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Re: Interface reality check


Does the regenerator you describe look something like this?

PMD -> PMA -> PCS -> XGXS -> XAUI -> XGXS -> PCS -> PMA -> PMD

I'm not sure this would be a device specified in the standard
even though it uses components defined by the standard. However,
let me see if I can follow through with your thought process.

In my opinion, the /A/K/R/ only exists between/within the
XGXS boundaries. It is used for alignment, jitter, etc., across
the 4-lane XAUI and has a useful purpose there. Others are of
the opinion that /A/K/R/ can be carried past these boundaries
with the only detrimental affect being the loss of PCS coding

I think your message is referring to yet another "future idle-
sequence". I presume this means additional codes beyond /A/K/R/
as opposed to simply a re-ordering of these same codes. Given
XAUI's randomness in the order of /A/K/R/, re-ordering these
same codes would not be obvious. So, the new codes required by
your "future idle-sequence" would require additional code space
and, in particular, would need to be defined during the standard
specification phase so the PCS would know what these codes are.
To get these codes defined during the specification phase of
the standard, you would not be making this a "future idle-
sequence" but another "present idle-sequence" and presumably,
this one would exist to fulfill a particular purpose that /A/K/R/
couldn't fill.

Allowing the receive state machines to treat unknown but valid
codes as idles is one thing but I don't know how to future proof
the transmit machines.

Have I mis-understood you? Can you please shed more light on
something I'm missing?


Osamu ISHIDA wrote:
> Dear Ben and Rich,
> At 8:33 AM -0500 00.4.1, Brown, Ben [BAY:NHBED:DS48] wrote:
> > Please, let's get some new blood in on this discussion! I feel
> > like we're in a vacuum.
> I would like to add another side dish for your Guinness;
> this is a bit reinforcement for XGXS to propagate /A/K/R/ rather
> than having to translate them to /I/.
> I have guessed the /A/K/R/ randomization in Rich's mail to work
> pretty well for EMI reduction, but still would like to reserve my
> last one cent to future idle-sequence up-grade by other standard
> such as fibre channel.  Also another peculiar application
> may utilize the /A/K/R/ sequence itself for some other purposes,
> such as field maintenance debugging tool hinted by Mr. Edward Chang.
> Once we carriers invest in a 10 Gigabit Regenerator that is a
> pair of two Attachment Units connected back to back with XAUI
> backboard interface, we hope the regenerator can enjoy the future
> up-grade benefits and can carry another idle sequences without any
> field upgrade operation.
> If XGXS on the regenerator does not propagate /A/K/R/ or any other
> interpacket gap sequences as it is, our investment may lose strong
> support of potential automatic field upgradability/interoperability.
> Cheers,
> Osamu
> ---------------------------------------
> Osamu Ishida
> NTT Network Innovation Laboratories
> TEL:+81-468-59-3263 FAX:+81-468-55-1282
> ---------------------------------------

Benjamin Brown
Router Products Division
Nortel Networks
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