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Re: XAUI and 64b/66b


I disagree with your direction on this issue for the same reason that I have
trouble with the lack of specification of an optional interface in 1000BASE-X
which is implemented in 100% of Ethernet products implementing 1000BASE-X. I may
be being politically incorrect in stating this, but I typically like products to
match specs.

I view XAUI as being a very prevalent 10 GbE interface, perhaps not as prevalent
as the serial side of the GbE Ten-Bit-Interface. Barring no other complete and
workable XAUI/XGXS proposals that meet the requirements of an optional XGMII
extender, my view is that the PCS should accommodate the optional XGMII extender
as well as operate properly without one. Since we'll have multiple PCS's
probably corresponding to PMA/PMDs, and one of the heavily backed (27 companies)
Serial PHY proposals endorse a 64B/66B PCS, I believe that this PCS should
support the optional XGMII extender which is specified to be PHY/PMD
independent. The Serial PHY proposal already does this and I see no benefit or
savings in cost, complexity, etc. in removing it. 

I also see no significant difference in complexity between converting between
XGMII and PCS 64B/66B codes whether or not the IPG includes only /I/ or /A/K/R/.

Best Regards,

"Benjamin J. Brown" wrote:
> Rich,
> Jonathan just sent me a note saying that I was even confusing
> him right now so I want to stop and ask my question again. I'll
> try to make this as clear as possible.
> In the layer diagram that Brad showed in Albuquerque, the XAUI
> was shown as an XGMII extender. To me this means that the
> reconcilation sub-layer speaks using XGMII language and the PCS
> listens using XGMII language. The XAUI can extend this interface
> by translating from XGMII to XAUI but it must translate back
> again before it gets to the PCS. The XGXS block is the translator.
> The 64b/66b proposal as written ignores the XGXS block between
> XAUI and the PCS. It is my contention that, though this would
> work, it is unnecessary and even burdensome to those implementors
> that choose to not use XAUI. 64b/66b would work equally as well
> without the XAUI specific control codes as they add nothing to
> the efficiencies of 64b/66b (that I can tell). The XGMII specific
> control codes are completely adequate for 64b/66b. In my opinion,
> a serial PCS should be specified as if XAUI didn't exist.
> I'll even go so far as to state that, in my opinion, even a
> parallel/CWDM PCS should be specified as if XAUI didn't exist.
> If this PCS turns out to be identical to the XGXS block then some
> implementors may choose to avoid the encode/decode/encode as
> specified in the standard, but I believe that is how it should
> be specified.
> Is the question/comment still confusing or do you merely disagree?
> Ben
> --
> -----------------------------------------
> Benjamin Brown
> Router Products Division
> Nortel Networks
> 1 Bedford Farms,
> Kilton Road
> Bedford, NH 03110
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> -----------------------------------------
Richard Taborek Sr.                 Phone: 408-845-6102       
Chief Technology Officer             Cell: 408-832-3957
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