Solution Architecture and Design
The reference solution architecture for end-to-end xHaul, shown in Figure 1, deploys a spine-leaf access topology (Fronthaul) and core, peering and services gateway roles comprising the xHaul infrastructure.
The network setup includes Segment Routing MPLS as the underlying technology, which spans across multiple ISIS domains and inter-AS connections. The access nodes are placed within an ISIS L1 domain, establishing adjacencies with L1/L2 HSR nodes. The L2 domain extends from the aggregation to the core segments of the network. To achieve seamless MPLS connectivity, BGP-Labeled Unicast (BGP-LU) is enabled at the border nodes.
To manage current network scale and allow future growth, two sets of route reflectors are used at CR1 and CR2, primarily serving the westward HSR (AG1) clients. AG1.1/AG1.2 act as redundant route reflectors specifically for the access Fronthaul segment. Inter-AS Option-B solutions are supported through Multi-Protocol BGP peering between the Services Aggregation Gateway router (SAG) and the HSR (AG1).
To ensure the performance and reliability of the network, the design proposes additional enhancements, including E-OAM performance monitoring and Flow-Aware Transport Pseudowire (FAT-PW) load-balancing. These enhancements help monitor the network performance and balance the traffic load efficiently.
Overlay Services
The overlay services in the network use different combinations of VLAN operations. These operations are applied to each Layer 2 service types, including EVPN, L2Circuit, VPLS, and L2VPN. Additionally, L3VPN services incorporate IPv6 tunnelling to validate 6vPE functionality.
As shown in Figure 1, inter-domain VPN Option-B is used at the HSR/AG1 region, and Inter-AS Option-C is used between the SAG and CR border nodes. These nodes are enabled by BGP-LU.
This combination of VPN’s is designed in a way to allow following traffic flows in the 5G xHaul network:
- Layer 2 eCPRI between O-RU to O-DU traffic flows – 5G Fronthaul
- Layer 3 IP packet flows between 5G O-DU and CU/EPC – 5G Midhaul and Backhaul
- Layer 3 IP packet flows between 4G CSR and EPC (SAG) – 4G L3-MBH
- Layer 2 flows between CSR (AN) to EPC (SAG) – 4G L2-MBH
- Layer 2 Midhaul flows emulating additional attachment segments – 4G Midhaul and Backhaul
For more detailed information about this architecture, contact your Juniper Networks representative.
Fronthaul Network Design and 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.
As shown in Figure 2, the Fronthaul network consists of ACX7000 series routers interconnected by high-capacity links. The ACX7100-48L serves as the CSR, providing connectivity between O-RU and HSR aspects of the RAN. 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.
Fronthaul Layer 2 Connectivity Models
There are several possible connectivity models between O-RU and O-DU, but for the purposes of this JVD, we’ve validated these two:
- EVPN-VPWS Single-Homed supporting dedicated MAC for eCPRI without redundancy
- EVPN-VPWS with A/A LAG DU attachment
Figure 3 illustrates the first connectivity model. In this scenario, the network utilizes EVPN-VPWS single-homing connectivity. This setup supports dedicated MAC for eCPRI without redundancy. Additionally, it uses Ethernet OAM with performance monitoring. Currently, Ethernet OAM with performance monitoring is supported for the single-homed configuration in this model.
Figure 4 illustrates the second connectivity model. In this scenario, the network uses two configurations between the CSR (AN3) and HSR-1/HSR 2:
- EVPN-VPWS with active-active multihoming
- EVPN-VPWS with Flexible Cross Connect (FXC) active-active multihoming
To enable traffic load sharing, an Active/Active Ethernet Segment Identifier (ESI) Link Aggregation Group (LAG) is established between the HSRs and the O-DU. This allows for balanced distribution of traffic. The links are bundled into an Active/Active EVPN ESI 10G Ethernet LAG between HSR-1 and HSR-2, as well as to the O-DU. The O-DU includes a two-member Aggregate Ethernet (AE) with both links actively carrying traffic.
In this scenario, eCPRI packets might arrive on either of the O-DU links from the HSRs. Similarly, eCPRI packets can be sent across either of the HSR-1 or HSR-2 uplinks to support active-active functionality. This setup ensures flexibility and redundancy in the network for improved performance.
Layer 3 Connectivity Models
We chose L3VPN protocol to facilitate Layer 3 connectivity between O-DU and vCU/vEPC elements of the 5G xHaul. The JVD proposes two different connectivity models between the Hub Site Router (HSR) and the O-DU, with both supporting L3 multihoming between O-DU and pair of HSRs:
- EVPN IRB anycast gateway with L3VPN, refer to Figure 5
- BD with IRB and static MAC/ARP with L3VPN, refer to Figure 6
- We tested both connectivity models independently and collected data on their coexistence and convergence. We validated that both models are effective in facilitating the necessary connectivity between the HSR and O-DU.
For further details about the testing for these connectivity models, contact your Juniper Networks representative.
VLAN Operations
The ACX7000 series offers a wide range of VLAN operations. The proposed VLAN operations specifically cater to EVPN eCPRI-emulated traffic flows and support various normalization scenarios:
- Untagged frames
- Tagged (802.1q)
- Dual-tagged (802.1ad)
While the main emphasis of this JVD is on the Fronthaul segment, we also validated most of the VLAN operations for each VPN service type. To see the full test report, contact your Juniper Networks representative.