[j-nsp] LX Modules

[Richard A Steenbergen]

On Fri, Mar 03, 2006 at 10:03:31PM +0100, sthaug at nethelp.no wrote:
> > Specified TX power values are minimums and are usually on the conservative
> > side. It's common for a GBIC/SFP to push a 1-3 dbm more than what it is
> > rated.
> 
> That may well be the case - however, if this was enough to damage a
> significant number of LX SFPs when connected back-to-back, you would
> see warnings about back-to-back connections. I'm used to seeing such
> warnings for ZX GBICs and SFPs, never seen them for LX.
> 
> We use LX back-to-back in the lab all the time. Never had a problem
> with this.

There is a difference between a saturation threshold and a damage 
threshold too. LX for the most part is designed to work without requiring 
attention, unless you get some really funky optics. The stuff that you can 
actually DAMAGE is the longer reach ZX (aka Juniper LH) and beyond which 
has very high sensitivity, by putting two of them back to back. Hitting 
saturation won't generally hurt anything, it will just not pass traffic.

But yeah the range on optics can be significantly out of spec too. I 
recently got a batch of Cisco ER XENPAKs putting out +7dBm, far over spec. 
:)

-- 
Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
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