Description
The ProSe Discovery UE ID (PDUID) is a temporary, layer-2 identifier used exclusively for ProSe Direct Discovery procedures in 3GPP networks, starting from Release 13. It is assigned by the ProSe Function in the network core to a UE that is authorized for ProSe services. The PDUID is used in the actual discovery messages broadcast over the PC5 interface (the direct device-to-device radio link) and monitored by other UEs. It serves to mask the permanent UE identity (like IMSI or SUPI) for privacy and to provide a handle for the discovery process. There are two primary models: Model A ("I am here") where a announcing UE broadcasts its PDUID, and Model B ("Who is there?/Are you there?") where a discoverer UE broadcasts a PDUID containing information about the UE it is looking for.
Architecturally, the assignment and management of the PDUID involve several network functions. The UE requests authorization for ProSe Discovery from the ProSe Function via the PC3 reference point. Upon successful authorization, the ProSe Function may assign one or more PDUIDs to the UE, along with associated parameters like a validity timer and discovery filters. The PDUID is then used by the UE's ProSe Protocol stack to formulate discovery messages. At the physical layer, these messages are sent using specific physical channels and resources allocated for sidelink communication (e.g., in LTE's SL-DCH or NR's SL-SCH). The receiving UE's ProSe application layer processes the received PDUID, often applying discovery filters provided by the ProSe Function to determine if the discovered UE is of interest.
The role of the PDUID in the network is to enable secure, private, and efficient device discovery for Proximity Services. It acts as a temporary alias, preventing long-term tracking of a UE based on its discovery broadcasts. The ProSe Function can map the PDUID back to the real UE identity for network-assisted discovery or for charging purposes. In public safety scenarios, where network coverage may be absent (Out-of-Coverage), UEs may use pre-configured or self-assigned PDUIDs. The identifier is thus a key enabler for a wide range of applications from social networking (finding friends nearby) to critical communications for first responders, forming the initial step before establishing a direct ProSe Communication session.
Purpose & Motivation
PDUID was created to address the specific need for a privacy-preserving and network-managed identifier for direct device discovery in LTE and 5G networks. Prior to ProSe standardization, device-to-device discovery relied on ad-hoc methods like Bluetooth or Wi-Fi Direct, which lacked integration with cellular network security, subscription management, and wide-area coordination. There was no standardized way for a cellular network to facilitate discovery between its subscribers while maintaining control and privacy. The PDUID solves this by providing a temporary, network-issued handle.
The historical context is the 3GPP's work on Proximity Services, initiated to support public safety requirements and commercial D2D applications. A core challenge was enabling discovery without constantly exposing permanent, trackable identifiers over the air. The PDUID, along with the ProSe Function, was designed to solve this privacy problem. It also addresses scalability; the network can allocate different PDUIDs for different discovery purposes (e.g., different apps on the same UE) and manage their lifecycle, preventing identifier exhaustion or conflict.
Furthermore, PDUID enables network-assisted discovery optimization. By controlling the assignment, the network can help UEs filter irrelevant discovery messages, saving battery life and radio resources. It is a foundational element that allows the cellular network to extend its services to direct device-to-device links, creating a hybrid communication paradigm. This was a significant evolution from traditional cellular architectures where all communication was necessarily routed through a base station, enabling new low-latency and off-grid use cases.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (548 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-13, normative work from Rel-15.
In Release 15, the PDUID function was extended to support WLAN-based ProSe Direct Discovery as an alternative technology, introducing updates to the Announce, Monitor, and Match report procedures for both open and restricted discovery models. This included specific authorisation and semantic updates for WLAN Direct Discovery, alongside the introduction of ProSe Per-Packet Priority and Reliability parameters for enhanced ProSe QoS descriptions. The release also provided clarifications and corrections to procedures for ProSe communication and PCF discovery.
- 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 to ProSe Service Authorisation for WLAN Direct Discovery TS 24.334CR0298
- Updates to Announce request procedure for open WLAN based ProSe direct discovery TS 24.334CR0299
- Updates to Announce request procedure for restricted WLAN based ProSe direct discovery model A TS 24.334CR0300
+ 16 more changes
In Release 16, a specific correction was made to the "open ProSe direct discovery" procedure. This update addressed the technical implementation of ProSe Direct Discovery, which uses ProSe Application Codes over the PC5 interface. The change ensured the proper functioning of the discovery process where UEs announce or monitor for proximity using these codes.
