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Re: 16-bit 625Mbaud XGMII

I second this opinion. I think that 32 bit interface is reasonable too. I
would go to the extent
of using Saturn POSPHY3 or Utopia3 as XGMII signaling (why re-invent wheel
?) standard.


At 05:32 PM 3/20/00 -0800, you wrote:
>Curt Berg wrote:
>> Hi Jaime,
>> If I recall correctly, last time a 16 bit interface
>> was proposed, it was a differential interface. This would
>> take about the same amount of pins as a single ended 32 bit XGMII.
>> (Anyone know about a single ended PMA to PMD interface?)
>> For design simplicity a single ended 312.5 Mbaud is very much preferred.
>> -Curt Berg-
>> Extreme Networks
>You are rigth: the 16-bit interface would by of the LVDS-type.
>Sorry: I made a mistake.
>I do mind defining in the standard a XAUI that is not a
>simple extender, with a XGMII at its input and output.
>A XAUI that has a XGMII in only one side (the MAC) creates a
>compatibility and interoperability problem since the other
>side outputs encoded symbols, and everyone wants a
>different coder (8b/10b, 64b/66b,PAM-5, etc) for the PMD.
>in the optical fiber.
>On the other hand, a XAUI as a simple extender, with a
>XGMII on both sides, is of little value to anyone: adding
>one code on one side and then removing the coding in the
>other in order to insert the final coding that will be used
>in the PMD is useless. In the absense of a clear
> winning code over Copper, (and the presentations
>and discussions on the Reflector appear to indicate that this
>is the case and the various coding schemes on Copper seem
>to give reasonable eye openings - I ignore, for simplicity,
>packaging , EMI considerations, cost and maximum length),
>it makes more sense to use on the Copper medium the same
>coder as the one to be used on the optical fiber medium
>and avoid the multiplicity and complexity of coding/decoding
>in the XAUI with one coder and again coding for the PMD
>with another coding scheme. After all, it is much
>more important to use the optimum coding in the fiber, where
>we do not have spare SNR to play with.
>XAUI was introduced to solve the problem of sending
>10 Gbps over long distances on a Copper backplane.
>It is really a PHY for 10 Gbps over Copper. Spending
>a significant time to find out what is the best coding
>over Copper might not be the right direction. It should not
>be part of the 10 GbE standard that deals with finding
>the optimum coding/PMDs for optical fiber.
>The only specified interface should be the XGMII.
>Jaime E. Kardontchik
>Micro Linear
>San Jose, CA 95131
Best Regards,

Devendra Tripathi
XaQti Corporation
3100 De La Cruz Boulevard
Santa Clara, CA  95054
Phone: (408) 986-4380 Ext 103
Fax:	(408) 986-6050
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