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Between two server rooms on an office campus I have three pairs of fiber with an interconnect panel in the middle. Two of the three pairs were connected before I started here and are working. I cannot get a connection over the last pair for the life of me. I've tested all my patch cables and transceivers and I know they're all good, and I've had the fiber tested and it's good, so I have to assume maybe I've got an incompatibility somewhere?

The SFPs I'm using are 10Gbps/850nm multimode. The patch cables are OM1 2.0mm LC/ST. If I run from one switch to the other with an LC/LC or LC/ST - patch panel - LC/ST they get connected fine. Then if I try to run from one server room to the interconnect panel, no dice. I have tested both polarities to confirm that's not the issue. The cable that's running between that server room and interconnect panel is labeled 04/97 - FTB250MN which I believe refers to a 250um fiber diameter. Is that potentially the issue? I don't know but that might be singlemode fiber?

  • 10G needs OM3 or OM4. – Ron Trunk Aug 11 '20 at 18:37
  • I guess it works over short distances on OM1, is that right? So I just need different patch cables? How can I tell whether the cable running in the walls/conduit is OM1 or OM3/4? Just found this: "OM1 cable typically comes with an orange jacket and has a core size of 62.5 micrometers (µm). It can support 10 Gigabit Ethernet at lengths up 33 meters" I know that the initial run from the interconnect panel to the first server room is definitely less than 33m, it's just from one floor to the other, so this should work at least, no? – NaOH Aug 11 '20 at 19:17
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FTB250MN is a Corning number for tubing. You'll need to look inside the tubing for the actual fiber type.

What are the distances?

Fiber from 1997 is likely OM2 (50 µm core, 500 MHz·km @ 850 nm). 10GBASE-SR should work over OM2 for up to 82 m - but you do require OM2 patch cables. Mixing with OM1 (62.5 µm core) generally causes very high attenuation and seriously decreases the reach (possibly not more than 15 or maybe 20 m).

If the deployed fiber is OM1 or lower and the distance is too far you'll need to look at 10GBASE-LRM. Single-mode fiber requires single-mode transceivers (10GBASE-LR) for everything more than short runs.

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