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RE: Chapter 46: preamble length




Pat,

Are you catching the Thatcher disease? :-)  I figured that's what you meant,
but I'm sure others are glad for the clarification. 

Cheers,
Brad

		-----Original Message-----
		From:	pat_thaler@xxxxxxxxxxx
[mailto:pat_thaler@xxxxxxxxxxx]
		Sent:	Thursday, March 29, 2001 2:37 PM
		To:	pat_thaler@xxxxxxxxxxx; bradley.booth@xxxxxxxxx;
stds-802-3-hssg@xxxxxxxx
		Subject:	RE: Chapter 46: preamble length

		I meant to say "I agree with Ben." That is, our current PHY
specifications
		do not allow removal of preamble bytes.

		Pat

		-----Original Message-----
		From: pat_thaler@xxxxxxxxxxx [mailto:pat_thaler@xxxxxxxxxxx]
		Sent: Thursday, March 29, 2001 10:48 AM
		To: bradley.booth@xxxxxxxxx; stds-802-3-hssg@xxxxxxxx
		Subject: RE: Chapter 46: preamble length



		Brad,

		Since we seem to be taking a poll - I agree with Brad. Any
device causing
		preamble shrinkage in 10 Gig Ethernet would be
non-compliant. All the data
		manipulating physical layers (meaning those that handle
encoding and
		decoding) have state machines specifying how the encoding
takes place and
		those state machines show that when data is received, the
data is encoded
		and sent. We have text that explicitly allows deleting idles
and, in some
		circumstances, ordered sets. We don't have any text allowing
deletion of any
		kind of data and the layers below the RS have  no knowledge
of preamble.
		WIS, the PMAs, and the PMDs do not do deletion.

		Furthermore, we have made sure that there are plenty of
idles available for
		deletion. On the other hand, preamble is only 8 bytes and
deletions can only
		be done in 4 byte chunks. If devices were relying on the
ability to delete
		preamble, there is only one chance per frame so if a device
higher on the
		stack deleted one, there are no chances per frame.

		If you believe that the current draft text allows deletion
of preamble, then
		it also allows deletion of an arbitrary 4 bytes of data
because there is no
		text in any of the PCS clauses that treats preamble
differently than any
		other data byte.

		Also, note that if a device deleted preamble, it would be a
different kind
		of deletion. Normally deletion happens to a column of idle
or an ordered
		set. Neither of the preamble containing columns is deletable
because one
		contains the /S/ and the other contains the SFD. An
implementation deleting
		preamble would have to delete some bytes from one column and
some from the
		next column combining the ends of the columns to make a new
column.

		Regards,
		Pat