Description
A Data Radio Bearer (DRB) is a fundamental construct in the radio protocol stack of LTE (E-UTRAN) and 5G NR (NG-RAN). It represents a logical connection or "pipe" over the air interface (Uu) specifically dedicated to transporting user plane data for a particular service or application flow. Each DRB is configured with a specific set of protocol layers and parameters that define how data is processed, protected, and transmitted between the UE and the Radio Access Network (RAN) node—the eNodeB in LTE or the gNB in 5G NR. The DRB is the point where QoS differentiation is physically enforced on the radio link.
The establishment and configuration of a DRB are controlled by the RAN node via RRC (Radio Resource Control) signaling. When a UE initiates a data session (a PDU Session in 5G or an EPS Bearer in LTE), the Core Network (5GC or EPC) requests the setup of a QoS flow (5G) or an EPS bearer with specific QoS characteristics (QCI/5QI, ARP, GBR, etc.). The RAN node translates this request into the configuration of one or more DRBs. A key function is QoS mapping: the RAN maps multiple QoS flows (in 5G) or Service Data Flows (in LTE) that share similar QoS requirements onto a single DRB. Each DRB is associated with a specific 5QI/QCI value, which dictates its treatment in terms of scheduling priority, packet delay budget, and error loss rate.
Technically, a DRB is realized through the configuration of the Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), and Medium Access Control (MAC) layers. PDCP provides header compression, ciphering, and integrity protection. RLC handles segmentation, concatenation, and error correction through ARQ. MAC performs scheduling, logical channel prioritization, and multiplexing of multiple DRBs (and SRBs) onto the shared transport channels. The physical layer (PHY) then transmits the data over the air. The DRB is identified by a DRB ID, and its lifecycle—setup, modification (e.g., for handover or QoS change), and release—is managed dynamically to match user data activity and mobility events, ensuring efficient use of radio resources while meeting the required service quality.
Purpose & Motivation
The DRB concept was introduced with LTE in 3GPP Release 8 to provide a flexible and efficient mechanism for delivering IP-based services with guaranteed Quality of Service (QoS) over the radio link. It addressed limitations of previous 3G systems where the mapping between core network bearers and radio channels was less flexible. The primary problem it solves is the efficient translation of core network QoS requirements into concrete radio resource allocation and treatment.
In pre-LTE systems, radio bearers were often tied more rigidly to specific services. The DRB, coupled with the QCI (QoS Class Identifier) framework, created a standardized, granular way to apply different packet forwarding behaviors (scheduling, queue management, etc.) based on service type (e.g., voice, video, web browsing). This enables network operators to prioritize latency-sensitive traffic like VoIP over best-effort traffic, improving user experience. Furthermore, the DRB's dynamic nature allows the network to establish bearers on-demand as services are activated, conserving radio resources when not needed. In 5G NR, the purpose evolved to support an even more flexible QoS model with QoS Flows. The DRB acts as the RAN's container for these flows, allowing efficient aggregation and reducing signaling overhead. It is a critical enabler for network slicing at the radio level, as different slices can be supported by different sets of DRBs with distinct QoS profiles, isolating performance between slices.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (60 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-8, normative work from Rel-15.
In Release 15, key DRB enhancements included the introduction of PDCP duplication for increased reliability and the PDCP suspend procedure, with specific operations clarified for sidelink and over the E1 interface. The release also enabled an increased number of E-UTRAN data bearers and introduced corrections and clarifications to PDCP structure, re-establishment, and transmission procedures.
- Introduction of New Radio Access Technology in TS 36.300 TS 36.300CR0998
- Enabling MBMS Bearer Event Notification TS 36.300CR1138
- Introduction of increased number of E-UTRAN data bearers TS 36.321CR1286
- Introduction of PDCP duplication TS 38.323CR0009
- Clarification to Sidelink PDCP Duplication TS 36.321CR1396
- CR on PDCP duplication related operations in sidelink LCP procedure and resource reselection procedure TS 36.321CR1432
+ 17 more changes
In Release 16, the DRB function was enhanced with the introduction of the EHC (Evolved Header Compression) feature for LTE PDCP and support for PDCP duplication with more than two entities for both the E1 and F1 interfaces. The release also introduced the UE Radio Capability Mapping procedure for EN-DC and included various corrections addressing PDCP re-establishment, security, and operation for both LTE and NR, particularly concerning IIoT (Industrial IoT) scenarios.
