FTTO vs FTTB

FTTO (Fiber to the Office) and FTTB (Fiber to the Building) are two access network architectures that both bring optical fiber into a building, but they terminate the fiber at different points and serve different user models. FTTB stops the fiber at the building's boundary—typically the basement or a telecommunications room—and uses the building's existing copper infrastructure to reach individual offices, apartments, or units. FTTO extends the fiber all the way to the office or workspace, providing a dedicated optical connection to the end user without any copper segment in between.

The distinction is not merely about where the fiber ends. It determines the bandwidth available to each user, the symmetry of the connection, the service-level guarantees that can be offered, and the cost structure for both the operator and the subscriber. FTTB is a shared architecture: the fiber capacity is distributed among the building's tenants through copper, and each tenant's performance depends on the copper loop length, the number of active users, and the quality of the in-building wiring. FTTO is a dedicated architecture: the fiber is reserved exclusively for one organization, and the full capacity of the link is available at all times, in both directions.

FTTB was widely deployed as an intermediate step when operators wanted to bring fiber closer to the user without the cost and disruption of reaching every office. It leverages existing copper infrastructure, which lowers deployment cost and shortens installation time, but it limits the achievable bandwidth and creates a bottleneck in the building's internal wiring. FTTO eliminates that bottleneck by extending fiber to the workspace, and it is increasingly the architecture of choice for enterprises that depend on high-bandwidth, low-latency, and symmetrical connectivity.

This guide examines both architectures in depth: their topology, fiber termination points, bandwidth and symmetry characteristics, service-level commitments, in-building distribution, cost structures, application scenarios, and the migration path from FTTB to FTTO.

1. What Is FTTO?

FTTO, or Fiber to the Office, is an access network architecture in which optical fiber runs from the operator's network directly to the office or workspace of the end user. The fiber terminates at an Optical Network Terminal (ONT) or optical network unit (ONU) inside the office, and the full capacity of the fiber link is reserved exclusively for that organization.

FTTO is a point-to-point architecture. There is no passive optical splitting between the operator's equipment and the customer premises, and no sharing of the fiber with other subscribers. The connection is dedicated, which means the bandwidth is guaranteed and symmetrical: the upstream and downstream capacities are identical, and they are available at all times regardless of what other users are doing on the network.

1.1 FTTO Characteristics

• Fiber reaches the office: The optical fiber terminates inside the workspace or office.

• Dedicated connection: The fiber is reserved exclusively for one organization; no sharing with other tenants.

• Guaranteed bandwidth: The contracted bandwidth is available at all times, in both directions.

• Symmetrical: Upload and download speeds are identical.

• SLA-backed: Contractual guarantees for availability and fault restoration.

• Higher cost: Dedicated infrastructure and SLA commitments result in higher monthly fees.

• Future-proof: The fiber can support higher speeds by upgrading the equipment at each end.

• Best for: Enterprises, government agencies, campuses, and businesses with mission-critical connectivity needs.

2. What Is FTTB?

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

The most common FTTB implementation uses VDSL2 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 office or apartment. In buildings with coaxial cable infrastructure, FTTB may use DOCSIS or MoCA over coax.

FTTB is a shared architecture. The fiber capacity is distributed among the building's tenants, and each tenant's performance depends on the copper loop length, the number of active users, and the quality of the in-building copper. The copper loop from the building's distribution point to each office is typically 20 to 100 meters, which is shorter than in FTTC or FTTN but still imposes a bandwidth limit that fiber does not have.

2.1 FTTB Characteristics

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

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

• Shared bandwidth: The fiber capacity is shared among the building's tenants.

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

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

• Limited symmetry: Upstream bandwidth is typically lower than downstream.

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

• Best for: Existing multi-tenant buildings with usable copper, price-sensitive tenants, transitional deployments.

3. Architecture: Point-to-Point vs Building-Level Distribution

The fundamental architectural difference between FTTO and FTTB is the network topology and the point at which the fiber terminates.

3.1 FTTO Architecture

FTTO is a point-to-point architecture. Each office or organization has a dedicated fiber connection to the operator's network. There is no passive splitting between the operator's equipment and the customer premises. The fiber runs from the operator's point of presence (PoP) or central office directly to the ONT inside the office.

