Continuing on my recent theme of 5G assessment, I want to look today at the relationship between 5G, SDN, and NFV. Because 5G evolution is considered a given in the industry, many vendors in the SDN and NFV space have been eager to link their wares to 5G as a means of insuring they’re not trapped by slow discrete SDN and NFV adoption. Can SDN and NFV be pulled through by 5G, or would the linkage be as likely to slow 5G down?
We have to start with what’s almost a standard disclaimer, which is that the details of 5G architecture won’t be completely defined until Release 16, which isn’t due until mid-2020. The core architecture, however, will be available with Release 15 late in 3Q18. That means that we’re not really going to know the exact nature of 5G for about a year and a half. Even given that vagueness offers an unparalleled opportunity for positioning agility among vendors, that’s still a long time in the future.
The high-level model of 5G (an example is found HERE) envisions a five-layer structure with a Business Services Layer on top, then a Business Functions Layer, an Orchestrator layer next, then a Network Function Layer, and an Infrastructure Layer on the bottom. Operators who own infrastructure would implement all five layers, while those who offered “virtual network operator” or “over-the-top” services would implement the top two and would access infrastructure via a specifically called-out Northbound Interface exposed by the Orchestrator layer.
The NBI is important here because it’s the most specific (in most diagrams, the only specific) inter-layer interface that’s defined in the preliminary model. The presumption is that NBI-exported features (which I’ve been calling “behaviors”) are assembled into “vertical business functions” that are then combined within the Business Functions Layer to create retail services. Thus, in 5G, the NBI represents the boundary between what I’ve been calling the “service domain” and “resource domain”, referencing SDN/NFV or virtualization architectures. Below Orchestration, the Network Function layer presumably exports Network Functions for composition into my “behaviors”. These are assembled from the raw infrastructure.
Orchestration is a familiar NFV concept, of course, and many of the models of NFV orchestration map fairly nicely to the Orchestration layer of 5G. It also maps to AT&T’s ECOMP, Verizon’s SDN/NFV architecture, and a bunch of OSS/BSS models. In fact, the position of the Orchestration layer in 5G seems to make it clear that this isn’t NFV MANO—it has to deal with more generalized deployment processes. That’s where the ambiguity in the relationship between 5G and NFV comes in.
A Virtual Network Function is a hosted cousin of the Physical Network Function from which it is derived, according to classic NFV ISG thinking. It’s my view that the 5G model’s presumption is that a given “network function” in either it’s “V” or “P” flavor would be abstracted equivalently and exposed identically, so that the Orchestration process could use them interchangeably. From this, it’s clear that there is no reason why 5G couldn’t be built from infrastructure in which nothing was virtualized at all, as long as whatever PNFs were there were exposed correctly. All that means is that the function as a device could be deployed and managed.
In this approach, 5G orchestration is indeed NFV-like, but not like the ISG flavor of NFV that focuses explicitly on virtual function deployment. Instead it’s like the top layer of the ECOMP model, the Master Services Orchestrator or MSO. That means that from operators’ perspectives, 5G architecture and NFV depend on a common high-level concept of service orchestration. NFV does not define it, but it needs it. 5G will presumably define it, at least in terms of its NBIs.
You don’t need NFV to do the 5G architecture, but that doesn’t necessarily mean that NFV would have no value in 5G. To understand what the value could be, we have to look at the differences between VNFs and PNFs.
PNFs, meaning devices, are real boxes that tend to be put somewhere and sustained there until they break or a network topology change requires they be moved. Their functionality is typically fairly static, meaning that while they can be updated to add features their main mission is consistent. A “router” can have protocols and features added to it, but it typically stays a router.
VNFs, as hosted versions of PNFs, could also be viewed this way. You could build a network of routers or router instances, and if we assume that the hosting of the instances supported the performance requirements of the mission, the two would be equivalent. There are many missions of VNF that would be like this, and this mission is really more like that of a cloud-hosted router element than a VNF because none of the complexity of deployment or redeployment really applies to it. Virtual boxes of this type stay put like their PNF counterparts.
What would validate a VNF versus a PNF is dynamism. If a network of VNFs could benefit from different node placements and topologies, you can create those different models by simply re-instantiating and re-connecting, presuming you have a rich resource pool that’s highly interconnected. 5G doesn’t necessarily demand this kind of thing, however, and it will be difficult to say how much 5G would preference it versus another earlier network model for applications like IoT. We don’t have the details of 5G service or its architectural framework yet, nor will we for that year-and-a-half period.
But it’s SDN that is the big deal for 5G in my view, though it’s not clear just what “SDN” we’re talking about. Network slicing, as I noted earlier this week, is a multi-tenancy issue. SDN can support that in any OpenFlow, tunneling, or overlay model. To me, the big question about the value of 5G is how valuable network slicing will turn out to be. In addition, SDN could be a big part of a modern vision of mobility management to replace the old EPC concepts of previous wireless generations. A supercharged mobility management strategy could almost justify 5G on its own. We don’t need NFV for either of these, but we could sure use SDN.
We can’t wait forever, though. As I noted at the start of this blog, even foundation specs for 5G are a year and a half away, and the industry isn’t waiting. We’re already seeing things like the “fronthaul” movement in fiber, rich deployment of edge dark fiber to feed microcells in urban areas. Will an industry sit around and wait for formal specs when they have assets that could be exploited? An outrun standard is an irrelevant standard, except insofar as it drives industry attention and moves markets. 5G could be another indication that formal standardization just cannot keep up with the information age, and if that’s true then it’s the ad hoc market reaction to 5G and not 5G itself that we have to watch for SDN/NFV impact.