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Re: Interface reality check


Thank you for your efforts.  I still don't see why the WAN compatible PHY
should be burdened with all of these add on complexities, in addition to an
additional ~3% of bandwidth loss.

Thank you,
Roy Bynum

----- Original Message -----
From: Rick Walker <walker@xxxxxxxxxxxxxxxxx>
To: <stds-802-3-hssg@xxxxxxxx>
Sent: Friday, April 07, 2000 6:55 PM
Subject: Re: Interface reality check

> Dear Roy,
> > True 64B/66B supports all of the "Ethernet packet signalling semantics"
> > BEFORE it encodes the 802.3 frames.  But quite simply, after it is
> > it is no longer octet aligned.  The WAN compatible PHY is octet aligned.
> > ANSI T1X1 and ITU standards are also octet aligned.  It has nothing to
> > with control codes or any other issue.  For example your 1500 octet
> > Ethernet MAC frame becomes 1546.875 octets after it is encoded with
> > This type of octet alignment failure may cause other problems in octet
> > aligned signaling schemes.  I noticed this octet alignment failure in
> > looking at the possibility of using IPG compression with 64B/66B to help
> > reduce the additional ~3% transfer bandwidth loss.
> It is well known to logic designers how to build what is colloquially
> as a "gearbox".  Even though the code is defined on 66 bit boundaries,
> it is easy to actually transport it as octets.  As long as SONET can
> reliably transport octets, then the RX gearbox reconstructs the 66bit
> codewords with no problem.
> You can see such a structure converting 33 bit words into 16 bit words in
> the last 64b/66b presentation slides.  It should be trivial to see how
> a similiar structure can convert from 66 bit words to a sequence of 8 bit
> words.
> So, in summary, we only need to use SONET as a stripped down octet
> mechanism.  It never needs to know about the underlying 66-bit structure.
> Best regards,
> --
> Rick Walker