[c-nsp] Cisco SFP

[Buhrmaster, Gary]

> What are the implications of using a GLC-ZX-SM module to light a
> stretch of 20 - 30km? Would I need to add an attenuator, given that 20km is well
> below the 70km limit?


As always, the answer is "it depends", because
it is the optical power, not distance, but usually
if the link is <~25km you can expect to need an
attenuator.  The typical transmit is ~ 0-5dBm,
and the max receive power is ~ -3dBm.  If you
overload the receiver, you could damage the
device, or shorten is life, or cause various
physical link errors to be reported as the
optics is overloaded.  So, in all cases,
measure the received power, and add in the
needed attenuation.

Reference:  
http://www.cisco.com/en/US/prod/collateral/modules/ps5455/ps6577/product_data_sheet0900aecd8033f885.html

Gary