The process of virtualizing the telco network has proved longer and tougher than many had hoped, and is still in a very embryonic state for more operators – apart from a few Asian frontrunners which have invested in very hand-crafted systems like SK Telecom’s.
Other operators have been waiting for full standards and open interfaces to reduce the cost, risk and complexity of running their core, transport and RAN network functions in software on commoditized hardware. That longer-than-hoped wait will delay some of the hoped-for cost benefits of 5G, since most early 5G deployers will start rolling out their systems using conventional architecture, especially in the RAN.
Verizon, however, claims to be making significant progress towards a virtualized RAN (vRAN). AT&T – generally seen as the more advanced, or certainly the more vocal, telco in matters of virtualization and open frameworks – has said the RAN will come at the end of its multiyear roadmap, but its rival may get there earlier.
Bill Stone, VP of technology planning and development at Verizon, told the recent FierceWireless Next Gen Wireless Networks Summit that the telco has already deployed a “first step” towards vRAN. This involved virtualizing some functions in the upper layer, or Layer 3, of the network, within Verizon’s own cloud architecture.
This is not all about 5G, though it will go hand-in-hand with New Radio roll-out as that progresses. Some of the benefits of vRAN come from having a common set of functions in the centralized, white box baseband unit (BBU), which can work with remote radio units (RRUs) supporting different standards, and potentially from different vendors. This gives the MNO flexibility to swap new radios in and out only as required, rather than engaging in a complete upgrade.
“We’re going to proceed down that path with 5G NR as we get in into the NR deployment phase now,” Stone said. “We’re also going to … virtualize the upper layers for LTE as well.”
One of the many challenges in vRAN is to decide which network functions are appropriate to be centralized, and which are better left at the cell site. The 3GPP 5G standards set out eight options, with varying degrees of centralization, though only a few of these are likely to be adopted at scale. Functions which require low latency – mainly those in the lower layers of the network – often work better if left close to the user, even though that compromises some of the extreme efficiencies of a fully centralized topology. As edge compute starts to be integrated into some telco networks, there is likely to be a swing back towards decentralization to support some of the low latency industrial or immersive applications that are seen as important to the 5G and the edge compute cases.
However, Stone said Verizon is working with its vendors—Ericsson, Samsung and Nokia—to virtualize the lower layers of its network too, saying: “We’re looking at it in two steps, where we virtualize the upper layers first, and then the lower layers second.”
This is building on existing work Verizon has done in centralized RAN (cRAN), which similarly splits baseband processing from remote radio units, allowing several RRUs to share a BBU, but which does not virtualize the functions with NFV. The centralized unit often sits at the base of a tower rather than in the cloud. Verizon already has thousands of cRAN hubs throughout the USA, which may prove valuable locations for edge compute deployments and for creating relatively localized vRANs, in which the cloud functions and infrastructure are pushed out to the tower.
In February, Verizon said it was working with Nokia and Intel on a new vRAN architecture, building on the cRAN hubs. This was trialled in Oklahoma City, with the virtualized baseband functions running on Nokia’s AirScale cloud base station server, based on Intel’s Xeon processors. Verizon has also run vRAN trials with Ericsson and Samsung as part of its broad Open RAN initiative in 4G and future 5G.
Nicola Palmer, the operator’s chief network engineer, said then: “We have thousands of these cRAN hubs throughout the US. They’ve already been identified. They are built out and equipped. And we have been in the process of centralizing those baseband units.” She explained that, as a result, 15 to 50 centrally managed cells could work together, using LTE-Advanced features like remote electrical tilt (RET), which can point an antenna array toward high traffic areas during the day and then tilt them up at night to improve coverage.
The next step is to “do a lot more … The cRAN hubs become vRAN hubs, and now you can communicate across cRAN hubs. … You can scale horizontally instead of vertically.”
Like many operators, Verizon and Palmer are keen to open up their supply chains. Where one vendor, such as Ericsson, provides an end-to-end system, “you basically have an Ericsson market,” Palmer said, adding: “Our view is that you need to have those pieces disaggregated. By separating hardware and software, you can get best of breed on each one. And that allows us, for example, to take a Samsung radio with an Ericsson baseband. … And that allows us to play the suppliers against each other. And to their strengths, to be honest.”
But many operators remain sceptical about vRAN. Orange’s director of spectrum strategy and planning, Yves Bellego, said the French telco’s vRAN trials had been strong technically but had failed to show any major business benefits.
“We did not go beyond trials or a proof of concept because of the business case,” Bellego said. “As of today it remains cheaper and simpler to upgrade each and every site.”