HR's Brown: Longtime Coexistence for LTE & 5G Core Networks

It's probably a bit snarky to call the non-standalone (NSA) 5G network core a training wheels approach. But it wouldn't be totally inaccurate: Like a bike with four wheels, NSA allows many advantages of the fully fledged product without some of the deeper complexities.

In part one of this Q&A, Heavy Reading Principal Analyst Gabriel Brown told Telco Transformation that that the two approaches -- standalone and non-standalone -- will coexist well into the future. That, of course, is the successful approach the industry took in the migration from 3G and LTE. In part two, Brown will talk mor about the evolution of 5G.

Telco Transformation: Could you define precisely what you mean by the 5G-core network as a level set for the discussion?

Gabriel Brown: Often, we talk about 5G in terms of how well the 5G radio performs. But to actually deliver service, you really need an end-to-end system architecture. The core network is basically responsible for things like session management, mobility management, security, authentication, quality of service... all these kinds of things.

TT: There are two different approaches to the core network: The stand-alone and the non-stand alone. My understanding is the non-standalone is something that came about relatively recently.

GB: I don't know if that's quite the story. The idea behind non-standalone is to enable an early launch. The driver of 5G is a completely new system architecture. It has a lot of complexity and a lot of hard problems to solve. In the meantime, a lot of operators had a much more aggressive schedule for deployment and operation. They said, "We can make this a lot simpler by going with the existing LTE core." This is the so-called non-standalone mode. So, essentially, connecting 5G radio access to a 4G core network.

You can take away a lot of complexity and actually launch much faster. The idea has been around for a couple of years, at least.

TT: Quick revenue generation while the hard parts are in development. What’s not to like?

GB: When you first introduced 4G, users had a fallback onto 3G. It's the knowledge that the coverage can be quite limited in the initial period. So you're going to have a sense at least of a dual network strategy. By anchoring the subscriber onto the 4G core, you can remove an enormous amount of complexity from 5G itself and still have the ability to handover between the different racks, the different radio activities.

So now it looks like we are going to commercial launches somewhere around 2019. One of the reasons that's possible is that we have the 5G radio that will provide user-plane services. We won't need to have all the signaling and other advanced functionality. One of the things that makes it attractive is the basic architecture of a master cell for LTE and, then, a 5G serving cell that's already been specified for 4G. Where before you'd have a small cell or something like that as a serving cell for 4G. So, actually a little of the work has already been done to enable this. And, so, for an operator that wants to launch in 2019 or 2020, this is pretty compelling.

TT: Can you give me a flavor for the trade-offs between those two options?

GB: In simple terms, upgrading 4G core to support 5G is going to make deployment faster. It's going to be simpler. What you're giving up, probably, is some of the more advanced 5G services. They are going to need a bit of time to mature in any case. Some of the ultra-low latency mission-critical applications are examples.

What I think will likely happen in practice is that operators will have to make some investment in the 4G core even though the architecture and specifications are in good shape. They're still going to have to invest some resources and upgrade the existing core to take on 5G.

TT: It seems that the wireless industry is getting accustomed to these switchovers?

GB: Actually, over time you could probably see more of a migration than a hard switch over. So you might start to see a combined or a common 4G/5G core... It's pretty hard to know at this point, but certainly there are quite a few vendors and some operators thinking about how to do more of a smooth transition rather than a direct cut over. They want to make the migration as painless as possible, but at some point, there does need to be a kind of hard switch over.

TT: Are there any dangers to this approach?

GB: One of the sorts of concerns about NSA mode is that if it becomes very successful in a short period of time you'll end up with quite a lot of handsets in the active user base that work in that mode, but which don't support the required signaling for the full 5G core. What happens to all those devices? They're probably going to be premium tier devices for premium customers. It's going to be very difficult to abandon them. So, there's uncertainty and a bit of concern in that direction. For that reason, if it's popular, you're probably going to have to maintain the 4G core for some period anyway.

TT: Can they introduce a generation of phones that can be upgraded to move with a carrier from NSA to SA?

GB: That’s uncertain. It’s possible but not clear how practical it is at this stage.

TT: Has a pattern emerged: Have carriers begun making actual choices between SA and NSA or is this still kind of conceptual?

GB: It's hard to say how many have committed publicly, but companies such as T-Mobile and AT&T that are talking about their 5G launches are pretty much going to have to do that in NSA mode. It's similar for some of the Korean operators and Japanese operators. And we know quite a few of the big European operators also like this approach.

— Carl Weinschenk, Contributing Writer, Telco Transformation