- Introducing EHC in LTE PDCP TS 36.323CR0278
- PDCP duplication with more than 2 entities for E1 stage 2 TS 38.460CR0039
- PDCP duplication with more than 2 entities for F1 stage 2 TS 38.470CR0067
- Introducing UE Radio Capability Mapping procedure for EN-DC TS 36.300CR1314
- LTE PDCP corrections for NR IIOT TS 36.323CR0286
- Correction for PDCP status report TS 36.323CR0287
+ 11 more changes
In Release 17, enhancements for Data Radio Bearers (DRBs) focused on support for new architectural functions and protocol corrections. Key developments included introducing support for User Plane IP in EPC-connected architectures using NR PDCP and providing specific corrections for PDCP in the context of Layer 2 UE-to-Network (L2 U2N) Relay, SideLink Relay (SL relay), and NR Multicast/Broadcast Service (MBS). These updates also encompassed clarifications and corrections for PDCP control PDUs, sequence number settings, and entity establishment procedures for various bearer types.
- Introducing support of UP IP for EPC connected architectures using NR PDCP TS 36.300CR1353
- Introducing support of UP IP for EPC connected architectures using NR PDCP TS 38.323CR0085
- Correction on PDCP Control PDU for UDC feedback TS 36.323CR0304
- Corrections on E1 bearer context management function for NR MBS TS 37.480CR0002
- Correction on PDCP for SL relay TS 38.323CR0093
- PDCP Corrections for MBS TS 38.323CR0096
+ 8 more changes
In Release 18, key enhancements for the DRB function included the introduction of NR sidelink PDCP duplication and the specification of PDCP SN gap reporting. These were complemented by necessary corrections to the PDCP SN gap report procedure and to the handling of the Delay Critical Indication from PDCP to RLC.
In Release 19, the primary enhancements for the Data Radio Bearer (DRB) function were focused on introducing and correcting Packet Data Convergence Protocol (PDCP) specifications for Extended Reality (XR) services. These changes aimed to optimize the DRB's performance for XR traffic, which is part of the broader Evolved Packet System bearer management. The work involved specific PDCP procedure enhancements to better support the low-latency and high-reliability requirements of XR applications over the E-UTRAN radio access bearer.
Explore further
Broader topics and technologies where DRB plays a role.
Defining Specifications
3GPP specifications that define or reference DRB, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 26.114 vj10 | IMS Multimedia Telephony Media Handling | Rel-19 |
| TR 33.853 vh00 | Study on User Plane Integrity Protection | Rel-17 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |
| TS 36.314 vj00 | E-UTRA Radio Measurements Specification | Rel-19 |
| TS 36.321 vj00 | E-UTRA MAC Protocol Specification | Rel-19 |
| TS 36.323 vj00 | PDCP Protocol Specification | Rel-19 |
| TS 36.360 vj00 | LTE-WLAN Aggregation Adaptation Protocol | Rel-19 |
| TS 36.361 vj00 | LWIP Encapsulation Protocol Specification | Rel-19 |
| TS 36.509 vh40 | EPC Special UE Conformance Testing Functions | Rel-17 |
| TS 37.470 vj00 | W1 Interface Introduction for ng-eNB | Rel-19 |
| TS 37.480 vj00 | E1 Interface General Aspects and Principles | Rel-19 |
| TR 37.901 vf10 | UE Application Layer Data Throughput Performance | Rel-15 |
| TS 38.323 vj00 | Packet Data Convergence Protocol (PDCP) | Rel-19 |
| TS 38.460 vj00 | E1 Interface General Aspects and Principles | Rel-19 |
| TS 38.470 vj10 | F1 Interface Introduction | Rel-19 |