Recommended 1Gb SFP for ~115km?

Justin M. Streiner streiner at cluebyfour.org
Wed Aug 4 06:45:37 CDT 2010


On Wed, 4 Aug 2010, 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.

I just lit a ~110km fiber span with gigabit gear in the last few weeks, 
and I ended up going with an external line driver because the native 
Cisco options wouldn't work, for a variety of reasons.  I would have 
preferred to plug directly into the 6509s I have at each end, but it 
wasn't feasible.

I ended up going with gear from Transition Networks.  Pricing was pretty 
reasonable and their customer service has been great so far.  There are 
some things with the management interface that I'm not too crazy about, 
but nothing that was a show-stopper.  The driver has a 2-port SFP module 
that takes the LX12 long-haul signal in one side we drop it out the other 
side as 1000baseSX to drop into the 6509s.  Works like a charm.

I also looked at kit from MRV and Metrobility.  The MRV stuff looked good 
too.

Having said all that, you need to take into account the engineering 
characteristics of the fiber span, to make sure you choose gear that will 
live within the attenuation and dispersion limits that physics, fiber 
quality, splice quality, etc will impose upon you.

On the 110km span I just lit, I used the G.652 spec as a guide and figured 
for 0.2 dB/km of attenuation at 1550 nm and 0.5 dB of loss for each 
connector, which got me an estimated loss budget of about 23 db, and the 
span tested out better than that.  With an additional cross-connect at 
the one end I'm still at about 22.5 dB end to end.  The LX12 optics I used 
from Transition have a link budget of 32 dB, so we have a bit of 
headroom.

jms




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