Description
The 5G ProSe UE-to-Network Relay is a critical component in the 3GPP Release 19 ProSe architecture. It is a 5G ProSe-enabled User Equipment (UE) that acts as a relay between one or more 5G ProSe Remote UEs and the 5G core network (5GC). Its primary function is to extend network coverage to UEs that are out of direct coverage or to improve service reliability by providing an alternative path. The relay UE connects to the network via the Uu interface (standard cellular link) and communicates with Remote UEs via the PC5 interface (sidelink). It forwards user plane and control plane traffic between the Remote UEs and the network, effectively acting as a Layer-3 router or a transparent IP relay.
The Relay UE performs several key functions: it discovers and authenticates with the network, advertises its relay capability, and allows Remote UEs to discover and connect to it. It maintains a ProSe context and manages the relayed connections, including IP address allocation (if acting as a DHCP server or using prefix delegation) and QoS enforcement. It also ensures security by establishing a secure PC5 link with each Remote UE and encapsulating their traffic towards the network. The relay can support multiple Remote UEs simultaneously, multiplexing their traffic over its Uu connection.
Architecturally, the Relay UE interacts with the 5GC through the N3 interface (for user plane) and N2 interface (for control plane) via the RAN. The 5GC identifies the relayed traffic and applies appropriate policies. The Relay UE may be mobile, and it can hand over between cells while maintaining the relayed connections. It also supports relay selection and reselection for Remote UEs to ensure continuous connectivity. In Release 19, the Relay UE is defined in TS 23.304, with protocol aspects in TS 24.554 and management in TS 32.277.
The Relay UE can operate in both in-coverage and out-of-coverage scenarios (though it must have network coverage itself to relay). It can be a dedicated relay or a UE that also serves its own applications. For public safety, the Relay UE may be a vehicle or a handheld device carried by a first responder. For commercial use, it could be a smartphone sharing its connection with nearby devices. The Relay UE's capabilities include supporting IP, Ethernet, and unstructured data, and it can handle multiple Remote UEs with different QoS requirements.
In summary, the 5G ProSe UE-to-Network Relay is essential for extending 5G network reach and enabling critical communications in areas without direct coverage, forming a cornerstone of the 5G ProSe feature set.
Purpose & Motivation
The 5G ProSe UE-to-Network Relay was created to address the need for extended network coverage and reliable communication in scenarios where direct network access is unavailable or unreliable. Traditional cellular networks rely on direct UE-to-base-station links, which can be compromised in disasters, remote areas, or indoor environments. The relay concept allows a UE with network connectivity to share it with other UEs, effectively creating a mesh-like extension. This is particularly important for public safety (e.g., police, fire, medical) where communication must continue even when infrastructure is damaged. It also supports commercial use cases like coverage extension for IoT devices or wearables. By introducing this relay in Release 19, 3GPP provides a standardized, interoperable solution that leverages 5G's high data rates and low latency, overcoming the limitations of earlier ProSe (LTE) relays which had less flexibility and performance.
What changed in its specifications
The latest release-to-release comparison of specifications that define 5G ProSe UE-to-Network Relay. Each summary describes the whole specification, not only this term.
Rel-19 adds multi-hop NR sidelink relaying through Intermediate UE-to-Network Relay entities, with discovery, QoS and link handling clauses. It also adds path switching between direct and indirect paths via Layer-2 UE-to-Network Relay, and ProSe support for SNPNs and CAG use in PNI-NPNs.
Full comparison in TS 23.304 →Rel-19 adds multi-hop NR sidelink UE-to-network relay with new direct link establishment procedures and discovery IEs. It extends 5G ProSe to SNPNs, adding SNPN identification, authorisation checks, and PC5 relay indications. It also adds multi-hop relay configuration over PC5 and charging-related abbreviations and content type values.
Full comparison in TS 24.554 →Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (3 CRs across 1 releases). Complements the general historical overview above with the evidence-based evolution of this function.
- Update on 5G ProSe UE-to-Network Relay Discovery additional parameter to support 5G ProSe in SNPN TS 24.554CR0665
- Updates to Common identifiers for 5G ProSe UE-to-Network Relay TS 23.304CR0545
- Resolving the EN related to receiving cause value #15 "security procedure failure of 5G ProSe UE-to-network relay" for multi-hop UE-to-network relay TS 24.554CR0854
Defining Specifications
3GPP specifications that define or reference 5G ProSe UE-to-Network Relay, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.304 vk10 | 5G Proximity Services (ProSe) Stage 2 | Rel-20 read |
| TS 24.554 vk10 | 5G ProSe Protocols and Procedures | Rel-20 read |
| TS 32.277 vj20 | Charging Management for Proximity Services (ProSe) | Rel-19 read |