User Info ID (ProSe Discovery User Information Identifier)

Description

The User Info ID is an identifier defined in 3GPP Release 19 for use in 5G Proximity Services (ProSe) discovery procedures. It is configured for Model A and Model B Group Member Discovery, 5G ProSe UE-to-Network Relay Discovery, and 5G ProSe UE-to-UE Relay Discovery. These discovery models are the standardized mechanisms by which ProSe-enabled UEs find each other, find group members, or find relay UEs that can extend their connectivity. The User Info ID serves as a piece of user-related information that is carried or matched during these discovery procedures to help identify or filter the appropriate discovery targets.

The identifier can be used for either public safety or commercial applications. Its configuration is governed by the policy of the Home Public Land Mobile Network (HPLMN) or is allocated by the ProSe application server. This dual-source allocation reflects the two deployment models for ProSe: operator-controlled (where the HPLMN policy dictates the identifier values and usage) and application-controlled (where an external ProSe application server provisions the identifier). The flexibility allows ProSe to serve both mission-critical public safety communications and commercial proximity-based services.

In the context of discovery, the User Info ID is one of several parameters that a UE can include in discovery messages or use to filter incoming discovery announcements and responses. For Model A discovery, a UE announces or queries using discovery parameters that may include the User Info ID; for Model B, a UE sends a request and another UE responds, with the User Info ID helping to match the request to the correct responder. For relay discovery, the User Info ID can help identify the relay or the remote UE in the discovery exchange. This enables more precise and context-aware discovery than would be possible with only low-level identifiers.

A notable characteristic of the User Info ID is that the definition of its values is explicitly out of scope of the 3GPP specification. This means 3GPP defines the identifier's role, configuration sources, and usage in discovery procedures, but does not mandate a particular format, encoding, or value space. Instead, the value semantics are left to the HPLMN policy or the ProSe application server. This design choice gives operators and application providers the freedom to define identifiers that suit their specific service requirements, while ensuring interoperability at the procedural level.

The User Info ID is specified in 3GPP TS 23.303 (Proximity-based services; Stage 2) and TS 23.304 (Proximity based Services in 5G System; Stage 2). It was introduced in Release 19 and carried over unchanged into Release 20. Its introduction reflects the ongoing evolution of ProSe from LTE-based proximity services toward comprehensive 5G ProSe capabilities, including relay support that is essential for extending 5G coverage to UEs outside network coverage.

Purpose & Motivation

The User Info ID was created to support the enhanced discovery requirements of 5G ProSe, particularly for group member discovery and relay discovery. As ProSe evolved from its LTE origins into the 5G System, the discovery procedures became more sophisticated, supporting Model A and Model B discovery, UE-to-Network relaying, and UE-to-UE relaying. These procedures needed a flexible, user-related identifier that could be used to match discovery requests with the right targets, beyond what low-level identifiers could provide.

Previous ProSe discovery mechanisms in LTE relied on a more limited set of identifiers and discovery parameters. With 5G ProSe, the scope expanded to include relay discovery for coverage extension and more granular group-based discovery. The User Info ID addresses this by providing a configurable identifier that can carry application- or operator-defined user information relevant to discovery. This allows, for example, a public safety user to discover only members of their own group, or a commercial user to discover a relay that matches their service profile.

By leaving the value definition out of scope, 3GPP ensured that the identifier could adapt to diverse deployment scenarios without requiring specification changes. The HPLMN policy or ProSe application server can define values appropriate to the service, whether for mission-critical push-to-talk groups, commercial proximity marketing, or relay selection. This balance between standardized procedure and flexible value space is what makes the User Info ID a practical tool for 5G ProSe deployments.