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Ben,
This is exactly the conclusion I came to - that the alignment will
be in a different layer this time (compared to comma detect in the
PMA).
So if the 64b/66b PCS needs to do its own alignment, it sounds like it
would be important for the PCS to have a link initialisation
sequence (which hopefully could be kept very simple). Because
it could be near-impossible to align to 0/1 1/0 sync bits, without
also having assistance from specific Types. So to facilitate code
alignment (locally and link partner), there will need to be some
well-defined codewords to sync to. Perhaps this could be handled in
the IPG, by searching for
ZZZZ/ZZZZ = KKKK/RRRR or RRRR/KKKK or AAAA/KKKK ....
(with exact matching of the 7-bit types)
- and then follow-on by checking a few sequential codeword boundaries
to verify the framing is correct (further 0/1 or 1/0 checks).
This places a requirement on the minimum IPG length. And the PCS
would only gain alignment in between packets. But this should be okay.
Does anyone see a requirement for the PCS to define link-init
codewords (eg break-link + handshake) ?
Regards,
Una
-----Original Message-----
From: Brown, Ben [BAY:NHBED:DS48] [mailto:bebrown@xxxxxxxxxxxxxxxxxx]
Sent: 10 April 2000 14:57
To: stds-802-3-hssg@xxxxxxxx
Subject: code-word alignment location
Una,
I thought I'd throw in a response to your aside using a new thread.
> Una Quinlan wrote:
>
> [ Aside: Does PCS codeword alignment belong in the PMA/WIS or the PCS?].
>
In 1000Base-X, code-word alignment (to the comma) occurred in the PMA.
With a break down (from the Uni-PHY proposal) of PMD - PMA - WIS - PCS,
the PMA cannot provide alignment. The WIS needs to align on A1/A2. From
this, the WIS provides byte aligned data to the PCS. If the PCS
is 64b/66b, this byte alignment is useless and 66b alignment is done
to the 1/0 or 0/1 sync bits. The PMA can't participate in any of this
because the WIS is optional and both the WIS and PCS require different
alignment mechanisms. Implementations can do anything they want but the
standard needs to keep these separate.
Ben
--
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Benjamin Brown
Router Products Division
Nortel Networks
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Kilton Road
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