FTTH vs FTTB

Fiber to the Home (FTTH) and Fiber to the Building (FTTB) are two access network architectures that both use optical fiber in the access segment, but they differ in where the fiber terminates and how the signal reaches the subscriber. FTTH brings fiber all the way to the individual living unit—a house or an apartment. FTTB stops the fiber at the building's boundary, typically in the basement or a telecommunications room, and uses existing copper or coaxial infrastructure to distribute the signal to each unit within the building.

The distinction is not merely about where the fiber ends. It determines the bandwidth available to each subscriber, the cost and complexity of deployment, the operational model for the service provider, and the migration path to future speeds. FTTH offers the highest performance and the cleanest upgrade path, but it requires new in-building wiring and a higher upfront investment per subscriber. FTTB leverages existing in-building copper, which lowers deployment cost and shortens installation time, but it limits the per-subscriber bandwidth and creates a bottleneck in the building's internal wiring.

The choice between them depends on the target market, the building type, the existing infrastructure, and the service provider's business model. In greenfield deployments and single-family homes, FTTH is almost always the right choice. In multi-dwelling units (MDUs) with existing copper infrastructure and a price-sensitive subscriber base, FTTB can be a pragmatic intermediate step. In many real networks, the two architectures coexist: FTTH for new builds and premium subscribers, FTTB for existing buildings where the cost of rewiring is prohibitive.

This guide examines both architectures in depth: their network topology, physical layer characteristics, bandwidth and latency performance, deployment requirements, cost structures, application scenarios, and the migration path from FTTB to FTTH.

1. What Is FTTH?

FTTH, or Fiber to the Home, is an access network architecture in which optical fiber runs from the operator's central office (or a remote optical line terminal) all the way to the individual subscriber's living unit. The fiber terminates at an Optical Network Terminal (ONT) inside the home or apartment.

The dominant FTTH technology is the Passive Optical Network (PON). A PON uses a point-to-multipoint topology in which a single optical fiber from the OLT is split by passive optical splitters to serve multiple subscribers—typically up to 32 or 64 ONTs per OLT port. The PON consists of three elements: the OLT at the central office, the passive Optical Distribution Network (ODN) comprising fibers, splitters, and connectors, and the ONT at the subscriber premises.

At the ONT, the optical signal is converted to electrical form for distribution within the home via Wi-Fi or Ethernet. FTTH delivers dedicated optical connectivity to each subscriber, with no sharing of the in-building infrastructure.

1.1 FTTH Characteristics

• Fiber reaches the living unit: Optical fiber terminates inside the home or apartment.

• Dedicated optical path: Each subscriber has a dedicated fiber from the splitter to the ONT.

• Highest bandwidth: Supports GPON, XG-PON, XGS-PON, and emerging 50G-PON.

• Future-proof: Upgrade path to higher speeds requires only replacing the ONT and OLT optics.

• Higher deployment cost: Requires new in-building fiber cabling to each unit.

• Best for: Single-family homes, greenfield MDUs, premium subscribers.

2. What Is FTTB?

FTTB, or Fiber to the Building, is an access network architecture in which optical fiber runs from the operator's central office to a point inside the building—typically the basement, a telecommunications room, or a street cabinet near the building. From that point, the signal is distributed to individual units using the building's existing copper or coaxial infrastructure.

The most common FTTB implementation uses VDSL or G.fast over the existing twisted-pair telephone wiring in the building. A DSL access multiplexer (DSLAM) or a G.fast distribution point unit (DPU) is installed at the fiber termination point, and the existing copper pairs are used to reach each apartment. In buildings with coaxial cable infrastructure, FTTB may use DOCSIS or MoCA over coax.

FTTB is often described as a hybrid fiber-copper architecture. The fiber provides high-capacity transport to the building, while the copper infrastructure provides the final drop to each unit. The result is a shared bandwidth model: the fiber capacity is shared among the building's subscribers, and each subscriber's speed is limited by the copper technology and the distance from the distribution point.

2.1 FTTB Characteristics

• Fiber reaches the building: Optical fiber terminates at a building-level distribution point.

• Copper in-building distribution: Existing twisted-pair or coaxial cable reaches each unit.

• Shared bandwidth: Fiber capacity is shared among the building's subscribers.

• Lower deployment cost: Leverages existing in-building copper infrastructure.

• Faster installation: No new in-building wiring required for basic service.

• Limited upgrade path: Copper infrastructure becomes the bottleneck at higher speeds.

• Best for: Existing MDUs with copper infrastructure, price-sensitive markets.

