Description
Provide Subscriber Information (PSI) is a standardized service within the 3GPP core network architecture, defined as part of the Mobile Application Part (MAP) protocol and later the Diameter-based Sh and S6a/S6d interfaces. It is a network-initiated procedure where a requesting node, such as a Gateway Mobile Location Centre (GMLC), a Service Capability Exposure Function (SCEF), or a Lawful Interception node, queries the subscriber's home database – the Home Location Register (HLR) in 2G/3G or the Home Subscriber Server (HSS) in 4G/5G – to obtain specific information about a subscriber.
The procedure involves a well-defined request/response message exchange. The requesting entity sends a PSI message (e.g., MAP_PSI or Diameter PSI-Request) containing the subscriber's identifier (like MSISDN or IMSI) and an indication of the information required. The HSS/HLR processes the request, which typically involves checking the requester's authorization against subscriber privacy settings and regulatory requirements (e.g., for location services). Upon successful authorization, the HSS/HLR responds with a PSI-Answer message containing the requested data. This data can include a wide array of information: the subscriber's current serving network node (MSC, SGSN, MME, AMF), the subscriber's state (e.g., attached, detached), location information (if available and permitted), subscribed services, and IMSI-MSISDN mapping.
Key components in the architecture include the Requesting Node (the client of the service), the HSS/HLR (the server holding the data), and the relevant signaling interfaces. For 4G/5G, the primary interface is the S6a (between MME and HSS) and Sh (between Application Server/SCEF and HSS), using the Diameter protocol. The HSS acts as the central repository and policy enforcement point, ensuring that subscriber data is provided only to authorized network functions based on the subscriber's consent and network policies.
PSI's role is critical for enabling numerous value-added and regulatory services. It is the backbone procedure for network-based location services, allowing a GMLC to find out which Mobility Management Entity (MME) or Access and Mobility Management Function (AMF) is serving a target UE before issuing a location request. It is also used for restoring subscriber data in case of MME failure, supporting SMS delivery routing, facilitating lawful interception provisioning, and enabling service capability exposure for third-party applications. Its evolution across releases has seen it adapt from circuit-switched MAP to packet-switched Diameter, and its integration with new network functions like the SCEF and Network Exposure Function (NEF) in 5G, maintaining its position as a fundamental subscriber data access service.
Purpose & Motivation
The PSI service was created to address the fundamental need for authorized network entities to access centralized subscriber information in a standardized, secure, and controlled manner. In early cellular networks, different network nodes (like switches and service platforms) required subscriber data to perform their functions, but ad-hoc methods of sharing this data were inefficient and insecure. PSI provided a unified, protocol-based mechanism for querying the master subscriber database (HLR), solving problems related to service triggering, routing (e.g., for SMS or voice calls), and the nascent field of location-based services.
The historical motivation stems from the separation of the subscriber database (HLR) from the switching functions in GSM architecture. This separation created the need for a signaling service to connect them. PSI, as part of the MAP protocol, was one of the key services enabling this distributed architecture. It solved the limitation of having subscriber data siloed or replicated inconsistently across network elements. By centralizing data in the HLR and providing controlled access via PSI, network operators could ensure data consistency, simplify service deployment, and implement subscriber privacy controls.
As networks evolved through 3G, 4G, and 5G, the purpose of PSI expanded. It became essential for enabling regulatory services like lawful interception, where authorities require network attachment information. The drive towards service exposure and network APIs for third-party developers further leveraged PSI (via the SCEF/NEF) to provide subscriber status information to authorized applications, fueling the creation of new services. Thus, PSI has endured as a critical enabler, evolving from a basic network operations tool to a key component in service delivery, security, and innovation across the entire 3GPP system evolution.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (199 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-4, normative work from Rel-15.
In Release 15, enhancements to the Provide Subscriber Information (PSI) function were introduced through new capabilities for calling number verification using signature verification and attestation information. The release also added support for conveying slicing assistance information and detailed slicing information during handover procedures. Furthermore, it included clarifications and corrections for delivering access network information during IMS calls in 5G dual connectivity scenarios.
