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  • What’s the difference between passive optical networks (PON) and active optical networks (AON)?

1 Nov 2019, 9:43

What’s the difference between passive optical networks (PON) and active optical networks (AON)?

There’s a lot of talk about fiber optics, fiber-optic networks, and broadband, but the way they can be constructed is where the real conversation starts.

The main network may well always be fiber but there are alternatives when it comes to connecting the last mile. “The last mile” is the last few hundred meters nearest the consumer’s home or the business premises of the end-user. More than likely, this will use fiber to the home (FTTH) or curb (FTTC), where the final few meters consist of copper cables. All together these variants are known as FTTx.

Fiber has proven to be an expensive connection, it’s simply too expensive to run a dedicated and direct link all the way to each end-user. If there’s already an existing copper telephone cable that’s running to each home it will make it cheaper for the last few meters. It will, however, make the connection slower.

Considering all that, how are we supposed to construct our network so that fast fiber is able to reach the very endpoint, the end-user? Not only that but without the cost of everyone needing their own private connection.

What are AON and PON?

There are two common ways this problem can be solved, both based on the principle of splitting the signal so that each fiber from the central office in the network’s core is shared between multiple end-users. The two methods are called Active Optical Networks (AON) or Passive Optical Networks (PON), and in both cases, the split into individual fibers for each user happens fairly close to the customer; within a few kilometers at most.

The key difference between AON and PON is how the signal is split between the multiple fibers going to each customer. AONs use active, electrically powered devices to direct the appropriate signal only to the relevant customer - you can see this below in the diagram. Ethernet is commonly used, and a switching device will typically route signals to up to about 500 customers.

In contrast, a PON uses optical splitters, which require no electrical power, to send the signal to each customer. Each switching cabinet can handle up to 128 end users. You can see from the diagram that each customer also receives signals intended for someone else, so encryption ensures privacy is maintained. For upstream signals sent back from customers, these are combined into one signal at the switching cabinet, typically using Time Division Multiple Access (TDMA). The PON also uses wavelength division multiplexing (WDM) to carry both upstream and downstream traffic over single-mode fibers.

Benefits of each approach

PONs have a number of key advantages; for a start, because they don’t require electrical power for the splitter, they have lower installation and operating costs than AONs. They also use less energy, and less network infrastructure, than AONs, and are highly reliable. Compared to the copper wiring that is being replaced by fiber, using PONs means the fiber is smaller, easier to manage, and more secure than the legacy cabling it replaces.

On the other hand, AONs enable the fiber ‘last mile’ link to operate over longer distances than with a PON: typically, up to around 70 to 100km, compared to about 20km for PONs. Troubleshooting and finding a problem is easier with AONs than with PONs, because each fiber is carrying signals dedicated to one customer. AONs also don’t suffer from the drop-in speeds that PONs experience at peak times, due to multiple customers’ traffic being sent down each fiber.

Reliability is essential

Both AON and PON are widely used today. Whichever approach is chosen, the key factor in building a successful fiber-optic network is reliability. Connectors are an essential part of the FTTx network, and by working with a vendor such as Bulgin, you can be assured of choosing a rugged, dependable connector that will handle harsh outdoor environments.

4000 Series Fiber connector from Bulgin

The 4000 Series Fiber connector offers reliable performance regardless of the application environment. Its industry-standard LC interfaces feature color-coded O-rings and washers for ease of identification. Mounting body options include Flex, Flex In-Line and Rear Panel styles.

The ideal solution for where ease of connection, space, and appearance are important considerations.

Visit for expert advice on optical fiber connectors.

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1 Nov 2019, 9:43