3. Architecture Comparison

The fundamental architectural difference between FTTH and FTTB is where the optical-to-electrical conversion happens and what medium carries the signal to the subscriber.

In FTTH, the entire access path is optical. The signal remains in the optical domain from the OLT to the ONT, with passive splitters providing the point-to-multipoint connectivity. In FTTB, the optical path ends at the building, and the signal is converted to electrical form for distribution over the existing copper infrastructure.

4. Bandwidth and Speed

Bandwidth is the most visible difference between the two architectures. FTTH provides dedicated optical bandwidth to each subscriber, while FTTB shares the fiber capacity among the building's subscribers and is limited by the copper in-building distribution.

4.1 FTTH Bandwidth

FTTH supports the full range of PON technologies. GPON provides 2.5 Gbps downstream and 1.25 Gbps upstream, shared among up to 64 subscribers on a PON tree. XG-PON provides 10 Gbps downstream and 2.5 Gbps upstream. XGS-PON provides 10 Gbps symmetrical. 50G-PON, currently being standardized, will provide 50 Gbps symmetrical.

In practice, FTTH packages typically offer 100 Mbps to 1 Gbps per subscriber, with premium packages offering 2 Gbps, 5 Gbps, or even 10 Gbps. Because each subscriber has a dedicated fiber from the splitter, the bandwidth is not shared with other subscribers on the same PON tree.

4.2 FTTB Bandwidth

FTTB bandwidth is limited by the copper technology used for in-building distribution. VDSL2 provides up to 100 Mbps downstream and 40 Mbps upstream over short distances (typically up to 300 meters). G.fast provides up to 1 Gbps downstream and 500 Mbps upstream over very short distances (typically up to 100 meters). DOCSIS 3.1 over coax can provide up to 1 Gbps downstream in a shared configuration.

The actual speed depends on the distance between the subscriber's unit and the distribution point, the quality of the copper pair, and the number of subscribers sharing the same binder. In a typical MDU, VDSL2 speeds range from 20 to 80 Mbps, while G.fast speeds range from 200 to 800 Mbps depending on loop length.

5. Latency and Performance

Latency and jitter are critical for real-time applications such as video conferencing, cloud gaming, and remote collaboration. The two architectures differ in the latency introduced by the in-building distribution.

FTTH introduces very low latency because the signal remains in the optical domain from the OLT to the ONT. The only latency contributions are fiber propagation (approximately 5 microseconds per kilometer) and the PON protocol overhead, which is typically in the range of tens to hundreds of microseconds depending on the PON technology and the upstream scheduling.

FTTB introduces additional latency in the copper distribution segment. VDSL2 and G.fast use complex modulation and forward error correction, which add processing delay. The retransmission and interleaving used to combat impulse noise on copper pairs also add latency. In practice, FTTB latency is typically 5 to 20 milliseconds higher than FTTH latency for the same application, depending on the copper technology and the loop length.

6. In-Building Distribution

The in-building distribution is where the two architectures diverge most significantly. FTTH uses optical fiber to each unit; FTTB uses the existing copper infrastructure.

6.1 FTTH In-Building Distribution

FTTH requires a fiber cable from the building's entry point to each living unit. In a new building, this fiber can be pre-installed in conduits during construction, making the installation straightforward and cost-effective. In an existing building, the fiber must be routed through existing cable ducts, along corridors, or through wall penetrations—a process that can be disruptive and expensive.

The fiber used for in-building distribution is typically single-mode fiber with a bend-insensitive design, allowing it to be routed around tight corners. The fiber terminates at an ONT inside each unit, which provides Wi-Fi and Ethernet connectivity for the subscriber's devices.

6.2 FTTB In-Building Distribution

FTTB leverages the existing copper infrastructure in the building. In most MDUs, this is twisted-pair telephone wiring that was installed for voice service. The copper pairs run from the building's telecom room to each unit's telephone outlet.

The FTTB distribution point—a DSLAM or G.fast DPU—is installed in the telecom room and connected to the fiber. The existing copper pairs are then used to carry the broadband signal to each unit. The subscriber connects a VDSL or G.fast modem to the telephone outlet to receive the service.

The advantage of FTTB is that no new in-building wiring is required. The existing copper pairs are reused, and the installation can be completed without entering individual units. The disadvantage is that the copper infrastructure limits the achievable bandwidth and may be degraded or poorly maintained.

7. Deployment and Construction

Deployment complexity and construction requirements differ significantly between the two architectures.

