Description
Integrated Access and Backhaul (IAB) is a key architectural innovation in 5G New Radio (NR) that allows a single radio node to simultaneously function as an access point for User Equipment (UE) and as a relay node for backhaul traffic. An IAB node consists of two logical components: a Mobile Termination (IAB-MT) and a Distributed Unit (IAB-DU). The IAB-MT acts as a UE towards its parent node (another IAB node or an IAB donor), establishing a wireless backhaul link. The IAB-DU functions as a gNB-DU towards its child nodes (which could be UEs or other downstream IAB nodes), providing the radio access interface. The IAB donor is a gNB that provides network access to the IAB nodes and contains a Central Unit (CU) that controls the entire IAB topology.
The operation relies on sophisticated resource partitioning and multiplexing. Time, frequency, and spatial resources are dynamically allocated between access and backhaul links to prevent self-interference and optimize capacity. This is managed by the IAB donor CU through F1 application protocol (F1-AP) over the backhaul RLC channels. Key protocols are adapted: the IAB-MT uses the NR Uu interface stack (SDAP, PDCP, RLC, MAC, PHY) to connect upstream, while the IAB-DU uses the NR F1 interface stack to connect to the donor CU, with the backhaul RLC channel serving as the transport network layer. Routing in the IAB network is topology-aware, with the donor CU managing BH RLC channel establishment and BAP (Backhaul Adaptation Protocol) routing for efficient hop-by-hop forwarding of user plane data.
Deployment scenarios are flexible, supporting multi-hop topologies (tree, mesh) to extend coverage deep indoors or into remote areas. The IAB node uses the same 5G NR spectrum and waveforms for both functions, ensuring a unified, spectrum-efficient air interface. Key technical challenges addressed include topology management, route selection, discovery and integration of new IAB nodes, and robust resource management to handle the compounded latency and capacity constraints of multi-hop wireless paths. IAB is a cornerstone for rapid, cost-effective 5G network densification.
Purpose & Motivation
IAB was created to solve the critical economic and logistical challenge of providing high-capacity fiber backhaul to every small cell in a dense 5G network. Deploying fiber to every streetlight, traffic light, or building facade for ultra-dense networks (UDN) is prohibitively expensive and time-consuming. IAB provides a wireless self-backhauling solution, allowing operators to deploy nodes rapidly where only power and a mounting location are available, using the already-licensed radio spectrum for connectivity.
Historically, microwave links were used for wireless backhaul, but they operated in dedicated, often expensive spectrum bands with separate equipment. IAB integrates this function directly into the 5G NR standard, using the same baseband and RF hardware for access and backhaul. This dramatically reduces deployment costs, site acquisition complexity, and time-to-market. It is particularly motivated by the need for enhanced Mobile Broadband (eMBB) and massive IoT deployments in urban canyons, stadiums, factories, and temporary event sites.
Furthermore, IAB enables flexible network topologies that can self-organize and self-heal. In a mesh configuration, it provides resilience against link failures by offering alternative paths. It addresses the limitations of previous relay technologies in LTE, which were often less integrated and inefficient. By being a native part of the 5G NR standard from Release 16 onwards, IAB ensures vendor interoperability, efficient spectrum use through dynamic resource sharing, and seamless integration with the 5G core network, making network densification economically viable for the 5G era.
Classification
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (283 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 16, the IAB function was formally introduced for both 5GS and EPS, defining an architecture where an IAB-node combines a gNB-DU and a UE function (IAB-UE) to relay traffic via NR Uu backhaul links to an IAB-donor. Key enhancements included new signaling, such as the IAB-Indication in RRC connection establishment for EPS to enable MME selection and authorization based on subscription data, and support for IAB operation in EN-DC mode. The release also specified the handling of OAM traffic and established that IAB performs layer-2 relaying using the F1 interface, supporting multi-hop backhauling and dynamic topology updates.
- Support for IAB in EPS TS 23.401CR3555
- Support for IAB indication and authorization in EPS TS 23.401CR3570
- Introduction of the IAB support in 5GS TS 23.501CR1522
- Handling of IAB-indication to 5GC TS 23.501CR1901
- Handling of OAM traffic for IAB-node TS 23.501CR1902
- Support of IAB operation in EN-DC mode TS 23.501CR1903
+ 108 more changes
In Release 17, key IAB enhancements included the introduction of specific MAC CE configurations via RRC signaling, support for control-plane and user-plane separation (CP-UP separation), and mechanisms for control-plane-based congestion mitigation and indication within the IAB network. The release also provided clarifications for IAB operation within EN-DC architectures and for NR satellite access, alongside various performance criteria and measurement definitions. These updates built upon the foundational layer-2 relaying and multi-hop backhauling architecture defined for IAB-nodes and IAB-donors.
- Big CR to TS38.174 for Rel-17 IAB enhancement TS 38.174CR0024
- Introduction of IAB enhancements TS 38.300CR0389
- CR to 38.321 introducing Integrated Access and Backhaul for NR Rel-17 TS 38.321CR1171
- CR to 38.321 on Integrated Access and Backhaul for NR Rel-17 TS 38.321CR1266
- Introducing Enhancements to Integrated Access and Backhaul for NR TS 38.331CR2811
- Introducing IAB MAC CE Configurations in RRC TS 38.331CR3194
+ 55 more changes
In Release 18, the primary new development for IAB was the formal **introduction of mobile IAB**, extending the feature to support relay nodes in motion. This required the definition of new RF, RRM, and demodulation core requirements for these mobile nodes, as detailed in updates to the 38.174 series of specifications. Furthermore, enhancements were made to support procedures like RACH-less handover for mobile IAB and updates across multiple layers, including RRC (38.321), F1 (38.340), and NGAP (38.413/38.473), to integrate this new capability.
