Passive Wave Primer

Tue Oct 13 21:00:53 UTC 2020

From the perspective of a large carrier, spectrum is an operational nightmare. At a former $dayjob it was an “offering” in the sense that we had deployed it, told customers we offered it but wouldn’t actually deploy it anymore. 

Logistically there are a lot of potential points of failure once you got beyond the distance threshold where mid-line amps would be required, and as alluded to here, no big carrier would want to take on risk to the network that they’re not in control of. There’s not much sense in doing it in shorter-distance scenarios when most folks needing enough bandwidth to even have the conversation are going to be able to run their own optical systems across dark fiber at that distance anyway. The customers that we talked to about it were almost exclusively other carriers that wanted to use the muxes they had in inventory (aka not the same platform as the photonic layer) without the burden of deploying/managing a lot of amps but had no issue taking OTN or even LAN PHY in bulk when push came to shove. 

FWIW, and I understand these terms have become fungible over time, the scenario above is spectrum from the perspective of the photonic layer owner and alien wave from the perspective of the customer. As the photonic layer owner, alien wave would generally be thought of as 1) accepting a handoff as a WDM-specific channel of light, whether on fixed or tunable optics, not a standard 1310/1550, and, typically but not necessarily, 2) accepting a signal that is framed as OTN, not LAN PHY or WAN PHY.  

For the record, the OP’s query about passive wave would suggest PON/GPON or similar low-power CWDM for short-haul use, and not spectrum or alien wave, both of which are decidedly non-passive. 

Dave Cohen
craetdave at gmail.com

> On Oct 13, 2020, at 4:24 PM, Brandon Martin <lists.nanog at monmotha.net> wrote:
> 
> On 10/13/20 4:01 PM, Mike Hammett wrote:
>> It seems incredibly simple to do, depending on the capabilities of your platform.
>> What am I missing?
> 
> If the span between the mux/demux pair is entirely passive, it's fairly straightforward.  That's going to limit distances to around 80km or so with conventional systems or maybe 120km with systems designed entirely around modern coherent optics.
> 
> If there are photonic devices in the span, you now have customer-supplied light being part of the rainbow that those photonics have to handle.  Balancing things at amplifiers requires careful coordination with the customer (or adding a separate managed/monitored VOA for each alien wave which somewhat defeats the point).  You end up with a scenario where a customer can do something screwy and potentially affect other waves on potentially multiple spans which your big-name carriers are obviously completely freaked out by.
> 
> It's obviously possible, but the operational headache seems large enough that the major mid-haul and long-haul carriers I've talked to (all North America and all midwest, for that matter), don't seem to want to sell it despite all the major optical transport platform vendors not just supporting it by heavily pushing it.
> 
> I really do hope it becomes a real product that I (as a smaller, local island operator) can buy, but it just doesn't seem to be there yet at least in my region.
> -- 
> Brandon Martin