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lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1

1 edit
reply to spectrumhead

Re: SFP module for 100km

said by spectrumhead:

There is a -32db loss on the path.

We have tried now HP SFP J4860C but it didint link up.

I found basic specs for the HP and it says max 70km, so it was not suitable to begin with for your 90km link.
»h30094.www3.hp.com/product/sku/3673147

*** I am curious what tool/method you used to determine that the path has -32dB total loss. Anyway, assume that the contribution to this number from the actual 90km fiber run stays exactly the same and is out of your control.

But you do a very good job splicing the two endpoints and you also have newer design SFP modules with lower losses ... you can easily deduce that you WILL end up with a bit more system margin.

So in my opinion there is no need to buy the most expensive 200km/41dB LX20 module. The 160km/37dB LX16 you chose should be OK. Just to be safe, work out a 30-day return/exchange privilege before you buy.


spectrumhead

join:2009-05-03
@lutful
32 dbi loss was measured by the owner of the fiber pair recently. Actually the enginner told me that it is around -30 but it will be better for me to consider it like it is -32 for some reason i dont know.

The price I have got from a reseller is 1250$ per SFP. Is it too expensive or are there any cheaper options out there that I may consider ?

switchman

join:1999-11-06

1 edit
said by spectrumhead:

@lutful
32 dbi loss was measured by the owner of the fiber pair recently. Actually the engineer told me that it is around -30 but it will be better for me to consider it like it is -32 for some reason i don't know.

The price I have got from a reseller is 1250$ per SFP. Is it too expensive or are there any cheaper options out there that I may consider ?

37 db is plenty of budget. I would be a lot more comfortable if they gave the specs for the SFP. If you look at the finisar site, you can see an example of what I am talking about for specs.

You could also get an amp use it. Something like this, »www.finisar.com/products/optical···cro-EDFA, in their 1RU package. Then pair it up with a DWDM sfp in you switches. This way if the SFP fails, you have a wide source to select from.

What wavelength did they shoot the fiber with, 1310 or 1550. If it was 1550, then that is not very good fiber or it has a lot of splices or connectors in the path.

When you look at optics you look at the Min TX launch power. That in combination with the min rx sensitivity gives you you link budget. The actual TX power of your SFP will be between the Min and Max value there is no guarentee as tothe actual launch power. It will probably be around+2 or +3, but you can't count on it.

JDSU also makes good stuff.

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1

1 edit
Finisar is an excellent brand.

I also agree that OP needs to get official specs for the chosen 160km SFP to make sure (minimum TX power - RX sensitivity) comes out a few dB higher than the 30-32dB loss on this fiber.

OK, I was looking at marketing spec for Transition TN-SFP-LX modules.

TN-SFP-LX5 [50 km/31.1 mi.] Link Budget: 19.0 dB
TN-SFP-LX8 [80 km/49.7 mi.] Link Budget: 24.0 dB
TN-SFP-LX12 [120 km/74.6 mi.] Link Budget: 32.0 dB
TN-SFP-LX16 [160 km/99.4 mi.] Link Budget: 37.0 dB
TN-SFP-LX20 [200 km/124.3 mi.] Link Budget: 41.0 dB

My hunch is that the RX sensitivity is the same for all modules and they are only increasing TX power for the increased range and link budget guarantee. If RX sensitivity was -30dBm across the modules, minimum TX power would have to be +7dBm for LX16 and +11dBm for LX20 ... which boggle my mind. Definitely worth asking for their complete technical specs.