- Information flows for interconnection group configuration TS 23.280CR0110
- Calling number verification using signature verification and attestation information TS 29.165CR0959
- Deferred System Information Acquisition for PEO TS 43.064CR0120
- Clarification on access network information during IMS call in 5G dual connectivity scenario TS 23.228CR1191
- Renaming of "MCPTT emergency state cancel" and corrections to information flow TS 23.379CR0107
- Slicing assistance information TS 38.300CR0024
+ 33 more changes
In Release 16, the PSI function was enhanced to support Mission Critical services, introducing the ability to query and report location information based on a functional alias. It also gained the capability to provide a list of MCPTT group members who did not acknowledge a group call request and to report user affiliation status information from the group management server.
- Functional alias information query TS 23.280CR0185
- Location information reporting based on functional alias TS 23.280CR0203
- Provide list of MCPTT group members who did not acknowledge the group call request TS 23.379CR0191
- User configuration for functional alias information query for MCPTT TS 23.379CR0195
- Proposal for affiliation status information in group management server TS 23.280CR0165
- Preconfigured regroup information in dynamic data TS 23.280CR0192
+ 24 more changes
In Release 17, the PSI function was enhanced to support the provision of new information types, including activated functional alias information for group servers, Quality of Experience (QoE) information transfer, and disaster roaming information. It also introduced specific support for SNPNs with independent IMS providers and added details to location information reports and notifications, including for emergency alert requests. Furthermore, the release included corrections and clarifications to existing procedures such as location information cancellation, MBMS suspension reporting, and UE positioning assistance.
- Providing activated functional alias information to the group controlling server TS 23.280CR0207
- Additional details to the Location information report TS 23.280CR0243
- Additional details to the Location information notification TS 23.280CR0244
- Add missing server to server information flows for group calls TS 23.379CR0239
- Support of QoE information transfer TS 38.473CR0826
- Clarification to location information cancel subscription TS 23.280CR0262
+ 22 more changes
In Release 18, the PSI function was enhanced to support new Mission Critical (MC) services capabilities, specifically for sharing location information across multiple MC systems through on-demand, triggered, and subscription-based procedures. It also introduced support for ad hoc group call information flows involving multiple MCPTT systems and expanded location-related features, including user-configurable restrictions on location dissemination and MCPTT user profile parameters for location information. Furthermore, updates were made to provide application lists based on UE Device Capabilities (DC) and to manage binding information for DC applications.
- Binding information of DC Application with DC - 23.228 TS 23.228CR1266
- Provide application list based on UE DC capabilities TS 23.228CR1294
- MCGWUE 3GPP access network related location information management TS 23.280CR0300
- Sharing location information across MC systems (functional model) TS 23.280CR0322
- Sharing location information across MC systems (on-demand) TS 23.280CR0323
- Sharing location information across MC systems (triggered) TS 23.280CR0324
+ 59 more changes
In Release 19, the PSI function was enhanced to support the provision of third-party user identity information in IMS, including its associated procedures and the verification process. It also introduced new capabilities for requesting and reporting specific location information for MC service users, both on-demand and periodic, and expanded the use of MC service group IDs for location requests. Furthermore, the release added procedures for setting users and groups as recording targets and included new information elements for ad hoc group emergency alerts and calls.
- Support of third party user identity information in IMS TS 23.228CR1478
- Procedure for supporting of third party user identity information in IMS TS 23.228CR1524
- Corrections to MC service emergency alert cancel request information flow TS 23.280CR0469
- MC service group ID(s) usage for location information request TS 23.280CR0532
- Location reporting information obtained from the PLMN operator (LTE) TS 23.280CR0569
- Requesting specific location information of MC service user on-demand or periodic TS 23.280CR0609
+ 27 more changes
In Release 20, the PSI function was updated to support the "Provide User Info ID during MC service user authentication procedure," introducing a new information element for mission-critical services. Additionally, the release included editorial clarifications and corrections for server-to-server messages and information flows related to MCPTT (Mission Critical Push-To-Talk) and ad hoc group calls.
