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I am just learning about the outlay of my worksite which has a multi block setup (physical buildings) each connected by their own fibre connection to the main aggregation switch.

I am in the process of figuring out what kind of fibre each connection is, because the buildings have been build over the years and so the fibre type is different.

I am using this image as a reference to ask my question - it seems to be a common table I have seen on multiple websites.

enter image description here

So if I have a connection in my switch that comes up as OM1 550/OM2 550 and the distance is 102m,then the max speed I can transfer across that would be 1Gb/s (please correct me if I am wrong)

But assuming I have that right then OM3 / 300m (up to) would give me 10 Gb/s

QUESTION

Now I have several fibre connections that are OM1 150m / OM2 300m and I am not sure what to make of the max speed capabilities.

What are the length & speed limitations of OM1 150m / OM2 300m ?

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The achievable link rate depends not only on the fiber grade but also on the exact technology/physical layer variant you use.

OM2 is specified with 500 MHz·km for both 850 and 1300 nm. According to the specifications, OM2 is good for up to 550m 1000BASE-SX, 82m 10GBASE-SR, 220m 10GBASE-LRM (might be expensive, depending on vendor), or 300m 10GBASE-LX4 (very expensive and obsolete/hard to get). Depending on the exact fiber quality and insertion losses, some reach stretching is often possible.

OM1 is specified with only 200/500 MHz·km (850/1300 nm), so 1000BASE-SX's reach decreases to 275m and 10GBASE-SR's to mere 33 m. 10GBASE-LRM uses 1300 nm wavelength, so it's the same reach as over OM2.

Note that what the switch displays most likely just reflects the transceiver requirements, not the actual fiber that is used. Obviously, you need to inspect the cable to make sure of the fiber grade at hand.

Unless it's OM1, your installation should be good for 1000BASE-SX but the upgrade path to 10GBASE-LRM may be expensive. Cheaper 10GBASE-SR seems unlikely to work.

If your fiber is deployed in an empty tube you should seriously plan to replace it. Single-mode fiber (OS2) has no dispersion limitations, so it should be preferred between buildings.

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  • Thanks for the explanation - that makes a bit more sense :-) So the tranceiver is that the SFP module? and if so does that mean that with OM2 / 300m it can go a higher speed at a longer distance then if the SFP module is a lower quality?
    – jwknz
    Sep 27, 2022 at 18:13
  • Yes, SFP modules are transceivers. 300m over OM2 is only good for 1 Gbit/s (1000BASE-SX). In case you can get 10GBASE-LX4 transceivers, those would also work but they're largely obsolete and very pricey. it can go a higher speed at a longer distance then if the SFP module is a lower quality? doesn't make sense to me, sorry.
    – Zac67
    Sep 27, 2022 at 18:33
  • Sorry I miswrote what I meant - lower quality I was referring to slower modules. But I get that slower module does not equal lower quality.
    – jwknz
    Sep 27, 2022 at 18:53
  • Yes, basically slower link speed means longer reach, but there are more parameters, so that's not always the case. -LRM uses a more efficient wavelength than -SR, increasing the reach. -LX4 uses four wavelengths to quarter the symbol rate, also significantly increasing the reach.
    – Zac67
    Sep 27, 2022 at 19:05
  • Flexoptix claim they achived 640 meters over old OM1 with a regular LR optic and a mode conditioning patch cord. Obviously YMMV, but it seems it's well worth actually testing stuff before spending huge sums of money ripping out and replacing fiber. Oct 3, 2022 at 12:08

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