FTTH Tutorial: Network Architecture, Configuration, and Technologies

Fiber to the Home (FTTH) is a key technology in delivering high-speed internet directly to homes and businesses. This tutorial explores the essential aspects of FTTH, including network architecture, configuration and the various technologies involved, such as AON, PON, EPON, and GPON.

Earlier telecommunication networks were using optic fiber cables for connectivity between exchanges across the sea. This has been replaced with an all-fiber network. This concept provides connectivity between user premises and the service provider using fiber optics. It has become more popular because of higher bandwidth and cheap cost. Moreover, it is a reliable and secure way of communication compared to wireless networks.

Fiber optic networks have evolved very quickly, and service providers are deploying different fiber configurations based on different applications. It is designed as FTTx, where ‘x’ stands for the final terminating point on the user side. ‘x’ can be Home, Premise, Building, Curb, or Node. Based on this, there are different terminologies for fiber optic deployment configurations. They are:

• FTTH (Fiber to the Home)
• FTTP (Fiber to the Premise)
• FTTB (Fiber to the Building)
• FTTN (Fiber to the Node)
• FTTC (Fiber to the Curb)

FTTH is a type of fiber-optic communication delivery in which the optical fiber runs from a central point directly to individual buildings, such as residences or businesses. This contrasts with technologies where fiber runs to the curb or node and then uses coaxial cables or copper wires to complete the connection.

FTTH Configuration

As shown in Figure 1, the basic elements of the fiber optical network are OLT, ONU, and ODN.

• Optical Line Terminal (OLT): Located at the service provider’s central office, the OLT is the endpoint hardware device in a passive optical network.
• Optical Network Unit (ONU) / Optical Network Terminal (ONT): These devices are located at the user’s premises and connect to the OLT via the optical fiber.
• Optical Distribution Network (ODN): This network connects the OLT and the ONT, consisting of optical fibers, splitters, and connectors.

In this FTTH configuration, a modem is used at the user premises which converts the optical signal to an electrical signal and vice versa. The user’s computer is connected to the network using an ethernet card.

FTTH Architecture Diagram

A basic diagram includes the OLT at the central office connected via optical fibers to an ONU/ONT at the subscriber’s premises, often passing through a splitter. This shows the high-level layout of a typical FTTH network.

• Active Optical Network (AON): In AON, each user has a dedicated fiber connection back to a switch in the provider’s network. AON uses electrically powered equipment, such as Ethernet switches, to manage data.
• Passive Optical Network (PON): PON uses unpowered splitters to divide a single optical fiber into multiple signals to serve multiple premises. This reduces the number of fibers needed but shares bandwidth among users.

The major deployment consideration for telecom service providers is to decide on the FTTH architecture. There are two categories of architectures: Active Optical Network (AON) and Passive Optical Network (PON). These AON and PON are explained below.

Configuring an FTTH network involves several key steps, focusing on both hardware setup and network management.

OLT Configuration

• Defining Services: OLTs are configured to define the services (e.g., internet, voice, video) that will be delivered to the ONUs/ONTs.
• Bandwidth Management: Quality of Service (QoS) settings ensure that bandwidth is allocated efficiently, prioritizing traffic as needed.
• Security: Implementing encryption and other security measures to protect the data transmitted over the network.

ONU/ONT Configuration

• Service Provisioning: This involves setting up the ONU/ONT to receive the defined services from the OLT.
• Firmware Updates: Keeping the ONU/ONT updated with the latest firmware ensures it operates efficiently and securely.

Splitter Configuration

• Splitter Placement: Determining the optimal location for splitters is crucial for minimizing signal loss and ensuring a robust connection.
• Signal Testing: Testing the signal strength at various points in the network to ensure that it meets the required standards.

AON vs PON: Active vs. Passive Optical Networks

AON is a point-to-point FTTH architecture. This type uses active devices and connects the OLT (Optical Line Terminal) placed at the central office with the ONT (Optical Network Terminal) placed at the user premises using a dedicated cable. The distance can be about 80 Km, and the fiber cable provides full bi-directional communication. Figure 2 depicts a typical active star ethernet (ASE) architecture, which is a point-to-point architecture. This ASE architecture reduces cost due to the sharing of the fiber cable.

PON is a point-to-multipoint FTTH architecture. This configuration is used for various applications including voice, video, data, etc. This configuration uses an optical splitter to connect the OLT located at the service provider side with multiple ONUs located at the user premises. Optical splitters are available in different configurations viz. 1:4, 1:8, 1:16, 1:32, 1:64, etc. As the name suggests, this architecture uses all the passive components between OLT and ONUs. No electronic or electrical active components are used. There are two benefits to this type of architecture: easy maintenance and lower cost. The typical distance between the OLT and ONU is about 35Km.

As shown in Figure 3, transmission from the user premises to the service provider is referred to as uplink and from the service provider to the user premises is referred to as downlink. In the uplink, TDMA is used and in the downlink, TDM is used. TDMA stands for Time Division Multiple Access and TDM stands for Time Division Multiplexing.

EPON (Ethernet PON) and GPON (Gigabit PON) are two main types of PON technologies, each with its unique characteristics.

EPON (Ethernet Passive Optical Network) Technology

• EPON is based on the Ethernet standard (IEEE 802.3) and delivers data in Ethernet frames.
• Speed: Typically supports speeds of up to 1 Gbps.
• Use Case: Widely used in Asia, particularly for delivering triple-play services (internet, TV, and voice) over a single fiber.

GPON (Gigabit Passive Optical Network) Technology

• GPON, defined by ITU-T G.984, delivers data using the Generic Framing Procedure (GFP) and supports multiple services including voice, video, and high-speed data.
• Speed: Supports up to 2.5 Gbps downstream and 1.25 Gbps upstream.
• Use Case: Popular in North America and Europe for its high data rates and ability to handle a mix of services efficiently.

There are different standards which are evolving under PON based on ethernet technology advancement. They are EPON(Ethernet PON) and GPON(Gigabit Ethernet PON).

Comparison between PON vs EPON vs GPON

Summary

Understanding the intricacies of FTTH, including network architecture, configuration, and the differences between AON, PON, EPON, and GPON, is crucial for anyone involved in designing or managing fiber-optic networks. Each technology offers its own set of advantages and challenges, and the choice between them depends on specific network requirements, cost considerations and regional preferences. This guide provides a foundation for further exploration into the world of FTTH, ensuring that you are equipped with the knowledge to make informed decisions about your network infrastructure.