Passive and Active Optical Networks – What is the difference

Passive and Active Optical Networks – What is the difference

Fibre optic wires are minuscule strands made of plastic or glass which are designed to carry virtual information at very high speeds.

As optical fibre transmits via light, the signal is not weakened easily and avoids electromagnetic interference. The signal is therefore very stable, ensuring high-quality broadband Internet access suitable for real-time high-definition multimedia services.

As this data travels across the fibre connection, it needs a way to be directed so that the correct information arrives at its intended destination.

There are to alternate network designs that make fibre broadband connections possible – active and passive optical networks. Each design offers a way to separate data and set it upon its intended route to arrive at the proper place. Passive and Active networks comparatively have their advantages and disadvantages depending on their purpose.

AON (Active Optical Network)

An Active Optical Network (AON) utilises 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 fibre is routed to the end users premises.

  • Subscribers have a dedicated fibre optic strand.
  • Uses active components like amplifiers, repeaters, or shaping circuits to manage signal distribution
  • AON networks can cover a range to about 100 km, a PON is typically limited to fibre cable runs of up to 20 km
  • Flexible solution suitable for businesses
  • Higher building cost as active networks requires more fibre

PON (Passive Optical Network)

A Passive Optical Network (PON), however, does not have electrically powered equipment and rather makes use of optical splitters to separate and collect optical signals that move through the network. A PON shares optical fibre strands from portions of the network and the equipment is only really powered by the ends of the signal.

  • Shares fibre optic strands for a portion of the network.
  • Because the bandwidth in a PON is not dedicated to individual subscribers, data transmission speed may slow down during peak usage times in an effect known as latency. Latency quickly degrades services such as audio and video, which need a smooth rate to maintain quality.
  • Uses optical splitters to separate and aggregate the signal
  • Every time the signal is split two ways, half the power goes one way and half goes the other therefore PON networks have a shorter range of coverage limited by signal strength.
  • Power required only at the ends
  • Rigid solution suitable for residential
  • PONs have a low building cost with lower maintenance costs
  • PONs also make it difficult to isolate a failure when they occur.
  • Types of PON:
  • EPON – Ethernet PON (Symmetrical)
  • GPON – Gigabit PON (Asymmetrical)

Hybrid systems can also be formed that utilise both active and passive networks in some FTTH systems.