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Re: Unified PMD vs. Unified PHY


The survey showed that there appears to be support for a unified
WAN and LAN PHY. That's wonderful. However, there will be nothing
in the standard that dictates how this is implemented.

PHY vendor A may choose to design a single part for those
system vendors that want to develop a single product for
applications that want the flexibility of selecting LAN
or WAN at a later date.

PHY vendor B may choose to design separate parts for those
system vendors that are willing to support multiple products
in order to make the LAN product marginally lower cost than
the WAN (due to the unnecessary Sonet framing and overhead).

The standard will allow both implementations. The market
will decide to award one or even both of the above applications
as they may both have a place.


Roy Bynum wrote:
> Bruce,
> Given my earlier question about why the option of a unified PMD with
> separate LAN and WAN PHYs, and the other issues of the weighting of the
> options in the question, I tend to suspect the validity of the survey
> results.  As you might remember, the motion that carried with overwhelming
> support was for a limit of seven PMDs with only an attempt to reduce below
> that, and the PMD was separated from the PCS/PMA in the motion that carried.
> As it is, half of the "UniPHY" options failed against the separate LAN/WAN
> PHYs option.  It means that there is a limit to the support for the
> "UniPHY".   The bandwidth costs of the "UniPHY" proposals currently before
> the group, may limit that support even more.
> I think that the issue of the PMD carries a lot more weight than does the
> PCS/PMA portion of the PHY.  Given that proposals are in place that would
> allow a LAN PHY at 10.0 Gb MAC transfer rate to operate at only ~4% higher
> baud than a WAN PHY, a unified PMD set could be defined, with separate LAN
> and WAN PHYs.  Combine this with the need to add WAN overhead processing
> that would not be needed in a LAN PHY, the "UniPHY" could be well over the
> 10% higher cost limit that the survey results defined.
> What I do find interesting is that the survey placed a LAN only PHY just
> above a WAN only PHY, both at the bottom of the option results, below a very
> high cost "UniPHY".  This means that there will be WAN support in 10 Gigabit
> Ethernet.  This is very different than what the "powers that be" thought at
> this time last year would be happening.
> I personally do not want to burden a LAN PHY, that could be implemented
> inside buildings and campus environments, with the management capabilities
> of a WAN PHY.  There may be situations that warrant it, but it should be a
> distinct option that is available to the implementers.  I think that the LAN
> only oriented people should be allowed to develop the LAN PHY as they
> thought they wanted it to be last year.  This would allow the WAN PHY people
> to concentrate on their issues and stop having to deal with the same
> encoding "options" from the LAN people time and again.
> Thank you,
> Roy Bynum
> ----- Original Message -----
> From: Bruce Tolley <btolley@xxxxxxxxx>
> To: Roy Bynum <rabynum@xxxxxxxxxxxxxx>; Benjamin J. Brown
> <bebrown@xxxxxxxxxxxxxxxxxx>; 802.3ae <stds-802-3-hssg@xxxxxxxx>
> Sent: Tuesday, March 14, 2000 2:13 PM
> Subject: Re: Unified PMD vs. Unified PHY
> >
> > At 08:33 AM 3/14/00 -0600, Roy Bynum wrote:
> > >  I think that the original compromise and
> > >the objectives as stated are correct, there needs to be seperate LAN and
> > >PHYs.
> >
> >
> > Roy:
> >
> > I think in the first part of your statement you hit the nail on the head.
> Goal #9 (Define two families of PHYs) was a compromise that came out of
> several meetings that was aided by the bridge diagram originally proposed by
> Howard Frazier.
> >
> > Many folks have since expressed displeasure with the idea of a bridge but
> the picture gave the members of the study group a way to understand and
> bound the problem.
> >
> > The goal of two PHYs agreed upon in York was as much political statement
> as it was a technical statement. There was a strong feeling up to the
> meeting in York of the need to limit the problem, define the goals, and get
> on with the work.
> >
> > It was always clearly stated that the goals were not written in stone and
> we might come back to revise them.
> >
> > Given the basis of the findings from survey conducted by Jonathan, I
> conclude that there is strong support among the members of the task force to
> seriously investigate the concept of the UniPHY.
> >
> > Bruce
> >

Benjamin Brown
Router Products Division
Nortel Networks
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Kilton Road
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