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FTTH terminology: The basics


Keeping track of fiber optic terminology is tricky.

When it comes to discussing FTTH deployments, there are additional definitions and concepts that are important to know as a network developer. Below is a snapshot of the most important terms to help you get started.

For a more thorough glossary, check out Corning’s excellent PDF.


Although not specific to FTTH technology, you need to understand attenuation.

Attenuation refers to a reduction in signal, or signal loss, within data cables. It’s calculated by comparing the strength of an input signal to the strength of an output signal. Typically reported in decibels per foot, attenuation is impacted by several variables, including cable length, wire size, and the presence of other networks.

Fiber optic cables have very low attenuation and can transmit signals over much longer distances than copper wires.

Passive Optical Network (PON)

Passive optical networks (PONs) are one of the two primary ways through which telecommunication signals are delivered to end users.

PONs are different from active optical networks (AONs) in that they utilize point-to-multipoint architectures. Optical splitters are used to route signals from a single fiber cable to many end users. Fiber-to-the-curb or fiber-to-the-building networks are typically PONs.

PONs can be categorized into two sub-groups: Ethernet PONs and Gigabit PONs.

Ethernet Passive Optical Network (EPON)

An Ethernet passive optical network (EPON) uses wavelength division multiplexing (WDM) to send digital data both upstream and downstream. The technology is highly useful as it relies on Ethernet packets and eliminates the need for asynchronous transfer mode (ATM) cells. EPONs are commonly used in Europe and Asia.

Gigabit Passive Optical Network (GPON)

Similarly to how EPONs work, Gigabit PONs also use WDM to transmit data bidirectionally. However, GPONs use ATM elements and are the most widely used for FTTH deployments in the U.S. today. Typically, GPONs are more expensive than EPONs to deploy.

Gigabits per second (Gbps)

Gigabits per second is the most commonly used data-rate metric used when discussing telecommunication capabilities. One gigabit per second equates to 125 megabytes or 1,000,000,000 bits per second.

Fiber cables can transmit data 40 kilometers at 10 gbps, compared to copper wires which can only send data 100 meters at 1 gbps.

Optical Network Terminal (ONT)

Also referred to as modems, optical network terminals are the hardware components used to translate light signals from fiber cables into electronic signals for wireless routers to interpret. ONTs connect to fiber optic terminal points in consumer homes in FTTH networks.

Optical Line Terminal (OLT)

Optical line terminals (OLTs) are the hardware endpoints of PONs that serve two primary purposes: signal conversion and multiplexing coordination.

OLTs are the sites at which electrical signals from service providers and optical signals from PONs are converted in the consumer’s home. OLTs also communicate with optical network terminals (ONTs) to coordinate multiplexing with other conversion devices.

Optical Return Loss (ORL)

Optical Return Loss is a measure of how much signal is reflected in relation to an original output. Throughout an optic line, signal may be lost as a result of mismatched terminating loads or other discontinuities in the network.

Remember, this is just a starter list of terms. As you dive deeper into FTTH technology, you will expand your vocabulary significantly beyond this resource.


Topics: Fiber to the home (FTTH), Fiber optic networks, Fiber planning and design, Fiber

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