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RE: PMD discussion

Walt (and others who have responded in the interim),

Although I am encouraged that the group will come to some agreement without
delaying our schedule, there is still some way to go.  Given the breadth of
the 5 objectives set forth, it seems almost certain that a 3-PMD set will
leave at least one objective being greatly under-optimized.  I would hate
for that to be the highest volume product.  Following the theme of
optimizing for each space presented Thursday by Steve Haddock (and departing
from his presentation of only 3 spaces), I would see the following as the
optimal solutions for each Objective.  Given the concensus that the 2km and
10km objectives are best served by a common PMD, we are really discussing 4
distinct Objectives.  Most of the debate is focused on the shorter-distance
objectives, so this note focuses on them.  I recommend the 4-PMD set below.

SMF up to 40km - 1550nm Serial

SMF up to 10km (incl 2km) - 1310nm Serial

MMF up to 300m - 850nm Serial

Installed MMF up to 100m - 850 CWDM

Highest Volume Product Space
The highest-volume product space here is almost certainly the MMF up to
300m.  This is due to most of the transceivers being put into new products
with new fibers.  An interesting comment was made last Thursday regarding
100Mb Ethernet in which 3 PMDs were spec'd in order to accommodate TX grade
cable as well as the installed base of T2 and T4 cable.  Subsequently the T2
and T4 were more or less abandoned and virtually the entire market went for
the TX-based PMD.  [I did not participate in that process; this is my
interpretation of the comments made last Thursday.  If this is inaccurate, I

Cost "Survey"
There have been several comments today regarding costs of different PMDs.
The cost comparisons which I (and Paul K) presented were NOT the result of
an "unscientific survey."  They are the average of estimates which were
circulated on the reflector.  No one was excluded from presenting their own
numbers.  I believe a great deal of thought was put into each estimate.  Are
the numbers accurate? Of course not.  Are they all consistent enough to
represent the general picture (which is how they were presented)?
Absolutely.  They have been presented publicly and privately with no voiced

Relative Costs of Serial and WDM
It has been suggested and sometimes even stated outright that a WDM solution
will be as low-cost or even lower-cost than a serial solution.  This is
unsupportable.  I put this question to (and look for responses from) vendors
who have manufactured and sold transceivers in any reasonable volume.
(These are the ones who know transceiver costs better than anyone.)  Does
your optical subassembly cost more than your ICs?  In expectation of a
unanimous "Yes" to that question, comes the next question.  In order to move
to higher performance levels while minimizing the cost increase should you:
1) increase the complexity of your optics; or 2) increase the complexity of
your ICs?  This is why we aren't seriously discussing a WDM-only set of
PMDs.  WDM is a good way to get more data over a fiber than otherwise
possible - but it's used only when simpler approaches cannot be used.  As
for the ICs, there were a lot of IC vendors at the meeting having aggressive
goals and impressive capabilities.  Assuming a "market entry" for 10GbE
products at the end of this year, it is reasonable to forecast that the cost
to produce a serial product will be less than its equivalent WDM product at
the time of market entry or within 6 months after that.  I.e. for
essentially the entire product lifetime.

The 4 PMDs recommended above are not biased in order to favor my company's
choice of PMDs; rather my company's choice of PMDs is based on a hard view
of the markets and technologies required to address them in an economical


-----Original Message-----
From: Walter Thirion [mailto:wthirion@xxxxxxxxxxxx]
Sent: Sunday, May 28, 2000 11:58 AM
To: '802.3ae'
Subject: PMD discussion

First of all, thanks to everybody that presented PMD proposals at the last
meeting. I've sent my presentation to David Law, so it should be available
on the web site in the next couple of days.

In listening to the discussion after my presentation and then going around
and talking to people, it feels to me like we're starting to converge. Not
there, yet, but making progress.

The equipment manufacturers made it pretty clear they would like to see no
more than 3 PMDs in the standard. The PMD vendors have some concern that
using only 3 PMDs may sub-optimize certain objectives, however, they could
support the 3 PMD position if it is made clear which 3 PMDs the equipment
oems want.

Based on an informal straw poll and anecdotal evidence, my opinion is the
first choice would be the set:
850 nm WWDM
1310 nm WWDM
1550 nm Serial

If that set isn't feasible, then the 2nd most popular choice is:
850 nm WWDM
1310 nm Serial
1550 nm Serial

Thoughts, feedback?

Walter Thirion
Chair, IEEE 802.3ae PMD Sub-Task Force
301 Congress Ave.
Suite 2050
Austin, Texas 78701
Voice:	512-236-6951
Fax:	512-236-6959