7.1 FTTH Deployment

FTTH deployment in an MDU requires fiber to be routed from the building's entry point to each living unit. This involves installing a fiber riser cable through the building's vertical shafts, pulling fiber along each floor's corridor, and splicing or connecting the fiber to each unit's drop cable.

In new construction, the fiber can be installed during the building's construction, with minimal additional cost. In existing buildings, the installation is more complex and may require drilling through walls, routing cable along corridors, and installing new cable trays or conduits. The process is labor-intensive and may require coordination with building management and residents.

7.2 FTTB Deployment

FTTB deployment is simpler and faster. The fiber is pulled to the building's telecom room, where the DSLAM or G.fast DPU is installed. The existing copper pairs are then connected to the distribution point, and service can be activated for each subscriber by connecting their unit's copper pair to the DSLAM port.

The installation does not require entering individual units, which reduces disruption and simplifies logistics. The service can be activated remotely, and the subscriber can self-install the VDSL or G.fast modem by connecting it to the existing telephone outlet.

8. Cost Comparison

The cost structure differs significantly between the two architectures, with FTTH having higher upfront costs but a clearer long-term upgrade path.

8.1 FTTH Cost

FTTH cost includes the outside plant fiber, the OLT port, the in-building fiber cabling, and the ONT in each unit. The in-building fiber cabling is the primary additional cost compared with FTTB: it requires labor for routing, splicing, and connectorization, and it may require new cable trays or conduits.

The ONT in each unit adds equipment cost, but this is comparable to the VDSL/G.fast modem that the subscriber would need in an FTTB deployment. The ongoing operational cost of FTTH is low, and the network can be upgraded to higher speeds by replacing the ONT and OLT optics, without touching the in-building fiber.

8.2 FTTB Cost

FTTB cost includes the outside plant fiber, the OLT port, the DSLAM or G.fast DPU in the building, and the subscriber's VDSL/G.fast modem. The in-building copper infrastructure is already installed, so there is no cost for new in-building cabling.

The DSLAM or DPU is shared among the building's subscribers, so the per-subscriber equipment cost is lower than an ONT. However, the copper infrastructure has a limited lifetime and may require maintenance or replacement as it ages. Upgrading to higher speeds requires installing new fiber to each unit, which is the same cost as a greenfield FTTH deployment.

9. Service Scenarios

The choice between FTTH and FTTB depends on the target market and the building type.

9.1 FTTH Service Scenarios

• Single-family homes: FTTH is the natural choice; no in-building distribution is required beyond the drop to the ONT.

• Greenfield MDUs: New construction can include in-building fiber at minimal additional cost.

• Premium subscribers: Subscribers requiring gigabit or multi-gigabit speeds, low latency, and symmetrical bandwidth.

• High-ARPU markets: Markets where subscribers are willing to pay for the highest performance.

• Future-proof deployments: Networks designed for long-term evolution to 10G, 50G, and beyond.

9.2 FTTB Service Scenarios

• Existing MDUs with copper infrastructure: Buildings with usable twisted-pair or coaxial wiring where rewiring is expensive or disruptive.

• Price-sensitive markets: Markets where subscribers prioritize low monthly fees over maximum speed.

• Rapid deployment scenarios: Situations where service must be activated quickly without unit-by-unit installation.

• Intermediate step to FTTH: FTTB can be deployed as a temporary solution while FTTH migration is planned and funded.

• Buildings with difficult fiber routing: Older buildings where routing fiber to each unit is technically challenging or prohibitively expensive.

10. Standards and Ecosystem

FTTH and FTTB are both supported by mature international standards, but they draw on different technology ecosystems.

10.1 FTTH Standards

FTTH is standardized by ITU-T (G.984 GPON, G.987 XG-PON, G.9807 XGS-PON, G.9804 50G-PON) and IEEE (802.3ah EPON, 802.3av 10G-EPON). These standards define the PON protocols, the optical parameters, and the management interfaces. The FTTH ecosystem includes a broad range of OLT and ONT vendors, with equipment available from many suppliers.

10.2 FTTB Standards

FTTB uses copper-based technologies standardized by ITU-T (G.993 VDSL2, G.9700/G.9701 G.fast) and CableLabs (DOCSIS 3.1). These standards define the copper modulation, the spectrum management, and the management interfaces. The FTTB ecosystem includes DSLAM and DPU vendors, as well as CPE modem vendors.

11. Migration from FTTB to FTTH

FTTB is often deployed as an intermediate step toward FTTH. The migration path from FTTB to FTTH follows a natural progression as bandwidth demand grows and the copper infrastructure reaches its limits.

