What Is a Passive Optical Network (PON)?

■ Understanding Passive Optical Networks (PONs): Architecture, Standards, and Applications

Passive Optical Network (PON) is a telecommunications solution that makes use of fiber-optic cable to provide bandwidth network access to end users with no active components in the carrier's route between a central office of the provider and the end user. This architecture has the capacity to afford high-bandwidth over large distances without solution to old copper wires; it provides an option for the future that will lower maintenance cost of these traditional systems.

■ PON versus copper-based connection systems

Unlike the conventional copper-based networks, like DSL or coaxial cable, that depend on electric signals and are disturbed by electromagnetic flux, PONs employ optical links instead; this implies much more bandwidth and transmission distance. Copper systems need a higher number of active components, which include amplifiers, in order to transmit their signals over long distances. This factor makes it harder to plan and maintain a copper network. On the other hand, PONs use passive optical splitters and hence have no power supply, which greatly reduces operation expenses.

■ Passive vs. Active Optical Networks

PONs fall under the passive optical category, as there are no powered components between the central office of the service provider and the customer's premises. Electricity, on the other hand, makes up the active optical networks (AONs), which incorporate powered equipment like switches and routers within the distribution path. AONs have scalable capabilities, can route anything, and give close to total control. However, they require electrical power and a complicated infrastructure. PONs, on the other hand, are comprised of a simple design, are low-power consuming, and have fewer failure points.

■ Common FTTx Configuration

The abbreviation FTTx embraces related models of fiber installations, varying by how deep the fiber penetrates to an end user, including:

• FTTH (Fiber to the Home): Fiber optics goes all the way to the housing premises.

• FTTB (Fiber to the Building): Fiber reaches at a building’s point of entrance, supplying users through Ethernet or coaxial cable.

• FTTC (Fiber to the Curb): Fiber stops at the edge of the pavement or nearby street cabinet, usually within a few hundred meters from the place, further carried via twisted pair or coaxial cables.

• FTTN (Fiber to the Node): Fiber at the central node within the vicinity, moving on to the last-mile delivery via copper wiring.

This configuration offers several alternatives that find bandwidth, cost, and complexity as mutually exclusive.

■ PON Network Components

A typical PON consists of the following key components: 

• Feeder cable: Running from the central office (CO) or originating point of cable; it has the aggregated signal from the provider to bring new services.

• Fiber distribution hub (FDH): It serves as the linking point for feeder cables with distribution cable and utilizes optical splitters, which act as a cross-connection point.

• Distribution cable: From FDH to Network Access Point (NAP). They often comprise several fibers.

• Drop Cable: This wire connects NAP to the Network Interface Device (NID) within the dwelling place. It normally carries a single fiber for each subscriber.

• NAP (Network Access Point): Outside enclosure in which individual fibers are spliced to connect to higher fibers from drops.

• NID (Network Interface Device): Customer's premises terminal. Fiber ceases here and connects to the end-user's Optical Network Terminal (ONT).

• Each connection between the components in a PON report is formed by the use of passive components with no electrical needs, such as optical couplers and splitters.

■ Standards and Protocols

The two major PON standardization documents, issued on international level, are as follows.

ITU-T G.984 and G.987: These are the GPON and XG-PON standards from the International Telecommunication Union, with GPON supporting downstream rates up to 2.5 Gbps, and upstream rates of 1.25 Gbps.

IEEE 802.3: It is the IEEE standard specifying Ethernet Passive Optical Network (EPON) and 10G-EPON for 1 Gbps (EPON) or 10 Gbps (10G-EPON) symmetrical speeds for both upstream and downstream traffic.

■ Optical Transceivers

Optical transceivers, the key elements in PON systems, must follow the specifications of the physical layer as defined in the GPON and EPON standards:

1000BASE-PX10:

• Reach of up to 10 km.

• Transmission at 1310 nm and receiving at the 1490 nm wavelength,

• This transceiver is a common means or way of conveying information in a passive network.

1000BASE-PX20:

• You could be traveling for 20 km or more.

• Same wavelengths as 1000BASE-PX10.

• This transceiver is used in a passive network.

■ RF over Fiber

Besides providing broadband connectivity, a PON may be used for transmitting RF over Fiber (RFoF) signals as well, such as 1)

• Analog video distribution, especially in multi-dwelling units (MDUs).

• Wireless antenna backhaul allowing radio signals to travel long distances with minimal application range.

Radio frequency signals are transmitted via optical modulation for:

RFoF grants long links for CATV and mobile wireless services by preserving signal quality and upholds various frequencies.

■ Conclusion

Passive Optical Networks are transforming the access network by giving increased speed, reliability, and expansion of broadband connections and at the same time reducing the power need and the maintenance service. With homogenized designs, effective optical units, and support for all types of FTTx connections, PONs turns to be a perfect solution for modern living spaces, work places, and industries.

Contact us for more information

James is a technical manager and associate at Zion Communication. 

Specializes in Optical Fiber communications,  FTTH Solutions, 

Fiber optic cables,  ADSS cable, and ODN networks.

james@zion-communication.com

+86 13777460328