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Re: Interface reality check


See comments below:

Rich Taborek wrote:
> The issue is not whether XAUI encodings are required for 64B/66B, the issue is
> whether either the MAC needs to signal the PHY with anything other than Idles or
> the PHY itself needs to signal over the medium.


> I completely forgot about the obvious case of ERROR, where the MAC transmitter
> or the PHY at any point in the link needs to replace a data or control code with
> an ERROR code. In order to support this proposed function, 64B/66B must
> transport /E/ codes in addition to /I/ codes across the medium.

Of course, and don't forget /S/, /T/ and /D/.

> Note that Gigabit Ethernet also signals Break Link and Remote Fault through the
> use of Config words, which are essentially a control encoding different than the
> GbE idle stream. Several folks including Mr. Howard Frazier and myself have
> already alluded to the benefit and compatibility of supporting Break Link and
> Remote Fault for 10 GbE.

This is a good example of codes in addition to those required by the
MAC/RS. So this means there is precedent to send information across the
link other than that information which comes from/to the MAC via the RS.
However, these codes are only used as a startup (Auto-Neg) or to
signal error conditions (remote fault & break link). They are not
present between every packet.

> This makes for a potential requirement to signal at least three control codes
> besides /I/, /T/, /S/ and /D/ across 64B/66B and the medium. A further
> requirement is to support the transport of these codes through the optional
> instantiations of the PCS Service interface.

I agree that these codes may need additional encoding to go across
something such as XAUI. I don't agree that this additional coding
cannot be removed at the end of the XAUI.

> One way I'll propose to do this cleanly is to have the RS receiver treat /A/K/R/
> the same as /I/. In fact, all codes other than /T/, /S/, /D/ and /E/ could be
> treated as /I/ by the RS receiver until those other codes are defined by 10 GbE.
> No translations by the PCS, including 64B/66B, would be necessary.

It's not a matter of this translation being necessary. I keep getting
the feeling that you're trying to make the PCS "easier" by "keeping"
the /A/K/R/ rather than converting them back to /I/. If all
used XAUI than this could indeed be considered "easier". However, if
not going to force the use of XAUI then "keeping" /A/K/R/ is not
necessarily "easier". Am I reading you incorrectly?
(The above quotes are for emphasis. They are not meant to imply that
you've used these words.)

> Whaddya think?

I'll reserve judgement until I see the full proposal.


Benjamin Brown
Router Products Division
Nortel Networks
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Kilton Road
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