CWDM link: 1310 nm channel works, new 1471 nm channel carries no traffic despite good light levels
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Two service providers shared a fibre with CWDM multiplexers. The existing 1310 nm channel worked, but after adding a 1471 nm channel the transmitting side saw frames leave (confirmed with packet captures) while the far end received nothing, even though light levels looked normal. The provider had already disconnected the whole fibre for testing, which took down the working transit channel as well. The poster asked how to isolate whether the fault was in the SFPs, jumpers, mux filters or the fibre.
- Transceivers: CWDM SFP 1471 nm, CWDM SFP 1310 nm
- Form factor: SFP
Symptoms / messages:
no traffic received on new CWDM channel
light present but link dead
Comments 2
Measure received power per wavelength with a CWDM-capable power meter and compare with the SFP receiver spec; test jumpers and SFPs individually.
Bring both ends together with short jumpers and proper attenuators to rule out the fibre and the mux; note that CWDM SFPs sometimes fail for no obvious reason.