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I have been having problems with a link flapping only when working with the AXM763 Module, but when I change 1G module it works without problems. Also there other 2 links with the same configuration working with the AXM763 10G.

I understand that the distance between my buildings is avobe the maximum distance, But How can I explain that 2 of those links work and only one fails.

I was reading cisco documentation and fiber specs and I found Mode Conditioning Patch cables are required for 10GBASE-LRM SFPs working on OM1 MMF because those cables reduce the effect called differential mode delay (DMD).

And I was thinking that this might help me with my problem, Can anybody help me with this problem? If it could work or not or if I missunderstood the Mode Conditioning Patch Cables.( I am not an expert in fiber)

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10GBASE-LRM will only go so far over legacy multi-mode fiber. Officially, its reach is 220 m over 500 MHz·km fiber, 243 m could just about work when everything else is perfect.

A mode conditioning patch is worth a shot but I wouldn't bet on it - 10G-LRM is designed for MMF and should already launch accordingly. If you've got some 10G-LR transceivers at hand it's also worth a try with mode conditioning.

Edit: As ilkkachu has pointed out, MCPs should be used with FDDI and OM1/2 MMF fiber as specified in IEEE 802.3 Table 68-3 and by various vendors. 802.3 alternatively suggests launching into those fibers without MCP but with a pretty focused "encircled flux" (at least 30% power within 5 µm radius, 81% within 11 µm) - the same as with OM3/4. I guess that clears up why using MC patches helped in your case. It seems you need the right kind of mode-conditioning patches as well. Only OM3/4 "laser optimized" fiber seems to be good w/o MCP for full reach.

If everything fails and redeploying modern fiber is not an option you should look out for 10GBASE-LX4 transceivers - they're expensive but if you can get them they're pretty much guaranteed to work (official reach is 300 m over legacy fiber).

Also, redeployment may be much cheaper when it's possible to pull preterminated fiber - you can get that very reasonably priced from many vendors. Use either OM4, OM5, or switch to OS2 altogether, especially when using budget transceivers.

Another (suboptimal) approach is to use aggregated gigabit links with or without WDM.

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  • Thank you very much. I will try the Mode Conditioning Patch, this Switch model does not have LX4 transceivers. I might also give it a try with the 10G-LR. I looked for re running new fiber but it is underground and it cost around 8000usd for OM4 12 strands.
    – NetOps2021
    Aug 13, 2018 at 20:39
  • I was afraid the cable's buried - the usual procedure back then, rather than the empty tube nowadays where you could just pull another cable. You can get 200m preterminated 12-strand OS2 for 300 € or even less...
    – Zac67 ♦
    Aug 13, 2018 at 20:54
  • I know, We were seriously thinking about running a pre-terminated fiber, but since the fiber is buried that would be hard and we could damage the fibers while pulling them.
    – NetOps2021
    Aug 13, 2018 at 22:27
  • I decided to try the Mode Conditioning Patch Fiber Cables, the link came up instantly, Its been around 2 weeks and the link works without errors. Thank you.
    – NetOps2021
    Aug 22, 2018 at 17:49
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    I checked and you're right: IEEE 802.3 Tabe 68-3 lists MCPs for FDDI and OM1/2 MMF. Thx!
    – Zac67 ♦
    Oct 23, 2018 at 11:08
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The point of a mode conditioning cable is to refocus the laser, this is traditionally used when using larger diameter multimode cable with single mode transceivers. basically the multimode cable has a lot more area for the light to disburse than a single mode cable.

For you application OM1 and 2 were never designed to handle 10Gig transfer rates over larger distances, the smaller diameter OM3 and 4 are really the types designed to push those 10Gig rates over longer distances. What the mode conditioning cable will do is to refocus the disbursed beam into something the receiving transceiver can read.

As for why 2 of the 3 are working. Well because you are just past the recommended limit any manufacturing deformities can cause the light to diffuse faster. At normal distances this wouldn't be an issue, but I suspect that because these runs are longer than the recommended 220m you are seeing some deformity in the glass.

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But How can I explain that 2 of those links work and only one fails.

Because everything has variability, so when you are pushing the limits sometimes things work, sometimes they don't.

And I was thinking that this might help me with my problem

I would say it is certainly worth a try. A couple of mode conditioning patch cords are much cheaper than ripping out and replacing the fiber plant.

(p.s. in your diagram one of the mode conditioning patch cords is incorrectly shown, the singlemode fiber goes to the transmit port on the transciever while the multimode fiber goes to the infrastructure cabling)

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I decided to try the Mode Conditioning Patch Fiber Cables, the link came up instantly, Its been around 2 weeks and the link works without errors.

Thank you.

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  • You should accept your answer so that the question doesn't keep popping up forever, looking for an answer.
    – Ron Maupin ♦
    Aug 22, 2018 at 17:48

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