AON vs PON Networks: What's the Difference and How to Make Choice?

Fiber to the home (FTTH) is a system which installs optical fiber from a central point directly to individual buildings, including residences and apartments. The deployment of FTTH has come a long way before subscribers adopt optical fibers instead of copper lines to achieve broadband Internet access. There are two basic paths to deploy high-speed FTTH networks: active optical network (AON) and passive optical network (PON). Then AON vs PON networks: what's the difference and how to make the wise choice?

What Is AON Network?

AON (active optical network) is a point-to-point network structure in which each subscriber has its own fiber-optic line that is terminated on an optical concentrator. AON network covers electrically powered switching equipment, such as a router or a switch aggregator, to manage signal distribution and direction signals to specific customers. The switch directs the incoming and outgoing signals to the proper place by opening and closing in various ways. The reliance of the AON network on Ethernet technology makes interoperability among vendors easy. Subscribers can select hardware that delivers an appropriate data transmission rate and scale up as their needs increase without the need to restructure the network. However, the AON network requires at least one switch aggregator for each subscriber.

In an active optical network, three key devices play pivotal roles in facilitating more intricate communication schemes: amplifiers, transponders, and modulators.

Amplifiers

Amplifiers play a crucial role in enhancing the intensity of light traveling through optical fiber cables. They come in two main types: analog and digital. Analog amplifiers, while more cost-effective, are commonly utilized in various settings, including large buildings such as data centers and hospitals. On the other hand, digital amplifiers employ lasers instead of LEDs to generate light, providing advanced capabilities for specific applications.

Transponders

Transponders serve as signal converters, transforming signals from one format to another. For instance, if you intend to transmit a television signal over a phone line, a transponder is essential to convert it into a telephone signal. This conversion enables seamless connectivity, allowing you to directly plug your telephone into the wall jack.

Modulators

Modulators share similarities with transponders but operate in reverse. Instead of converting signals from one format to another, modulators alter the wavelength of an optical signal. This capability is particularly useful when, for example, you need to transmit a red laser beam over a blue fiber. In such a scenario, a modulator comes into play, converting the red laser beam into a blue laser beam to ensure compatibility with the optical medium.

What Is PON Network?

Different from AON networks, PON (passive optical network) is a point to multipoint network structure in which passive optical splitters are used to separate and collect optical signals. The fiber optic splitters allow the PON network to serve multiple subscribers in a single optical fiber without the need to deploy individual fibers between the hub and the end-users. As its name shows, the PON network does not include electrically powered switching equipment and shares fiber optic strands for portions of the network. Powered equipment is required only at the source and receiving ends of the signal.

In a typical PON network, there are several important products and devices that collectively form the PON architecture, providing efficient optical communication and making it a common and effective architecture for delivering broadband access services.

OLT (Optical Line Terminal)

The OLT is the central device in a PON, responsible for sending and receiving optical signals to the user side. It is typically located in the service provider's central office or data center and manages the entire PON network.

ONU (Optical Network Unit) or ONT (Optical Network Terminal)

The ONT/ONU is the user-side device installed in residences or business premises. It receives optical signals from the OLT and converts them into electrical signals for use by terminal devices. The ONT often functions as a home gateway, providing phone, television, and internet services.

OLT Modules and ONU Modules

These OLT & ONU Modules are for slot-based OLT and ONU devices, allowing network operators to expand or upgrade their PON network as needed.

PLC splitters

The PLC splitters combine multiple optical signals into a single output, or take a single optical input and distribute it to multiple separate outputs. These splitters for PON are bi-directional. To be clear, fiber signals can be sent downstream from the central office, broadcast to all users. And signals from the users can be sent upstream and combined into one fiber to communicate with the central office.

AON vs PON Network: Differences and Selection

Both PON and AON networks make up the fiber backbone in FTTH systems that allow people and businesses access to the internet. Before choosing between a PON or an AON, it's necessary to make clear the differences between them.

AON vs PON Networks: Signal Distribution

When it comes to the AON vs PON network, the main difference between them is the way the optical signal is distributed to each customer in the FTTH system. In an AON system, the subscribers have a dedicated fiber-optic strand, which allows them to get the same bandwidth that isn't shared. While in a PON network, users share the fiber optic strands for a portion of the network in PON. This makes active optical networks more efficient than passive optical networks. Also, it allows AON networks to support greater numbers of users.

AON vs PON Network: Cost

The biggest ongoing expense in a network is the cost of the powering equipment and maintenance. Compared with the AON network that is a powered network, PON makes use of passive components that require less maintenance, and no power is needed. So PON is less expensive than AON.

AON vs PON Networks: Coverage Distance and Applications

AON can cover a distance range of up to 90 km, while PON is usually limited by fiber cable runs of up to 20 km. This means that the PON subscribers must be geographically closer to the originating signal.

In addition, there are some other factors to consider if it is relevant to special applications or services. For example, radiofrequency and video services will be deployed, then a PON is typically the only practical solution. If all services are Internet Protocol-based, however, either a PON or an AON could be appropriate. If there are longer distances involved and providing power and cooling to active components in the field could pose a problem, then a PON may be the best choice. Alternatively, if the target customer is commercial or if the project involves multiple dwelling units, then an AON network may be a better fit.

AON vs PON Networks: Which Do You Prefer for FTTH?

When choosing between a PON or an AON, it is essential to consider what services are going to be delivered over the network, the overall network topology and who the primary customer will be. Many operators deploy a blend of the two networks under different circumstances. However, with the increasing demand for interoperability and scalability for networking, there is a tendency that network architecture would allow any fiber to be used interchangeably in either a PON or AON application as future needs dictate.

Ultimately, the choice between AON and PON depends on your specific requirements and constraints. Both architectures have their advantages and limitations, and the best choice for FTTH will vary based on the unique characteristics of the deployment.