Nokia laid claim to the world’s first fully cloud-based 5G vRAN, deployed with a US operator which is almost certainly Verizon in Dallas.
Details were sparse, but the roll-out used a combination of central cloud-based functions and those based on distributed units at the cell site – an architecture which is increasingly looking more viable for 5G than the fully centralized vision of the original China Mobile concept of Cloud-RAN. But this is unlikely to have met the full definition of a 5G vRAN yet – those goalposts keep moving, but no vendor or operator has yet claimed to be able to deploy a pure cloud-native, containerized RAN, and that is likely to be the next goal..
Of all the technologies which have been touted as transformational in mobile network economics, the virtualized RAN (vRAN) has been the one with the biggest promises and the slowest progress. The industry has to hope that this is a case of a tortoise, making a slow but steady path towards a genuinely game-changing destination – and not a Galapagos turtle, large and impressive but doomed to an evolutionary dead end. Because the vRAN really is key to the promised cost economics and service flexibility that will make 5G a different beast from 4G. It will be essential to full cloud networks and to network slicing.
It seems that we have been waiting for many, many years for the vRAN. It is eight years since China Mobile published its seminal white paper setting out its concept of a green, low-opex Cloud-RAN and the industry leapt on this as the architecture that would change the economics of mobile broadband. Yet in 2019, there are very few vRANs in evidence.
The original idea, that vRAN would become mainstream with LTE, has died – there were a few deployments in Korea and Japan, but they were proprietary and expensively engineered. In fact, most first-phase 5G RANs are being deployed in the conventional way.
The apparently slow progress is partly because the goalposts keep changing, as they do with any kind of virtualized telecoms network. There was early confusion between two concepts, both of which have been referred to as C-RANs or Cloud-RANs. One was centralized RAN, which usually has nothing to do with the cloud but does involve multiple radio heads sharing a centralized baseband controller, with varying degrees of disaggregation between software and hardware. This was one step on from the division of the base station between the baseband unit (BBU) or base station hotel and the remote radio unit (RRU); and it has been deployed in macro networks and particularly in small cell clusters.
The other was the true Cloud-RAN or vRAN, in which some or all of the baseband functions are not only centralized and shared, but deployed in software as virtual network functions (VNFs) on cloud infrastructure. This is a far more daunting prospect. Standard servers need a great deal of acceleration to be able to cope with the demanding digital processes of a RAN; some ‘vRANs’, as a result, have been quite proprietary, with non-standard VNFs running on separate, but specialized and expensive, boxes. Even companies trying to do a vRAN on common cloud infrastructure have had to invest large amounts of time and money in tuning and retuning the hardware and software to run together so that they could deliver anything close to the performance of a dedicated RAN – the much-vaunted Rakuten deployment being an example.
Other challenges complicate and delay the roll-out of a macro vRAN, such as how the digital functions should be split between the cloud and the cell site (there has been a backlash against full centralization because low latency functions need to be closer to the user). In future architectures, some of those cell site functions could run on edge cloud nodes rather than on proprietary appliances, but those platforms are not mature yet. That sums up the problem with vRAN – just as one set of enablers stabilizes, the industry moves on with its demands. So now, in the RAN and the core, operators are reluctant to deploy virtual machines on OpenStack cloud infrastructure, because this approach is now seen as cumbersome and old-fashioned. Better to wait for full cloud-native, container-based designs, which will be far more flexible and automated, and should do away with much of the upfront tuning – but which are not fully commercially available yet.
So when will the first fully open, cloud-native, macro vRAN be switched on? Nokia is claiming the crown, saying that it has delivered “the world’s first commercially deployed cloud-based 5G RAN”, in North America.
It did not name the operator, though it seems most likely to be Verizon. A tweet from the official Nokia account, a few days after the initial announcement, indicated that the advantages of the commercial 5G vRAN had been showcased in Dallas at a Verizon Enterprise event.
This tweet, and the fact that the news was announced in a blog post by Mark Atkinson, head of Nokia’s 5G and small cells business unit, suggest that the vRAN is not a macro layer deployment but an urban small cell roll-out geared to enterprise. Atkinson said Nokia’s cloud base station had been used “in one of the busiest cities in the USA” to “split traffic to ensure each connection gets the service it needs”.
