Why is 5G transport such a big deal for network operators?

With 2G/3G/4G radio access network (RAN), the approach for backhaul started with radio frequency (RF) planning and design. Once the RF planners determined the optimal RAN design, the RAN team would send longitude/latitude specifications for where the radio sites need to be installed, to their infrastructure team. The Infrastructure team would look at those desired locations and assess which assets and facilities like real estate, power, and of course backhaul connectivity might be available at the desired RAN site location.  It’s a rare case when all three are available at the desired site location when needed. Then, the negotiations begin. Based on where infrastructure assets are, and how long it might take to get them deployed and ready, the RF planners invariably revise their RF radio designs, sometimes there are several iterations. Eventually, after unsatisfying compromises, the deployment starts.

While a bit clunky and inefficient, mobile network operators (MNOs) were able to make this approach work mainly due to the fact the RAN architecture—Distributed RAN (D-RAN)—is relatively homogenous. With the D-RAN architecture in 2G/3G/4G networks:

• All radio system elements are fully contained at the same physical site.
• Backhaul connectivity is a simple access link (fiber or microwave) to an aggregation router connected to a multiservice IP/optical transport network.
• RAN traffic is treated as over-the-top traffic, alongside all other traffic coming from enterprise and residential access networks.
• RAN traffic is terminated at the packet core location (mobile switching office).

It’s a relatively straightforward process of matching up self-contained D-RAN sites to locations where the MNO can get the real estate, power, and connectivity at the lowest cost, while minimizing impact to RAN performance.

Enter 5G Transport (So what is different about 5G that makes the approach above insufficient?)

5G changes the game for backhaul. In fact, it’s changing so much that we can’t really use mobile backhaul as a generic term any longer. Mobile backhaul is just one part of broader solutions for RAN connectivity in 5G. With 5G, RAN architectures are evolving. D-RAN sites that we know and love today will disaggregate and virtualize, giving rise to new RAN architectures. D-RAN will not go away, rather it will be augmented by Centralized RAN (C-RAN), Virtual RAN (V-RAN), and Elastic RAN (E-RAN) architectures.

Figure:  Impact of 5G on Transport Networks

These new RAN architectures have come about because they offer MNOs flexible and efficient ways to:

• Deploy their new 5G spectrum.
• Improve RAN performance through better use of their spectrum assets.
• Densify their networks with new radio technologies.
• Deliver 5G use case and applications to subscribers.

Each of these new RAN architectures come with new interfaces as defined by 3GPP. Furthermore, each of these interfaces come with varying requirements for connection capacity and latency. So, in addition to the backhaul connections for the S1 and X2 interfaces we know and love, 5G introduces new network segments like fronthaul with CPRI 8, CPRI 10, and eCPRI interfaces, and additional new interfaces for specific 5G use cases like F1 and E5 interfaces.

Another major change coming is with timing and synchronization.  With 5G, Time Division Duplex (TDD) radios are being deployed alongside and among other TDD and FDD radios. TDD radios are highly dependent on a reliable phase and time synchronization source to operate properly. If you lose the local GPS, you only have an hour before you lose the TDD radios. And these TDD radios will be driving the vast majority of the capacity at radio sites. Synchronization backup over backhaul is a must.   More about timing and sync in 5G networks in this blog, 5G is all in the timing.

With 5G, capacity for backhaul connections will need to be upgraded as 5GNR in mid-band and high-band spectrum is deployed in a variety of form factors. Fronthaul networks for common public radio interface (CPRI) transport being deployed today using dark fiber, will evolve to Ethernet-based transport technology. And, logical networks for Virtual RAN have yet to be built.

Network security will also become increasingly important.  With new technologies and architectural change discussed above comes with new attack surfaces and risks. Service providers must carefully evaluate the potential threats, adapt security strategies and implement proper security measures to protect the infrastructure, assets and end users.

Network management, operation and administration of the transport network will change as well.  In addition to new physical layer interfaces to manage and control, 5G comes with an overlay network, and more virtual network functions to connect. Simply put, the way we as an industry approached managing discrete domains in the past just won’t scale efficiently and effectively for 5G. To deliver on the promise of 5G, transport network management tools and processes must evolve and keep pace with the 5G network as it evolves.

So, with 5G, it’s not just backhauling RAN traffic over the top of IP/optical transport networks.  It’s an entirely new game called 5G Transport.

Learn more about Ericsson’s 5G Transport solutions here.