GLC-LH-SM transciever - distance over 10km

[cmihaylov_2]

Hi, we have a 1000BASE-LX/LH SFP (GLC-LH-SM), which is supposed to be used for

distances of up to 10 km over SMF.

Have someone tried using it at something close to this prescribed limit -

for example 11 or 12 km distance? Will the link be flapping too much.. will it work at all?

Thanks

[paolo bevilacqua]

You have to try yourself, different types and years of manufacturing can change the results. Also the number of splices do influence power budget.

[Tom Randstrom]

As Paola has mentioned, you will have to try to confirm.

A lot will depend on the quality of the fiber links you will be using.  The biggest issue would be if there were a lot of connectors in the link; sometimes encountered when the fiber runs through many building, with connectors to allow access to the fiber.  Connectors can have high losses.  Otherwise, a singlemode fiber link with fusion splices has a very low loss. Do you have any information regarding the actual loss of the fiber links that you will be using?

The GLC-LH-SM transceiver have quite a bit of operating margin.  However, it won't be supported by Cisco above 10km.  

Tom

[Alexei Andoni]

A quick test will certainly give you some initial evaluation, but be aware it also can produce wrong expectation.
The 1000BASE-LX/LH has a large Transmit Power tolerance according to its specs:

  Transmit Power (dBm) = -3 to -9.5
  Receive Power Range (dBm) = -3 to -20

As you can see the transmit power could vary 6.5 dB (from -3 to -9.5). That depends on 1000BASE-LX/LH sample to sample.
Therefore the link might work with some 1000BASE-LX/LH samples, which have Transmit Power of -3 dBm, and at the same time it won't work with samples which Transmit Power is -9.5 dBm.

Having said the above, the best approach would be to measure the link loss (including: fiber, connectors, patch-cords, optical distribution frame, etc..) and compare the result with the power budget of the 1000BASE-LX/LH. In this case the total span loss must be less than 10.5 dB. You might want to add about 3 dB optical margin to total loss, as normally fibers increase their attenuation with age (not mentioning about getting a new splice).

PS: 12 km distance is feasible.

Alex