Rakuten spills beans on software revamp and why Cisco hasn't gone

Granite Rapids. It sounds like a hazardous stretch for white-water rafting. But in the turbulent world of telecom technology, it's a forthcoming processor architecture from Intel that marks the next destination for Rakuten. Through Mobile and Symphony – its two telecom ventures – the Japanese company seems to have paddled smoothly alongside the US chips giant ever since plunging into the murky waters of the radio access network (RAN). But Granite Rapids, appropriately enough, could be harder to navigate.

When Rakuten Mobile built its network in Japan, it paired Cascade Lake and Ice Lake, two older Intel platforms, with software written by Altiostar, a US company it subsequently bought (before rebranding the product to SymRAN), inside its central and distributed units (CUs and DUs). At the time, it had little choice. Processor alternatives for the virtual RAN did not exist beyond Intel. Altiostar, moreover, had built its software on FlexRAN, an Intel reference design that still works only with Intel's chips.

But several years later, the market looks quite different. Intel has moved from Ice Lake to Sapphire Rapids, the architecture now shipping, and it plans a commercial launch of Granite Rapids next year. And Intel is no longer the only boat on the water. Chip companies including AMD, Marvell, Nvidia and Qualcomm have all pushed off with some kind of product offer.

It has set off a technological shakeup on the RAN side at Rakuten. Sharad Sriwastawa, the CEO of both the Mobile and Symphony businesses, is now pursuing a two-track software strategy, he revealed to Light Reading at Mobile World Congress (MWC) last week. "We initiated two projects this year," he said. "One is going for Granite from FlexRAN and the other is taking the entire stack and porting this to AMD or other chipsets."

Beyond Intel

In moving to Granite Rapids, some adaptation is necessary because Intel's products increasingly rely on hardware "accelerators," customized silicon, to handle the most demanding software functions. With Sapphire Rapids, Intel stumps up hardware and code to accelerate the resource-hungry FEC (forward error correction). All other software, written by independent software vendors, is hosted on Intel's central processing units (CPUs). But Granite Rapids goes further, pitching an accelerator for various enigmatically named functions like fast Fourier transform (FFT) and sounding reference signal (SRS), besides FEC.

This seems like a tacit acknowledgement by Intel that ordinary CPUs will not be able to keep pace with the demands of 5G RAN software. But it also means Rakuten cannot simply copy and paste its old code, even if the changes are not dramatic, according to Sriwastawa. "The software will have to change and adapt, but it's not useless," he said.

His initial plan was adaptation for the architecture now shipping. But Intel's sprint through technology generations means that plan has also changed. "Everything was done with Sapphire Rapids – the design, especially for the next-generation DU – but now we're moving to Granite Rapids," said Sriwastawa.

More dramatically, on its other software track, Rakuten is examining competitors to Intel, including AMD and "inline" accelerators. Where Intel is attempting to keep as much software as possible on the CPU, inline moves the whole of Layer 1 – the category of most demanding functions – to separate customized chips, typically hosted on cards that can be plugged into a server. Marvell, Nvidia and Qualcomm have all announced inline offers in the last couple of years.

Sriwastawa seems eager to assess the results of research he carries out this year before making any firm commitments one way or the other. But Rakuten cannot simply tweak Layer 1 software written for Intel's x86 processors to work on these custom chips. It would probably need an entirely new set of code in parallel, and that could necessitate additional investments.

A more economical option, potentially, would be to rely on a third party like Qualcomm, whose Layer 1 inline accelerator comes with both hardware and all the requisite software. Rakuten flagged a RAN partnership with Qualcomm as far back as February 2022, although little seems to have come of it so far. Nevertheless, Rakuten could theoretically combine Qualcomm's Layer 1 code with its own existing software for less resource-hungry Layer 2 and 3 functions to avoid major software investments.

All of this, of course, would be done with customers of Symphony in mind. Today, they include telcos such as Germany's 1&1, now building a fourth mobile network in Europe's largest economy. But under new plans unveiled at MWC, SymRAN will be available for a licensing fee to manufacturers of radio units (RUs) and systems integrators, including telcos that want to play this role.

"We don't have a huge sales team, and there are these RU manufacturers who are strong in their own territory, especially considering 5G enterprise use cases," said Sriwastawa. Systems integrators, meanwhile, will be able to license software, combine it with an RU and pitch the combination to operators, he explained.

Rocky road

How the FlexRAN-based domestic RAN of Cascade Lake and Ice Lake servers will evolve is less clear. But other parts of the Rakuten Mobile network are also due for an overhaul. When the telco launched its inaugural 4G service in April 2020, it did so on a Cisco 4G core and cloud platform provided by IBM-owned Red Hat. That was far from ideal, said Tareq Amin, Sriwastawa's predecessor, in June of that year. By October 2021, Rakuten would have fully migrated to a 5G standalone (SA) core provided by Japan's NEC, he said. And Cisco would not survive the shift.

Red Hat was also put on death row after Rakuten bought Robin.io, a rival Kubernetes platform, in February 2022. Amin reckoned he could halve costs by switching from a Red Hat service based on OpenStack, an aging open-source virtualization platform, to Robin.io. A few months later, he told publications including The Mobile Network and TelecomTV that he would also remove a Linux-based operating system (OS) provided by Red Hat. The plan there was to introduce Rocky Linux, an OS alternative that – in Amin's view – remained truer to the open-source faith.

