Re: [8023-10GEPON] [FEC Superating] - kickoff preso
Frank,
To start with, thanks for putting these slides together. It's a very good
start to getting the discussion going.
Here is a list of the defined interfaces in the existing 802.3ae standard:
- XGMII is a 32-bit wide interface that runs at 156.25 MHz * 2
- XAUI is a 10-bit wide interface that runs at 3.125 GBd
- XSBI is a 16-bit wide interface that runs at 644.53125 MHz
- PMD is a serial interface that runs at 10.3125 GBd
For the FEC with a higher line-rate, we could have something like this:
- FEC/PMD is a serial interface that could run at 11.049 GBd
The increase in baud rate is needed to account for the added parity bytes.
If we go with the higher line rate, will we need a buffer to add/delete
idles in order to adapt between the different line speeds?
I recognize that there is an existing mechanism mentioned in Clause 49 that
can help with this (49.2.5 for Transmit, 49.2.11 for Receive). I think that
with either the line-rate or MAC-rate modification there will still need to
be additional idle insertion/deletion within the PHY. In one case we are
adding idles to decrease the data rate to account for the parity insertion,
and in the other case we are adding idles to adapt between clock boundaries
and/or rates.
If we choose to go with a line-rate modification, than we are probably going
to be forced to go with an existing rate. I haven't heard anyone propose
that we use a line rate not currently used by any other applications. If
that is the case, then would that restrict us to the exact FEC algorithms
already being used at those higher rates? There may be more flexibility in
selecting an FEC algorithm if we stick to the 10.3125 rate.
From yesterday's ad-hoc call, it looks like we may be going with a 29dB
channel loss and up to 3dB in additional penalties, for a 30dB-32dB power
budget, so we need to keep that in mind, too.
- Eric Lynskey
-----Original Message-----
From: Frank Effenberger [mailto:feffenberger@HUAWEI.COM]
Sent: Wednesday, January 31, 2007 12:32 PM
To: STDS-802-3-10GEPON@LISTSERV.IEEE.ORG
Subject: [8023-10GEPON] [FEC Superating] - kickoff preso
Dear All,
I have put together the following presentation on the issue of FEC and
line-rate vs. MAC-rate modification. I tried to include in these slides all
the arguments I have heard favoring one method or the other. If I have
forgotten your favorite, you can shoot an Email to me, and I'll add it to
the list.
You may also note that the last slide, entitled "Reaching a decision" is
blank. I don't know a truly objective way to solve this problem... It seems
to me that when you stack up the pros and cons, these two schemes are pretty
equal.
One last thought: The one 'hard' (objective) con for the super-rating scheme
is the loss of 0.3 dB of sensitivity. The one 'hard' con for the sub-rating
scheme is the loss of bandwidth (7% lost). How can we put these two items
on a common comparative base? Usually, the common denominator in these
situations is cost, so...
What is the relative system cost increase due to 0.3dB optical loss?
What is the relative system cost increase due to a 7% capacity loss?
If someone wants to hazard an answer to these questions, please do.
Regards,
Frank E.