Description
The Non-3GPP Connection (N3C) is a protocol sublayer introduced in the 5G New Radio (NR) user plane protocol architecture, operating between the Service Data Adaptation Protocol (SDAP)/Packet Data Convergence Protocol (PDCP) layers and the underlying non-3GPP access technology's link layer. It functions as an adaptation layer, allowing the upper layers of the 5G radio protocol stack (specifically PDCP) to operate independently of the lower-layer characteristics of a non-3GPP radio link. The N3C entity resides in both the User Equipment (UE) and the network side (e.g., in a gNB-CU or a dedicated node supporting multi-RAT). Its primary role is to map PDCP Protocol Data Units (PDUs) onto the service data units of the non-3GPP link layer, handling aspects like segmentation, reassembly, and in-sequence delivery if the non-3GPP link does not natively provide these services.
Architecturally, N3C is part of the broader Multi-Radio Dual Connectivity (MR-DC) and Access Traffic Steering, Switching, and Splitting (ATSSS) framework. When a UE is configured with a non-3GPP connection as a secondary cell group or a path for traffic splitting, the gNB uses the N3C layer to manage the data flow over that link. The N3C layer may add its own header to the PDCP PDU, containing sequence numbers and length indicators necessary for the adaptation function. This enables the PDCP layer to maintain its core functions—such as ciphering, integrity protection, and duplicate detection—consistently, whether the underlying physical transport is 5G NR, LTE, or a non-3GPP technology. The specifications (e.g., TS 38.322, 38.323) define the precise procedures for N3C establishment, reconfiguration, and release, as well as its interactions with the RRC layer for control.
From an operational perspective, the N3C layer abstracts the vagaries of the non-3GPP link, presenting a more reliable and ordered data pipe to the PDCP layer. This is crucial for maintaining the end-to-end QoS and reliability expectations of 5G services when using heterogeneous access. For instance, if the non-3GPP link is a high-latency satellite connection, the N3C layer's buffering and sequencing mechanisms help mitigate the impact on the overall data flow. By standardizing this adaptation layer, 3GPP allows for the incorporation of a wide variety of non-3GPP radios into the 5G RAN framework in a clean, modular way, without requiring changes to the core PDCP protocol for each new access type.
Purpose & Motivation
The N3C was developed to address the growing need for deep, layer-2 integration of non-3GPP access technologies into the 5G RAN, going beyond the core network integration provided by N3AN. Previous approaches, like LTE-WLAN Aggregation (LWA), required specific adaptation and were limited in scope. The 5G vision of truly integrated multi-RAT operation, especially for ATSSS, demanded a more generic and flexible solution that could work with various non-3GPP links (e.g., Wi-Fi 6/7, satellite, private networks) as if they were native 3GPP radio links from the upper-layer perspective.
Its purpose is to solve the technical problem of protocol stack mismatch. Non-3GPP technologies have their own MAC and PHY layers with different characteristics (frame sizes, reliability mechanisms, absence of in-order delivery). N3C provides the necessary 'glue' to allow the 5G NR PDCP layer, which is designed for the 3GPP MAC/PHY, to function correctly over these disparate links. This enables advanced RAN features like packet duplication for ultra-reliability or intelligent traffic splitting across 3GPP and non-3GPP paths to be implemented seamlessly. The creation of N3C is motivated by the drive towards network convergence at the radio level, allowing operators to build more robust, high-capacity, and efficient radio networks by harnessing the best characteristics of all available wireless technologies in a tightly coordinated manner.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (76 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the specification introduced the **PDCP suspend procedure** and made numerous corrections and clarifications to PDCP functionality, including aspects of PDCP duplication configuration, re-establishment, and status reporting. These changes also involved the handling of the PDCP sequence number during data forwarding and its association with RLC for radio bearers configured with PDCP duplication. Furthermore, the release included updates on RRC connection release triggered by upper layers and security for RRC connection release.
