TransAtlantic 40 Gig Waves

Tue Aug 18 05:28:16 UTC 2009

On Mon, 17 Aug 2009, Rod Beck wrote:

> Rod, do you know if the 40G waves increased the spectrum efficiency of 
> your fiber? On land systems they pretty much break even, i.e. you can 
> have a 100GHz 40G channels or 4x25GHz 10G channels but at the end of the 
> day you still get the same amount of signal out of the fiber. I don't 
> know whats being done on undersea cables though. Eventually this will 
> get better too, and 40G will become the "native" wavelength standard 
> with 10G being muxed onto them, similar to what we saw with the 
> transition from 2.5G->10G 10 years ago.

Think of this as the natural progression equivalent to the evolution of 
speed over phone lines, from 300bps to 56k, ie use of DSPs to get more out 
of the available spectral capacity.

10G is generally pretty simple NRZ, 40/100G is much more complex using 
multiple bit per "baud" and/or polarization.

<http://www.ripe.net/ripe/meetings/ripe-55/presentations/lothberg-40-gb-to-my-mother.pdf>

(around page 34 is where the stuff you're asking about comes in)

My guess is that 100G will be available and being rolled out before 40G is 
widely used, thus we'll wont see much 40G in DWDM systems, at least not 
with the current encoding standards (because they don't fit directly into 
10G systems as they have higher requirements).

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