IAB Architecture Explained: SA with 5GCN vs EN-DC Mode in 5G
IAB Architecture in 5G: SA Mode vs EN-DC Mode
As 5G networks keep growing, service providers are challenged with ensuring strong backhaul connectivity to support the increased number of small cells. Traditional backhaul methods usually depend on fiber or microwave connections, which can get pretty pricey and complicated to set up in urban and suburban areas. To address this issue, 3GPP introduced IAB (Integrated Access and Backhaul) in Release 15, allowing the same wireless spectrum to serve both access (connecting to users) and backhaul (linking base stations).
The image uploaded compares two scenarios for IAB deployment:
(a) IAB-node in Standalone (SA) mode with 5GCN
(b) IAB-node using EN-DC (E-UTRAN New Radio Dual Connectivity)
Now, let’s dive into the architecture and what it means for real-world 5G setups.
What is IAB (Integrated Access and Backhaul)?
IAB is a versatile network design where the same radio interface (NR Uu) is used for:
Access: Connection between gNB and UEs.
Backhaul: Connection among gNBs or IAB-nodes arranged in a multi-hop structure.
This design cuts down the need for a lot of fiber installation, speeds up network densification, and lowers costs.
IAB in SA Mode with 5GCN (Figure a)
In a Standalone (SA) deployment, the 5G network operates with the 5GC (5G Core Network) instead of the LTE EPC.
Key Components:
gNB (Next-generation NodeB): Connects directly to the 5GC via NG interfaces (NG-C for control plane, NG-U for user plane).
IAB Donor (gNB): Serves as the primary node that connects to the 5GC and provides backhaul for downstream IAB-nodes.
IAB-nodes: These act as relay nodes using the same NR spectrum for both user access and backhaul, connecting hierarchically through NR Uu (the radio interface) and F1 interface.
Architecture Highlights:
NG Interface: Links gNBs directly to AMF/UPF in the 5GC.
Xn Interface: Facilitates communication between gNBs.
NR Uu Links: Carry both access and backhaul traffic wirelessly.
F1 Interface: Connects IAB-nodes to the IAB donor (similar to DU to CU split).
This arrang ement allows for a pure 5G environment where the entire control and user plane is based on the 5G Core, offering low latency and advanced 5G features.
IAB in EN-DC Mode (Figure b)
In the EN-DC (E-UTRAN New Radio Dual Connectivity) setup, the architecture combines LTE EPC and 5G NR. This is a Non-Standalone (NSA) deployment, with LTE eNBs and Me NBs (Master eNBs) taking on central roles.
Key Components:
eNB/MeNB (Master eNB): Provides LTE connectivity and anchors the control plane to the EPC (via S1 interface).
SgNB (Secondary gNB / IAB donor): Adds NR user plane capacity and acts as the donor for downstream IAB-nodes.
IAB-nodes: They connect to the donor gNB using NR Uu (for backhaul) and the F1 interface.
EPC (MME/S-PGW): Continues to function as the core network, handling signaling and user plane via S1 interfaces.
Architecture Highlights:
S1 Interface: Links EPC with LTE eNBs and MeNB.
X2/X2-C Interface: Connects LTE eNBs with gNBs for coordination.
NR Uu Links: Utilized by IAB-nodes for both access and backhaul.
F1 Interface: Connects the donor SgNB with the downstream IAB-nodes.
In this case, LTE provides the control plane, while NR mainly boosts user plane throughput.
Comparison: IAB SA with 5GCN vs IAB EN-DC
Feature IAB with SA (5GCN)IAB with EN-DC Core Network5G Core (AMF/UPF)LTE EPC (MME/S-PGW)Anchor Nodeg NB (Standalone)Me NB (LTE)Donor Node gNBSg NB Access Interface NRU uNR Uu (plus LTE Uu for EN-DC)Backhaul InterfaceF1 + NR UuF1 + NR Uu Control Plane Anchored in 5GCAnchored in LTE EPC Use Case Pure 5G deployment Transitional (NSA) deployment
Benefits of IAB Architecture
Cost Efficiency: Reduces reliance on fiber rollout.
Faster Deployment: Perfect for urban densification where small cells are a must.
Scalability: Supports multi-hop layouts (donor → IAB-node → further IAB-node).
Flexibility: Functions well in both Standalone (SA) and Non-Standalone (NSA/EN-DC) modes.
Enhanced Coverage: Boosts 5G service reach in hard-to-access areas using wireless backhaul.
Challenges in IAB Deployment
Even though IAB simplifies backhaul installation, it does have its hurdles:
Spectrum Sharing: Since backhaul and access share the same spectrum, it could affect capacity.
Latency: Multi-hop setups might increase overall latency.
Resource Management: It's crucial to manage spectrum allocation between access and backhaul effectively.
Standardization Evolution: IAB is still evolving, with improvements anticipated in 3GPP Release 16 and beyond.
Real-World Applications of IAB
Urban Areas: Deploying 5G small cells without extensive fiber infrastructure.
Temporary Setups: Quick installations for special events, disaster recovery, or rural connectivity.
Enterprise Networks: Private 5G networks can leverage IAB for internal connections without massive infrastructure costs.
Why IAB is Critical for 5G Evolution
Merging Access and Backhaul: IAB combines access and backhaul into one unified system, unlike traditional networks.
Facilitating 5G Densification: It supports the large-scale deployment of small cells that mmWave 5G requires.
Smooth Transition: Works seamlessly with both EPC (EN-DC) and 5GC (SA).
Future-Proof: Prepares the groundwork for advanced use cases like network slicing and URLLC when integrated with 5GC.
Conclusion
The IAB architecture is crucial for next-gen 5G installations, tackling cost and scalability challenges in backhaul deployment.
In SA mode with 5GCN, IAB offers a pure 5G environment, featuring ultra-low latency and top-notch capabilities via direct 5GC integration.
In EN-DC mode, IAB aids in a smooth transition from LTE to 5G, making the most of the current EPC and LTE anchors while enabling NR for backhaul.
For telecom professionals, grasping IAB concepts is vital, as it stands out as one of the most practical solutions for 5G densification, expanding coverage in rural areas, and economical deployment.