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Use Case and Reference Architecture

The 5G xHaul architecture encompasses three physical segments: Fronthaul, Midhaul, and Backhaul as shown in Figure 1.

The primary focus of the JVD is on providing design options and performance validation of the Fronthaul network considered in the context of the end-to-end converged 5G xHaul network.

Figure 1: 5G xHaul Reference Network A diagram of a computer network Description automatically generated

Fronthaul segment enables Layer 2 connectivity between Open Radio Unit (O-RU) (cell site) and Open Distributed Unit (O-DU) (shown as RU and DU in Figure 1) in the radio access network (RAN), 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. The current solution for 5G Fronthaul transport is based on O-RAN Alliance architecture [ORAN-WG9.XPSAAS.0-v00.01].

The advancement of the RAN involves different architectures for 4G, including distributed, centralized, and virtual setups, which need to coexist with the 5G disaggregated O-RAN. These diverse ecosystems provide flexibility for the placement of components like O-DU and O-CU. This JVD does not cover all possible scenarios but closely aligns with O-RAN split 7.2x, where the O-RU connects to the CSR and the O-DU is located within the HSR infrastructure. If needed, additional insertion points can be implemented to support disaggregation between the Midhaul and Backhaul segments by extending appropriate services.

Figure 2 (as proposed by the O-RAN Alliance), summarizes the deployment scenarios for the RAN according to the ITU-T for simultaneous support of 4G and 5G.

Figure 2: RAN Deployment Scenarios for Simultaneous Support of 4G and 5G A screenshot of a cell phone Description automatically generated

Figure 3 shows an end-to-end 5G xHaul network, modeled after common topology [O-RAN.WG9.XPSAAS-v02.00], which defines four segments of transport infrastructure: access, pre-aggregation, aggregation, and transport core.

Figure 3: 5G xHaul Network Topology A diagram of a network Description automatically generated

Topology Definitions:

  1. Access: ACX7100-48L as DUT (AN3), ACX7100-48L (AN1), ACX710 (AN2) cell site routers.
  2. Pre-Aggregation: ACX7509 (AG1.1) and ACX7100-32C (AG1.2) DUT hub site routers.
  3. Aggregation: MX204s (AG2.1/AG2/2), MX10003 (AG3.1), MX480 (AG3.2) aggregation routers.
  4. Core Network: PTX1000 (CR1) and MX10003 (CR2) core routers. MX10003 (SAG) services router.

The network topology in this use case combines Seamless MPLS and ISIS Segment Routing technologies. These technologies enable the support of multiple 5G and 4G services, such as:

  • Layer 3 VPN (IPv4 and IPv6)
  • Ethernet VPN–virtual private wireless service (EVPN-VPWS)
  • EVPN Flexible Cross Connect (EVPN-FXC)
  • L2VPN
  • L2Circuit
  • Border Gateway Protocol-Virtual Private LAN Service (BGP-VPLS)