- What’s a 5G Transport Service?
- VPN Services
- Transport Services Across MCN
- Summary
- References
This chapter is from the book
This chapter is from the book
This chapter is from the book
Transport Services Across MCN
In addition to the commonly used VPN technologies discussed in this chapter, a plethora of networking technologies and connectivity protocols can be used to provide transport services. Some of these technologies include L2TPv3, GRE, DMVPN (which uses multipoint-GRE), Generic Network Virtualization Encapsulation (GENEVE), Network Virtualization using Generic Routing Encapsulation (NVGRE), and Overlay Transport Virtualization (OTV); however, they are virtually never used as the primary connectivity mechanism in an MCN. There might be a few outlier scenarios and use cases where some of these technologies may be applicable (such as L2TPv3 for L2 connectivity over a non-MPLS IP-only underlay, or GRE to provide Layer 3 overlay), but overall such instances are few and far between. Virtually all modern networks use a combination of overlay technologies discussed in this chapter—L2VPN VPWS, L3VPN, EVPN, and VXLAN—in various MCN domains. The choice of the VPN protocol used is dependent on product support, feature richness, deployment simplicity, and sometimes based on golf course discussions between organizational leaders.
Unless L2 connectivity is required explicitly by the endpoint(s), MPLS L3VPNs are the preferred connectivity mechanism within an MCN. As mentioned previously, one such example is the explicit use of L2VPN for RU and DU connectivity through the fronthaul, which is typically provided through traditional VPWS or EVPN VPWS-based pseudowires. In contrast, L3VPN is preferred for midhaul and backhaul as well as for management connectivity across all xHaul domains, as specified in the O-RAN Packet Switched xHaul Architecture specifications.19
As mentioned previously in Chapter 5, “5G Fundamentals,” the O-RAN architecture defines four planes of operations for any modern-day MCN:
The management plane (M-Plane), which provides RU management functions such as software maintenance and fault management
The control plane (C-Plane), which is used for control messaging regarding RF resource allocation for functions such as scheduling, multi-radio coordination, beamforming, and so on
The user plane (U-Plane), which carries the actual mobile user data
The synchronization plane (S-Plane), which provides timing and synchronization between RAN components
Transport network connectivity for all these planes of operations is provided by the VPN technologies described throughout this chapter.
A separate L3VPN instance is used for M-Plane connectivity to ensure management traffic is kept separate from other traffic on the network. C-Plane traffic and U-Plane traffic are closely related, as they both pertain to mobile user traffic. As such, they may have their own separate VPN instances or share a VPN instance with separation provided by using different IP subnets, depending on the RAN vendor implementation. The VPN instance for end-to-end C-Plane and U-Plane is composed of VPWS (traditional EoMPLS based or EVPN based) in the fronthaul and L3VPN in the midhaul and backhaul. This could change to end-to-end L3VPN-based C- and U-Planes if the RU and DU start supporting L3 connectivity in the future. Figure 8-14 illustrates the VPN services and their implementation.
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FIGURE 8.14 Transport Services Across Various Planes of Operations
While traffic from other planes uses VPN overlay for transport, S-Plane is implemented natively as part of the transport infrastructure. This is due to the nature of synchronization traffic, where better accuracy could be achieved if transport network elements (that is, routers) along the traffic path participate in the synchronization process. The next chapter will discuss the details of timing and synchronization as well as its importance and implementation in the 5G networks.