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Re: One common type of 64B/66B PCS?


I like this proposal very much, though I disagree with a number of the 
points you are making. The current design already allows for a dual mode 
PHY. It requires 2 transmit clock sources for a dual mode PHY which will 
need to be switched when moving form the 10GBASE-R and 10GBASE-W modes. The 
advantage to using the same clock source for both is that a dual mode PHY 
will require only a single clock source.

I certainly disagree that the number of interface types would be reduced 
from 4 to 7. The reason we have 7 interface types is because there is no 
ability to autodetect between 10GBASE-R and 10GBASE-W. Since the 10GBASE-R 
and 10GBASE-W are incompatible due to the added bytes and scrambler of the 
WIS the only way they could be treated as the same interface type is if we 
had a standard way to autodetect between them. The current standard has no 
way to connect 10GBASE-R to a 10GBASE-W and have them automagically resolve 
the coding and proceed to communicate. It will require human intervention 
to configure 10GBASE-R or 10GBASE-W even if a single clock source is used.



At 06:38 PM 4/20/2001 +0200, Luigi.Ronchetti@xxxxxxxxxx wrote:
>Hi all,
>did you ever think about the possibility to have only one type of
>64B/66B PCS (the same circuit for 10GBASE-R and 10GBASE-W)?
>Consider to have only one type of PCS that can remove (add) idles as
>for WIS applications and can integrate (as option) the SONET framer:
>the upper interface of this PCS may connect to the RS through the
>XGMII or this PCS may connect to an XGXS sublayer.
>The XGXS and the RS provide the same service interface to this PCS.
>The lower interface of this PCS connects only to the PMA sublayer
>to support the same PMD.
>When the SONET framer inside this PCS is bypassed (or it is not
>present), the nominal rate of the PMA service interface is 622.08
>Mtransfers/s which provides capacity for the MAC data rate of about
>9.65 Gb/s.
>When the SONET framer inside this PCS is used, the nominal rate of
>the PMA service interface is again 622.08 Mtransfers/s which instead
>provides capacity for the MAC data rate of about 9.29 Gb/s.
>In both cases the MAC uses IFS stretch mode to ensure that there
>will be enough idle time that the PCS can delete idles to adjust to
>the lower rate, with two different values for ifsStretchRatio (about
>221 bits instead of 104 bits for the first case).
>Since the data rates are now the same and there is only one PMA
>interface connection, there are no more additional constraints.
>Here a list of Con's and Pro's (for sure it is not exhaustive):
>---- Con's ----
>1) the LAN "useful" bit rate for 10GBASE-R is reduced by 3.5%
>2) need to introduce a new ifsStretchRatio value for that
>3) ...
>++++ Pro's ++++
>1) only one type of 64B/66B PCS is needed (two ASICs with the same
>    pinout, one with, the other without the SONET framer, can be
>    hosted by the same PCB)
>2) only one type of REFCLK (622.08MHz) for serial PMA is needed
>3) PMA REFCLK is always independent from XGMII_TX clock
>4) PMA and PMD, just characterized for SONET, can be used without
>    the need of further investigations/tests (for example the
>    10Gig MSA module or an OIF defined VSR can be used for both
>    LAN/WAN application)
>5) there is now the possibility to have an automatic adaptation of
>    the 10GbE interface to LAN or WAN applications, depending on
>    what is in between the two peer interfaces, or by presetting
>    (for an PCS with SONET framer inside, of course).
>  As a consequence there will be only 4 physical types instead of 7
>6) proprietary WDM solutions are able to better transport both LAN
>    and WAN signals because of 3R regeneration is now allowed,
>   (reclocking with a "standard" SONET clock is now possible)
>... and if, because of points 2) and 3), the PMA REFCLK is generated
>locally with an accuracy of at least 20ppm ...
>7) no synchronization problems (PJC thresholds reached) will be
>    reported when 10GbE WAN is transported over an SONET network
>8) the emerging OTN is now able to transport both 10GbE LAN and WAN
>    signals without the need of "special" adaptation
>9) ...
>Waiting for your comments to complete the above list,
>best regards,
>    Luigi Ronchetti

Paul A. Bottorff, Director Switching Architecture
Enterprise Solutions Technology Center
Nortel Networks, Inc.
4401 Great America Parkway
Santa Clara, CA 95052-8185
Tel: 408 495 3365 Fax: 408 495 1299 ESN: 265 3365
email: pbottorf@xxxxxxxxxxxxxxxxxx