Passive Optical Network (PON): Delivering Fiber Optic Connectivity

Learn about Passive Optical Networks (PONs) and how they bring fiber optic internet to homes and businesses. Understand the components of a PON system, how it works, and the advantages of this technology for high-speed data transmission.

Passive Optical Network (PON)

What is a Passive Optical Network (PON)?

Passive Optical Networks (PONs) are widely used by telecommunications providers to carry fiber optic cables and messages almost all the way to the final customer. Depending on where the PON ends, it can be referred to as fiber to the curb, fiber to the building, or fiber to the house.

How Does a Passive Optical Network Operate?

A PON system consists of an Optical Line Terminal (OLT) located at the main office of the communication company and multiple Optical Network Units (ONUs) closer to the end customers. Typically, one OLT can connect up to 32 ONUs. The term "passive" refers to the fact that once the signal is transferred across the network, optical transmission doesn’t require any active electrical components or energy. In contrast, active optical networks rely on powered equipment to transmit data along the fiber cables.

In a typical PON setup, fiber cabling is distributed up to 20 kilometers from the central office, and a passive optical splitter divides the signal into multiple ONUs. The fiber link is then terminated near the customer’s delineation point, allowing the ONU to provide a network handoff through Ethernet or copper connections for easy connection to the customer’s Local Area Network (LAN).

Types of Passive Optical Networks

At the optical level, all PON systems have similar potential capacities. However, the electrical layer, which controls the connection and allocates bandwidth, sets limits on the downstream and upstream speeds. Early PON systems were based on Asynchronous Transfer Mode (ATM) or cell switching protocols, known as APON (ATM PON). APON systems were later evolved into BPON (Broadband PON), which is still in use today. The usual downstream capacity of APON or BPON networks ranges from 155 Mbps to 622 Mbps, with BPON being the more common configuration.

PONs assign bandwidth to multiple users using optical splitters and wavelength division multiplexing (WDM) technologies. Additionally, PONs can serve as a network trunk uplink, connecting a neighborhood, building, or residential Ethernet line to a larger system, such as a community antenna television network.

Ethernet-based PONs have now replaced ATM-based PONs. For example, Gigabit PON (GPON) provides a variety of bandwidth options, including asymmetric transfer speeds of 1.25 Gbps downstream and 2.5 Gbps upstream, as well as symmetric capabilities of 622 Mbps for both directions. GPON is commonly used in fiber-to-the-home (FTTH) networks.

Modern PON technologies, such as 10G-PON, offer even higher speeds. This Ethernet-based system offers 2.5 Gbps upstream and 10 Gbps downstream speeds. Future developments are expected to achieve speeds up to 80 Gbps with the Next-Generation PON2 (NG-PON2) standard from the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T).

Advantages and Drawbacks of PONs

Advantages:

  • Cost-effective compared to other broadband distribution systems.
  • No need for electrically powered midspan devices.
  • Leverages existing fiber optic infrastructure.
  • High throughput rates and multiple upgrade pathways.
  • Regarded as a secure network technology.
  • Can operate over long distances (up to 20 kilometers) from the central office.

Drawbacks:

  • Requires a large-scale fiber rollout.
  • Larger networks may become less efficient due to significant management traffic overhead between the central office and individual ONUs.
  • Distance limitations in comparison to active powered network systems.