Re: [8023-10GEPON] [FEC Superating] - kickoff preso
Frank,
I think you might be conflating the loop timing issue with some other issue raised earlier.
The point I intended to raise about loop timing is that the upstream frequency of 1.25 GHz is fixed already, and in the asymmetric 10/1 case the ONU needs to derive the upstream clock from the downstream signal. Of course how easy or difficult it is to do that depends both on the dividability of the downstream frequency by 1.25 Ghz and also on the jitter of the downstream signal.
11.25 Ghz (rather than 11.049 GHz) would be fine. Can XFI/SPI components go that fast?
- Jeff
-----Original Message-----
From: Frank Effenberger [mailto:feffenberger@HUAWEI.COM]
Sent: Monday, February 05, 2007 6:02 PM
To: STDS-802-3-10GEPON@listserv.ieee.org
Subject: Re: [8023-10GEPON] [FEC Superating] - kickoff preso
All,
I don't think that clock management is so strong an advantage for one scheme over the other. In all the cases, in all the technologies, there are a set of frequencies that are phase-locked to each other. Dividers and PLLs do a fine job of inter-converting them. One is not much harder than the other, unless we choose a poor frequency for the super-rating. We should be more careful!
Just as a for-example, the 11.049 GHz happens to be 15/14ths of 10.3125.
Those are reasonably small clock dividers, and not a big problem to implement. Note that this division builds on top of the 33/32nds clock ratio of 64b66b. If we go with super-rating, then I see no reason to maintain the redundant framing bit. Rather, I think we would look for a clock relationship from the FEC super-rate directly to the 10G base rate.
In any case, I will add the item to the list, for completeness sake.
Regards,
Frank E.
-----Original Message-----
From: Jeff Mandin [mailto:Jeff_Mandin@PMC-SIERRA.COM]
Sent: Monday, February 05, 2007 9:19 AM
To: STDS-802-3-10GEPON@LISTSERV.IEEE.ORG
Subject: Re: [8023-10GEPON] [FEC Superating] - kickoff preso
Frank hi,
Loop-timing for the asymmetric 10/1 case would appear to be another "pro"
for the subrating scheme.
The ONU can - perhaps - use the recovered 10.3125 clock to derive one of
312.5 Mhz (divide by 33), and then use a PLL to generate the upstream rate (multiply by 4). With 11.1 Gb/s XSBI this would probably be much more difficult.
- Jeff
-----Original Message-----
From: Frank Effenberger [mailto:feffenberger@HUAWEI.COM]
Sent: Wednesday, January 31, 2007 10:32 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.