What are ROADMs? Everything you need to know | Neos Networks

What are ROADMs?

  • Neos Networks
What are ROADMS?

What are ROADMs?

Until recently, Optical network solutions were hard to change. The routes traffic took were fixed and inefficient and bandwidth was not being optimised. That was until Reconfigurable Optical Add-Drop Multiplexers (ROADMs) came along.

Before ROADMs, optical network operators have faced the challenge of extending and modifying their networks. A ROADM is a piece of software that provides the ability to remotely provision traffic from a Wavelength Division Multiplexer (WDM), at the wavelength layer, without the need for network redesigns and can be done in almost real-time. This means that assigning how the entire bandwidth will function does not need to be done at the deployment stage – it can be configured and changed as and when it is needed.

ROADM Technology

When ROADM technology was first launched its functionality was as an add/drop design whereby one wavelength would be added or dropped from a network at a time, ROADMs can now route and reroute any wavelength in any direction – this is known as CDC-ROADM. Where previously ROADMs were only really used in long-haul Dense WDM (DWDM) networks, as the need for greater capacity has increased it is now also more commonly found in major metropolitan networks too.

How do ROADMs work?

ROADMs have a number of components to help ensure greater efficiency for a fast and responsive network:

  • Wavelength Selective Switch (WSS) – this is the part that enables a wavelength to be switched. The network manager can route any wavelength to and from any port to seamlessly change connectivity as needed.
  • Optical Channel Monitoring (OCM) – This monitors the optical power of each wavelength to ensure they are operating as efficiently as possible.
  • Variable Optic Attenuators (VOAs) – configures the power level of each wavelength to minimise signal loss.


ROADMs give you more flexibility in that you can select and then reselect a particular wavelength to add or drop. This is particularly useful if you have unpredictable or changeable traffic volumes. 

As point-to-point networks, DWDMs are well suited to transferring large amounts of data from one data centre to another.

ROADMs carry a higher initial cost than DWDMs. However, as the traffic load increases, with even just the addition of a few wavelengths per link, ROADMs quickly become more economical than DWDMs.

An added bonus of ROADMs is that you can implement ‘multi-degree’ networking, with several fibre paths per node connecting to other sites. So if one fibre path goes down, you can simply steer traffic along another path.

ROADMs are now the most common type of optical network deployed.

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Optical connectivity FAQs

Take a look at our FAQs for Optical connectivity

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    Optical Wavelengths are high capacity methods of transporting data from one point to another, using fibre optics.

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  • What are ROADMs?

    Until recently, Optical networks were hard to change. The routes traffic took were fixed and inefficient and bandwidth was not being optimised. That was until Reconfigurable Optical Add-Drop Multiplexers (ROADMs) came along. Discover more about ROADMs.

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    The lowest latency on a fibre network is achieved when distances between two sites are short, with as few exchanges in between as possible.