- DNN Replacement as PCF discovery factor for the AMF TS 29.513CR0122
- Update of PCF discovery by the AF for eSBA TS 29.513CR0142
- Correction of PCF discovery via BSF to consider eSBA binding principles TS 23.503CR0326
- Correction of CHF discovery to consider eSBA binding principles TS 23.503CR0376
- Correction of PCF discovery via BSF to consider eSBA binding principles - AF/NEF/SCP re-selection functionality (23.503) TS 23.503CR0385
- Correct open ProSe direct discovery TS 29.343CR0031
+ 1 more changes
In Release 17, enhancements for the PDUID function included its reporting change by the PCF and its integration into new procedures for 5G ProSe UE-to-Network Relay discovery, such as being included in the relay discovery solicitation message. Furthermore, the PDUID's role was extended within security procedures, including the direct link security mode control and re-keying procedures for UE-to-network relay. These updates were part of broader ProSe enhancements like DRX support for direct discovery and the introduction of a ProSe application traffic descriptor.
- Identifiers for Layer-2 UE-to-Network Relay discovery TS 23.304CR0020
- DRX support for direct discovery and communication and L3 relay TS 23.304CR0024
- BSF enhancement on PCF Discovery for dynamic AM policy TS 23.503CR0506
- ProSe Policy TS 23.503CR0533
- URSP enhancement for the 5G ProSe UE-to-Network Relay support TS 23.503CR0569
- Reporting Change of PDUID by the PCF TS 23.503CR0573
+ 129 more changes
In Release 18, the PDUID function was enhanced to support integrated discovery within UE-to-UE Relay operations, as indicated by the new work item "Identifiers for Discovery integrated into PC5 unicast link establishment." This introduced new identifier structures and procedures specifically for relay discovery, enabling a UE to discover potential relay UEs using ProSe Direct Discovery mechanisms over the PC5 interface.
- 5G ProSe Communication via U2U Relay TS 23.304CR0125
- UE-to-UE Relay Discovery TS 23.304CR0131
- 5G ProSe UE-to-UE Relay reference architecture TS 23.304CR0144
- 5G ProSe UE-to-UE Relay reselection TS 23.304CR0148
- UE-to-UE Relay with Integrated Discovery TS 23.304CR0150
- 5.2.X 5G ProSe UE-to-UE Relay Discovery TS 23.304CR0155
+ 197 more changes
In Release 19, the PDUID function was enhanced to support ProSe operations within Standalone Non-Public Networks (SNPNs) and for multi-hop relay scenarios. This included updates to the 5G ProSe Discoverer request procedure and the announce request procedure for restricted discovery Model A to function within SNPNs. Furthermore, new identifier specifications were introduced to support 5G ProSe Multi-hop UE-to-UE Relay for non-IP PDU types.
- ProSe support for NPNs TS 23.304CR0436
- Authorization and Provisioning for 5G ProSe multi-hop Relays TS 23.304CR0444
- Enhancement of 5G ProSe Capability for multi-hop Relays TS 23.304CR0445
- Functional Entities enhancements for 5G ProSe multi-hop Relays TS 23.304CR0448
- Update on ProSe U2U Multihop Relay for non-IP PDU TS 23.304CR0450
- Support ProSe U2N Multihop Relay TS 23.304CR0451
+ 174 more changes
In Release 20, the PDUID function was enhanced to support new 5G ProSe capabilities for multi-hop UE-to-UE relay and MANET multicast for IP-based communication. These enhancements extended the ProSe architecture to facilitate more complex, multi-hop discovery and communication paths between UEs. This allowed ProSe-enabled UEs to establish and utilize relay chains for both direct discovery and communication, building upon the existing ProSe Direct Discovery and Communication procedures.
- 5G ProSe Enhancements to support MANET multicast for IP based 5G ProSe Layer-3 Multi-hop UE-to-UE Relay TS 23.304CR0565
Explore further
Broader topics and technologies where PDUID plays a role.
Defining Specifications
3GPP specifications that define or reference PDUID, 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 23.304 vk00 | 5G Proximity Services (ProSe) Stage 2 | Rel-20 |
| TS 23.503 vk00 | 5G Policy and Charging Control Framework | Rel-20 |
| TS 24.334 vj00 | ProSe Protocols and Procedures | Rel-19 |
| TS 24.554 vj40 | 5G Proximity Services (ProSe) Protocols | 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 29.513 vj40 | 5G PCC Signalling Flows & QoS Mapping | Rel-19 |
| TS 29.534 vj20 | 5G Access & Mobility Policy Authorization Service | Rel-19 |
| TS 29.555 vj10 | 5G Direct Discovery Name Management Services | Rel-19 |
| TS 29.557 vj20 | 5G AF ProSe Service Stage 3 Protocol | Rel-19 |
| TS 29.559 vj40 | 5G PKMF Service Based Interface Stage 3 | Rel-19 |