In a campus environment, FTTO can be deployed as a passive optical LAN (POL). A central OLT in the campus equipment room connects via fiber to passive splitters, which distribute the signal to ONUs in each office or on each floor. Each ONU provides Ethernet, Wi-Fi, and voice interfaces for the end devices in that office. This is sometimes called FTTO in the enterprise campus sense, and it uses PON technology within the campus rather than dedicated point-to-point fiber to every desk.

3.2 FTTB Architecture

FTTB is a building-level architecture. The fiber terminates at a distribution point inside the building—typically the basement or a telecommunications room. From that point, the signal is distributed to individual offices or units using the building's existing copper infrastructure.

The FTTB distribution point contains a DSLAM or G.fast DPU that converts the optical signal to an electrical signal for transmission over the copper pairs. The copper pairs run from the distribution point to each office's telephone outlet. The subscriber connects a VDSL or G.fast modem to the outlet to receive the service.

4. Fiber Termination Point and User Boundary

The point at which the fiber terminates determines the user boundary and the performance that can be guaranteed.

In FTTO, the fiber terminates inside the office. The user boundary is the ONT or ONU in the workspace. The operator is responsible for the fiber all the way to the office, and the performance is guaranteed at that point. The user's internal network begins after the ONT, and the operator's responsibility ends there.

In FTTB, the fiber terminates at the building's distribution point. The user boundary is the copper outlet in the office. The operator is responsible for the fiber to the building and the DSLAM/DPU, but the performance depends on the in-building copper, which may be owned by the building owner and may be of variable quality. The operator cannot guarantee the same performance as FTTO because the copper segment is outside its direct control.

5. Bandwidth and Symmetry

Bandwidth and symmetry are the most visible performance differences between FTTO and FTTB.

5.1 FTTO Bandwidth and Symmetry

FTTO provides dedicated, symmetrical bandwidth. A business that subscribes to 500 Mbps FTTO receives 500 Mbps in both directions, at all times, regardless of what other businesses are doing on the network. FTTO connections can scale from 100 Mbps to 10 Gbps symmetrical, and the bandwidth can be upgraded smoothly without replacing the fiber infrastructure.

The guaranteed bandwidth is critical for business applications that depend on consistent performance: VoIP telephony, video conferencing, cloud-based ERP and CRM systems, remote backups, and multi-site data synchronization. When the network is the lifeline of the business, "up to" speeds are not sufficient.

5.2 FTTB Bandwidth and Symmetry

FTTB bandwidth is shared among the building's tenants and limited by the copper in-building distribution. VDSL2 provides up to 100 Mbps downstream and 40 Mbps upstream over short distances. G.fast provides up to 1 Gbps downstream and 500 Mbps upstream over very short distances. The actual speed depends on the distance between the office and the distribution point, the quality of the copper pair, and the number of tenants sharing the same binder.

FTTB is typically asymmetrical: the upstream bandwidth is lower than the downstream. This is acceptable for residential use, where most traffic is downstream, but it is a limitation for businesses that need to upload large files, synchronize data to the cloud, or run server applications.

6. Service Level Agreement

The service level agreement is one of the most consequential differences between FTTO and FTTB, and it is often overlooked when comparing monthly fees.

6.1 FTTO SLA

FTTO includes a contractual Service Level Agreement with precise commitments. A typical FTTO SLA includes availability guarantee of 99.9 percent or higher, guaranteed restoration time (GTR) of 4 to 8 hours, and financial penalties if the operator fails to meet these commitments. Some FTTO offerings also include proactive 24/7 monitoring by a Network Operations Center.

The financial impact of an SLA is not just the penalty clause—it is the operational certainty it provides. A business that knows its network will be restored within 4 hours can plan its operations accordingly.

6.2 FTTB SLA

FTTB typically operates on a best-effort basis. There is usually no contractual guarantee of restoration time, and the operator is not financially penalized for extended outages. In practice, FTTB restoration can take several days in the event of a copper fault or equipment failure. This may be acceptable for residential tenants, but it is not acceptable for businesses whose operations depend on network availability.

Some operators offer business-grade FTTB with a limited SLA, but the SLA is typically less stringent than FTTO because the copper segment is outside the operator's direct control.

