Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Re: XAUI and 64b/66b


I've also responded to Mr. Walt Thirion in a similar manner: 

The XGMII proposal describes an OPTIONAL physical interface consisting of 32
data bits, 4 control bits and one clock signal in each data direction.

The XGXS/XAUI proposal describes an OPTIONAL coding and physical interface
consisting of 4 serial signals in each data direction.

Calling  XGXS/XAUI an "XGMII extender" is somewhat deceiving. If both the XGMII
and XGXS/XAUI are voted in as OPTIONAL 10 GbE interfaces, a 10 GbE device may
choose to implement XGXS/XAUI and not the XGMII. Such an implementation is
viewed by many as potentially being the most cost effective 10 GbE intra-cabinet
interconnect. Note that XAUI is viewed by its supporters (24 companies in
Albuquerque and more have signed up already) as a generic, low-cost,
chip-to-chip interconnect.

XGXS/XAUI goes a long way towards satisfying the 5th PAR criteria of Economic
Feasibility for the intra-cabinet interconnection portion of the 10 GbE
standard. Much more so than does the XGMII. This is because the XGMII is a high
pin count, high power (more termination resistors req'd), short distance,
non-jitter-attenuating interface. 

This being said, for NRE, I would be glad to develop you a chipset with an XGMII
on either side and XAUI interface between the chips. Is this something that you
would have an application for? Also if you don't like 8B/10B, I can do SLP
coding instead since the ends would still be XGMII. Is the latter part something
that you would have an application for?

BTW, can you please define what you mean by "larger form factor chassis"? Since
XAUI has fewer signals, it enables smaller form factors and/or greater port

Best Regards,

Roy Bynum wrote:
> Walter,
> As a non-vendor participant, representing an industry that will buying a
> large amount of these interfaces, I would like to reiterate your comments.
> XAUI is being presented as an optional PHYSICAL DISTANCE EXTENDER for the
> XGMII not an optional additional sublayer between the RS and the PCS.  This
> means that XAUI is inside the XGMII.
> As an optional physical distance extender XAUI will give vendors more
> flexibility to build larger form factor chassis.  Why they would do that in
> an era when customer would like to see the form factor reduced is a mystery
> to me, but it is an option.  As long as it remains optional, it also means
> that vendors do not have to use XAUI when their chassis/ASIC form factor
> does not require it.  As a customer this gives me more options from diverse
> vendors that remain interoperable.  It has the effect of increasing the
> overall market for more vendors and more customers.
> I have attached a slide that represents what I understand the XAUI was
> presented to be.  Perhaps this will help explain my understanding and
> provide a better center for the discussion.
> Thank you,
> Roy Bynum
> ----- Original Message -----
> From: Walter Thirion <wthirion@xxxxxxxxxxxx>
> To: HSSG <stds-802-3-hssg@xxxxxxxx>
> Sent: Friday, March 17, 2000 7:01 PM
> Subject: RE: XAUI and 64b/66b
> >
> > Rich,
> >
> > Without reiterating all of the points Ben made, I think the following
> > paragraph from Ben really summarizes it:
> > ______________________________________________________________
> > The picture does tend to get confusing. However, if the XAUI
> > is an extension of the XGMII, and the XGMII isn't "there" how
> > can a XAUI be "there"? This does seem silly. However,
> > architecturally, I think these layers are required to avoid
> > a certain amount of confusion.
> > ______________________________________________________________
> >
> > We have been using the XGMII as the architectural interface between the RS
> > and the PCS. Granted it is optional and, therefore, implementors are free
> > to use some other i/f. However, in the standard, we can't just assume
> > magic happens between the layers, so the XGMII has been put in that role.
> > If XAUI had been presented (and accepted) first, then maybe we would be
> > having a different discussion.
> >
> > So I recommend we leave XGMII as the specified i/f and allow XAUI to
> > transparently extend it. Transparently means you can't tell whether XAUI
> > is present or not and, therefore, the PCS gets XGMII signals when XAUI
> > is present just as it would when XAUI is not present.
> >
> > Walt
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