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16 February 2021

The true open source RAN needs a tier one champion to become a reality

The ‘open source RAN’ remains the stuff of dreams, even according to some of the challenger vendors that are making progress in opening up the cellular ecosystem. Some of this relates to the difficulty of applying classical open source models, as epitomized by the frameworks of the Apache Foundation, to chips and other hardware (see separate item). But even when it comes to the software element of the virtualized RAN (vRAN), there is very little work being done on RAN network functions that could be downloaded for free to any baseband or radio unit.

For those that believe a true open source model is the best way to throw open the doors to the RAN market, a depressing sight is that of the WiFi sector. The WiFi ecosystem is undoubtedly more open than that of cellular, with a diverse set of vendors of access points and other elements. The openness has helped make WiFi equipment affordable and applicable to a huge range of use cases. But the IEEE and WiFi Alliance, which publish the specifications, are conventional standards organizations; open source efforts such as OpenWrt have been fragmented in their impact; and in many higher end systems, proprietary embedded software remains the norm.

Of course there is plenty of open source code in use in mobile networks, not least in various flavors of the Linux operating system and in elements of NFV and containerisation infrastructure. But so far, opening up the RAN to a broad base of software developers is being achieved through reference platforms rather than pure open source platforms.

These may be defined and distributed by open organizations such as the Open Networking Foundation (ONF), or by individual vendors that open up their platforms in order to achieve broad impact for their products and services. An example of the latter is Intel’s FlexRAN software reference stack, which has been extensively used in early vRAN developments and trials.

The emerging RAN Intelligent Controller (RIC) is one of the areas where the two approaches are playing out. While the O-RAN Alliance and the ONF are creating open RIC platforms for which many third parties can develop xApps, Intel is working with VMware’s RIC to do the same – an instance of the chip giant building interfaces to other companies’ products to extend the reach and functionality of FlexRAN, with the aim of making it a de facto standard through sheer ubiquity.

Release 1.0 of ONF’s SD-RAN promises a “complete open source RAN solution for developers” spanning the key O-RAN elements – the nRT RIC, the radio unit, distributed unit and central unit (RU/DU/CU), and a framework for developing xApps, the concept underpinning the RIC. This can be implemented entirely virtually or on reference white box hardware. A fledgling SDK is being shared with the O-RAN Software Community (the open source wing of the O-RAN Alliance) to support and promote availability of interoperable xApps that can work with a selection of nRT-RIC implementations.

The RIC is important, in its near-real time flavor, because it potentially opens up critical RAN management functions that were previously embedded. However, it will have to prove it can perform these very demanding functions at the same level as integrated solutions before it will be adopted in large networks. And that barrier to open source is even greater when it applies to the whole radio software, as the demands of 5G get ever-more stringent.

Some argue that the only way that radio software – of sufficient capability to win operator trust for their macro networks – would be made available under a general open source licence would be if a giant like Intel triggered the move. If Intel open sourced FlexRAN, it would be gambling on achieving the kind of dominance of the ecosystem that IBM did with some of the IT technologies it committed to open source in the 1990s.

But it might just split the industry – after all, AT&T put its xRAN code into open source, but while that was a catalyst for O-RAN, that has moved away from general open source licensing. And IBM was, though wounded, still the king of IT back in those days, so its action was more akin to Ericsson open sourcing its radio platform than Intel.  A hypothetical open FlexRAN would still need the big RAN vendors on board, just as O-RAN will to achieve maximum scale, and we are still waiting to see the outcome of the game of ‘who blinks first’ between the operators and the largest vendors (with Nokia playing both sides).

In a recent interview with SDxCentral, Steve Papa, CEO of O-RAN vendor Parallel Wireless, said: “Maybe open source in radio is all about the chicken and the egg, and someone like Intel needs to step up and catalyze it. Otherwise all you’re doing is creating proprietary stovepipes. FlexRAN, if it’s only for Intel processors, well someone else is going to build one for other processors. And the operators lose; in fact, open RAN moves slower, moves slower for Intel as well.”

He added: “We need people that want to accelerate open RAN to step up and accelerate it by contributing some of this stuff to open source for the radio.”

For now, ‘open’ organizations focused on the RAN are adopting a hybrid approach. ONF, for instance, uses a combination of elements, some defined by open source organizations and some by standards bodies. Some of its platforms, such as the Open Network Operating System (ONOS) are fully open source and subject to the Apache process. Others rely on licensed technologies.

It offers its developments under two main models:

  • Technical specifications include ONF’s reference designs and OpenFlow portfolio of standards, and are licensed under the Foundation’s RAND-Z (reasonable and non-discriminatory) IPR policy for licensing.
  • Technical recommendations, which are normative documents that define APIs, data models, protocols, information models and similar. These are open source under the Apache 2.0 system and may be freely used if formally cited, not altered, and not commercially sold.

When Telecom Infra Project (TIP) was first established by Facebook, it was billed as an open source initiative to drive commonality and scale economics into the telco network. But it became clear that a more nuanced approach was needed to attract companies that had developed highly differentiated contributions. Many small vendors – as well as many operators – remain concerned by the risks that open source brings in terms of quality, control and patent licensing.

One of the start-ups that was chosen, in 2017, to be incubated by Orange under the TIP ecosystem acceleration center (EAC) program was Amarisoft, whose CEO Franck Spinelli said at the time: “We don’t want to let our technology go for nothing. We want money for that.” While Facebook (and others) have open sourced their own contributions to the project, the option of licensing under RAND (reasonable and non-discriminatory) principles is open to any working group or member, and in 2017, Facebook initiated a new TIP group specifically to support RAN licensing.

Meanwhile, the O-RAN Alliance has a two-string approach familiar from the IT industry (and Android), in which an open source community exists alongside a more commercially driven structure. O-RAN started life combining the efforts of two groups, xRAN foundation and Cloud-RAN Alliance, and its current incarnation shows the heritage of both. The former was hosted by the Linux Foundation with seed code open sourced by AT&T, while the latter was more closed.

The O-RAN Software Community is an open source grouping that sits alongside the O-RAN Alliance, and last month published its ‘Cherry’ software release. Cherry contains new functions aligned with O-RAN specifications including the E2, A1 or O1 interfaces, and new service management & orchestration (SMO) elements.