194
- Transfer Information of MA PDU Session between AMFs TS 29.518CR0211
- RIM Information Transfer procedure TS 29.518CR0240
- Updating support for subscription-based access restriction TS 29.518CR0261
- V2X information in UE Context TS 29.518CR0289
- Monitoring Event Information TS 29.518CR0350
+ 1 more changes
In Release 17, the SARI function was enhanced to support Multicast Broadcast Service (MBS) by introducing MBS Service Area Information for location-dependent MBS sessions. This allows the network to manage service area restrictions specifically for MBS traffic. Furthermore, the release included updates to ensure that relevant service area and session management information is properly conveyed within the Namf_MBSBroadcast and Namf_MBSCommunication service-based interfaces.
- NF discovery based on SUCI information TS 29.518CR0444
- PRA Information update TS 29.518CR0483
- Analytics subscription information TS 29.518CR0536
- N2 MBS Session Management Information in Namf_MBSBroadcast API TS 29.518CR0684
- N2 MBS Session Management Information in Namf_MBSCommunication API TS 29.518CR0685
- MBS Service Area Information for Location dependent MBS session TS 29.518CR0718
+ 5 more changes
In Release 18, the SARI function was enhanced to support **Network Slice Replacement** alongside area restrictions during UE mobility, as indicated in the CR title. The specification updates clarify that the AMF must store and transfer **access and mobility management (AM) policy information** within the UE context, particularly when received from the PCF during such replacement procedures. Furthermore, the handling of **N2 information** was refined, including the transfer of a callback URI for N2 Information Notification within the UeContextCreateData structure during inter-AMF UE context transfer.
- A2X information in UE Context TS 29.518CR0935
- Slice Usage Control Information in UE Context TS 29.518CR0939
- Updates on the RAN Timing Synchronization Status Report related N2 information TS 29.518CR0968
- Update on delivery of N2 information for rangingsl TS 29.518CR1003
- Subscription to TSS information Reporting using Namf_NonUeN2MessageTransfer TS 29.518CR1009
- Remote UE Indication in Location Information TS 29.518CR1086
+ 5 more changes
In Release 19, the SARI function was enhanced to include slice information for active PDU sessions during inter-PLMN handover, ensuring service continuity. Additionally, the release clarified the storage and transfer of access and mobility management policy information within the UE context. It also introduced the ability for an NF Service Consumer, such as an LMF, to provide routing information within the N1N2MessageTransfer service operation.
- Clarification on Storage and Transfer of Access and Mobility Management Policy Information in UE Context TS 29.518CR1181
- DNN and Slice information for Communication Failure Event TS 29.518CR1146
- Addition of LMF routing information to N1N2MessageTransfer Service Operation TS 29.518CR1274
- Slice Information for Active PDU Session during inter-PLMN Handover TS 29.518CR1297
Explore further
Broader topics and technologies where SARI plays a role.
Defining Specifications
3GPP specifications that define or reference SARI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 29.518 vj50 | AMF Service Based Interface Protocol | Rel-19 |