Yet most of these plans have not come to fruition, Sriwastawa revealed to Light Reading at MWC. For a start, Cisco is still Rakuten's core network provider, with Nokia providing IMS (Internet Protocol multimedia subsystem) technology and Oracle introduced for policy and charging. NEC is not in the mix. "We didn't go on that route because we decided not to do SA," said Sriwastawa. A lack of SA-compatible handsets for the Japanese market and Rakuten's own spectrum constraints largely explained that decision, he said.

Red Hat is also still a supplier to Rakuten, according to a senior executive at the IBM subsidiary. "They went and they bought Robin.io, they bought Altiostar and they tried to put somebody else's Linux in there – aka Rocky – and they're still running real-time RHEL [Red Hat Enterprise Linux] in that system and they're still buying our technology and our support," said Ian Hood, Red Hat's chief technologist for global service providers, when he met Light Reading at MWC.

Sriwastawa's ultimate objective remains identical to Amin's – to run the whole network on the Robin.io platform. "This makes life very easy from an operational perspective, from a skillset perspective, from a hardware perspective, with a single SKU [stock-keeping unit] for hardware," he said. "If we want to be lean, that is the approach we have to take."

The challenge is persuading third-party application developers to play along. Next year, Sriwastawa hopes to begin the long-delayed SA-related overhaul of the core network, and Rakuten is in talks with numerous vendors about this, including Cisco. But the two companies, evidently, have not seen eye to eye. "The way they want to do 5G core is on their core hardware, on UCS [Unified Computing System] – that is their strategy," said Sriwastawa.

He rates the level of "cloud agnosticism" – meaning the ability to host software applications in any cloud environment – as "not that great" when it comes to the RAN. In other domains, though, Rakuten continues to work on testing with numerous third parties, including Nokia, the provider of the IMS application. "Nokia is migrating from CBAM [CloudBand Application Manager]," said Sriwastawa, with reference to Nokia's in-house platform. "It is on CBAM today and we're migrating it to Robin.io."

Coverage conundrum

The Finnish vendor will have a somewhat beefed-up role at Rakuten Mobile after landing a contract with it to provide 700MHz-compatible radios for a much-needed coverage boost. Having previously lacked any low-band spectrum – good for penetrating buildings and wide-area coverage – Rakuten last year struck a deal with KDDI, its long-standing roaming partner, for use of sub-1GHz frequencies. Then, in October, it secured a 3MHz sliver of 700MHz spectrum from Japan's government.

It is this spectrum that Rakuten will bring into use with Nokia, pairing its SymRAN software with the Finnish company's radios in an example of open RAN, where different vendors are combined at the same mobile site. "We'll start deploying from June this year," said Sriwastawa. Rollout will proceed slowly because the 700MHz spectrum is still subject to broadcasting interference in some parts of the country, but the plan is to be "surgical, wherever we have a coverage hole," said the Rakuten executive.

He is sticking to earlier guidance on costs, which is that Rakuten can spend as little as 54.4 billion Japanese yen (US$370 million) on 700MHz rollout over a ten-year period. From a financial perspective, then, this is no game changer for Nokia. Where Rakuten might eventually have to spend much more is on 5G coverage, which remains "low" across swathes of the country, including Tokyo, Sriwastawa admits. It is evident in site numbers, too. At the end of last year, Rakuten had 60,940 4G macro cell sites in service but only 11,592 5G ones.

"5G sites are low, especially in Tokyo, because we are interference-limited," said Sriwastawa. "So even if we deploy sites, we cannot transmit at full power." The interference is caused by the proximity of spectrum to frequencies still used by satellite services. By next year, however, regulators may finally have addressed the problem.

This could be a mixture of bad news and good news for Rakuten. Bad because a new wave of spending on 5G rollout in Tokyo might hinder company efforts to end losses and eventually turn a healthy profit. Good because Rakuten already claims to have massive MIMO, an advanced 5G technology, working at its current 5G sites, where it has paired NEC radios with SymRAN software.

NTT Docomo, the market leader, has not made investments in this technology, according to both Sriwastawa and Tommi Uitto, the head of the mobile business group for Nokia, a Docomo supplier. Japan's biggest telco has avoided massive MIMO partly because it likes to mix products from different vendors at its mobile sites, Uitto told Light Reading at MWC. Pairing vendors remains difficult in massive MIMO, even with new open RAN specifications, he said.

Sriwastawa also brushed off suggestions that its relatively poor 5G coverage puts it at a competitive disadvantage. "Not just for us but for any operator in Japan, 5G is lagging big time because of this interference," he said.  

He has reason to be happier about a recent uptick in subscriber numbers. After struggling to grow its base of customers for many months, Rakuten added 840,000 in the final quarter of 2023 to finish the year with about 6 million. It needs between 8 million and 10 million to break even, it has said, and believes that target is achievable by the end of 2024.

Yet the improvement in the final quarter of 2023 was driven largely by low-spending customers in the business sector, said Sriwastawa. Success in the mainstream consumer market will be critical if Rakuten Mobile is to thrive.