Basics of 5G Transport Network Architecture

The advent of 5G technology is set to revolutionise the way we connect, and at its core lies a sophisticated transport network architecture. This architecture is designed to support the varied requirements of 5G’s advanced services and applications.

As we migrate from the legacy 4G to the versatile 5G, the transport network must evolve to accommodate new deployment strategies influenced by the functional split options specified by 3GPP and the drift of the Next Generation Core (NGC) network towards cloud-edge deployment.

The Four Pillars of 5G Transport Network

1. Fronthaul: This segment of the network deals with the connection between the high PHY and low PHY layers. It requires a high bandwidth, about 25 Gbit/s for a single UNI interface, escalating to 75 or 150 Gbit/s for an NNI interface in pure 5G networks. In hybrid 4G and 5G networks, this bandwidth further increases. The fronthaul’s stringent latency requirements (<100 microseconds) necessitate point-to-point (P2P) deployment to ensure rapid and efficient data transfer.

2. Midhaul: Positioned between the Packet Data Convergence Protocol (PDCP) and Radio Link Control (RLC), the midhaul section plays a pivotal role in data aggregation. Its bandwidth demands are slightly less than that of the fronthaul, with UNI interfaces handling 10 or 25 Gbit/s and NNI interfaces scaling according to the DU’s aggregation capabilities. The midhaul network typically adopts tree or ring modes to efficiently connect multiple Distributed Units (DUs) to a centralized Control Unit (CU).

3. Backhaul: Above the Radio Resource Control (RRC), the backhaul shares similar bandwidth needs with the midhaul. It handles both horizontal traffic, coordinating services between base stations, and vertical traffic, funneling various services like Vehicle to Everything (V2X), enhanced Mobile BroadBand (eMBB), and Internet of Things (IoT) from base stations to the 5G core.