RE: XAUI/XGXS Question
Rich,
If MaxSkew=40 Bits and all /R/ columns are removed, then the size of the
IPG is 8 characters (=80 bits) which is exactly twice the skew. In this
case, there is ambiguity. Isn't it more safe to increase the gap between two
/A/ columns to 32 (In fact any even number bigger than 16 will be fine)
Best Regards
Boaz
> -----Original Message-----
> From: Rich Taborek [mailto:rtaborek@earthlink.net]
> Sent: Monday, May 15, 2000 4:52 AM
> To: HSSG
> Subject: Re: XAUI/XGXS Question
>
>
>
> Boaz,
>
> The worst case XAUI/XGXS lane-to-lane skew anticipated is
> approximately 39 bits.
> Skew sources included in this figure are described in:
> http://grouper.ieee.org/groups/802/3/ae/public/mar00/taborek_1
> _0300.pdf, slide
> 16. The same slide indicates that the minimum distance
> between adjacent /A/'s is
> 160-bits. Since /A/ spacing is more than 4 times the worst
> case skew, there is
> no ambiguity in determining which which /A/ code-groups are related.
>
> The current proposal accounts for even the case of removal of
> all /R/ columns.
> Performing deskew on the column including the Start-of-Frame
> delimiter requires
> that both MAC devices transmit frames. This is not required
> for the current
> proposal since /A/s are present in the IPG and in the absence
> of packets.
>
> Best Regards,
> Rich
>
> --
>
> Boaz Shahar wrote:
> >
> > Hi Rich,
> > Recalling from your March presentation that the Max skew
> between two lanes
> > is 8 Characters (80 bit), and that the distance between two
> adjacent /A/'s
> > is 16 Characters.
> >
> > 1.So, in this case, how should one know Which /A/ is this?
> (That is, if a
> > certain lane exceeds the other in 8 characters or delayed
> after the other in
> > 8 characters it looks the same)
> >
> > 2.Suppose some /R/'s were dropped in the middle due to
> clock tolerance
> > compensation. The result is that the distance between two
> adjacent A's is
> > smaller than 16 characters. In this case its even more
> problematic to
> > distinguish between delayed lane to an exceeding one.
> >
> > Can it be solved by:
> > 1.Enlarging the gap between /A/'s
> > 2.Doing de-skew on the /S/ and /Dxx.y/ code-words
> >
> > Thank you,
> > Boaz
>
> -------------------------------------------------------
> Richard Taborek Sr. Phone: 408-845-6102
> Chief Technology Officer Cell: 408-832-3957
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>