Fiber to the home (FTTH) has begun to receive the attention of global telecommunications companies, and technology has developed rapidly. Active optical networks (AON) and passive optical networks (PON) are two major systems that make FTTH broadband connections cost-effective. PON solutions are more common in most FTTH deployments.
This article will introduce the basic knowledge of PON, mainly involving basic components such as OLT, ONT, ONU, ODN and related technologies.
Detailed Explanation of PON: Definition, Standards and Advantages
Passive optical network refers to an optical fiber network that utilizes point-to-multipoint topology and optical splitters to transmit data from a single transmission point to multiple user endpoints. In contrast to AON, multiple customers pass through optical fiber branch trees and passive splitters/ The combiner unit is connected to a single transceiver and operates entirely in the optical domain, with no power supply in PON architecture.
There are currently two main PON standards: Gigabit Passive Optical Network (GPON) and Ethernet Passive Optical Network (EPON).
Their topologies are basically the same. As the first choice for many FTTH deployment scenarios, the PON solution has several outstanding advantages:
Lower power consumption
Requires less space
higher bandwidth
Higher level of security
Easier to install and expand
Reduce operating and administrative costs
PON Structure and Components
In a Gigabit Ethernet Passive Optical Network (GEPON) system, the service provider has an optical line terminal (OLT) at the central office and multiple optical network units (ONUs) or optical network terminals (ONTs) near the end user. as a beam splitter (SPL). In addition, ODN (Optical Distribution Network) is also used for transmission between OLT and ONU/ONT.
Optical Line Terminal (OLT)
The OLT is the starting point of the passive optical network and is connected to the core switch via Ethernet cables.
The primary function of the OLT is to convert, frame and transmit signals for the PON network and coordinate optical network terminal multiplexing to share upstream transmission.
OLT equipment generally includes a rack, CSM (Control and Switch Module), ELM (EPON Link Module, PON card), redundant protection-48V DC power module or a 110/220V AC power module, and fans.
In these parts, the PON card and power supply support hot swapping, while another module is built in. The OLT has two floating directions: upstream (distributing different types of data and voice traffic from users) and downstream (acquiring data, voice,
Optical Network Unit (ONU)/Optical Network Terminal (ONT)
The ONU converts optical signals transmitted through optical fibers into electrical signals. These electrical signals are then sent to individual subscribers.
Typically, there is some distance or other access network between the ONU and the end user's residence. Additionally, the ONU can send, aggregate, and collate different types of data from customers and send it up to the OLT.
Collation is the process of optimizing and reorganizing data flows for more efficient delivery. The OLT supports bandwidth allocation, allowing smooth floating transfer of data to the OLT. This data often arrives in bursts from customers. The ONU can be delivered in a variety of ways and Cable type connection such as twisted pair copper wire, coaxial cable, fiber optic or via Wi-Fi.
End user equipment can also be called optical network terminal (ONT). In fact, ONT is essentially the same as ONU. ONT is an ITU-T term, and ONU is an IEEE term. They belong to different standards bodies and both refer to the GEPON system. User side equipment, but in practice, there is a little difference between ONT and ONU based on their location.
Optical Distribution Network (ODN)
ODN is an integral part of the PON system and provides the optical transmission medium for the physical connection of the ONU to the OLT at a distance of 20 kilometers or more.
Within an ODN, fiber optic cables, fiber optic connectors, passive optical splitters, and ancillary components work together.
ODN is specifically divided into five sections: feeder fiber, optical distribution point, distribution fiber, optical access point and introduction fiber.
The feeder fiber starts from the optical distribution frame (ODF) in the central office telecommunications room and terminates at the optical distribution point for long-distance coverage.
The distribution fiber from the optical distribution point to the optical access point distributes optical fiber to the area next to it, and introduces optical fiber to connect the optical access point to the terminal (ONT) to realize fiber-to-the-home. In addition, ODN is essential for PON data transmission. Path, its quality directly affects the performance, reliability and scalability of the PON system.
OLT, ONU or ONT, ODN are the main components of GEPON systems and are currently widely used in FTTH applications. The reduced wiring infrastructure (no active components) and flexible media transmission help make passive optical networks more suitable Home Internet, voice and video applications. In addition, passive optical networks can also be applied to university campuses and commercial environments to provide cost-effective solutions. As PON technology continues to advance, its potential applications are also expanding.
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