I agree that the APL sublayer should
ideally be defined in a very general way. That is to say, in a perfect world,
it would support aggregation of channels with various (i.e. – mixed) bit
rates. That being said, this raises some interesting challenges. For example,
the striping (or splitting) ratio across the channels will not be uniform –
for every ten bits (or bytes) sent down a 10G channel, only one could be sent
down a 1G channel. Is there any precedent for managing something like this? If
not, does anyone have any idea whether this is even feasible?
From: Myles Kimmitt
Sent: Wednesday, August 09, 2006
Subject: Re: [HSSG] Topics for
My point was that the APL should try to be broader than an
nx10G sublayer (at least architecturally) because there are applications that
could take advantage of higher speed links, especially over time. Try to get
more mileage out of the sublayer.
I wasn't proposing that 802.3 get involved in any WAN
links - it was just an example of how economics skew in different
All that you say about dispersion is true but 25G dispersion
would be 2.5 times better than 40G. Beauty is in the eye of the beholder.
----- Original Message -----
Sent: Wednesday, August
09, 2006 7:56 PM
Subject: Re: [HSSG] Topics
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.
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08/09/2006 05:05 PM
Myles Kimmitt <mylesk@xxxxxxxxxxx>
Re: [HSSG] Topics for Consideration
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
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.
> I have listed dilemma we are facing:
> - Implementing 100 Gig in the near term means
> - 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
> All these means we should either define some
sort of scalable
> architecture or just define LAG method and do
not define any PMDs!
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