01-29-2012 07:14 AM
We have a customer who bought an IBM SAN40B (Brocade 5100) with LW SFP for 30Kms, and extende fabric. Their two sites will be to 25 Kms separated. Now the dark fiber provider aks if an attenuation of -15db is ok, or not.
Could someone help me to answer the question? Is the proposed link ok, or needs better specs (attenuation)?
01-29-2012 08:09 AM
That depends, HP states (through HP supportcase) powerlevels off -12 (measured by the switches themselfes), as the lowest which should run ok.
If your SFP's are powerfull enough to compensate for the loses on the fibers you should be ok.
Only way to find out is to test, before putting it in production
01-30-2012 05:35 AM
please look in the Spec of your SFP.
The Powerbudget of the SFP should be more then 15dB.
You can calculate the Powerbudget in the following way:
Tx(min) - Rx(min) = Power-Budget of the SFP. Then add all Attenuation you have (Connectors, Patchpanels, etc.) plus 3dB of reserve.
If your SFP has an Powerbudget of approx. 19 to 20dB it will work perfect.
01-30-2012 02:49 PM
SFP is Brocade, ELWL 30Kms 4Gbps, their spec says "
Wavelength: 1285 to 1345 nm
Spectral width: 1 nm
Average power: 0 to 5 dBm
RIN: -118 dB/Hz
maxOptical return loss: -12 dB minimumOMA: 850 μW, -0.7 dBm
Wavelength: 1260 to 1600 nm
Average power: 0 dBm
Optical return loss: -12 dB
Unstressed sensitivity: 29 μW, -18.0 dBm
3 dB cutoff maximum: 5 GHz
This means that the total attenuation supported is 12dB? This is about just 30Kms of singlemode fiber with 0,4dB per KM.... no space for splices or similar!
01-30-2012 10:55 PM
I think this SFP will work.
You have unstressed sensitivity of -18.0dBm.
So if you transmit with min. of 0dBm and then you have attenuation of 12dB you get -12dBm.
Additional 6dB for reserve.