Re: [8023-10GEPON] [FEC Superating] - kickoff preso
Jeff,
The loop timing clause refers to PMA. There is no 1.25GHz PMA clock. Please, see PMA section 36.3.3:
"Two recovered clocks, PMA_RX_CLK<0> and PMA_RX_CLK<1>, which are at 1/20th the baud (62.5 MHz), and 180вк out-of-phase with one another, are used by the PMA to latch the received 10-bit code-groups."
10G PMA operates on 16-bit wide words. It runs at 644.53125 MHz without FEC. The challenge is to find a new "nice" PMA rate (line rate divided by 16) such that 62.5 MHz clock could be derived from it.
Glen
> -----Original Message-----
> From: Jeff Mandin [mailto:Jeff_Mandin@PMC-SIERRA.COM]
> Sent: Tuesday, February 06, 2007 1:41 AM
> To: STDS-802-3-10GEPON@LISTSERV.IEEE.ORG
> Subject: 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.