CWDM question


We are doing a fiber link between us and another SP using CWDM.

There is traffic flowing just fine at the 1310 wave, and have recently added a
1471 wave.

On the 1471 wave there are some problems with it. From our perspective, and we
have packet captured this, we are transmitting data to them, but they say they
are not seeing anything. We are receiving from them, and while we show that
packets are leaving our interface to them, they are getting nothing at all.

There are good light levels between the two locations and do not understand
why they are not seeing traffic from us even though we are sending it. Our packet
counters show we are transmitting to them and receiving from them.

Is it possible to have RX and TX light and things appear to be ok, but have the
RX on their side fubar in some way that it is not operating correctly in that our
traffic is not reaching them?


Are you using fixed optics or tunables? Are transponders involved for the CWDM side then you have “client optics” at 850nm or 1310? Is there a filter involved? Do you have a light meter? What do the optics show for the various light levels and frequencies involved?

- Jared

Fixed optics, there are no transponders, just a passive mux. No filters, though there is a pad on our side.
Light levels on our side are good and within spec. I have been trying to find out from the SP what theirs
are at presently, but when the circuit was first lit levels were taken and found to be within spec on both

Only 1310 and 1471 in use.

We are 800+km away from the site so its hard to get some hands/eyes there at present.


That is whats next. They took down the whole fiber instead of just the 1471 wave to test
which killed transit...grrr..

They say their tx/rx are within spec.

Next is jumpers and sfp swaps I guess.


If you're also doing 1310 does that mean there's a splitter cable inline
with the passive mux? If so, some are cheap and don't filter well outside
of the 1550 band.

Another possibility is that the fiber you're using has higher attenuation at 1471nm than at 1310. While 1471 is outside of the 'water peak' band (E band - 1360-1460nm, centered at 1383nm, iirc), the type of fiber could could still have higher attenuation that runs into the S and O bands.

If replacing optics doesn't solve the issue, you'll probably need a test set that can test specifically at 1471 nm.