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I also like Jack’s perspective
foundation. And I have to agree that a common small port form factor
would be valuable. Regarding the PMD cost comparisons, I also
agree that picking a common cost basis could eliminate translation problems
that come with use of different bases. For PMD relative costs I am fine
with choosing either 10GE SR or LR because I don’t quite appreciate Chris’
concerns over the danger in using LR as the basis. But if there is a
problem, it seems like it could be avoided by eliminating the bit/sec factor and
instead using simple cost. However, there is still the issue of picking
the point in the supply chain at which the baseline cost is chosen. It
could be at the level of the transceiver manufacturer, or up one level to the
switch manufacturer, or off on another branch to distributors, or up one level
again to the end user. There can be substantial differences in these
costs, which is what likely gives rise to the “order of magnitude”
perception disparity that Chris mentioned. While we are forbidden to talk
about it, it is the 500 pound gorilla in the room. In some cases it tips
the scales lightly and in other cases it leans its full weight. Yet this
weight is what is creating a 100GE market acceptance barrier in data center
deployments. While there is clear cost reduction
potential in reducing the multimode lane count based just on the improvement in
media cost, the benefit of defining a new single-mode solution may depend largely
on the gorilla, for if we go to a parallel solution the media will only get
more costly. So for me the biggest cost question is whether defining a
new single-mode solution moves the gorilla from leaning heavily to leaning
lightly. While I’d like to agree to use cost
at the transceiver maker level as the basis, it cannot address this big question.
If used it will likely result in highly distorted perceptions and projections
because it ignores the order-of-magnitude problem. The only point in the supply
chain where transceiver costs and cabling costs come together is at the end
user level. This dilemma is hitting me squarely as I try to further my
work on the “Kolesar_Kalculator”. I continue to wonder
what good this tool will do if the PMD cost and cable cost are in two different
silos without a common basis to bring them together, for it is the combination
of the two that defines the total channel cost that we must optimize. I
need to find a way to appease the gorilla. If only Fay Wray were here…
From: Chris Cole
[mailto:chris.cole@xxxxxxxxxxx] Hello Jack, Nice historical
perspective on the new reach space. Do I interpret your
email as proposing to call the new 150m to 1000m standard 100GE-MR4? J One of the problems
in using today’s 100GE-LR4 cost as a comparison metric for new optics is
that there is at least an order of magnitude variation in the perception of
what that cost is. Given such a wide disparity in perception, 25% can either be
impressive or inadequate.
Using these
reference baselines, in order for the new reach space optics to be compelling,
they must have a cost structure that is referenced to a fraction of 10GE-SR
(VCSEL based) cost, NOT referenced to a fraction of 10GE-LR (DFB laser based)
cost. Otherwise, the argument can be made that 100GE-LR4 will get to a fraction
of 10GE-LR cost, at similar volumes, so why propose something new. Chris From: Following last week's
meetings, I think the following is relevant to frame our discussions of
satisfying data center needs for low-cost low-power interconnections over
reaches in the roughly 150-1000m range. This is a "30,000ft
view,"without getting overly specific. Throughout GbE, 10GbE,
100GbE and into our discussions of 100GbE NextGenOptics, there have been 3
distinct spaces, with solutions optimized for each: Copper, MMF, and SMF. With
increasing data rates, both copper and MMF specs focused on maintaining minimal
cost, and their reach lengths decreased. E.g. MMF reach was up to 550m in GbE,
then 300m in 10GbE (even shorter reach defined outside of IEEE), then 100-150m
in 100GbE. MMF reach for 100GbE NextGenOptics will be even shorter unless
electronics like EQ or FEC are included. Concurrently, MMF solutions have
become attractive over copper at shorter and shorter distances. Both
copper and MMF spaces have "literally" shrunk. In contrast, SMF
solutions have maintained a 10km reach (not worrying about the initial 5km spec
in GbE, or 40km solutions). To maintain the 10km reach, SMF solutions evolved
from FP lasers, to DFB lasers, to WDM with cooled DFB lasers. The 10km
solutions increasingly resemble longer-haul telecom solutions. There is an
increasing cost disparity between MMF and SMF solutions. This is an
observation, not a questioning of the reasons behind these trends. The
increasing cost disparity between MMF and SMF solutions is accompanied by
rapidly-growing data center needs for links longer than MMF can accommodate, at
costs less than 10km SMF can accommodate. This has the appearance of the
emergence of a new "reach space," which warrants its own optimized
solution. The emergence of the new reach space is the crux of this discussion. Last week, a straw
poll showed heavy support for "a PMD supporting a 500m reach at 25% the
cost of 100GBASE-LR4" (heavily favored over targets of 75% or 50% the cost
of 100GBASE-LR4). By heavily favoring the most aggressive low-cost target, this
vote further supports the need for an "optimized solution" for this
reach space. By "optimized solution" I mean one which is free from
constraints, e.g. interoperability with other solutions. Though
interoperability is desirable, an interoperable solution is unlikely to achieve
the cost target. In the 3 reach spaces discussed so far, there is NO
interoperability between copper/MMF, MMF/SMF, or copper/SMF. Copper, MMF and
SMF are optimized solutions. It will likely take an optimized solution to
satisfy this "mid-reach" space at the desired costs. To
repeat: This has the appearance of the emergence of a new "reach
space," which warrants its own optimized solution. Since the reach target
lies between "short reach" and "long reach," "mid reach"
is a reasonable term Without discussing
specific technical solutions, it is noteworthy that all 4 technical
presentations last week for this "mid-reach" space involved parallel
SMF, which would not interoperate with either 100GBASE-LR4, MMF, or copper.
They would be optimized solutions, and interest in their further work received
the highest support in straw polls. Given the high-density environment of
datacenters, a solution for the mid-reach space would have most impact if its
operating power was sufficiently low to be implemented in a form factor
compatible with MMF and copper sockets. Cheers, Jack |