PON networks explored

PON is a term that is often mentioned in networking discourse and one that garners a lot of interest specifically for discussions regarding Fiber-to-the-X (FTTX) networks. In this article, we explore the elements of a PON network and how it has become a key contributor for fiber networks.

Network structure

In a fiber network, downstream data (in the form of light signals) travels from the network to the central offices of a local loop. The central offices are then responsible for distributing data among the subscribers in the network, in what is referred to as the “last mile” portion of the network.

There are different pathways that can be utilized to distribute the data among the subscribers in a network. The two types of networks are: Active Optical Networks (AON) and Passive Optical Networks (PON).

PON explored

AON networks use a point-to-point topology meaning that each subscriber line requires a dedicated fiber. In contrast, PON networks are point-to-multipoint in which single fibers can be shared among different subscribers.

One of the defining characteristics of a PON network is that it utilizes “unpowered” equipment in its architecture. For this reason, it is referred to as a “passive” network, whereas AON networks are called “active” networks because they require “powered” components.

PON architectures feature the deployment of splitters, which are unpowered optical devices with prisms that duplicate and split a single light source into multiple beams of light. The ability to take a single input and turn it into multiple outputs allows PON networks to use only a single fiber to serve multiple pathways simultaneously. The light signal can be split into ratios of 1:28, 1:32, 1:64 depending on network needs.

OLT

Unique to PON architecture is an OLT (Optical Line Terminal), which is a collection of specialized hardware that is housed in the central office. The OLT performs key functions such as:

1. Convert the electrical signals used by service-provider equipment into the light signals that are transmitted back-and-forth via fiber.

2. Coordinate the multiplexing of the PON system. OLTs leverage WDM (Wave-Division Multiplexing) to combine signals together and send them across the fiber, passing through the optical splitters, and onwards to the ONUs (Optical Network Unit) or ONTs (Optical Network Terminal), which are devices located near end user premises. Once the signals reach the ONUs or ONTs, the combined signal is separated back into their original states and distributed among the subscribers in a fiber network.

Pros vs Cons of PON

Pros:

Reduced power consumption

The obvious benefit of a PON network is the reduced power consumption it provides compared to active networks. Whereas an AON may require amplifiers, modulators, transponders, etc., all of which are powered components, PON consolidates network functions with the simple deployment of optical splitters. 

Lower network complexity

Removing the need for active equipment also decreases the operational complexity to configure and maintain these networks. When using an AON configuration, each port on a switch has to be routed to a specific user line, which increases the maintenance costs and requires careful monitoring of specific lines. With PON, each switch port can support up to four users on a single fiber.

Easier upgrade path

Scalability is also a huge advantage for PON as the optical distribution network can remain virtually untouched when upgrading to newer standards. The only hardware that needs to be replaced in an upgrade is the endpoint equipment at the ONUs. 

Cons:

Reach limitations

PON does not require implementation of any amplification equipment to operate and while that is an advantage on the power consumption aspect, it limits the range in which downstream signals can travel to in the last mile portion of the network.

However, using the combination of DWDM amplified channels (10G, 25G or 100G) and remote OLTs, it is possible to extend the reach to distant customers and mitigate this disadvantage of amplifying xPON signals.

Latency issues

PON can serve a higher number of users at once with its point-to-multipoint topology, but it also means there is potential for high traffic in the network. This can lead to some latency issues in the network, which could hinder network performance. Latency issues can be addressed through the use of better network designs.

While there are many benefits to utilizing a PON network, there are also areas where AON pathways are better suited for a network. Suitable deployments for each network are contingent on the network needs and the resources that service providers possess when building a fiber network. 

Variants of PON

Service providers have a variety of options when it comes to PON. There are a number of PON variants that can fit a modern infrastructure. Such variants include:

EPON

EPON is a variant of PON that uses Ethernet packets for data transfer and adheres to the traditional IP protocol when sending data. It offers 1Gbps data rates. 

10G-EPON

As its name suggests, the 10G-EPON ups the data rate to 10Gbps, making it an upgrade over its base EPON counterpart. 

GPON

GPON is a PON network that boasts gigabit data rates, breaking the gigabit threshold and making it an excellent fit for modern broadband networks. GPON offers 2.5Gbps downstream speeds/ 1.25 upstream speeds. 

XG-PON

XG-PON is an upgrade over GPON as it offers 10Gbps data rates. 

XGS-PON

Compared to XG-PON which offers one-way 10Gbps data rates, XGS-PON is symmetrical, meaning it supports 10Gbps data rates for both upstream and downstream data transfer. This gives it an advantage over the other PON deployments, making it an excellent fit with FTTH networks. It also offers a significantly more flexible migration path. XGS-PON operates at different wavelengths downstream/upstream, allowing it to be integrated on the same fiber as GPON. 

Learn more about Axiom PON solutions

Axiom carries a full lineup of PON solutions that supports a full PON ecosystem. We offer:

Transceivers

• PON OLT, ONT and ONU transceivers 

• GPON, EPON and XGSPON OLT transceivers pairable with multiple Axiom GPON, EPON and XGSPON ONT/ONU transceivers (with or without MAC Address) at the end user side

• Transport data upstream and downstream for triple play services

Splitters (1xN) 

• Mini, ABS, LGX or Rack Units

• Deployable in any PON network to split one signal into multiple downstream broadcast signals

• Support for EPON, GPON, BPON, FTTX, FTTH, etc.

Fiber Drop Cables

• Designed to assist operators in maximizing existing fiber infrastructures inside and outside

• Fully customizable and available in different fiber drops and connectors

Axiom Virtual OLT

Axiom recently announced the launch of Axiom Virtual OLT. The turnkey solution is vendor-agnostic, representing a paradigm shift in the PON ecosystem. With Virtual OLT, the architecture is disaggregated so that both hardware and software are not confined to vendor-specific standards, unlocking the integration of white box equipment in PON access networks. Virtual OLT unlocks the vendor-lock for OLT hardware, unleashing the full potential of PON for FTTX. 

To learn more about PON solutions for Axiom, contact: www.axiomupgrades.com