Fiber to the Home (FTTH) Network: Choosing the Right FTTH Network Architecture | Corning

Darin Howe
Published: August 15, 2024

There’s never been a better opportunity for telecommunications service providers to bring broadband connectivity to the unserved and underserved. Thanks to the 2021 Infrastructure Investment and Jobs Act, $65 billion in federal funding is available to help service providers build new networks and extend high-speed internet access to the millions of Americans.

The most forward-looking solution for delivering this connectivity is building a fiber optic network, with four main fiber-to-the-home (FTTH) architectures to consider. Each architecture has tradeoffs in terms of upfront costs, engineering, inventory, maintenance, restoration, and future expandability. However, it's important to note that there are numerous variables at play when operators decide on the network architecture for their FTTH build. Based on our industry experience and expertise in assisting operators to build state-of-the-art FTTH networks, we will delve into the key considerations for each architecture.

Based upon my 15-plus years of experience in assisting operators to build state-of-the-art FTTH networks, I’ve put together the following guidelines, key considerations, and relevant comparison for each architecture.

Home Run FTTH architecture provides the highest bandwidth capability, as well as the best foundation for future needs. Within this architecture, operators have the option to either avoid using a splitter, which maximizes bandwidth for each subscriber, or implement a splitter at the signal source in the central office (CO) or headend. The latter approach helps to effectively distribute costs.

Advantages:

• Optimal bandwidth without the use of a splitter: With an unsplit Home Run architecture, each subscriber benefits from a dedicated link, receiving up to 100% of the signal from the source. This setup enables service providers to offer the highest internet speeds. However, to effectively distribute costs, operators typically opt to split their Home Run network in the CO or headend.
• Easier upgrades and maintenance: Since fiber optic cabling has virtually limitless bandwidth, the path to offering customers increased capacity with a Home Run architecture is simply a matter of upgrading the equipment at either end of the fiber run. And, since there’s less equipment used, there are fewer elements in the network to test, monitor, and manage.

Trade-offs:

• High upfront cost, slower installation: Home Run networks have the highest upfront cost due to the amount of materials and labor required and may take longer to build. Higher-fiber-count cables require more splicing and more installation costs from larger ducts. In addition to running a dedicated fiber for each subscriber, it’s usually recommended to include spare fiber in cables during the initial build to support additional needs or customers that may emerge down the road, such as a new business or wireless network equipment.
• Repairs and restoration: Home Run networks will have more cable with higher fiber counts distributed throughout the Outside Plant (OSP) portion of the network. These cables and the associated splices will take longer to repair and restore if the network is damaged.

The most common network architecture in the United States and Canada is Centralized Split (CS), in which a single split point is added between the CO and the end customers. This architecture is popular due to its balance of upfront cost, bandwidth capability, and future expandability.  

Advantages:

• Lower cost, faster installation: CS architecture provides a lower cost alternative to Home Run by reducing the amount of fiber needed to pass homes. Rather than running individual fibers to every subscriber, CS deploys lower fiber-count feeder cables to a centralized fiber distribution housing (FDH) located closer to subscribers. A splitter is then placed at the FDH transitions feeder fibers into distribution fibers that provide a dedicated connection between the FDH and each home. Since less fiber is used in the feeder, less upfront labor is needed for splicing, resulting in lower costs and shorter build times.
• Geographical flexibility: In CS architecture, splitters and optical line terminal (OLT) ports are typically deployed and utilized as take rate increases. Additionally, split ratios could be adjusted as needed to accommodate network needs like longer reach or to improve OLT efficiency. This approach provides financial benefits and flexibility across a range of geographical densities.
• Success-based deployment: Deploying splitters on a success-based approach as service is turned up for homes enables deferment of splitter costs and efficient OLT port utilization.

Trade-offs:

• There is a higher cost to the CS architecture, particularly relative to distributed architectures, as its rich fiber distribution needs more splicing and has higher placement cost.
• More equipment: The centralized cabinets that typically house the splitter in CS architecture are often large and require a dedicated pad, large vault, or pole space in addition to a splice location. This may require permitting or access to space on the right-of-way which adds cost and time for deployment. It can also be expensive and time-consuming to repair or expand these locations.
• Testing and troubleshooting: The centralized FDH can provide a testing point for certifying and troubleshooting the network. This can require extensive time and effort in the field to test the feeder and distribution networks.

