Re: Alien Waves

[Mark Tinka <mark@tinka.africa>]

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.