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Re: Comma Characters


The history is that some old SerDes initially designed for Fibre Channel
but slated for use in Gigabit Ethernet only supported one version of
comma. I believe that you are correct in stating that the specific
version was the positive comma version, also referred to as comma+ and
corresponding to the bit pattern 0b0011111. The Gigabit Ethernet
1000BASE-X PCS protocol is designed to emit both comma versions in order
to be "friendly" to all SerDes parts.

Clause 48, 10GBASE-X PCS is specified to statisitically emit an equal
number of both comma versions. The PCS implicitly requires the
generation and detection of both comma versions. The big difference
between 10GBASE-X and 1000BASE-X is that the 10GBASE-X does not require
comma detection in the PMA.

Personally, I don't believe that anything needs to be added to the
Clause 48 to clarify this point since it is the "obvious" way that an
8B/10B protocol should work. Please go ahead and submit a comment if you
feel otherwise.  

Best Regards,

Brian Cruikshank wrote:
> In Clause on page 261, the /COMMA/ is referred to being
> defined in clause 36.
> In this section, both a positive and negative comma are defined.
> I believe that in 1 GE devices, usually only positive commas were
> recognized.  Is this enough to be 1 GE and 10 GE compliant?
> In a IPG over 20 bytes, both commas will probably exist.  In
> sustained minimum IPG, the positive comma occurrence may be random.
> Do positive commas occur often enough?
> Maybe this detail should be stated?
> /Brian Cruikshank
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