- Introduction of PDCP duplication TS 38.323CR0009
- Clarification of PDCP functionality TS 38.300CR0053
- Correction of handling of PDCP SN during Data Forwarding TS 38.300CR0150
- Introduction of PDCP duplication TS 38.321CR0185
- Corrections to PDCP specification TS 38.323CR0002
- Corrections to PDCP specification TS 38.323CR0006
+ 22 more changes
In Release 16, enhancements for Non-3GPP Connections (N3C) included support for PDCP duplication with more than two entities and introduced a release with redirect for connection resume procedures triggered by NAS. The release also provided clarifications and corrections for PDCP duplication, particularly for Industrial IoT (IIoT) and NR-Dual Connectivity (NR-DC) scenarios, and addressed handling during RRC reconfiguration and re-establishment.
- PDCP duplication with more than 2 entities for F1 stage 2 TS 38.470CR0067
- Stage-2 CR for clarifications of Rel-16 PDCP Duplication TS 38.300CR0263
- Release with Redirect for connection resume triggered by NAS TS 38.300CR0338
- PDCP SN issue for EPC to 5GC handover TS 38.300CR0347
- PDCP security issue about duplicate detection TS 38.323CR0032
- NR PDCP corrections for NR IIOT TS 38.323CR0049
+ 13 more changes
In Release 17, enhancements were made to PDCP for Non-3GPP connections, specifically introducing support of UP IP for EPC connected architectures using NR PDCP. Furthermore, the release included several corrections and clarifications for PDCP operation in relay scenarios, such as for SL Relay and L2 U2N Relay, and for Multicast Broadcast Services (MBS). These updates also addressed PDCP initialization for MRB and handling during PC5 connection release in RRC re-establishment.
- Introducing support of UP IP for EPC connected architectures using NR PDCP TS 38.323CR0085
- Introducing support of UP IP for EPC connected architectures using NR PDCP TS 38.331CR2904
- Correction on PDCP for SL relay TS 38.323CR0093
- PDCP Corrections for MBS TS 38.323CR0096
- Correction on PDCP for L2 U2N Relay TS 38.323CR0097
- MBS corrections for PDCP TS 38.323CR0102
+ 7 more changes
In Release 18, the enhancements for the Non-3GPP Connection (N3C) function primarily involved corrections and clarifications to Packet Data Convergence Protocol (PDCP) duplication procedures when operating over multi-path relay links, including those using sidelink relay or N3C indirect paths. The release introduced specific handling for PDCP Sequence Number gap reporting and made corrections related to the RLC layer for multi-path relay with N3C. These updates also included corrections for the delay critical indication from PDCP to RLC and for PDCP packet discard in the context of multicast/broadcast service path updates.
- Introduction of NR sidelink PDCP duplication in TS 38.323 TS 38.323CR0126
- Correction to PDCP duplication description for L2 MP using SL relay or N3C indirect path TS 38.300CR0989
- RLC correction for multi-path relay with N3C TS 38.322CR0063
- PDCP SN gap reporting TS 38.323CR0139
- Correction for Delay Critical Indication from PDCP to RLC TS 38.323CR0144
- PDCP SN Gap report Corrections TS 38.323CR0147
+ 6 more changes
In Release 19, enhancements and corrections were introduced for the Packet Data Convergence Protocol (PDCP) layer, specifically targeting Extended Reality (XR) traffic. This included corrections to the PDCP configuration for Signalling Radio Bearers 4 and 5 (SRB4 and SRB5). Additionally, a Stage-2 correction was made for the Xn connection management related to Wireless Access Backhaul (WAB).
Explore further
Broader topics and technologies where N3C plays a role.
Defining Specifications
3GPP specifications that define or reference N3C, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.321 vj00 | NR MAC Protocol Specification | Rel-19 |
| TS 38.322 vj00 | NR Radio Link Control (RLC) Protocol | 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 38.401 vj10 | NG-RAN Architecture Specification | Rel-19 |
| TS 38.470 vj10 | F1 Interface Introduction | Rel-19 |
| TS 38.473 vj10 | 5G F1 Application Protocol (F1AP) | Rel-19 |