Description
The E-UTRAN Radio Access Bearer (E-RAB) is a fundamental concept in the Evolved Packet System (EPS) architecture, representing a logical transport path for user plane data with specific Quality of Service (QoS) characteristics. It is established between the User Equipment (UE) and the core network's Serving Gateway (S-GW) for the EPS, or the User Plane Function (UPF) in 5GC. An E-RAB is uniquely identified by an E-RAB ID and is essentially the concatenation of two underlying bearers: the Radio Bearer (RB) across the Uu (air) interface between the UE and the eNodeB/gNB, and the S1 bearer (or N3 bearer in 5G) across the S1-U (or N3) interface between the eNodeB/gNB and the S-GW/UPF. The core network, specifically the MME (or AMF in 5G), is responsible for the establishment, modification, and release of E-RABs based on session management requests, typically triggered by a PDN connection establishment or a dedicated bearer activation procedure initiated by the Policy and Charging Rules Function (PCRF) or Policy Control Function (PCF). The eNodeB/gNB is responsible for the radio resource management aspect, mapping the QoS requirements of the E-RAB (e.g., QCI, ARP, GBR, MBR) onto appropriate radio configurations, scheduling algorithms, and link layer protocols to meet the required performance. The E-RAB's lifecycle is tightly coupled with the UE's mobility; during handover procedures, E-RABs are managed to ensure service continuity, with the target node preparing resources before the source node releases them. This bearer-centric architecture provides a clear separation between control and user planes and enables efficient, QoS-aware traffic handling across the entire radio access and core network path.
Purpose & Motivation
The E-RAB was introduced with LTE in 3GPP Release 8 to provide a streamlined, all-IP bearer model for packet-switched services, replacing the more complex and circuit-switched oriented bearer concepts of 2G/3G (like Radio Access Bearers and Radio Bearers in UMTS). Its primary purpose is to establish a clear, QoS-guaranteed pipe for user data traffic that spans the radio access network and connects seamlessly to the core network's transport tunnels. This solves the problem of providing consistent, end-to-end service quality for diverse applications (e.g., VoIP, video streaming, web browsing) over a shared packet infrastructure. By defining the E-RAB as the key subscriber- and service-specific data path, the network can apply precise traffic management, prioritization, and charging policies. The architecture also decouples the radio-specific configurations from the core network transport, simplifying network evolution and allowing for independent optimization of the radio and transport layers. The E-RAB concept is central to the EPS's goal of achieving higher data rates, lower latency, and more efficient resource utilization compared to previous 3GPP systems.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (72 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, the primary new introduction for the E-RAB function was the support for an increased number of EPS bearers, specifically enabling the use of up to 15 bearers per UE. This required corresponding UE capability signaling and network support, including modifications for bearer requests during Tracking Area Update (TAU) procedures. The release also introduced clarifications and corrections for E-RAB level QoS parameter handling and procedures related to bearer management in EN-DC (E-UTRA-NR Dual Connectivity) scenarios.
- Per EPS bearer, RAN selection of DC (or non-DC) usage TS 23.401CR3258
- Feature definition for supporting 15 EPS bearers TS 23.401CR3396
- UE Capability for supporting 15 EPS bearers TS 23.401CR3419
- Network support for increased number of bearers TS 23.401CR3420
- Introduction of New Radio Access Technology in TS 36.300 TS 36.300CR0998
- Enabling MBMS Bearer Event Notification TS 36.300CR1138
+ 24 more changes
In Release 16, the E-RAB function was enhanced to support a new **Ethernet Type Bearer**, extending dedicated bearer establishment for Ethernet traffic in the EPC. The release also introduced the **UE Radio Capability ID** into signalling procedures to optimize radio capability handling and added the **PSCell ID** parameter to the E-RAB modification procedure for further mobility enhancements.
