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Re: Unified PMD vs. Unified PHY




Rich,

I take exception to your comment below, "the LAN does not support SONET."  I
don't know where you learned the OSI model, so here is a lesson.  SONET is a
layer 1 media transport encoding scheme, of the same function as 8B10B, with
additional features.  Ethernet is a layer 2, data link protocol.  Since
Ethernet is a layer 2 protocol, it should be able to run on any layer 1
signal encoding seheme that we want it to.  Since P802.3ae is full duplex,
it does not matter what the signal encoding scheme is for LAN applications.
Since the LAN implimentations are normally directly from data switch to data
switch, there are no other functional restrictions, on the transport
encoding scheme such as legacy transport facilities implemenations.  The
PCS/PMA could be anything.  It could be somebody's "gobledy goop", as long
as it does what it is supposed to do.  That includes 8B10B only,
8B10B/64B66B, frame stuffing/SONET/SDH/frame, 8B10B/64B66B/SONET/SDH, or
PAM5.  In other words, the "LAN" does not care what you put on  the full
duplex point to point fiber link.   Making the statement that the "LAN" does
not support SONET" is either a case of a lack of knowledge, or a severe case
of hubris.  The "LAN", as we normally discuss it, is defined by the 802.3
Ethernet MAC protocol, not the transport encoding scheme.  The "LAN" can
support anything that we want it to, including SONET/SDH.

Personally, I do not think that adding ~3% additional overhead to the WAN
compatible PHY, just so you can continue with an encoding scheme that you
have an emotional attachment to, is justified.  When ~3% average transfer
rate can be recovered by IPG compression using a frame stuffing scheme, it
become even less justifed.  The real alternative for a unified PHY is the
WAN compatible PHY, because it will already support the LAN as well, with
only an average ~2% transfer bandwidth penalty.

If you are honest about wanting a LAN only PHY at 10.00 Gb, seperate from a
WAN/LAN compatible PHY at ~9.8Gb, then you can have the LAN with a block
encoding of 8B10B or 8B10B/64B66B and a WAN/LAN compatible PHY with frame
stuffed, scramble encoding using the SONET/SDH format.  If you are honest
about wanting a PHY that is compatible with both the LAN and WAN
implimentations at less than 10% additional cost, then you want the LAN/WAN
compatible PHY with a modified version of the Nortel frame stuffing using
scramble encoding with the SONET/SDH format.

Thank you,
Roy Bynum

----- Original Message -----
From: Rich Taborek <rtaborek@xxxxxxxxxxx>
To: HSSG <stds-802-3-hssg@xxxxxxxx>
Sent: Saturday, March 25, 2000 8:53 PM
Subject: Re: Unified PMD vs. Unified PHY


>
> Roy,
>
> Thanks for the clarification. It appears that you are now in agreement
with Mr.
> Andreas Bechtolsheim's original statement that the UniPHY proposed by Mr.
Howard
> Frazier, et. al. affects the transport of Ethernet over SONET to the tune
of
> only 3% (3.125% to be exact) overhead. I also agree that this is a
compromise
> with the WAN compatible PHY, which is not LAN compatible.
>
> I have a few additional comments below:
>
> Jonathan, Question for you below.
>
> --
>
> Best Regards,
> Rich
>
>
> Roy Bynum wrote:
> >
> > Rich,
> >
> > A LAN only PHY that is at 10Gbps transfer rate is exactly what I am
talking
> > about.  The proposed "UniPHY" is ~3% less than the original proposal for
a
> > WAN compatible PHY which, as you pointed out, is less than the original
LAN
> > PHY to start with.
>
> This appears to be a good compromise. Full 10 Gbps for the LAN and only 3%
> penalty for the WAN.
>
> > As far as a unified PHY is concerned, no one has said that the WAN
> > compatible PHY could not be used in a privately owned fiber systems,
like
> > the LAN PHY.
>
> I have absolutely no problem with this.
>
> > The WAN compatible PHY just has ~5% less MAC transfer rate. As far as I
> > I know, there has never been a presentation that would only work in the
> > WAN, ie. a WAN only PHY.  This understanding makes the WAN compatible
> > PHY functional as a reduced rate LAN PHY.
>
> The WAN PHY is not compatible with the LAN since it is speaks SONET. The
LAN
> does not transport SONET. The LAN transports Ethernet (in most cases). Am
I
> missing something?
>
> > In other words, the unified PHY that Jonathan Thatcher is wanting is
> > already the WAN compatible PHY.
>
> Jonathan,
>
> Can you shed any light on this?
>
> > I think that the preferences that came out of the survey that Jonathan
> > indicates that the majority of the group would prefer the WAN compatible
PHY
> > because it will support both the LAN and WAN implimentations at only ~5%
> > overhead cost.  From what I have been able to determine, the actual
> > implementation costs seem to be about the same.  The second alternative
is
> > seperate LAN only and WAN compatible PHYs.
>
> What survey are you referring to? The only survey I know of:
> http://grouper.ieee.org/groups/802/3/ae/public/mar00/brown_1_0300.pdf,
shows a
> WAN PHY in dead last place and a UniPHY in first place.
>
> The second alternative is again a UniPHY with a 10% penalty.
>
> The third alternative endorses separate LAN only and WAN compatible PHYs.
>
> > Thank you,
> > Roy Bynum
> >
> > --
> > >
> > > Roy,
> > >
> > > I believe that you have overhead sources twisted a bit.
> > >
> > > All proposals for the LAN PHY support a MAC data transfer rate of 10
Gbps.
> > > are you referring to when you say ~10% slower?  The only thing that's
> > > limiting the MAC's accepted 10 Gbps data rate is legacy SONET OC-192c
> > > and it's inherent overhead.
> > >
> > > Best Regards,
> > > Rich
> > >
> > > --
> > >
> > > Roy Bynum wrote:
> > > >
> > > > Andreas,
> > > >
> > > > The real question is, do we need a LAN PHY that is ~10% slower than
the
> > > > 10.000 Gigbit transfer rate that was so important in June, July,
> > > > September, and November of 1999?  Did all of that support for 10.000
> > > > Gigabit suddenly disappear?  It makes me very suspicious.  The
> > > > additional ~3% loss to the WAN compatable PHY is a seperate issue.
> > > >
> > > > Thank you,
> > > > Roy Bynum
> > > >
> > > > --
> > > > >
> > > > > Roy,
> > > > >
> > > > > the question is do we need to create two separate PHY standards
> > > > > because of a 3% difference in transmission efficiency.
> > > > >
> > > > > If you look at the results of the Albuquerque straw poll,
> > > > > the majority of 802.3ae appears to answer this question with "no".
> > > > >
> > > > > Andy
>
> -------------------------------------------------------
> Richard Taborek Sr.                 Phone: 408-845-6102
> Chief Technology Officer             Cell: 408-832-3957
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