Distributed Split (DS) architecture takes the CS philosophy a step further by adding an additional split point between the CO and subscribers. This is a more cost-effective method for bringing connectivity to less densely populated areas but has limitations in terms of maximum bandwidth and future expandability.

Advantages:

• Leaner distribution: DS gives service providers a cost-effective way to bring broadband connectivity to areas with fewer subscribers, or geographies in which competition with other service providers limits the take rate. DS utilizes less fiber than the above architectures, resulting in lower upfront material and labor costs along with faster installation time.
• Reduced access point size: Compared to CS architectures, which requires substantial space for a central fiber distribution housing to accommodate a 1:32 or even 1:64 splitter, DS architecture distributes the splitting over multiple tiers. So, instead of a single 1:32 splitter, a DS network can send a feeder cable from the CO to a 1:8 splitter, which then sends a feeder cable to a 1:4 splitter (or vice versa), resulting in the same 1:32 ratio. This allows the splitters to be housed in smaller closures or terminals that can be placed in hand holes. or hung on aerial lines, rather than in large above-ground cabinets.
• Smaller cables in Distribution: Distributed Split networks can utilize a 12 or 24-fiber cable through most or all the Distribution network which opens up low-cost deployment options like self-support deployment in aerial installs and the use of smaller ducts in underground installs.

Trade-offs:

• Less flexibility: Because of the added split level, DS networks have less flexibility to provide service reconfigurations in the future. The lower fiber count in cables typically results in less surplus fiber available for more demanding network needs such as businesses and wireless networks.
• Greater complexity: The addition of a second level of splitters means more equipment to maintain and document records, as well as more points to troubleshoot in the event of service disruptions. More OLTs have to be deployed on day one and are therefore less efficient.
• Changes for existing operators: A change from Centralized Split or Homerun architecture may require time to train and adapt inventory along with changes to mapping and IT systems.

Distributed Tap or Optical Tap (OT) architecture is a fiber-lean FTTH architecture, and thus has the lowest initial cost but the least room for future expansion. This architecture uses an uneven or unbalanced optical tap which typically feeds a symmetrical splitter (1:2, 1:4, or 1:8) to pass fibers to the home. The second output from the tap feeds back into the main fiber to pass power down to the next optical tap. A single fiber can be used to feed many combined tap or splitter locations in series. Power ratios in the uneven optical taps are engineered to optimize power down the series of taps.

Advantages:

• Lowest cost, comparatively quick installation: Distributed tap requires the lowest upfront investment in materials and labor and is fast to deploy. Plug-and-play options speed up deployment and, if splicing is chosen, it lowers the splice count significantly because much of the network can be deployed with 1 to 4 fiber cables.
• Ease of repair: This approach depends on common components that can be quickly replaced or repaired. When leveraging a plug-and-play solution, jumpers and terminals can be stocked and easily replaced if damaged.
• No large cabinets or housings: Distributed tap networks can be deployed with small terminals or closures to reduce the cost of deployment via smaller handholes or easier aerial attachment options.

Trade-offs:

• More upfront planning: While faster to install, distributed tap networks require careful planning to ensure sufficient optical power can traverse the often substantial distances to the final endpoint in the chain of optical taps. This complex engineering to optimize power can lead to a higher number of SKUs for more efficient design options.
• Reduced flexibility: Distributed tap networks are typically designed with fewer spare fibers and offer less flexibility for nonresidential subscribers. Therefore, if a new housing tract or factory is built in the area, the network may be unable to service them without deploying more fiber.
• Total cost: Distributed tap networks can be more costly to deploy than other architectures, driven by electronics inefficiency, underestimating future growth, more complex engineering costs, and the added cost of overlapping cables. However, splice-based designs can be attractive for rural deployments, depending on splicing costs.

While certain FTTH architectures lend themselves better to connecting certain geographies and customers, there is no hard-and-fast rule when it comes to selecting the best fit.

When weighing your options, it’s critical to look far into the future: because of its near-limitless bandwidth capacity, fiber optic infrastructure should be viewed as a long-term investment.

As such, when you weigh the total costs it’s usually best to choose a more fiber-rich architecture, as these permit a greater degree of expansion and flexibility in the future. Typically, the higher upfront costs can be more than offset by the reduced need for augmentation down the line. And with the wealth of infrastructure subsidies available today, there may never be a better opportunity to build a fiber-rich network for the future.

Regardless of your FTTH architecture choice, Corning offers a broad portfolio of solutions to maximize the value proposition of your network investment.

To learn more about FTTH network design click here.