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RE: bit ordering on XSBI vs SFI-4


What you're proposing is to change the standard to match an implementation.
To me, it is merely how companies implement/document the bit ordering that
is the key focus of this discussion.  I personally feel that the standard
should avoid performing any bit order swapping, as the standard could easily
outlive implementations and documentation of the interface.  Don't forget
that 2 years from now, 802.3ae will be merged into the collective 802.3
document, and we should maintain consistency with that document.

I know that this could cause some confusion about how to connect a component
with an XSBI to a component with an SFI-4 interface, but I believe that can
easily be alleviate in a note, an annex or in a white paper.  My choice
would be for the latter.  It's simpler, it's cleaner, and it keeps the
Ethernet standard consistent.


		-----Original Message-----
		From:	David Kabal [mailto:dkabal@xxxxxxxxxxxxx]
		Sent:	Wednesday, March 28, 2001 2:01 AM
		To:	stds-802-3-hssg@xxxxxxxx
		Subject:	RE: bit ordering on XSBI vs SFI-4


		Actually, I think SFI-4 and XSBI were always intended to be
the same. The
		divergence is unfortunate, but only really caused by the bit

		XSBI is new to Ethernet, but has been around the rest of the
industry for a
		while. Let's borrow the bit ordering since we borrowed the
interface as
		well. I think our early mistake was not to recognize and
enshrine the
		origins of this interface by copying it faithfully.

		Since changes to clause 49, 50, and 51 seem very to be less
palatable, I
		would like to propose an alternate approach which I think
would satisfy the
		ultimate desire of every module vendor: not to confuse our

		Since the XSBI is a physical instantiation of a service
interface, can we
		not name the bits differently on the physical interface than
they are named
		on the logical one? For instance:

		logical service interface -> physical instantiation
		tx_data-group<15:0> map to xsbi_tx<0:15>
		rx_data-group<15:0> map to xsbi_rx<0:15>

		Thus, the physical instantiation, and the physical
instantiation only, will
		have bits which have a name that matches the intended bit
order. The service
		interface will preserve Ethernet bit ordering in this
proposed change. I
		think this satisfies the original purpose behind the change
proposed by
		Justin and then alternately by me. This would only affect
clause 51, and a
		short explanation and diagram would show the mapping between
the two,
		differently named sixteen bits.

		David Kabal

		Phone:	303-530-3189 ext. 272
		Fax:	303-527-4968

		-----Original Message-----
		From: owner-stds-802-3-hssg@xxxxxxxx
		[mailto:owner-stds-802-3-hssg@xxxxxxxx]On Behalf Of Booth,
		Sent: Tuesday, March 27, 2001 9:04 PM
		To: stds-802-3-hssg@xxxxxxxx
		Subject: RE: bit ordering on XSBI vs SFI-4

		I've remained quiet on this, but I support Pat's position.
This is an
		Ethernet standard, and we should work to maintain Ethernet
		throughout.  This may lead to some confusion with products
specified for
		SFI-4, but XSBI is not SFI-4.  There is no standard that we
can reference
		for SFI-4, so we should maintain Ethernet bit ordering.  The
10 Gigabit
		Ethernet draft should remain consistent with previous
versions of Ethernet,
		and companies building SFI-4 and XSBI compliant parts will
need to figure
		out how to address this in their product literature.  Or in
other words,
		it's an implementation issue.


		 -----Original Message-----
		From: 	pat_thaler@xxxxxxxxxxx
		Sent:	Tuesday, March 27, 2001 4:01 PM
		To:	Jscquake@xxxxxxx;
		Subject:	RE: bit ordering on XSBI vs SFI-4

		The XSBI should not be labeled in terms of MSB and LSB. bit
significance has
		no meaning at that interface.
		Originally Ethernet was defined to send most significant
byte, least
		significant bit first. That is still the way the length
field is sent. On
		the other fields, we now leave defining byte order
significance up to the
		protocols obove Ethernet. If you look at the payload of a
64B/66B data
		block, the MSB is may the 8th data bit and the LSB may the
57th data bit.
		There is no meaning to bit significance when one looks at
quantities larger
		than a byte because it depends on the byte significance.
		When looking at the XSBI, bit significance becomes even more
		because byte boundaries may fall anywhere in the 16 bits.
The terms LSB and
		MSB have no relevance to the XSBI. 
		It seems that there are two ways of handling this and both
result in
		inconsistancy that will confuse some readers. 802.3 has
always numbered bits
		in primitives so that bit 0 was the first bit to be
transmitted and the
		highest numbered bit was the last bit transmitted. If we
		tx_data-group<0:15> and rx_data-group<0:15> work the
opposite way, we will
		be likely to confuse readers who are accostumed to the
convention used in
		the rest of the standard. 
		If SFI-4 numbers bits in the opposite order, then we have
two choices. 
		Number tx_data-group and rx_data-group opposite of the way
the other
		primitives such as TXD and RXD.
		Leave the tx_data-group and rx_data-group numbering as it is
and add a note
		that explains that tx_data-group<0> is the same as SFI's bit
15 and
		tx_data-group<15> is the same as SFI's bit 0. Does SFI
actually call their
		signals tx_data-group and rx_data-group? The explanation
will be clearer if
		the names are not exactly the same.
		It is less confusing to be consistant in bit numbering
within the standard
		and explain the difference between bit numbering of this
standard vs other
		related standards than to change our bit numbering order
somewhere in the
		-----Original Message-----
		From: Jscquake@xxxxxxx [mailto:Jscquake@xxxxxxx]
		Sent: Monday, March 26, 2001 1:28 PM
		To: Jonathan.Thatcher@xxxxxxxxxxxxxxxxxxxx;
		Subject: Re: bit ordering on XSBI vs SFI-4

		In a message dated 3/26/01 12:28:50 PM Pacific Standard
		Jonathan.Thatcher@xxxxxxxxxxxxxxxxxxxx writes: 

		Subj: RE: bit ordering on XSBI vs SFI-4 
		Date: 3/26/01 12:28:50 PM Pacific Standard Time 
		From:    Jonathan.Thatcher@xxxxxxxxxxxxxxxxxxxx (Jonathan
		Sender:    owner-stds-802-3-hssg@xxxxxxxx 
		To:    stds-802-3-hssg@xxxxxxxx 

		Before offering any opinion on this, I would like to know
what impact there 
		would be on measurement and test equipment, if any. 

		Clearly, a piece of equipment expecting a serial PRBS
pattern would need the

		bits in a specific order. No? 


		Hello All, 

		Let me state again that any changes (if any) would only be
in relabeling and

		is purely a logical construct. There was/is neven intention
to actually have

		Ethernet packets sending bit stream data out on a serial
link in a MSB first

		manner. If Pat (clause 49) or anyone else does see this as
becoming the case

		then I would back off from this effort and just leave things
as is. This 
		leaves the 
		user (customers of modules makers) to be careful in knowing
which bit is 
		sent out first on the link. Leaving things as is OR
relabeling the XSBI to 
		MSB should 
		never stop implementers. The serial PMA is a "dumb" device

		Just a try here to make a simple suggestion ... 

		If I relabeled the XSBI to have MSB transmitted first then
Pat coming out 
		from her clause could possible reword saying that the LSB
should be mapped
		the MSB of the XSBI in the case of a serial link. 

		Justin Chang 
		Quake Technologies, Inc. 
		2880 Zanker Road, Suite 104 
		San Jose, CA 95134 
		Tel: 408-922-6888 x108 
		Fax: 408-922-6827 
		email: justin@xxxxxxxxxxxxx