He added that, in the Nokia AirScale architecture, distributed units processed time-critical functions at the cell site, connected by Ethernet fronthaul to the radios, while non-real time functions were fully virtualized and run in a central cloud data center, presumably with fiber fronthaul.
“This flexible mix of local and cloud-based processing a real game-changer,” wrote Atkinson. “This means that we can combine performance, scalability and efficiency at its best – in the radio unit (RU), distributed unit (DU) and centralized unit (CU).”
This hierarchical architecture, in which processes are split between the DU and CU, is not new, but has evolved to address the concerns about adding latency by centralizing too many functions, potentially cancelling out the latency improvements of the 5G radio. Nokia has been a strong flagwaver for vRAN, although it has sometimes, like first mover operators, been wrongfooted by the changes in architectural thinking in this area. But with AirScale, it has been a strong supporter of vRAN, and is part of the multivendor Rakuten contract, working with Altiostar’s VNFs and NEC’s Massive MIMO antennas, among other elements.
Nokia has been working closely with Verizon on its vRAN roadmap. In May the operator demonstrated a fully virtualized RAN baseband, enabling edge computing, in its network in California, working with Nokia and Intel. An earlier trial, held in January in Houston, Texas, used MEC (multi-access edge computing) equipment and software in a 5G testbed and claimed to have cut latency in half.
Verizon has conducted vRAN trials, with all three of its 5G access network suppliers (Nokia, Ericsson and Samsung), and has made some implementations, particularly in localized small cell networks and in pre-commercial 5G. The first trials, in the first quarter of 2018, took place in Oklahoma City, with the virtualized baseband functions running on Nokia’s AirScale cloud base station server, based on Intel’s Xeon processors and its FlexRAN reference architecture, which supports the RAN stack running on servers.
The architecture builds on existing centralized, but non-virtualized, units which Verizon calls cRAN hubs.
Nicola Palmer, the operator’s chief network engineer, said at the end of last year: “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.”
Verizon has also started to virtualize some functions in the upper layer, or Layer 3, of the network, within its own cloud architecture. This is not all about 5G, though it will go hand-in-hand with 5G NR 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,” said Bill Stone, Verizon’s VP of technology development and planning, last year. “We’re also going to … virtualize the upper layers for LTE as well.”
Stone said Verizon is working with its vendors to virtualize the lower layers of its 5G network too.
“Now that we can separate the software from the underlying hardware, it gives us more flexibility, and it’s important because it reduces latency. We also believe over time this is going to become a more efficient and cost-effective configuration,” Stone added.
There is still a long road ahead to make vRANs mainstream, and easily deployable by operators without the technology prowess and budgets of Verizon. Many MNOs remain sceptical of the architecture, and even some vendors – notably Huawei, despite its early involvement in the China Mobile tests – have questioned whether it can deliver the promised automation and reduction in TCO and power consumption. At this year’s Mobile World Congress, T-Mobile USA’s CTO Neville Ray said the RAN is so much more complex now than when C-RAN was first mooted, that it is now extremely challenging to disaggregate hardware and software in the RAN.
Yet the RAN is by far the most expensive part of the mobile network to deploy and run, and without a radical change in architecture, it will he hard to roll out 5G in a way that can be cost-justified. The move to a cloud-native network, at least in the second phase of 5G, underpins a very large part of the 5G proposition, in terms of reducing TCO by leveraging cloud economics, and enabling full service flexibility and developments like dynamic slicing. If the case for vRAN cannot be made convincingly, in the macro as well as the small cell layer, the whole 5G story will need to be recast.
If Nokia can keep the faith, it stands to steal an advantage from Huawei and Ericsson, and it already seems aware of this with its vRAN trials (with Orange and others), and its support for open initiatives such as ORAN Alliance and Telecom Infra Project, which are working on, among other things, interoperable fronthaul interfaces which could reduce the cost of a vRAN by allowing CUs, DUs and RUs to be mixed and matched.