11.1 The Upgrade Trigger

The primary trigger for FTTB-to-FTTH migration is the subscriber's demand for higher bandwidth that the copper infrastructure cannot deliver. Common triggers include: subscriber requests for gigabit service, competitive pressure from FTTH providers, and the degradation of the copper infrastructure over time.

Before migrating, it is worth assessing whether the existing copper can be upgraded—for example, by deploying G.fast instead of VDSL2, or by shortening the copper loop by moving the DPU closer to the subscriber. If these measures are insufficient, FTTH becomes the appropriate solution.

11.2 The Migration Process

The FTTB-to-FTTH migration typically involves the following steps:

1. Assessment: Survey the building layout, identify the fiber routing path to each unit, and determine the equipment locations.

2. In-building fiber installation: Install fiber from the building's entry point to each unit. This may involve surface-mounted cable along corridors, through existing conduits, or through wall penetrations.

3. Splitter installation: Install passive optical splitters at the building's distribution point.

4. ONT installation: Install an ONT in each unit, connect the fiber, and configure the service.

5. Service migration: Migrate subscribers from the FTTB service to the FTTH service, either on a per-unit basis or as a building-wide cutover.

The migration is non-disruptive to the outside plant. The fiber from the OLT to the building remains unchanged; only the in-building distribution and the subscriber equipment are upgraded.

11.3 Coexistence and Upgrade Path

FTTB and FTTH can coexist in the same building during the migration period. The DSLAM or DPU continues to serve subscribers who have not yet migrated, while the new FTTH infrastructure serves those who have. This allows the migration to be phased, reducing disruption and spreading the cost over time.

The upgrade path from FTTB to FTTH is well understood, and the cost is primarily the in-building fiber installation. Once the fiber is installed, the network can be upgraded to higher PON speeds by replacing the ONT and OLT optics, without touching the in-building fiber.

12. Comparison Summary

13. Selection Framework

14. Emerging Trends

14.1 G.fast and Beyond for FTTB

G.fast has extended the life of FTTB by providing up to 1 Gbps over short copper loops. However, G.fast requires the DPU to be very close to the subscriber—typically within 100 meters—which means installing DPUs in the building's telecom room or on each floor. The cost and complexity of deploying G.fast DPUs in existing buildings can approach the cost of FTTH, reducing the economic advantage of FTTB.

14.2 50G-PON for FTTH

The next generation of PON technology, 50G-PON, is being standardized and will provide 50 Gbps symmetrical bandwidth per PON port. This will enable FTTH packages of 10 Gbps and beyond, with headroom for future applications. The in-building fiber installed for FTTH today will be capable of supporting 50G-PON and beyond, making FTTH the clear long-term choice.

14.3 FTTB as a Temporary Solution

In many markets, FTTB is being deployed as a temporary solution while FTTH migration is planned and funded. The FTTB infrastructure provides immediate broadband service, and the in-building copper is used until the fiber can be installed. This approach allows operators to generate revenue from existing buildings while building the business case for FTTH.

14.4 Regulatory and Policy Trends

Regulators in many countries are encouraging FTTH deployment by simplifying permitting, mandating fiber in new construction, and requiring building owners to provide access for fiber installation. These policies are reducing the cost and complexity of FTTH deployment, making it more attractive relative to FTTB.

15. Conclusion

FTTH and FTTB are two access network architectures that both use fiber in the access segment but differ in where the fiber terminates and how the signal reaches the subscriber. FTTH brings fiber to the living unit, providing dedicated optical bandwidth and the highest performance. FTTB stops the fiber at the building and uses existing copper infrastructure to reach each unit, providing lower bandwidth but lower deployment cost and faster installation.

The choice between them depends on the target market, the building type, the existing infrastructure, and the service provider's business model. FTTH is the clear choice for single-family homes, greenfield MDUs, and premium subscribers. FTTB is a pragmatic option for existing MDUs with usable copper infrastructure, price-sensitive markets, and rapid deployment scenarios.

The migration from FTTB to FTTH is a natural evolution as bandwidth demand grows and the copper infrastructure reaches its limits. The migration is non-disruptive to the outside plant, and the two architectures can coexist during the transition. The in-building fiber installed for FTTH today will support future PON generations, making FTTH the clear long-term choice.

As bandwidth demands continue to grow and new applications emerge, the limitations of copper-based FTTB will become increasingly apparent. FTTH provides the performance, the upgrade path, and the future-proofing that modern networks require. For service providers planning their access network strategy, FTTH should be the default choice wherever the economics allow.

16. Q&A