On 5/12/24 14:08, Mike Hammett wrote:

What are your experiences with alien waves, managed spectrum, spectrum as a service, etc?

Your outcomes will vary depending on whether this is deployed for terrestrial or subsea networks.

Subsea networks don't typically do alien waves, but rather, managed spectrum or spectrum sharing. This is especially the case on the newer SDM-based uncompensated submarine cable systems, where there is a huge volume of fibre pairs that makes this feasible, if not the most economical way to sell the asset to volume customers.

For terrestrial, alien waves were the original model, and in my opinion, the preferred one, because all the host network has to do is provide a port on their filter with a wavelength. The filter isolates the adjacent signals from one another, which improves launch OSNR. That said, managed spectrum and spectrum sharing are quickly replacing alien waves as the preferred deployment option for terrestrial networks, which can largely be blamed on advances for the same happening on the submarine side of things, even though the original idea was mostly driven by GEANT and a bunch of European NREN's back in the day.

Managed spectrum and spectrum sharing are more problematic because the chance of broadcasting bad noise to all other channels increases. Yes, major DWDM vendors now do have significantly improved optical power management systems (a spectrum controller, let's say) that will interact with the WSS in their ROADM, where the ROADM will set the centre frequency and its width, which helps to restrict any negative impact to launch insertion, and not toward the line side.

Different vendors will have different spectrum controller options that make managed spectrum and spectrum sharing services either simple or difficult to deliver on their specific type of gear. If it is something you want to be serious about, this will be the one time where PoC'ing all the vendors you are interested in is worth your time. It would also be useful to understand how each vendor supports things such as T-API (Transport-API) and other OpenROADM open architecture features to improve wavelength and optical power management characteristics between different vendors sharing a single OLS (Optical Line System). You may find that support for T-API and other OpenROADM standards may be spotty to non-existent with many vendors, but a vendor with a solid roadmap is certainly not a waste of your time.

Major traditional vendors like Ciena, Infinera, Nokia, Adva, Ribbon, and such, will have very extensive spectrum controllers, but they will come with the requisite $$ premium. Newer vendors whose platforms are based primarily on coherent pluggables approved by the MSA and OpenROADM will support alien waves, but may struggle to offer a comparable spectrum controller solution for managed spectrum and spectrum sharing, even if they may have a rudimentary ability to do so. Due diligence is highly warranted here, as the landscape is changing on a daily basis.

In essence, "virtual fibre pair services" (if I can call them that) is a matter of security, by way of total optical power control. What you want the vendors you consider to answer is:

If a spectrum customer erroneously provisions spectrum outside of their allocated bandwidth, how does the host network deal with that so that it does not impact any other spectrum customers on the same fibre pair?

How do you effectively restrict spectrum customers from only being able to access just their allocated spectrum, where a simple broadband splitter would not be sufficient for this?

How do you monitor the optical spectrum between each spectrum customer to ensure optimal optical performance on a per-spectrum-customer basis?

Especially for subsea applications, but nowadays, also for terrestrial ones; how do you monitor and manage optical power requirements for unallocated spectrum, including previously-allocated spectrum to a spectrum customer whose signal has now "disappeared" due to a failure of their own SLTE (Submarine Line Terminating Equipment) or transponder? In other words, ASE (Amplified Spontaneous Emission) noise loading capability.

Answering these questions makes it easier for interested parties looking to move away from procuring electrical bandwidth to, rather, procuring optical spectrum.

Hope this helps.

Mark.