[c-nsp] 10GE sanity check

[Mikael Abrahamsson]

On Sun, 18 May 2008, Tassos Chatzithomaoglou wrote:

> I had (accidentally) SFP 1000BaseLX/LH and 1000BaseZX talk to each other through SMF, regardless of 
> their different wavelengths (!).

10GBASE-LX4 is 4 times ~2.5 gig in a CWDM format, built into a single 
package, that's very different from 10GBASE-SR or LR which is single 
channel.

The difference between LX and ZX is mostly in the transmitter (1310 and 
1550nm respectively), even though the receiver is also more sensitive on 
the ZX, all receivers are wideband and will take most of the light from 
around 1200 or so, up to over 1600nm.

So if one wants to do ~20 km and LX doesn't work, one can usually do ZX at 
only one end, as 1550nm light only has half the attenuation of 1310nm 
light, which means more of the light get to the receiver for it to be 
enough with the ~ -18dB sensitivty of LX, you don't really need the ~24dB 
of ZX. The -24dB receiver on the ZX can be sensitive enough to receive the 
LX on the other end correctly.

Gigabit ethernet is mostly a play with attenuation and only attenuation, 
whereas on 10G things like dispersion and other factors start to be 
important as well.

-- 
Mikael Abrahamsson    email: swmike at swm.pp.se