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pcunite
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10G Fiber run of 700m, which SFP+ module and cable?

Sat Feb 06, 2021 5:13 am

I have an upcoming project to where I will require a fiber run in excess of 300m. Probably about 620 meters distance. I would like to be able to maintain a 10G link between the buildings if possible. I only have experience with 850nm Dual LC modules (like the S-85DLC05D) with 50/125 OM3 LC-LC style cabling. So, I welcome your guidance as this is new for me.

I see that MikroTik has the S+C47DLC10D in an 1470nm wavelength supporting 10km. There are 1490nm, 1510nm, 1530nm, 1550nm, 1570nm, 1590nm, and 1610nm variants. Which module should I go with and what cable type (I assume OS2 9/125 single mode)?

There is the S+2332LC10D pair, but these are 1270nm/1330nm wavelengths, so why should I choose them as they are not duplex?

The plan was to use two switches, the CRS328-24P-4S in the first building and a CRS326-24G-2S in the other. The CRS328 will have a S+85DLC03D for use with shorter runs using OM3 to other areas.

Thank you for your assistance.
 
onnoossendrijver
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Re: 10G Fiber run of 700m, which SFP+ module and cable?

Sat Feb 06, 2021 10:23 am

If you have duplex fibre, you should use something like https://www.fs.com/de-en/products/11555.html or https://mikrotik.com/product/xs_31lc10d.
For single fibre take the https://mikrotik.com/product/Splus2332LC10D, which is actually full duplex. Sending is done on a different wavelength as receiving.
Both options require 9/125 cable.
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mada3k
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Re: 10G Fiber run of 700m, which SFP+ module and cable?

Sat Feb 06, 2021 11:14 am

If you are not going to use CWDM (witch those different wavelenghts are for) then you should go with ordinary ~1310nm. And yes, above 300m you generally need to use single-mode.

If you are going to use dual fibre = XS+31LC10D
For single fibre ("BiDi") = S+2332LC10D

Of course almost all SFP:es works in Mikrotik. So the ones on FS.com will probably work fine as well.
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pcunite
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Re: 10G Fiber run of 700m, which SFP+ module and cable?

Sat Feb 06, 2021 11:29 pm

Thank you! This is very interesting. I do have the option of specifying the cabling. Can I use use simplex single strand LC-LC cables everywhere? Even for short runs? Naturally, I'll do what is cheaper, but to have BiDi duplex over single strand can I buy OS2 9/125, single strand single mode cables connected to the SFP+ S+2332LC10D module pair and always forgo OM3?

What is the rational for two strands (outside of redundancy or increasing bandwidth)?
 
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Re: 10G Fiber run of 700m, which SFP+ module and cable?

Sat Feb 06, 2021 11:51 pm

Probably nowdays there is no good reason to use two fibre strands for a duplex connection. Historically there were numerous reasons for that, two pretty important were these:
  • fibres used to have usably low attenuation in narrower wavelength bands around 1310 nm and around 1550 nm while attenuation in band between these two (as well as lower and higher) was high thus limiting usable length of connection.
  • optics was not so advanced. Optical filters were less selective making use of similar wavelengths impossible (and together with previously mentioned high attenuation band around 1390 nm this resulted in "standard" BiDi wavelengths of 1310/1550 nm). Optical filters were also larger which meant that including it in a small device such as SFP module was quite a challenge and thus much more expensive. And a BiDi module needs an optical filter to separate Tx from Rx.
Both problems meant that using single strand for duplex communications was reserved for special use cases. The price difference for a cable with double number of strands is usually not high. There are other (more or less) nuisances when using single strand (e.g. using complementary rather than same modules on both ends of connection which also means larger number of spare parts that should be at hand at any time).
Drawbacks of using single strand are not really here anymore. However when pulling a new cable one should always plan for expansion. But if there are strands available, why not using them (in pairs).
BR,
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onnoossendrijver
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Re: 10G Fiber run of 700m, which SFP+ module and cable?

Sun Feb 07, 2021 10:32 am

I believe the costs of fibre are really low. If it costs less than a few 100 euros/dollars extra for running 4 or even more strands, please consider doing that. You never know what you need it for. Doing it later is much more expensive. Also don't be cheap with the fibre quality. If adding just a few dollars extra gets you better cable that is able to do 100g.
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mada3k
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Re: 10G Fiber run of 700m, which SFP+ module and cable?

Sun Feb 07, 2021 11:41 am

If buying or deploying new (and self owned) cables, then duplex is the way to go. Simplex/BiDi usually makes most sense when leasing/renting dark-fibre.

You should also always plan for some spare fibre-pairs in case something new or some breaks and you can make a quick change to get it up running again.
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