Do tunable SFP+ modules actually exist, and can I use one on a box with no wavelength command
We are lighting a handful of channels over one metro pair with passive mux and demux at both ends, 100 GHz plan. Everything I can actually source is fixed-wavelength DWDM SFP+, a separate part number per channel, and keeping spares that way is getting silly.
- 10G aggregation at both ends, SFP+ cages only, no XFP anywhere in the estate
- passive DWDM mux/demux, 100 GHz spacing
- every DWDM SFP+ in the catalogues is a single fixed channel; the one tunable 10G part number I can find listed at all is DWDM-XFP-C, and that is an XFP
- one of the two boxes has no optics configuration under the interface at all
What other platforms seem to expose, against what I have here:
transceiver channel <n> # what some platforms use
wavelength <n> # ... or this, under the DWDM controller
(this box) # neither keyword exists under the 10G interfaceTried so far:
- went through the whole interface configuration tree looking for anything optics related, nothing there
- asked two suppliers for a tuunable SFP+ and got "we only stock fixed channels" from both
So, two questions. Do tunable SFP+ modules exist as a product at all, or is XFP the only 10G form factor that gets them? And if they do exist, is a host with no tuning commands a hard blocker, or is there a way around that?
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Comments 4
They exist. The reason the answer always sounds muddy is that two different properties get called "tunable" in the same breath.
One is tuning across the DWDM grid: a real tunable sits on the 50/100 GHz plan and covers something like 80 channels, so a single part number replaces your whole per-channel spares shelf.
The other is being able to reconfigure a module for a different host platform, which has nothing to do with wavelength at all, and is what a lot of the vendor tooling is actually about.
That second distinction is why your box having no wavelength command is a non-issue. A tunable SFP+ can be set externally through a control box before it ever goes near the switch. Once the channel is written into it, the host just sees an ordinary fixed-wavelength DWDM module and treats it like one, so there is nothing to configure on the platform side. You keep one SKU in stock and set the channel yourself at deployment time.
If the box on the other end does have the commands, by all means use them (transceiver channel on one flavour, wavelength under the DWDM controller on another), but it is a convenience, not a requirement.
The one thing I would still say: on a long span I would reach for a tunable XFP rather than SFP+, the budget on the smaller form factor tends to be tighter.
The last paragraph is the part I would push back on. There is no budget penalty for the smaller form factor here, tunable SFP+ and tunable XFP land at about the same receiver sensitivity, roughly -24 dBm, so the span comes out the same either way. Pick the form factor your cages give you rather than the one folklore says is stronger.
Two things worth watching instead. Mixing a 50 GHz tunable with 100 GHz fixed optics on the smae plan has caused real interop grief, so keep the whole span on one grid. And tunable modules have been seen reporting a channel number that does not match the wavelength they are actually transmitting on, XFPs in particular, so if your plan is 100 GHz have the parts preset to 100 GHz channels and verify on the mux port instead of trusting what the switch prints.
That settles it. The two shops I had been asking do not keep tunables at all, but a third one does, and they wrote the channels in with their control box before the modules shipped. Both ends came up as plain fixed-wavelength DWDM parts. The box with no optics commands does not care in the slightest, it sees a DWDM SFP+ and lnks, and the channeels landed where the mux expects them.
One SKU on the shelf, channel written at deployment. Exactly as described, thanks.
Preset modules being invisible to the host cuts both ways: the host also stops treating them as anything special, and monitoring built around short-reach optics starts shouting. Brocade FC switches on Fabric OS 7.x are the classic example, third-party DWDM SFP+ link fine and then the log fills with
Nothing wrong with the module. Fabric Watch ships a 50 mA ceiling for SFP bias current, which suits short-reach lasers, while a DWDM laser only gets interesting somewhere above 110 mA. So you raise the custom threshold instead of chasing the optic:
It needs a Fabric Watch licence, plus Extended Fabric for the long spans, and it is specific to Fabric Watch on FOS 7.x. The general lesson travels though: after DWDM optics go into a box that has only ever seen short-reach parts, check what its thresholds consider normal.