Knowledge
Difference Between Active Optical Network and Passive Optical Network
Fiber to the Home (FTTH) brings fiber connectivity directly to residential users, providing high-speed and reliable broadband access. Two common architectures used in fiber access networks are Active Optical Network (AON) and Passive Optical Network (PON).
Although both can be used to deliver fiber connectivity to end users, they differ in network architecture, equipment, fiber distribution, maintenance, and deployment requirements.
What Is AON?
AON stands for Active Optical Network. It commonly uses a point-to-point (P2P) architecture in which a dedicated fiber connection can be provided between the network equipment and an individual user.
Unlike a passive optical network, an AON uses powered network equipment within the access network to transmit, switch, or manage optical signals. Depending on the network design, this equipment may include Ethernet switches, aggregation switches, optical transceivers, or other active devices.
Because users can have dedicated fiber connections, AON can provide straightforward bandwidth allocation and network management. It can also offer flexibility when network operators need to upgrade equipment or expand capacity.
However, the use of powered equipment means that AON deployments require electrical power, equipment locations, and additional active-network infrastructure.
What Is PON?
PON stands for Passive Optical Network. It uses a point-to-multipoint (P2MP) architecture and is widely used in FTTH and other FTTx deployments.
The key feature of PON is that the optical distribution network (ODN) between the central office and users can use passive optical components, such as optical fiber, splitters, and connectors, without powered switching equipment in the distribution path.
A typical PON consists of three main parts:
- OLT (Optical Line Terminal): Installed at the central office or headend.
- ODN (Optical Distribution Network): Includes fiber cables, passive optical splitters, connectors, and other passive components.
- ONU/ONT (Optical Network Unit/Optical Network Terminal): Located at or near the end user’s premises.
How Does a PON Work?
In the downstream direction, the OLT sends optical signals through the ODN. A passive optical splitter divides the signal and distributes it to multiple ONUs or ONTs.
In the upstream direction, signals from multiple users are transmitted toward the OLT over the shared optical infrastructure according to the PON’s access-control mechanism.
This shared architecture allows one feeder fiber to serve multiple users, reducing the amount of feeder fiber and active equipment required in the access network.
For FTTH deployments, fiber optic splitters are therefore an important component of the PON architecture.
AON vs. PON: Key Differences
| Feature | AON | PON |
|---|---|---|
| Network architecture | Commonly point-to-point | Point-to-multipoint |
| Active equipment | Used within the access network | Mainly concentrated at network endpoints |
| Optical distribution | Dedicated connections are common | Fiber infrastructure can be shared |
| Splitters | Generally not required for P2P access | Passive optical splitters are commonly used |
| Power in distribution path | Requires powered network equipment | Passive ODN does not require powered equipment |
| Fiber utilization | Dedicated fiber per connection is common | One feeder fiber can serve multiple users |
| Maintenance | Active equipment requires power and maintenance | Passive ODN can simplify field infrastructure |
| Typical application | Enterprise/access networks and dedicated connections | FTTH and FTTx mass deployments |
AON vs. PON: Deployment Considerations
The choice between AON and PON depends on the network operator’s architecture, capacity requirements, available infrastructure, and operating model.
Fiber Distribution
AON commonly provides a dedicated optical path to each subscriber, which can simplify individual connection management.
PON shares part of the optical distribution infrastructure among multiple users. Passive splitters allow one feeder fiber to be distributed to several subscriber connections.
Equipment and Power
AON requires powered network equipment in the access network. This means that equipment locations need suitable power and environmental conditions.
PON moves much of the intelligence and active equipment toward the OLT and subscriber-side equipment, while the ODN can remain passive.
Maintenance
With AON, active switches and other powered equipment in the access network need to be monitored and maintained.
A PON ODN contains mainly passive components, so there are fewer powered devices in the field. However, fiber connections, splitters, closures, and other passive components still need proper installation and maintenance.
Network Expansion
AON can provide a dedicated connection for each user, which may make certain upgrades and bandwidth management approaches straightforward.
PON can scale by using different PON technologies, optical split ratios, and higher-capacity generations, subject to the limitations of the specific standard and optical budget.
AON and PON in FTTH Networks
Both AON and PON can support fiber access networks, but they use different approaches.
AON relies on active network equipment and commonly provides dedicated point-to-point connections. This can be suitable where dedicated connectivity and direct network control are important.
PON uses a shared point-to-multipoint architecture and passive optical distribution. Its use of passive splitters and shared feeder infrastructure makes it particularly common in FTTH deployments where many subscribers need to be connected from a central location.
Conclusion
AON and PON are two different approaches to building fiber access networks.
AON uses active equipment within the access network and commonly provides point-to-point connections. PON uses a point-to-multipoint architecture and passive optical components such as fiber splitters to distribute connectivity to multiple users.
