BT’s Open RAN trial: A mix of excitement and pragmatism

“We in telecoms, we don’t do complexity very well.” So says Neil McRae, BT’s managing director and chief architect.

He was talking about the trend of making network architectures open and in particular the Open Radio Access Network (Open RAN), an approach that BT is trialling.

“In networking, we are naturally sceptical because these networks are very important and every day become more important,” says McRae

Whether it is Open RAN or any other technology, it is key for BT to understand its aims and how it helps. “And most importantly, what it means for customers,” says McRae. “I would argue we don’t do enough of that in our industry.”

Open RAN

Open RAN has become a key focus in the development of 5G. Open RAN is backed by leading operators, it promises greater vendor choice and helps counter the dependency on the handful of key RAN vendors such as Nokia and Ericsson. There are also geopolitical considerations given that Huawei is no longer a network supplier in certain countries.

“Huawei and China, once they were the flavour of the month and now they no longer are,” says McRae. “That has driven a lot of concern - there are only Nokia and Ericsson as scaled players - and I think that is a thing we need to worry about.”

McRae points out that Open RAN is an interface standard rather than a technology.

“Those creating Open RAN solutions, the only part that is open is that interface side,” he says. ”If you think of Nokia, Ericsson, Mavenir, Rakuten and Altiostar - any of the guys building this technology - none of their technology is specifically open but you can talk to it via this open interface.”

Opportunity

McRae is upbeat about Open RAN but much work is needed to realise its potential.

“Open RAN, and I would probably say the same about NFV (network functions virtualisation), has got a lot of momentum and a lot of hype well before I think it deserves it,” he says.

Neil McRaeBT favours open architectures and interoperability. “Why wouldn’t we want to to be part of that, part of Open RAN,” says McRae. “But what we are seeing here is people excited about the potential - we are hugely excited about the potential - but are we there yet? Absolutely not.”

BT views Open RAN as a way to support the small-cell neutral host model whereby a company can offer operators coverage, one way Open RAN can augment macro cell coverage.

Open RAN can also be used to provide indoor coverage such as in stadiums and shopping centres. McRae says Open RAN could also be used for transportation but there are still some challenges there.

“We see Open RAN and the Open RAN interface specifications as a great way for building innovation into the radio network,” he says. “If there is one part that we are hugely excited about, it is that.”

BT’s Open RAN trial

BT is conducting an Open RAN trial with Nokia in Hull, UK.

“We haven’t just been working with Nokia on this piece of work, other similar experiments are going on with others,” says McRae.

McRae equates Open RAN with software-defined networking (SDN). SDN uses several devices that are largely unintelligent while a central controller - ’the big brain’ - controls the devices and in the process makes them more valuable.

“SDN has this notion of a controller and devices and the Open RAN solution is no different: it uses a different interface but it is largely the same concept,” says McRae.

This central controller in Open RAN is the RAN Intelligent Controller (RIC) and it is this component that is at the core of the Nokia trial.

“That controller allows us to deploy solutions and applications into the network in a really simple and manageable way,” says McRae.

The RIC architecture is composed of a near-real-time RIC that is very close to the radio and that makes almost instantaneous changes based on the current situation.

There is also a non-real-time controller - that is used for such tasks as setting policy, the overall run cycle for the network, configuration and troubleshooting.

“You kind of create and deploy it, adjust it or add or remove things, not in real-time,” says McRae. “It is like with a train track, you change the signalling from red to green long before the train arrives.”

BT views the non-real-time aspect of the RIC as a new way for telcos to automate and optimise the core aspects of radio networking.

McRae says the South Bank, London is one of the busiest parts of BT’s network and the operator has had to keep adding spectrum to the macrocells there.

“It is getting to the point where the macro isn’t going to be precise enough to continue to build a great experience in a location like that,” he says.

One solution is to add small cells and BT has looked at that but has concluded that making macros and small cells work together well is not straightforward. This is where the RIC can optimise the macro and small cells in a way that improves the experience for customers even when the macro equipment is from one vendor and the small cells from another.

“The RIC allows us to build solutions that take the demand and the requirements of the network a huge step forward,” he says. “The RIC makes a massive step - one of the biggest steps in the last decade, probably since massive MIMO - in ensuring we can get the most out of our radio network.”

BT is focussed on the non-real-time RIC for the initial use cases it is trialling. It is using Nokia’s equipment for the Hull trial.

BT is also testing applications such as load optimisation between different layers of the network and between different neighbouring sites. Also where there is a failure in the network it is using ‘Xapps’ to reroute traffic or re-optimise the network.

Nokia also has AI and machine learning software which BT is trialling. BT sees AI and machine learning-based solutions as a must as ultimately human operators are too slow.

Trial goals

BT wants to understand how Open RAN works in deployment. For example, how to manage a cell that is part of a RIC cluster.

In a national network, there will likely be multiple RICs used.

“We expect that this will be a distributed architecture,” says McRae. “How do you control that? Well, that's where the non-real-time RIC has a job to do, effectively to configure the near-real-time RIC, or RICs as we understand more about how many of them we need.”

Another aspect of the trial is to see if, by using Open RAN, the network performance KPIs can be improved. These include time on 4G/ time on 5G, and the number of handovers and dropped calls.

“Our hope and we expect that all of these get better; the early signs in our labs are that they should all get better, the network should perform more effectively,” he says.

BT will also do coverage testing which, with some of the newer radios it is deploying, it expects to improve.

“We've done a lot of learning in the lab,” says McRae. “Our experience suggests that translating that into operational knowledge is not perfect. So we're doing this to learn more about how this will work and how it will benefit customers at the end of the day.”

Openness and diversity

Given that Open RAN aims to open vendor choice, some have questioned whether BT’s trial with Nokia is in the spirit of the initiative.

“We are using the Open RAN architecture and the Open RAN interface specs,” says McRae. “Now, for a lot of people, Open RAN means you have got to have 12 vendors in the network. Let me tell you, good luck to everyone that tries that.”

BT says there are a set of flavours of Open RAN appearing. One is Rakuten and Symphony, another is Mavenir. These are end-to-end solutions being built that can be offered to operators as a solution.

“Service providers are terrible at integrating things; it is not our core competency,” says McRae. “We have got better over the years but we want to buy a solution that is tested, that has a set of KPIs around how it operates, that has all the security features we need.”

This is key for a platform that in BT’s case serves 30 million users. As McRae puts it, if Open RAN becomes too complicated, it is not going to get off the ground: “So we welcome partnerships, or ecosystems that are forming because we think that is going to make Open RAN more accessible.”

McRae says some of the reaction to its working with Nokia is about driving vendor diversity.

BT wants diverse vendors that can provide it with greater choice and benefit from competition. But McRae points out that many of the vendors’ equipment use the same key components from a handful of chip companies; and chips that are made in two key locations.

“What we want to see is those underlying components, we want to see dozens of companies building them all over the world,” he says. “They are so crucial to everything we do in life today, not just in the network, but in your car, smartphone, TV and the microwave.”

And while more of the network is being implemented in software - BT’s 5G core is all software - hardware is still key where there are are packet or traffic flows.

“The challenge in some of these components, particularly in the radio ecosystem, is you need strong parallel processing,” says McRae. “In software that is really difficult to do.”

“Intel, AMD, Broadcom and Qualcomm are all great partners,“ says McRae. “But if any one of these guys, for some reason, doesn’t move the innovation curve in the way we need it to move, then we run into real problems of how to grow and develop the network.”

What BT wants is as much IC choice as possible, but how that will be achieved McRae is less certain. But operators rightly have to be concerned about it, he says.