[c-nsp] Recommended 1Gb SFP for ~115km?

[Nick Hilliard]

On 04/08/2010 15:30, Abello, Vinny wrote:
> Any pointers on real world experience on this topic would greatly be
> appreciated. What are people using successfully out there as far as third
> party SFP's go to hit a distance of approximately 115km? This would be for a
> Catalyst 6506. Cisco's solution was a much more costly EDFA solution, but I
> see plenty of vendors that make SFP's for Gigabit Ethernet that range from
> 115km to 150km and more. I know these are not supported by Cisco and TAC
> won't troubleshoot if they are in the switch. I'm willing to work around
> that should I need TAC assistance on the switch. What works well for a
> single wavelength solution at this distance without having to switch to
> DWDM? This circuit will have duplex fibers.

This isn't really a Cisco question, but 115km takes a little bit of care.

First, you need an accurate attenuation measurement for both strands of the 
link - you can assume C band (1550).  Once you have this measurement, you 
will then be in a position to buy a transceiver which will fit your 
requirements. You can estimate the attenuation on the link, but this can 
cause problems if the estimation is wrong (which can happen if the fibre is 
duff quality).  You should also expect to have a chromatic dispersion 
penalty; this will remove a couple of dB from your link budget.

Once you've taken into account these things + any patching loss and all 
that, you'll end up with a link budget figure.  Add on a couple of dB to 
this for leg-room and this will be your operating optical attenuation 
budget.  This budget will enable you to pin down what sort of SFPs might 
actually work on your link.

Also make sure that the electrical output from the SFP port on the Cisco 
box is compatible with the electrical power requirements of the SFP.

In all likelihood, you're going to end up purchasing DWDM SFPs.  Get a good 
quality third party transceiver (Finisar, Opnext, etc) - they are worth the 
expense.

Nick