Convergence, the integration of wireline and wireless technologies into a single network infrastructure, gets a lot of attention for good reason. Operators need to reduce costs to maintain profitability in the face of increasing traffic and declining price per bit. There are significant economies of scale in both CapEx and OpEx by consolidating onto a single network. In our most recent post, we wrote about how edge computing affects the new service edge and why the service edge is moving much closer to the customer. This has a profound impact on the transport network.
The new service edge will also need to support convergence. We see three trends in convergence that we will look at in our next few posts.
The first is that 4G and 5G will coexist for some time. Backhaul connected a cell site to the network in 4G. With 4G, virtualized software could be used for functions that traditionally had been done in hardware. An individual function delivered as virtualized software is a Virtual Network Function (VNF). Disaggregation introduced fronthaul to the transport network.
In 4G LTE, eNodeB, the functions were disaggregated into the Remote Radio Head (RRH) and the Baseband Unit (BBU) for C-RAN implementations. Moving the BBU to a BBU hotel (such as a central office) eliminates a significant amount of equipment from the base station.
5G Next Generation RAN (NG-RAN) takes the cell site functions and breaks them down into multiple functions. 5G gNodeB functions are the Radio Unit (RU), the Distributed Unit (DU, and the Centralized Unit (CU). These interconnect via the transport networks and then connect to the core network. The DU and CU can be implemented as VNFs and centrally pooled for saving by not overprovisioning the cell site and keeping costs low. We discuss this in more detail in our white paper, The Future is Virtual: Routing in 5G Transport Networks.
MNOs have realized that costs needed to be reduced given the significant decline in revenue per bit. Cloud radio access network (C-RAN) showed that significant OpEx and CapEx reductions can be achieved with virtualization compared to traditional equipment deployments. In fact, a trial from China Mobile showed a 53% reduction in OpEx and 30% savings in CapEx.
Having a common wireless transport network makes it far simpler and cost-effective to operate the network without the need for costly overlay networks. To be able to converge 4G fronthaul and backhaul traffic with 5G fronthaul, midhaul, and backhaul traffic onto a network means supporting multiple interfaces, such as CPRI, Radio-over-Ethernet (RoE) encapsulation, eCPRI, and O-RAN interfaces.
Fortunately, these 4G/5G fronthaul and midhaul interfaces can leverage IP and packet technologies which allows these networks to use routing. Fronthaul requires strict levels of latency and jitter to ensure the successful transmission of packets across the fronthaul network. Similar technologies across midhaul and backhaul networks are leveraged to achieve the SLA requirements of new 5G use cases, such as urLLC. Routing features like hierarchical QoS, MPLS and segment routing are needed.
Next time we will look at the second trend, the convergence of wireline and wireless in the 5G transport network.