- Call forwarding for Ad hoc Group calls (information flows) TS 23.379CR0488
- Provide User Info ID during MC service user authentication procedure TS 23.280CR0708
- Resolving Editor’s Notes on server-to-server messages (MCPTT) information flows TS 23.379CR0503
- Void information flow in 10.19.2.3 TS 23.379CR0506
Explore further
Broader topics and technologies where PSI plays a role.
Defining Specifications
3GPP specifications that define or reference PSI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.079 vj00 | Support of Optimal Routeing (SOR) Phase 1 | Rel-19 |
| TS 23.179 vd50 | MCPTT Functional Architecture | Rel-13 |
| TS 23.206 v1700 | Voice Call Continuity (VCC) Functional Architecture | Rel-7 |
| TS 23.228 vj50 | IMS Stage-2 Service Description | Rel-19 |
| TS 23.280 vk10 | Common Architecture for Mission Critical Services | Rel-20 |
| TS 23.379 vk00 | MCPTT Functional Architecture | Rel-20 |
| TS 23.806 v1700 | Voice Call Continuity between CS and IMS | Rel-7 |
| TR 23.979 vj00 | PoC over 3GPP Systems Architectural Requirements | Rel-19 |
| TS 24.141 vj00 | Presence Service Protocol Details | Rel-19 |
| TS 24.147 vj00 | IMS Conferencing Protocol Details | Rel-19 |
| TS 24.173 vj00 | Multimedia Telephony Service and Supplementary Services in IMS | Rel-19 |
| TS 24.186 vj60 | IMS Data Channel applications | Rel-19 |
| TS 24.206 v1700 | Voice Call Continuity Between CS and IMS | Rel-7 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 24.259 vj00 | Personal Network Management (PNM) Protocol Details | Rel-19 |
| TS 24.406 v810 | Message Waiting Indication (MWI) Protocol | Rel-8 |
| TS 24.606 vj00 | MWI Service Protocol Description | Rel-19 |
| TS 24.819 v1700 | IMS Services via Fixed Broadband Access | Rel-7 |
| TS 24.841 v1600 | Presence Service IP Multimedia Subsystem | Rel-6 |
| TR 24.930 vj00 | IMS Session Setup Signalling Flows | Rel-19 |
| TS 25.331 vj00 | UTRAN RRC Protocol Specification | Rel-19 |
| TS 25.413 vj00 | Radio Access Network Application Part (RANAP) | Rel-19 |
| TS 26.237 vj00 | IMS for PSS and MBMS Control | Rel-19 |
| TS 26.506 vj20 | Real-Time Media Communication Architecture for 5G | Rel-19 |
| TS 26.510 vj10 | Media Delivery APIs for 5GMS and RTC Systems | Rel-19 |
| TS 26.522 vj30 | RTP for XR in 5G Systems | Rel-19 |
| TS 26.822 vj20 | 5G RTP Configurations Study Phase 2 | Rel-19 |
| TS 26.827 vc00 | IMS-based Streaming & Download Delivery Enhancements | Rel-12 |
| TS 26.854 vj00 | Study on Haptics in 5G Media Services | Rel-19 |
| TR 26.917 vj00 | TV Service Enhancements over 3GPP | Rel-19 |
| TS 29.118 vj10 | MME-VLR Interface for CS Fallback & SMS | Rel-19 |
| TS 29.165 vj10 | Inter-IMS Network to Network Interface (NNI) | Rel-19 |
| TR 29.949 vj00 | VoLTE IMS Roaming Architecture & Procedures | Rel-19 |
| TS 31.829 vd00 | ISIM Conformance Requirements Technical Report | Rel-13 |
| TS 32.250 vj00 | Circuit Switched Offline Charging | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.306 vj00 | NR UE Radio Access Capability Parameters | Rel-19 |
| TS 38.321 vj00 | NR MAC Protocol Specification | Rel-19 |
| TS 38.323 vj00 | Packet Data Convergence Protocol (PDCP) | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TS 38.415 vj10 | PDU Session User Plane Protocol | Rel-19 |
| TS 38.473 vj10 | 5G F1 Application Protocol (F1AP) | Rel-19 |
| TR 38.835 vi01 | Technical Report on XR Enhancements for NR | Rel-18 |
| TS 43.064 vj00 | GPRS Radio Interface Lower-Layer Functions | Rel-19 |