Myles,
I agree that there is a cost to consuming
wavelengths, and they should be used wisely. But a system that has
been engineered to support 10G rates cannot necessarily step up to higher
speeds, even if optically compatible with the existing DWDM grid and power
levels. The SM fiber's dispersion limited distance drops as the square
of the bit rate. For example, for externally modulated sources, if
the dispersion limited distance is 60 km at 10Gb/s, then at 25 Gb/s it
will be less than 10km. So channels that exceed this distance would
need to be dispersion compensated. Were you thinking that the higher
rates would be used only on shorter channels, or were you thinking
of dispersion compensation technologies as work-arounds? If the former,
then consider how it impacts the objectives. If the latter, it opens
up a whole set of issues.
Regards,
Paul Kolesar
CommScope EnterpriseŽ Solutions
1300 East Lookout Drive
Richardson, TX 75082
Phone: 972.792.3155
Fax: 972.792.3111
eMail: pkolesar@xxxxxxxxxxxxx
Myles Kimmitt <mylesk@xxxxxxxxxxx>
08/09/2006 05:05 PM
Please respond to
Myles Kimmitt <mylesk@xxxxxxxxxxx>
To
STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
cc
Subject
Re: [HSSG] Topics for Consideration
I would expand on the statement:
"Carrier want to leverage their existing DWDM layer which mean
baudrate in the 9.95-12.5 Gig".
There are two layers at which compatibility with existing DWDM systems
can
be achieved: the electrical layer (which this statement implies) and the
photonic layer. Compatibility at the photonic layer means interoperability
with existing DWDM wavelengths, optical filters, power leveling, etc. on
the same fiber. Is is likely that 25G (+7% FEC) NRZ optical signals are
compatible with many existing 10G NRZ DWDM systems. There is a premium
to
using many wavelengths in these systems and a 4x25G channel might well
be
cheaper and more wavelength efficient (as measured by GB/s/nm)than a
10x10G channel.
Such details are probably beyond the scope of the SG but I think it is
important to architect below the MAC to allow link speeds faster than 10G
within the APL which make sense in certain markets and will become more
economic and widespread over time.
-Myles
>
> I have listed dilemma we are facing:
> - Implementing 100 Gig in the near term means Nx10Gig
> - Implementing 100Gig in few years the right answer might be nx25Gig
> - Carrier want to leverage their existing DWDM layer which mean
> baudrate in the 9.95-12.5 Gig - If LAG implemented why not allow n
to be 4?
> - Operation with different width
> - Backward compatibility XAUI, LX4 ?
> - Greatest bandwidth demands (100+Gig) are on VSR links <50 m but
> the longer reach >10Km may be able to live with 4x10Gig.
>
> All these means we should either define some sort of scalable
> architecture or just define LAG method and do not define any PMDs!
>
>
> Thanks,
> Ali
>
>