If you want the quick and easy answer, the targeted maximum distance for the ONS 15454 SDH OC-12c LR/STM-4c LH 1310 card is 40km. This information is on page 2 of:
Network Cabling Physical Media Distances
http://www.cisco.com/warp/public/765/tools/quickreference/mediadistances.pdf
WARNING: LONG POST AHEAD. If you want to know more about this subject, continue reading; else skip it and do something more productive with your time.
How far you can really go is determined by the optical power and transmission wavelength of the interfaces at each end, and the attenuation in your cable system.
Predicting the actual maximum distance involves making several calculations, and a few assumptions. There is no exact maximum distance specified by any standard.
Knowing the optical transmit and receive power characteristics of the source and destination interfaces is your starting point. For this card, that's TX(max)=+2dBm, TX(min)=-3dBm; and RX(max)=-8dBm, RX(min)=-28dBm. This information can be found in:
Installing ONS 15454 SDH OC12 LR/STM4 LH 1310 Cards
http://www.cisco.com/en/US/products/hw/optical/ps2006/prod_installation_guide09186a00800f0104.html#xtocid4
With these figures, you can calculate your Link Loss Budget. This is the maximum amount of attenuation dB loss in your fiber span that will still allow a pair of optical elements to communicate with each other at minimum power levels. Link Loss Budget in this case is TX(min)-RX(min) or 25dB.
You can also calculate your Minimum Attenuation, which is the minimum amount of attenuation dB loss in your fiber span that is necessary for proper operation of your optical elements at maximum power levels. Minimum Attenuation in this case is TX(max)-RX(max) or 10dB. (That's the same 10dB mentioned in that .PDF file above.) At short distances, for example using a 2-meter patch cable, you must use at least a 10dB in-line attenuator on the RX port of each optical interface. At longer distances, the single mode fiber span may have sufficient attenuation that in-line attenuators are not needed.
So, as long as the optical dB end-to-end loss over your single mode fiber span does not exceed 25dB, your link will work. Here's where the assumptions (and more calculations) come into play.
You need to know the number of connectors/fiber terminations you have in the span, and estimate a dB loss for each; the cumulative total is known as connector loss.
You also need to know the number of fusion splices or joints in the span, and estimate a dB loss for each; the cumulative total of these is known as splice loss.
Finally, you need to know how many kilometers of single mode fiber are in your span, end-to-end, because there's attenuation in the fiber cable itself; knowing this, and what the specific cable attenuation rate is for your cable in dB per km at your transmission wavelength, you can calculate the cable attenuation loss.
As long as connector, splice, and cable losses added up do not exceed your link loss budget, then your link should work.
A helpful link:
Calculating the Maximum Hop Distances for 15454 Fiber Links
http://www.cisco.com/en/US/products/hw/optical/ps2006/products_tech_note09186a00800fd535.shtml
And here's some engineering "rules of thumb" we take into account when designing outside plant fiber cable installations:
* Since fiber doesn't come in one long continuous strand, but rather in reels, we figure there's a fusion splice at least every 6096 meters joining two pieces of cable.
* Also, in aerial cable installations (that is, fiber on telephone or power poles), we figure there's an extra 10% of cable up on the poles, above and beyond the distance measured between the two locations being connected, to allow for service loops (spare or slack cable in the event of a cable break).
* Also, plan on at least four splices being added to the span over its lifetime (necessary as you re-splice two ends of a broken cable).
Ultimately, all the calculations just tell you whether or not it is feasible. You have to measure the span end-to-end with an optical power meter; or better yet, an optical time domain reflectometer (OTDR). Only then will you know exactly what your dB loss is. The OTDR can tell you where you have problem splices, show you where fiber strands have been mis-spliced, or illustrate where strands are broken or damaged. OTDRs can be rather expensive, though, so either rent one, or pay a fiber optic cable installer to run the tests using one.
Hope this helps.
