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Question

Can i connect " SFP-10G-SR Module" one side and " SFP-10G-LR Module" other side?

  • 8 September 2019
  • 2 replies
  • 148 views

I have a customer who has ordered X670 as collapsed core and X440 as Edge. From X670 side customer ordered SFP-10G-SR Module and X440 (Dual 10GbE Upgrade License) ordered SFP-10G-LR Module.

My question is Can i connect " SFP-10G-SR Module" one side and " SFP-10G-LR Module" other side .

2 replies

Userlevel 2
Hi! (OK, this turned out to be a looong post... skip to the bottom if impatient 😉 )

You won't fry anything as the receivers will be OK with the low powers an LX, ER or even a ZR transmits with. Generally, those tx with 0 to +4 dBm (1 to 2,5 mW) and even if the receivers are specified to accept less (an SR somewhere around -1 dBm), the receiver will not fry. A ZR has an extremely sensitive receiver and some new and all old ones will fry if subjected to too high input power. Range is most commonly achieved with high receiver sensitivity, not high output power.

All receivers in (normal) SFPs accept light in a wide band, so even if an SR receiver is optimized for 850 nm, it will sense the light from an LR. Here my knowledge ends when it comes to LR vs SR compatibility. I think I've tried it sometime in the past, but it didn't work and I seem to recall that it is due to another signalling scheme/coding. If you're interested I can ask a vendor for more info.

For production use, I'd really recommend using the correct optics, but one can do tricks like using LR optics on multi mode to some extent. What really matters is the distance between the switches. SR cannot, will not and shall not go beyond 300 meters, and that is on 50 μm multi mode fiber (OM3 to OM5 only). If fiber distance is greater than that, you need LR optics. LRM may be an alternative, but that's a special case.

https://en.wikipedia.org/wiki/Multi-mode_optical_fiber
https://learn.extremenetworks.com/rs/extreme/images/10G-Base-X-Optics-DS.pdf

...skip to here ----->

Now, to answer your question, you really only have one option that is production quality. You ned to know which fiber type you use for each link. If you have, say 8 SR (MM) and 8 LR (SM) plugs, you can use the SR ones on up to four MM links (provided the length of the MM fiber is short enough) and the LR ones on SM fiber links. If MM fiber links are short enough, you can use LR plugs on those as well, but since I don't think there is a spec on the use of LR optics on MM fiber in the standards, I would not consider this production quality. 1000Base-LX is specified in the standard for up to 550 m on MM, but that's the 1 Gbpx version, not the 10 G.

If you come back with the fiber type(s) you have, I can provide guidance on what type of plug to use.

/Fredrik
Userlevel 3
Usually you don't do that.
You might fry the receiver of the SR module since the long range SFP is more powerful.
Additionally, both possibly don't work at the same wavelength anyway, in which case it can't work.
You should ask the customer what they intended to do.

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