- Big CR to TS 38.174 on RF core requirements for NR Mobile IAB TS 38.174CR0077
- Big CR to TS 38.174 on RRM core requirements for NR Mobile IAB TS 38.174CR0095
- BigCR for 38.174 addition of mobile IAB demodulation requirements TS 38.174CR0108
- Big CR on RRM performance requirements for NR Mobile IAB TS 38.174CR0114
- CR to TS 38.175 with mobile IAB introduction TS 38.175CR0035
- BigCR to TS 38.176-2 on RF conformance requirements for NR Mobile IAB TS 38.176CR0057
+ 92 more changes
In Release 19, the enhancements for Integrated Access and Backhaul (IAB) introduced standardized procedures for an IAB-node to connect to and be configured by a management system, formalizing these operational and maintenance aspects. The release also included corrections to performance requirements in the core specifications, specifically addressing out-of-band blocking co-location and EESS protection requirements for IAB-nodes. These updates build upon the existing IAB architecture where the IAB-node, comprising a gNB-DU and an IAB-UE function, connects to the network via an IAB-donor.
- Requirements for IAB-node connects to management system TS 28.314CR0002
- Use case IAB-node connects to management system TS 28.314CR0004
- Requirements for IAB-node configuration TS 28.531CR0245
- Use case IAB-node configuration TS 28.531CR0246
- Procedure for IAB-node configuration TS 28.531CR0247
- Management of IAB-node TS 28.540CR0048
+ 3 more changes
In Release 20, a specific enhancement was introduced for the management of the IAB-node, focusing on the procedure for NCI (NG-RAN Cell Identity) reconfiguration. This update builds upon the existing architecture where the IAB-donor-CU controls IAB-nodes via RRC and F1 interfaces, ensuring dynamic topology updates. The change refines the mechanisms for updating backhaul channels during mobility or reconfiguration events, which are handled transparently to end-user UEs.
- Rel-20 CR Update to management of IAB-node for NCI reconfiguration TS 28.540CR0052
Explore further
Broader topics and technologies where IAB plays a role.
Defining Specifications
3GPP specifications that define or reference IAB, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.401 vj50 | Evolved Packet System (EPS) Stage 2 Description | Rel-19 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TS 28.314 vk00 | Management and Orchestration - Plug and Connect | Rel-20 |
| TS 28.531 vk00 | Management and Orchestration | Rel-20 |
| TS 28.540 vk10 | 5G Network Resource Model (NRM) Management | Rel-20 |
| TS 28.875 vj00 | Study on IAB Node Management | Rel-19 |
| TS 29.272 vj40 | Diameter Interfaces for MME/SGSN | Rel-19 |
| TS 33.401 vj10 | EPS Security Architecture | Rel-19 |
| TS 33.501 vk00 | 5G Security Architecture and Procedures | Rel-20 |
| TR 33.824 vh00 | Security Study for NR Integrated Access & Backhaul | Rel-17 |
| TR 33.938 vj10 | 3GPP Cryptographic Inventory for 5G | Rel-19 |
| TS 36.304 vj00 | UE Idle Mode Procedures in E-UTRA | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 36.413 vj10 | S1 Application Protocol (S1AP) | 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 37.340 vj00 | Multi-Connectivity Operation Overview | Rel-19 |
| TS 37.483 vj10 | E1 Application Protocol (E1AP) | Rel-19 |
| TS 38.174 vj10 | NR Integrated Access and Backhaul Radio Spec | Rel-19 |
| TS 38.175 vj00 | EMC for NR IAB Nodes | Rel-19 |
| TS 38.176 vj20 | IAB Conformance Testing Specification | Rel-19 |
| TS 38.201 vj00 | NR Physical Layer General Description | Rel-19 |
| TS 38.211 vj10 | NR Physical Channels and Modulation | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.304 vj00 | UE RRC_IDLE and RRC_INACTIVE Procedures | Rel-19 |
| TS 38.321 vj00 | NR MAC Protocol Specification | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TS 38.340 vj00 | Backhaul Adaptation Protocol (BAP) Specification | Rel-19 |
| TS 38.401 vj10 | NG-RAN Architecture Specification | Rel-19 |
| TS 38.413 vj10 | NG Application Protocol (NGAP) | Rel-19 |
| TS 38.420 vj10 | Introduction to Xn interface specifications | Rel-19 |
| TS 38.423 vj10 | Xn Application Protocol (XnAP) specification | Rel-19 |
| TS 38.425 vj10 | NR User Plane Protocol Specification | Rel-19 |
| TS 38.463 vj00 | E1 Application Protocol (E1AP) | Rel-19 |
| TS 38.470 vj10 | F1 Interface Introduction | Rel-19 |
| TS 38.473 vj10 | 5G F1 Application Protocol (F1AP) | Rel-19 |
| TS 38.474 vj00 | F1 Interface User Plane Protocol | Rel-19 |
| TS 38.807 vg10 | NR beyond 52.6 GHz Study | Rel-16 |
| TR 38.808 vh00 | Study on NR above 52.6 GHz to 71 GHz | Rel-17 |
| TS 38.809 vg60 | IAB Radio Transmission & Reception Background | Rel-16 |
| TR 38.820 vg10 | NR; 7-24 GHz Frequency Range Study | Rel-16 |
| TR 38.864 vi10 | Technical Report on Network Energy Savings for NR | Rel-18 |
| TS 38.874 vg00 | Integrated Access and Backhaul for NR | Rel-16 |
