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Brad, Your statement “And, the connector for CX4 is different than the QSFP
being used for CR4; therefore, how likely is legacy support. These are
the types of things create extra work for maintenance and interpretation.” is
partially incorrect. There are two styles of connectors specified for CR4. Style-1
is the QSFP connector, but Style-2 is the mechanical mating interface defined
by IEC 61076-3, which is the same connector interface defined in 54.8.1 for
CX4. John From: Arthur Marris
[mailto:arthurm@xxxxxxxxxxx] Brad, Hugh, I hope you do not mind me
taking this discussion to the reflector but I think it would be useful to have
some input from the wider group. Brad, I sympathize with your view
point but what you suggest is a significant change to what has been in the
draft for a long time so I think it is appropriate for the proposed response to
be ‘reject’ and then discuss this in the task force meeting. To summarize I believe the
two sides of the argument are: Delete mention of 10GBASE-CX4 parallel
detect because: 1) It is out of scope 2) 10GBASE-CX4 and 40GBASE-CR4 are not compatible at the MDI Keep 10GBASE-CX4 parallel detect in
802.3ba because: 1) It is nice to have 2) If you ever did succeed in connecting 10GBASE-CX4 and 40GBASE-CR4
the AN block might indicate 10BASE-KX4 parallel detect if a Clause 48 PCS were
present. The present text in D2.0 can handle this scenario. Arthur. Arthur Marris From: Brad Booth
[mailto:bbooth@xxxxxxxx] In
Clause 45 for the 7.48.2 bit description in the table. Backplane
is different than copper cabling. While there is viability at the PCS and
PMA levels, the PMD and MDI also need to be considered. QSFP would be
used for CR4, but a QSFP will not connect to a CX4 connector; therefore, adding
support for legacy CX4 is unlikely to have broad market potential. Cheers, Brad From: Arthur
Marris [mailto:arthurm@xxxxxxxxxxx] Brad, Where is the
underlining of CX4 missing, could you give me the line number and page number? The issue as
I see it is that parallel detection is already described for the Clause 48 PCS
in Clause 73 and as 802.3ba extends Clause 73 beyond backplane to include
copper wiring there is a case for now including CX4 in parallel detection. Arthur. From: Brad
Booth [mailto:bbooth@xxxxxxxx] I
do agree with you Hugh that it was a shame that AN was not made available for
CX4. What
I don’t like is that this is a kludge. In reviewing this some more, I
noticed that the underlining of CX4 in 7.48.2 is missing. And, the
connector for CX4 is different than the QSFP being used for CR4; therefore, how
likely is legacy support. These are the types of things create extra work
for maintenance and interpretation. I
think this could be done correctly, but I believe that within the scope of this
project it is not as simple as being portrayed; hence the recommendation to
delete. Thanks, From: Hugh
Barrass (hbarrass) [mailto:hbarrass@xxxxxxxxx] Brad/Arthur, Firstly,
I didn't champion this function or the text supporting it, but I agree with the
general idea. I think
that including parallel detection within an autonegotiation function to support
legacy usage of the same media is the responsible thing to do. It was how we
worked in BASE-T autoneg, where it was well appreciated. I'm also glad that we
are ruling out parallel detection for the new PHY, so we avoid an equivalent to
the 100M parallel detection problem. Regarding
Brad's specific point: the legacy PHY needs no knowledge of autoneg. That's the
whole point of parallel detection for backward compatibility. Someone
implementing a new 40G only PHY will not link up with a legacy 10G PHY; someone
implementing a new 10G/40G interface will link with a legacy 10G PHY; someone
implementing a new 10G PHY may (or may not) choose to add autoneg in order to
detect a mis-connection with a 40G only system. Autoneg would have been
convenient if it had been added to 10GBASE-CX4 from the beginning, but as is
usually the case, the first users of a medium never seem to consider
"future compatibility." Bottom
line, I think that you should reject #565 Hugh. From: Brad
Booth [mailto:bbooth@xxxxxxxx] Arthur, The
legacy 10GBASE-CX4 port has no understanding of auto-negotiation. While
adding AN support for 10GBASE-CX4 may be viable, just adding a couple of
references to it in Clause 73 doesn’t enable it. For instance, someone
making a 40GBASE-CR4 port would read the Clause 73 and could add support for
10GBASE-CX4 AN. But someone making a 10GBASE-CX4 port would have no
reference to read Clause 73 or any reference in Clause 54 how it fits into the
architecture of the system; therefore, they are unlikely to add AN support. While
I agree that it is possible and it would be nice to have a way to do it, there
is no context for CX4 AN in Clause 54. If there is suggestion to open
that clause to add this function, then this has definitely gone beyond the
scope of the project. Cheers, Brad From: Arthur
Marris [mailto:arthurm@xxxxxxxxxxx] Brad,
I was not really clear in my original email. I meant 40GBASE-CR4 is using
Clause 73 AN which brings copper cabling into the 802.3ba scope.
At the moment my proposed response is: PROPOSED
REJECT. But
adding Clause 73 AN to copper cabling is in scope. There is now the possibility
of an end point using 40GBASE-CR4 connecting to a legacy 10GBASE-CX4 end-point.
but I am willing to be persuaded otherwise. Arthur. From: Brad
Booth [mailto:bbooth@xxxxxxxx] Arthur, Just
because the market is using Clause 73 auto-negotiation with copper cabling
doesn’t mean that adding this is within the scope of the project. When
something like this is added and it’s not done within the full context of
10GBASE-CX4. There are no edits to Clause 54 to make mention of this
function, so there is no context. While
adding things like this may appear to be helpful, experience has shown this is
where things get broken. Cheers, Brad From: Arthur
Marris [mailto:arthurm@xxxxxxxxxxx] Brad, You have submitted a TR
comment to remove mention of 10GBASE-CX4 parallel detect because –CX4 is out of
802.3ba’s scope. The reason I think this
is in scope is because Clause 73 auto-negotiation is now being used with copper
cabling for the first time. Hugh, Do you have any
comment on this? I think you championed adding this text in the first place. Arthur. |