Fibre Channel (SAN)

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New Contributor
Posts: 2
Registered: ‎01-29-2012

link specs for long distance

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)?

Valued Contributor
Posts: 931
Registered: ‎12-30-2009

Re: link specs for long distance

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

Regular Contributor
Posts: 164
Registered: ‎05-11-2011

Re: link specs for long distance

Hi,

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.

Regards Ralf

Kind Regards
Ralf
New Contributor
Posts: 2
Registered: ‎01-29-2012

Re: link specs for long distance

SFP is Brocade, ELWL 30Kms 4Gbps, their spec says "

Transmit (Tx):

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

Receive (Rx)

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!

Regular Contributor
Posts: 164
Registered: ‎05-11-2011

Re: link specs for long distance

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.

Kind Regards
Ralf

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