When to Deploy VDSL2 vs. GPON? Bell Labs Study Provides Answers

One of the great things about statistical analysis is that the more accurate information you can use as parameters and metrics, the more precise a determination you can make about what typically could be considered a hypothetical construct. In fact, unlike the recent lack of precision in U.S. presidential primaries which rely on human opinions, when it comes to outside plant planning for providing ultra-broadband networking infrastructure, there is a lot of useful information out there for doing rather precise calculations. In short, well-informed modeling can be extremely valuable.

Such is the case with a new study by Nokia’s Bell Labs (News - Alert) Consulting organization which takes a deep dive into the business case for both VDSL2 vectoring and GPON. It is a study which is already finding traction with fixed access providers as they seek to be fast to market and cost-effective in the planning and deployment of ultra-broadband plant and the services that use each. 

As outlined in a recent TechZine article about the study, VDSL2 and GPON study finds sweet spots, by Mohamed El-Sayed, Samrat Kulkarni and Robert Novo of Bell Labs Consulting, communications service providers (CSPs) can accurately determine the optimal use of both solutions long and shorter term. 

The study focused on comparing VDSL2 and GPON technologies where subscribers demand ultra-broadband access speeds across a range of serving areas with characteristics that varied according to various parameters, including Customer base; Area topology and morphology; Existing network and facilities; Cost factors; and Competition.

The authors explain that while they could not analyze every distribution area since there can be hundreds of thousands in a given fixed access network. Hence, as a first step, they determined what would constitute statistically valid representative areas. The key parameters were subscriber density, percentage of residential vs. business customers, and copper-loop quality. For each type, the fixed access technologies were evaluated to compare capital expenses, operational expenses, total cost of ownership (TCO), and the business cases. 

The study is filled with detailed comparisons of VDSL2 and GPON based on the parameters established. They are more than worth a careful examination as the criteria show there are great business cases for both. And, obviously the answer as to which one is best for a given scenario can be summed up in the phrase, “It Depends.” 

That said, without going into the details, a significant takeaway is that for “brownfield” situations, when all things are considered, VDSL2 is the way to go. This is illustrated in the chart below that shows a brownfield study result based on Bell Labs studies performed with customers in Latin America. As the authors note, in this example GPON barely breaks even in 5 years, and only if a portion of the customers subscribe to at least 50 Mbps. While with VDSL2, the service provider breaks even between 2 and 4 years, depending on the speeds offered.

VDSL2 versus GPON business case comparison

The case for a fiber-enriched diet

This is not to say that VDSL2 always beats out GPON. The authors point to additional analyses where fiber wins out over copper:

• In “greenfield” areas where it is most cost-effective to serve the premises with fiber.
• Distribution areas, such as commercial districts or business parks, where a significant percentage of subscribers are enterprises with demands that exceed the speeds that can be supported by the copper infrastructure.
• Areas with intense competition where the service provider wants to showcase services that require fiber and ultra-high access speeds.

So which technology choice is the way to go?

The authors of the study provide the following guidance:

In many cases, the choice may not be clear between one technology or another. Rather, subscriber bandwidth demands in different serving areas will require the flexibility to offer a mix of technologies concurrently.

Service providers will need to deploy copper and fiber access concurrently within the same network. Service providers also need to have the flexibility to quickly upgrade from VDSL2 to GPON, if and when demand increases, such as when a competitor enters an area currently served by an incumbent.

To paraphrase a common term used in the U.S., the study reveals the importance of “Know before you dig.”  

The comparisons show that in the short-term in brownfield situations, the business case and total cost of ownership (TCO) for VDSL2 over GPON is demonstrable. However, over the longer-term—depending on unique CPS conditions including costs (labor, fuel, etc.), revenues (customer base, competition), and even variations within particular serving areas— “every case should be closely analyzed individually.”  

Realities are that it would be great to have end-to-end universal optical connectivity. That said, having tools that enable sound planning to get from here to what could be a very distant all-optical future while remaining highly competitive in the process, as the study confirms, is a good place to start.