AON or PON – Which One Do You Choose for FTTH?

With consumers’ demand for high-speed bundled services, fiber-to-the-home (FTTH), a type of FTTx deployment, has been recognized as the ultimate solution for providing these services to the end users. In a similar vein as the “PC versus MAC” battle for supremacy in computing, there come two primary paths of FTTH—active optical network (AON) and passive optical network (PON), which wage the war for the preferred network. So, today, I’d like to introduce these two systems and make a brief comparison between them.

Definition of Active Optical Network

Active optical network (AON) is a point-to-point (PTP) structure, which means that each subscriber has their own fiber optic line that is terminated on an optical concentrator. An active optical network utilizes electricity powered switching equipment like routers or a switch aggregator to manage signal distribution and direction to the correct end users. These switches open and close to ensure that the outgoing and incoming messages are going in the right direction. In this design, dedicated fiber is routed to the end users premises. The following image shows an active optical network.

AON

Definition of Passive Optical Network

Unlike active optical network, passive optical network (PON) (shown in the picture below) does not have electrically powered equipment. It uses optical splitters to separate and collect optical signals that move through the network. A PON shares optical fiber strands from portions of the network and the equipment is only really powered by the ends of the signal. Typically, a passive optical network consists of an optical line termination (OLT) at the service provider’s central office and a number of network units (ONUs) near the customer premises.

PON-network

Comparison Between AON and PON

As optical fiber travels across the fiber connection, it needs a way to be directed so that the correct information arrives at its intended destination. AON and PON are two alternate network designs that offer appropriate ways to separate data and set it upon its intended route to arrive at the proper place. Each design comparatively has their advantages and disadvantages and the following part will make a comparison between them.

The arrangement of PON is a point-to-multipoint (PMP) network, which means that it will share fiber optic strands for portion of the network. So the transmission bandwidth of PON can be limited. But as for AON, a point-to-point structure, the bandwidth in each port is dedicated to each individual without sharing of it. Thus, higher bandwidth per port is possible through AON compared with PON. Besides, an AON can cover a range to about 100 km regardless of the number of subscribers being served, while a PON is typically limited to fiber cable runs of up to 20 km since the share of fiber optic strands for portions of the network needs PON subscribers to be geographically closer to the central source of the data. However, an active optical network requires at least one switch aggregator for every 48 subscribers and it is inherently less reliable than a passive optical network, since it needs power.

A PON only uses fiber and passive components like PON splitters and combines rather than active components like amplifiers, repeaters, or shaping circuits. Therefore, when running a passive optical network, the cost of building and maintenance are much lower, compared to an active optical network. And a PON is efficient, because its each fiber optic strands can serve up to 32 users. But each coin has two sides, a PON also has disadvantages when compared to an AON. For example, the bandwidth in a PON is not dedicated to individual subscribers, so data transmission speed may slow down during peak usage times in an effect known as latency. Latency quickly degrades service such as audio and video, which need a smooth rate to maintain quality. Furthermore, the splitters used in a passive optical network have no intelligence, and therefore they cannot be managed. Then you can’t check for problems cost effectively when a service outage occurs.

Summary

After reading this post, we have learned the merits and demerits of active optical network and passive optical network. And basically, passive optical network is a better choice for network operators who want to supply a very large number of subscribers, while active optical network is more suitable for private network operators, that either lay their own fiber optic infrastructure, or use debundled fiber optic lines (fiber local loops). Hope you can choose the appropriate one with the help of this passage.

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Optical Communication

Work as an English editor at FS.COM, a professional supplier and manufacturer of fiber cables.

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