[c-nsp] Single-mode GBIC question

[Matthew Crocker]

> I've combed the web with no luck to the answer of my simple  
> question....
>
> If you use SINGLE-MODE fiber and gbics for very short runs (same room,
> across the street), can you damage the GBICS?

If you use appropriately powered GBICs you won't harm your receivers

1000Base-LX is SM, 1310nm

To verify look at your two GBICs,  compare the transmit power of one  
GBIC to the maximum allowed receive power of the other.

According to http://www.cisco.com/en/US/prod/collateral/modules/ps5455/ps6577/product_data_sheet09186a008014cb5e_ps872_Products_Data_Sheet.html

The WS-G5486 1000BASE-LX GBIC transmits at -3 to -9.5 dBm and the  
receiver can receive between -3 and -19 bBm.  That means that even  
with 0 loss between a pair of WS-G5486 GBICs the transmit won't  
overpower the receiver.

WS-G5487 1000BASE-ZX on the other hand transmit at 5 to 0 dBm and  
receive at -3 to -23 dBm.  If you are using 1000BASE-ZX optics on a  
short run you are 1) wasting money on expensive GBICs and 2) require  
the use of attenuators to add dB loss to the link to protect your  
receivers.

>
>
> What has been your experience. Oversaturation? Life-shortening? We
> typically use SM towards the telco and MM for internal but have ran
> into some legacy fiber where it's SM internal. I have electronic
> background so terminology is familiar.
>
> thanks in advance
> -les
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