7. Latency and Performance Consistency

Latency is critical for real-time applications, and the two architectures differ in both average latency and consistency.

FTTO provides very low latency, on the order of just a few milliseconds, because the signal travels over a dedicated point-to-point fiber with no sharing and no contention. The latency is predictable and consistent, which is essential for VoIP, video conferencing, cloud gaming, and industrial control applications.

FTTB latency is also low in absolute terms, but it is less consistent. The shared copper distribution introduces contention and scheduling delays, especially during peak hours when multiple tenants are active. The latency experienced by an office using FTTB may be acceptable for browsing and email, but it is not predictable enough for business-critical real-time applications.

8. In-Building Distribution and Deployment

The in-building distribution is where the two architectures diverge most significantly, and it determines the deployment complexity and cost.

8.1 FTTO In-Building Distribution

FTTO requires fiber to be routed from the building's entry point or from the operator's network to each office. 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 office, which provides Ethernet and Wi-Fi connectivity for the organization's devices.

8.2 FTTB In-Building Distribution

FTTB leverages the existing copper infrastructure in the building. The FTTB distribution point—a DSLAM or G.fast DPU—is installed in the building's telecom room and connected to the fiber. The existing copper pairs are then used to carry the broadband signal to each office. 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 offices. The disadvantage is that the copper infrastructure limits the achievable bandwidth and may be degraded or poorly maintained.

9. Cost Comparison

The cost structure differs significantly between FTTO and FTTB, with FTTO having higher upfront costs but better long-term economics for high-bandwidth, mission-critical applications.

9.1 FTTO Cost

FTTO is more expensive than FTTB. The monthly fee for an FTTO connection is typically several times higher than an equivalent FTTB service, reflecting the dedicated infrastructure and the SLA commitments. The fiber is reserved exclusively for the customer, and the operator cannot amortize the cost across multiple subscribers.

However, the relevant comparison is not the monthly subscription price—it is the cost of network downtime for the organization. For a business where an hour of network unavailability translates into lost revenue, idle employees, or failed transactions, the FTTO premium is easily justified.

9.2 FTTB Cost

FTTB is the more economical option for building tenants, with monthly fees that are significantly lower than FTTO. The low cost reflects the shared infrastructure: the fiber, the DSLAM/DPU, and the copper distribution are amortized across many tenants. The operator can offer FTTB at a low price because the incremental cost of adding one more tenant to an existing building distribution point is minimal.

For a small office with basic browsing and email needs, FTTB may be sufficient. But as the business grows and its dependence on cloud services, VoIP, and remote collaboration increases, the limitations of shared bandwidth and best-effort SLA become apparent.

10. Application Scenarios

The choice between FTTO and FTTB depends on the organization's dependence on network availability, symmetry, and guaranteed performance.

10.1 FTTO Application Scenarios

• Corporate headquarters: Where network downtime directly impacts revenue, employee productivity, and customer service.

• Multi-site enterprises: Where reliable inter-site connectivity is essential for data synchronization, VoIP, and collaborative applications.

• Cloud-intensive businesses: Where applications run in the cloud and require consistent low-latency, symmetrical connectivity.

• Financial services: Where transaction processing and market data feeds require guaranteed bandwidth and low latency.

• Healthcare: Where telemedicine, medical imaging, and electronic health records depend on reliable connectivity.

• Education campuses: Where thousands of students and staff require high-bandwidth connectivity across multiple buildings.

• Government and public sector: Where service continuity and data security are paramount.

10.2 FTTB Application Scenarios

• Multi-tenant office buildings: Where many small businesses share the building and the cost of fiber to each office is prohibitive.

• Business centers and incubators: Where tenants need basic connectivity at low cost and can tolerate shared bandwidth.

• Residential MDUs: Where the building serves apartments and the tenants are residential subscribers.

• Hotels and hospitality: Where guest Wi-Fi and in-room connectivity are the primary requirements.

• Price-sensitive markets: Where tenants prioritize low monthly fees over guaranteed performance.

• Transitional deployments: FTTB can be deployed as an intermediate step while FTTO migration is planned and funded.

