Re: Interface reality check
Rick,
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
encoded,
> > 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
do
> > with control codes or any other issue. For example your 1500 octet
802.3
> > Ethernet MAC frame becomes 1546.875 octets after it is encoded with
64B/66B.
> > 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
known
> 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
transport
> mechanism. It never needs to know about the underlying 66-bit structure.
>
> Best regards,
> --
> Rick Walker