PON details: definitions, standards, and advantages:
he passive optical network refers to a fiber-optic network that uses a 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 are connected to a transceiver that operates entirely in the optical domain and has no power in the PON architecture through optical branching trees and passive splitter/combiner units.
At present, there are 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
Less space required
Higher levels of security
Easier to install and expand
Reduce operating and management costs
PON structure and components
In the Gigabit Ethernet passive optical network (GEPON) system, the central office of the service provider has an optical line terminal (OLT), and there are multiple optical network units (onus) or optical network terminals (ONT) near the end-user as an optical splitter (SPL). In addition, ODN (optical distribution network) is also used for the transmission between OLT and ONU / ONT.
Optical line terminal (OLT)
OLT is the starting point of passive optical network, which is connected to the core switch through Ethernet cable.
The main function of OLT is to convert, frame, and transmit signals for PON network, and coordinate the multiplexing of optical network terminals to share uplink transmission.
OLT equipment generally includes 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 fan.
In these parts, PON card and power supply support hot plug, and another module is built-in. OLT has two floating directions: upstream (allocating different types of data and voice traffic from users) and downstream (acquiring data, voice
Optical network unit (ONU) / optical network terminal (ONT)
ONU converts the optical signal transmitted through optical fiber into an electrical signal. These electrical signals are then sent to each subscriber.
Usually, there is a distance or other access network between ONU and the residence of end-users. In addition, ONU can send, aggregate, and sort different types of data from customers and send them up to OLT.
Collation is the process of optimizing and reorganizing data streams for more effective delivery. OLT supports bandwidth allocation and allows smooth floating transmission of data to OLT. These data usually arrive from customers in a burst form. ONU can be connected with cable types in a variety of ways, such as twisted-pair copper wire, coaxial cable, optical fiber, or 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, while ONU is an IEEE term. It belongs to different standard bodies and refers to the user side equipment in GEPON system. However, in practice, ONT and ONU are somewhat different according to their positions
Optical distribution network (ODN)
ODN is an integral part of PON system, which provides optical transmission medium for the physical connection between ONU and OLT at a distance of 20 km or more.
In ODN, optical cable, optical fiber connector, passive optical splitter, and auxiliary components cooperate with each other.
ODN is divided into five sections: feeder optical fiber, optical distribution point, distribution optical fiber, optical access point, and incoming optical fiber.
The feeder optical fiber starts from the optical distribution frame (ODF) in the telecommunication room of the central office and ends at the optical distribution point for long-distance coverage.
The distribution of optical fiber from the optical distribution point to the optical access point distributes the optical fiber to the area next to it. The optical fiber is introduced to connect the optical access point to the terminal (ONT) to realize the optical fiber into the home. In addition, ODN is an indispensable path for PON data transmission, and its quality directly affects the performance, reliability, and scalability of the PON system.
OLT, ONU or ONT, and ODN are the main components of GEPON system. At present, they have been widely used in FTTH applications. Reduced cabling infrastructure (without active components) and flexible media transmission help to make passive optical networks more suitable for home Internet, voice, and video applications. In addition, passive optical networks can also be applied to university campuses and business environments to provide cost-effective solutions. With the continuous progress of PON technology, its potential applications are also expanding