11. Migration from FTTB to FTTO

FTTB is often deployed as an intermediate step toward FTTO or FTTH. The migration path from FTTB to FTTO 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-FTTO migration is the tenant's demand for higher bandwidth and guaranteed performance that the copper infrastructure cannot deliver. Common triggers include: tenant requests for gigabit symmetrical service, competitive pressure from FTTO 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. If these measures are insufficient, FTTO becomes the appropriate solution.

11.2 The Migration Process

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

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

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

3. Splitter installation (campus POL): If deploying campus POL, install passive optical splitters at the building's distribution point.

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

5. Service migration: Migrate tenants from the FTTB service to the FTTO service, either on a per-office basis or as a building-wide cutover.

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

11.3 Coexistence and Upgrade Path

FTTB and FTTO can coexist in the same building during the migration period. The DSLAM or DPU continues to serve tenants who have not yet migrated, while the new FTTO 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 FTTO 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 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 FTTO for AI-Era Campuses

As AI applications move to the edge—local inference, video analytics, IoT—campus networks need higher bandwidth and lower latency. FTTO and POL architectures are evolving to support 50G-PON and Wi-Fi 7 backhaul, delivering 50 Gbps to the room and 10 Gbps to the access point. The two-layer FTTO architecture, with passive splitters replacing active aggregation switches, provides the bandwidth density and energy efficiency that AI-era campuses require.

14.2 FTTB as a Transitional Architecture

FTTB is increasingly seen as a transitional architecture. It served its purpose during the early years of fiber deployment, when the cost of reaching every office with fiber was prohibitive. As bandwidth demand grows and the limitations of copper become increasingly apparent, the migration to FTTO or FTTH is becoming unavoidable. FTTB will continue to serve price-sensitive and low-bandwidth environments, but it is not the long-term end state.

14.3 Passive Optical LAN in Enterprise

The enterprise version of FTTO—Passive Optical LAN (POL)—is gaining traction in campuses, hospitals, hotels, and commercial buildings. POL simplifies the campus network from a traditional three-tier design to a two-layer design, eliminating intermediate equipment rooms and reducing cabling by up to 80 percent. Energy consumption is reduced by 25 percent or more compared to traditional copper-based campus networks, and the network can be upgraded smoothly to 10G, 50G, and beyond without replacing the fiber infrastructure.

14.4 Copper Retirement Accelerates FTTO

The retirement of copper networks in many countries is accelerating the migration to fiber. Businesses that previously relied on copper-based services are moving to FTTO for their primary connectivity, driven by the superior performance, reliability, and future-proofing that fiber provides. As copper is retired, FTTB will become less viable, and FTTO will become the default choice for enterprise connectivity.

15. Conclusion

FTTO and FTTB are two access network architectures that both bring fiber into a building but terminate at different points and serve different user models. FTTB stops the fiber at the building's boundary and uses the existing copper infrastructure to reach individual offices or units, sharing the fiber capacity among multiple tenants. FTTO extends the fiber all the way to the office, providing a dedicated, symmetrical connection with guaranteed bandwidth and a contractual SLA.

The performance difference is significant. FTTB delivers shared, asymmetrical bandwidth limited by the copper in-building distribution—typically up to 100 Mbps with VDSL2 or up to 1 Gbps with G.fast. FTTO delivers dedicated, symmetrical bandwidth from 100 Mbps to 10 Gbps, with guaranteed performance and a contractual SLA. The difference in capability determines what applications the network can support and what services the operator can sell.

FTTB is cheaper to deploy because it reuses the existing in-building copper and shares the fiber capacity among multiple tenants. But FTTB has limited performance, no SLA, and a constrained upgrade path. FTTO has higher upfront costs and higher monthly fees, but it provides the guaranteed performance, symmetry, and reliability that mission-critical business operations require.

The choice between them depends on the organization's dependence on network availability and performance. For a multi-tenant building with light business use, FTTB may be sufficient. For an enterprise where network downtime translates directly into lost revenue, FTTO is the appropriate choice. The migration from FTTB to FTTO is a natural evolution as bandwidth demand grows and the limitations of copper become increasingly apparent.

As AI applications move to the edge and bandwidth demand continues to grow, the fiber-to-the-office model will play an increasingly central role in enterprise networking. FTTO provides the dedicated, symmetrical, low-latency connectivity that modern businesses require, and it offers a future-proof platform for decades of service evolution.

16. Q&A