[c-nsp] Single-mode GBIC question

[Richard A Steenbergen]

On Fri, May 30, 2008 at 01:18:25PM -0500, les wrote:
> 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?

Technically speaking, there is no reason that multimode fiber wouldn't be 
just as efficient at transmitting too much light. An MMF core is much 
wider than SMF so its actually easier to transmit "more" light, it's just 
that on MMF the core is so wide the light bounces around inside the fiber 
and makes it much harder to clearly decode the signal.

I assume what you actually mean is, is it possible for long reach optics 
(which one would normally use SMF with, in order to obtain those long 
distances) to transmit too much light and damage the GBICs? The answer is 
yes, but it's actually more a function of the receiving GBIC than the 
transmitting GBIC. The difference in TX power between a 10km LX optic and 
a 100km ZX optic are relatively minimal, but the 100km optic has a much 
more sensitive receiver. It's possible to blind an optic with an overly 
strong signal (you'll see bit errors before you see it just "go down"), 
but if you're going to cause damage it will be to a long haul optic with a 
very sensitive receiver.

Generally speaking, it's pretty hard to cause any problems with a 10km LX 
or LR optic (unless its transmitting WAY higher than spec, which does 
happen from time to time especially on 10GE optics), even if you're 
running back to back optics a few inches apart. When you start getting 
into 40km ranges you run the risk of blinding the receiver on short 
distances and causing errors, and at 70/80/100km optics you run the risk 
of damage if you hook them up back to back. In those cases, you should use 
an attenuator.

-- 
Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)