[c-nsp] Single strand SMF 10GbE

[Richard A Steenbergen]

On Mon, Jun 02, 2008 at 04:48:02AM +0800, Mark Tinka wrote:
> On Monday 02 June 2008, Arie Vayner (avayner) wrote:
> 
> > Hmm...
> >
> > Take a look here:
> > http://www.cisco.com/en/US/products/hw/optical/ps1996/pro
> >ducts_data_shee t09186a0080179158.html
> > http://www.cisco.com/en/US/prod/collateral/optical/ps5725
> >/ps1996/product _data_sheet0900aecd802be2f3.html
> >
> > This product (ONS 15216 Flexlayer filters) can be used
> > with most single mode 10GE links to multiplex both
> > signals (TX and RX) on a single fiber strand.
> 
> Funny, I had a feeling our SE told us this required 2-core; 
> or was that XFP?

Guys,

You can multiplex TX/RX onto a single strand of fiber on almost any WDM 
system, except for a rare handful which have components that only function 
in one direction. The glass itself carries light in both directions, so 
most people will just use two different colors for their TX on each side. 
There is no requirement that you receive a signal on the same frequency 
you are transmitting, and all optical receivers are pretty much wide-band 
and will process any color you send them, so long as you use a prism to 
split out a single wavelength first. Infact many people who have pairs of 
fiber will still build their systems this way with intentionally 
mismatched channels so that you can lose a single strand and still have 
half your channels functioning. It's not much protection against a fiber 
cut or anything, but it does let you do maintenances on a single strand at 
a time.

Also, technically speaking there is no requirement that you use different 
colors either. The photons don't interact with each other as they cross 
paths, but you run the risk of reflections being confused with actual 
signal coming from the other direction. If you really cared you could use 
polarization for a better seperation of the two signals, but for most 
people this isn't worth the trouble of the extra optical engineering, so 
they just use different colors in each direction.

-- 
Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
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