RE: XAUI/XGXS Question
OK, but there, in page 16 you wrote:
"40 UI deskew pattern neds to be 80 bits". I probably did not understand it
well. Can you help with that?
Thx.,
Boaz
> -----Original Message-----
> From: Rich Taborek [mailto:rtaborek@xxxxxxxxxxxxx]
> Sent: Monday, May 15, 2000 9:23 AM
> To: HSSG
> Subject: Re: XAUI/XGXS Question
>
>
>
> Boaz,
>
> The 39 bit maximum skew figure is deemed to be worst case and
> is already less
> than 1/4 the Align code-group (/A/) spacing.
>
> Skip column processing for an Ethernet link including two
> XAUI may result in the
> removal of two /R/ columns, reducing /A/ spacing to 140 bits.
> The same removal
> would not be required again for more than 13 maximum sized frames.
>
> In summary, a 160-bit spacing is overkill and more than
> adequate. There is no
> reason to increase the minimum /A/ spacing.
>
> Best Regards,
> Rich
>
> --
>
> Boaz Shahar wrote:
> >
> > 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@xxxxxxxxxxxxx]
> > > 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
>
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