Use Case and Reference Architecture
5G xHaul architectures must support stringent CoS to meet critical demands of delay sensitive traffic characteristics. The reference architecture encompasses: Fronthaul, Midhaul, Backhaul, and Core segments, and follows recommendations of Open Radio Access Network (O-RAN) Alliance transport network architecture (ORAN.WG9.XPSAAS-v02.00).
Figure 1 illustrates the physical segments of the 5G xHaul reference network, including the latency requirements. To confirm the effectiveness of the 5G xHaul and CoS reference architecture, we focused specifically on the Fronthaul segment, which is crucial for 5G technology.
In this architecture, the Fronthaul portion in the radio access network (RAN), connects the Open Radio Unit (O-RU) and Open Distributed Unit (O-DU), (shown as RU and DU in Figure 1), allowing them to communicate for control, data, and management traffic. It also ensures time and frequency synchronization between RAN elements. Because low latency is crucial (must be below 150µs from RU to DU), the Fronthaul segment has very few network elements, typically limited to one or two hops. Fronthaul devices must be able to deliver sub-10µs latency requirements.
Fronthaul Network Topology
The Fronthaul network deployment scenarios were carefully designed to support both the traditional 4G Mobile Backhaul and the evolution into the 5G network infrastructure over the same physical network. This approach allows MSOs to make a smooth transition from 4G to 5G without disrupting their existing services. They can gradually introduce the necessary changes and upgrades to accommodate the new requirements of 5G networks.
The Fronthaul network consists of ACX7000 series routers interconnected by high-capacity links. The ACX7100-48L serves as the Cell Site Router (CSR), providing connectivity between O-RU and Hub Site Router (HSR). The ACX7100-48L supports a range of port densities, including 47 ports of 10/25/50G + 1x10/25G and 6 x 400G (24x100G). The ability to support 400G access topologies is a key building block to the solution.
The ACX7100-32C and ACX7509 serve as the HSRs. The HSRs provide connectivity from the CSR to the O-DU, including pre-aggregation for Midhaul and Backhaul network segments. The ACX7100-32C supports 32 x 100G and 4x400G, and the ACX7509 supports three FPC variants (16x400GE, 4x200/400GE, and 20x1/10/25/50GE).