- Dedicated Bearers for Ethernet in EPC TS 23.401CR3498
- Adds UE Radio Capability ID in signalling procedures TS 23.401CR3503
- Dedicated Bearers for Ethernet in EPC - IOPS / LIPA / SIPTO@LN aspects TS 23.401CR3508
- Add new Use case related to QCI1 E-RAB establishment via Initial Context Setup into A2 TS 32.425CR0199
- Introduction of even further mobility enhancement in E-UTRAN TS 36.300CR1270
- Support of Ethernet Type Bearer TS 36.413CR1691
+ 24 more changes
In Release 17, specific enhancements were made to the E-RAB function, including the introduction of a new measurement for normally released QCI1 E-RABs initiated by the MME under Radio Link Failure conditions. Furthermore, clarifications and corrections were provided for the handling of UE radio capabilities for paging and the MME's handling of EPS bearer QoS parameters.
- Add new measurement related to number of the normally released calls (QCI1 E-RAB) initiated by MME in RLF detected conditions TS 32.425CR0201
- UE Security Capabilities signaling in E-UTRAN [UE_Sec_Caps] TS 36.300CR1359
- Correction to MME handling EPS bearer QoS TS 23.401CR3670
- Clarification on handling of UE radio capability for paging when MME changes TS 23.401CR3687
- Handling of radio capabilities across TN and NTN IoT TS 23.401CR3707
- Handling of UE Radio Capability for Paging TS 23.401CR3644
+ 1 more changes
In Release 18, the key update for the E-RAB function was the introduction of a configurable "Report Amount" parameter for M4, M5, M6, and M7 measurements specifically for E-UTRAN within the Minimization of Drive Tests (MDT) framework. This enhancement provides finer control over the volume of measurement reports collected by the network for radio resource management and optimization. The release also included a correction to the specification reference for the UE radio capability update procedure.
- Introducing Report Amount for M4, M5, M6, M7 measurements for E-UTRAN [ReportAmount_MDT_E-UTRAN] TS 36.413CR1876
- Introducing Report Amount for M4, M5, M6, M7 measurements for E-UTRAN [ReportAmount_MDT_E-UTRAN] TS 36.423CR1688
- Correcting the reference for UE radio capability update procedure TS 23.401CR3746
In Release 19, the key update for the E-UTRAN Radio Access Bearer function was the introduction of NB-IoT satellite information in E-UTRAN, specifically enabling E-UTRAN-to-NBIoTNTN functionality. This enhancement allows the system to incorporate satellite access network details for Narrowband IoT operations within the E-UTRAN context. Additionally, a correction was made to the UE Radio Capability Retrieval procedure to ensure accurate bearer management.
Explore further
Broader topics and technologies where E-RAB plays a role.
Defining Specifications
3GPP specifications that define or reference E-RAB, 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 23.401 vj50 | Evolved Packet System (EPS) Stage 2 Description | Rel-19 |
| TS 32.425 vj00 | E-UTRAN Performance Measurements | Rel-19 |
| TS 32.450 vj00 | E-UTRAN Key Performance Indicators (KPI) Definitions | Rel-19 |
| TS 32.451 vj00 | KPI Requirements for E-UTRAN | Rel-19 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |
| TS 36.401 vj00 | E-UTRAN Overall Architecture Description | Rel-19 |
| TS 36.410 vj00 | S1 Interface: General Aspects and Principles | Rel-19 |
| TS 36.413 vj10 | S1 Application Protocol (S1AP) | Rel-19 |
| TS 36.414 vj00 | S1 Interface User Plane Transport | Rel-19 |
| TS 36.420 vj00 | X2 Interface Introduction for E-UTRAN | Rel-19 |
| TS 36.423 vj10 | X2 Application Protocol (X2AP) Specification | Rel-19 |
| TS 36.424 vj00 | X2 Interface User Plane Transport Protocols | Rel-19 |
| TS 36.425 vj00 | X2 User Plane Protocol for Dual Connectivity | Rel-19 |
| TS 36.444 vj00 | M3AP Protocol Specification for M3 Interface | Rel-19 |
| TS 36.463 vj00 | XwAP Protocol Specification | Rel-19 |
| TS 38.423 vj10 | Xn Application Protocol (XnAP) specification | Rel-19 |