Description
The EPC ProSe User ID (EPUID) is a critical identifier within the 3GPP architecture for Proximity Services (ProSe), defined across specifications such as TS 23.303, TS 29.343, and TS 29.345. It uniquely identifies a user (more precisely, a ProSe-enabled subscriber) within the context of ProSe functions in the EPC. The EPUID is used by network-based ProSe entities—primarily the ProSe Function—to manage ProSe-related subscriber data, authorize ProSe capabilities, and facilitate direct discovery and communication between nearby UEs. It is distinct from other subscriber identifiers like IMSI or MSISDN, as it is specific to the ProSe service layer.
Architecturally, the EPUID is stored and managed within the ProSe Function in the subscriber's home network. When a UE registers for ProSe services, the ProSe Function allocates or maps an EPUID for that user. This identifier is then used in signaling between network functions, such as between the ProSe Function and the ProSe Application Server, or between ProSe Functions in different networks (for roaming scenarios). For direct discovery, a UE may broadcast a ProSe Application Code derived from its ProSe Application ID, which can be resolved by the network (using the ProSe Function) to the corresponding EPUIDs to enable discovery without revealing permanent identifiers over the air.
The EPUID plays a central role in the security and privacy of ProSe. It allows the network to authorize and track ProSe activities without necessarily exposing the user's permanent identity (IMSI) to other UEs or even to the application layer. The ProSe Function uses the EPUID to retrieve the subscriber's ProSe subscription profile from the HSS and to enforce policies. In direct communication (ProSe Direct Communication), the EPUID can be used within the network to establish security contexts and manage one-to-one or one-to-many communication groups. Its format and structure are defined to ensure global uniqueness within the ProSe domain, often constructed based on the user's subscription data.
Purpose & Motivation
The EPUID was introduced in 3GPP Release 12 as part of the standardization of Proximity Services (ProSe), which enables device-to-device discovery and communication. Its creation was motivated by the need for a dedicated, service-layer identifier that could support new use cases like public safety communications, social networking discovery, and commercial D2D services, without compromising user privacy or overloading existing core network identifiers.
It solved the problem of how to uniquely and securely identify users within the ProSe service framework. Using permanent identifiers like IMSI for over-the-air discovery would pose significant privacy risks. The EPUID provides an abstraction layer, allowing the network to map temporary ProSe codes or identifiers used over the radio interface to a stable network-internal user identity for authorization and management. This enables controlled discovery where the network can verify permissions before revealing a user's presence or contact information. The EPUID is fundamental to the network-controlled architecture of ProSe, distinguishing it from ad-hoc Wi-Fi Direct by providing carrier-managed security, billing, and interoperability.
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (9 CRs across 3 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-12, normative work from Rel-15.
In Release 15, the EPUID function was updated to support WLAN-based ProSe Direct Discovery as an alternative technology, with specific details for this procedure described in a new clause. Furthermore, the release introduced ProSe Per-Packet Priority and ProSe Per-Packet Reliability parameters to the ProSe QoS descriptions for direct communication.
- Inclusion of WLAN direct discovery technologies as an alternative for ProSe Direct Discovery: WLAN technology agnostic part TS 23.303CR0324
- Inclusion of WLAN direct discovery technologies as an alternative for ProSe Direct Discovery: NAN specific part TS 23.303CR0325
- Add PPPR introduction to ProSe QoS descriptions TS 23.303CR0328
- Updates for WLAN based ProSe Direct Discovery TS 29.345CR0053
In Release 16, the specification introduced clarifications for the EPUID (EPC ProSe User ID) function by correcting procedures for open ProSe direct discovery. This ensured the EPUID, which uniquely identifies a UE registered for ProSe, was correctly applied within the EPC-level ProSe Discovery process. The changes focused on aligning the use of this identifier with the direct discovery models, Model A and Model B, as defined in the ProSe framework.
- Correct open ProSe direct discovery TS 29.343CR0031
In Release 17, the EPUID (EPC ProSe User ID) function itself was not explicitly modified, but the release introduced foundational support for 5G ProSe and made corrections to the 4G ProSe Stage 2 procedures, which underpin EPC-level ProSe Discovery where the EPUID is used. Specifically, the corrections impacted the restricted discovery procedures and the associated technical figures within the ProSe security specification. Furthermore, security was enhanced for ProSe interfaces by introducing support for TLS version 1.3.
Explore further
Broader topics and technologies where EPUID plays a role.
Defining Specifications
3GPP specifications that define or reference EPUID, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.303 vj00 | Proximity Services (ProSe) Stage 2 | Rel-19 |
| TS 29.343 vj00 | PC2 Reference Point Stage 3 Specification | Rel-19 |
| TS 29.345 vj00 | Diameter-based PC6/PC7 interfaces for ProSe | Rel-19 |
| TS 33.303 vj00 | ProSe Security Specification for EPS | Rel-19 |