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Re: XAUI/XGXS protocol


Thanks for the reply.  I was trying to discern the definition of XGXS.
Your replies (below and to others) say, I think, that XGXS/XAUI/XGXS
is not, in fact, a symmetrical interface.  So it ought to be renamed
with an additional function (XGXS/XAUI/somethin' else).

I see your argument about the alignment characters being useful to
some PCS/PMA/PMD implementations.  Yet, things are getting sticky.
Wouldn't it be simpler to specify XGXS/XAUI/XGXS symmetrically?
Then, if some PCS/PMA wanted to use these characters, the design
(presumably contained within one chip) could collapse (i.e., remove) 
the redundant, reciprocal functions of deleting and re-adding these 
alignment characters?


Rich Taborek wrote:
> Mike,
> Comments below:
> Mike Jenkins wrote:
> >
> > Rich,
> >
> > I'm confused.  I will list what I think I've heard.  Please let
> > me know where I missed something:
> >
> >  * XGXS/XAUI/XGXS is proposed as an optional XGMII extender.
> >    That is, XGMII in and XGMII out.
> You're implying that XGMII is required and it's not. The GMII was optional in
> GbE and the XGMII is proposed as optional for 10 GbE. In the case that both are
> implemented, are you suggesting that the PCS-side XGMII is a 74 signal
> interface? Clearly it would be optional. Is anyone out there planning to
> implement this second XGMII (between the XGXS and PCS) and actually featuring
> it? If not, it shouldn't be documented this way in the standard.
> >  * The XGXS /A/ character (at least, and maybe others) is not
> >    a part of XGMII protocol, I believe.  But you are proposing
> >    leaving it in the data stream, encoding it, and shipping it
> >    out thru the PMD.
> /K/ or /R/ are neither part of RS protocol nor transported across the XGMII. The
> Reconciliation Sublayer only generates /I/'s.
> XGXS, XAUI and XGMII are supposed to be PMD independent. A WWDM or Parallel
> Optics PMD requires its PCS to support /A/, /K/, and /R/ to perform
> synchronization, deskew, alignment and clock tolerance compensation. This
> information must indeed be transported out through the PMD to enable the remote
> PCS receiver to perform all of the latter functions. Per my Albuquerque
> XAUI/XGXS proposal:
> slide 4,
> the XGXS acts as the PCS/PMA agent. Shipping /A/ over a Serial PMD does not
> affect the throughput, complexity, etc. of the Serial PMD over and above
> shipping /I/ but it certainly simplifies the task of the remote PCS in the case
> XAUI is present there.
> >  * Any device at the other end, then, must deal with such
> >    additional character(s), whether it employs XGXS/XAUI or not.
> For WWDM and Parallel Optics, this is required anyway. For the other PMDs it
> causes no pain whatsoever. You want to see pain, think of what you'd have to do
> at the remote end if the PMD is WWDM and the PCS is SLP to the XGMII (see the
> earlier notes in this thread).
> > It seems, at minimum, that the XGMII definition must be expanded
> > to include any extra characters defined in XGXS/XAUI.
> Not at all. The XGMII is a physical interface anyway. It's the Reconciliation
> Sublayer that defines codes.
> Notwithstanding, the RS speaks Idles only. Only Idles need be transported across
> the XGMII. Why do you say that the XGMII needs to know anything about
> XGXS-specific extra characters? Is this specifically because of your view that
> another XGMII must exist between the XGXS and PCS? If it hurts, don't do it.
> > Alternately, XGXS/XAUI should clean up what extra characters it
> > inserted in order to deliver the same data stream it was entrusted
> > to 'extend'.
> This is correct going from XGXS to the XGMII in the RS direction. In the XGXS to
> PCS direction, the PCS should just carry the special codes all the way up to the
> XGMII on the remote end.
> > Otherwise, this is like Microsoft's integrating their browser with
> > Windows -- all of a sudden you get it whether you want it or not.
> > Am I wrong?  Please help me understand.
> I use Windows '98 and Netscape. Works just fine for me :-)
> > Thanks,
> > Mike
> >
> >   ...
> > > 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.
> >   ...
> > --
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >  Mike Jenkins               Phone: 408.433.7901            _____
> >  LSI Logic Corp, ms/G715      Fax: 408.433.7461        LSI|LOGIC| (R)
> >  1525 McCarthy Blvd.       mailto:Jenkins@xxxxxxxx        |     |
> >  Milpitas, CA  95035      |_____|
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> --
> Best Regards,
> Rich
> -------------------------------------------------------
> Richard Taborek Sr.                 Phone: 408-845-6102
> Chief Technology Officer             Cell: 408-832-3957
> nSerial Corporation                   Fax: 408-845-6114
> 2500-5 Augustine Dr.        mailto:rtaborek@xxxxxxxxxxx
> Santa Clara, CA 95054  

 Mike Jenkins               Phone: 408.433.7901            _____     
 LSI Logic Corp, ms/G715      Fax: 408.433.7461        LSI|LOGIC| (R)   
 1525 McCarthy Blvd.       mailto:Jenkins@xxxxxxxx        |     |     
 Milpitas, CA  95035      |_____|