One common type of 64B/66B PCS?
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