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I have this multimode transceiver product: http://www8.hp.com/h20195/v2/gethtml.aspx?docname=c04168409&search=J4858C

I am going to use it on the following switch: http://www8.hp.com/h20195/v2/gethtml.aspx?docname=c04111401&search=J9727A

I was wondering if I could use the following fiber optic cable to connect to a same configuration at 200 meter distance (which has been cabled by an electrician and it is a multimode type but I don't know about the OM number) : LC-LC 0200 50/125µ OM3 Duplex 2m

What are the limitations in terms of bandwidth/distance? I really don't understand the MHz*km bandwidth thing.

4 Answers 4

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EDIT: Fixing answer now that I'm on a real laptop.

Yes, OM3 is just "laser optimized" multimode, it will work with both your optic and distance.

What are the limitations in terms of bandwidth/distance?

Max Distance @ 1Gbit/s (per the product page): 550m

This also lines up with the OM3 specification http://en.m.wikipedia.org/wiki/Multi-mode_optical_fiber#Types

I really don't understand the MHz*km bandwidth thing.

This is called modal dispersion, it's an inherent property of multimode fiber - it's basically the relationship between distance and bandwidth.

So first you need to understand that multimode fiber is named that way for a reason. There are multiple modes of light that are sent over the cable, so when light is transmitted it looks something like this:

enter image description here

All of those lines are the "modes".

Because they're using the entire width of the fiber, they "bounce" from "top to bottom" as you see in the picture. Modes traveling at the boundaries of the fiber travel faster, and modes traveling at the center travel a little bit slower. If you look at the picture where it says "Dispersion" you see that they don't quite arrive at the same time, this is a very very minute amount of time, however its enough to reduce bandwidth.

So for something like 1GB, because it doesn't need to carry as much data, it has much more tolerance for distance (550m). If you want it to carry 10GB, you need to compensate by shortening the distance because of this dispersion. I hope this helps.

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  • Thanks for the link. I just want to be sure that my transceiver will be compatible wizh OM3 because its specifications say: 50 µm core diameter, 500 MHzkm bandwidth but the OM3 says 1500 / 2000 MHzkm. What does that mean?
    – Truefalse
    May 19, 2015 at 12:19
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    This is directly from the transceivers product page: 62.5/125 µm or 50/125 µm (core/cladding) diameter, graded-index, low metal content, multimode fiber optic, complying with ITU-T G.651 and ISO/IEC 793-2 Type A1b or A1a, respectively; May 19, 2015 at 12:21
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    The first number in the 50/125, relates to the core size, 50 µm. This will work with your cable. May 19, 2015 at 12:23
  • Thanks @jordan-head, I was just scared that OM3 would only be compatible starting from 1500 MHz*km <- this may be nonsense XD
    – Truefalse
    May 19, 2015 at 12:27
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yes, you could use OM3 cable with J4858C, in fact, J4858C can be used with OM1, OM2 or OM3 but with a differenct distance.

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J4858C is a 1000BASE-SX transceiver. 1000BASE-SX is specified for 550 m reach over 500 MHz*km fiber (OM2). OM3 (1500 MHz*km) will probably go quite a bit further. So, yes you can!

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I refer you to the OSI stack definition. The distance is determined by the MAC (media access control) layer definition.

Specifically if you are using a 1GB MX (Multimode) SFP your distance is limited to 100m (330ft). You could be using the best quantum designed military grade fiber in the world and your distance limitation is still based on the timing characteristics of the MAC layer definition.

If you want to go to a longer distance you need to move to Single Mode Fiber and the matching SFP. Typically a SX or LX vs MX transceiver.

In the real world you can push the distance a bit... but the consequence is that the longer you go the greater number of dropped packets, which causes re-transmits, and subsequently your effective throughput goes down. This gets worse with higher traffic levels. Presumably you have a switch at each end of the fiber - when you have 24-28 devices at the far end of the link this could be significant.

To test the network throughput you do what's called a Pierf test. You generate traffic at one end and receive it at the other end. A simple ping test sends packets but doesn't hammer the network like what a Pierf test does

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    Link reach is entirely unrelated to the MAC/data link layer. "MX" is not a thing here. 1000GBASE-SX is specified for 550 m over OM2 MMF. Since fiber Ethernet is entirely P2P there's always exactly one node at each end. And you probably mean iperf3 for testing.
    – Zac67
    Nov 24, 2023 at 19:08

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