| Thread Links | Date Links | ||||
|---|---|---|---|---|---|
| Thread Prev | Thread Next | Thread Index | Date Prev | Date Next | Date Index |
|
Ali, While Chris seems in perfect agreement
with your suggestions, I’m having some interpretation trouble. Please
respond to these inquiries of clarification. In the first sentence you state “another
LR4 PMD”. Do you really mean LR4 (as in 10km) or do you mean “MR4”
(as in <1km)? If you mean the latter, as in “If there is an MR4
PMD out there…”, I would agree that a good comparative would be
40GBASE-LR4 for a CWDM approach. If you do not mean the latter, I am
confused and need clarification. The third sentence seems to make the
assumption that the new 100G MR4 PMD is based on CWDM. Perhaps you are
just trying to restate that the 40GBASE-LR4 PMD is a good (existing) cost
basis. If that is the case, once again I agree. If that is not the
case, please clarify. In your last sentence you assert that we
need to understand if a parallel fiber solution is even acceptable to distances
of 500 – 1000 m. The more accurate inquiry would be to ask if
parallel SM technology is acceptable at all. If the answer is yes, to what
distances, because according to my channel data it may never be deployed to
reaches of even 500 m. My point here is that one would not obtain an
accurate assessment of the customer’s position if the question were aimed
only at 500 – 1000 m channels. Regards, Paul From: Chris Cole
[mailto:chris.cole@xxxxxxxxxxx] Ali, Superbly framed! Chris From: Ali Ghiasi
[mailto:aghiasi@xxxxxxxxxxxx] Jack If there is another LR4 PMD out there the best starting point would be
40Gbase-LR4, look at its cost structure, and build a 40G/100G compatible PMD. We also need to understand the cost difference between parallel MR4 vs
40Gbase-LR4 (CWDM). The 40Gbase-LR4 cost with time could be assumed
identical to the new 100G MR4 PMD. Having this baseline cost then
we can compare its cost with 100GBase-LR4 and parallel MR4. The
next step is to take into account higher cable and connector cost associated with
parallel implementation then identify at what reach it gets to parity with 100G
(CWDM) or 100G (LAN-WDM). In the mean time we need to get more direct feedback from end users if
the parallel SMF is even an acceptable solution for reaches of 500-1000 m. Thanks, Ali On Nov 15, 2011, at 8:41 PM, Thanks for this input
Chris. I'm not
"proposing" anything here, rather trying to frame the challenge, so
that we become better aligned in how cost-aggressive we should be, which guides
the technical approach. As for names, "whatever works" :-) It
would be nice to have a (whatever)R4, be it nR4 or something else, and an
english name to go with it. The Structured Data Center (SDC) links you describe
in your Nov2011 presentation are what I am referencing, except for the
restriction to "duplex SMF." My input is based on use of any
interconnection medium that provides the overall lowest-cost, lowest-power
solution, including e.g. parallel SMF. Cost comparisons are
necessary, but I agree tend to be dicey. Present 10GbE costs are much better
defined than projected 100GbE NextGen costs, but there's no getting around
having to estimate NextGen costs, and specifying the comparison. Before the
straw poll, I got explicit clarification that "LR4" did NOT include
mux/demux IC's, and therefore did not refer to what is built today. My
assumption was a "fair" cost comparison between LR4 and (let's call
it)nR4 - at similar stage of development and market maturity. A relevant stage
is during delivery of high volumes (prototype costs are of low relevance). This
does NOT imply same volumes. It wouldn't be fair to project ER costs based on
SR or copper volumes. I'm guessing these assumptions are mainstream in this
group. That would make the 25% cost target very aggressive, and a 50% cost
target probably sufficient to justify an optimized solution. Power requirements
are a part of the total cost of ownership, and should be considered, but
perhaps weren't. The kernel of this
discussion is whether to pursue "optimized solutions" vs
"restricted solutions." LR4 was specified through great scrutiny and
is expected to be a very successful solution for 10km reach over duplex SMF.
Interoperability with LR4 is obviously desirable, but would a 1km-spec'd-down
version of LR4 provide sufficient cost/power savings over LR4 to justify a new
PMD and product development? Is there another duplex SMF solution that would
provide sufficient cost/power savings over LR4 to justify a new PMD and
product development? If so, why wouldn't it be essentially
a 1km-spec'd-down version of LR4? There is wide perception that SDC's
will require costs/powers much lower than are expected from LR4, so much lower
that it's solution is a major topic in HSSG. So far, it looks to me like an
optimized solution is probably warranted. But I'm not yet convinced of that,
and don't see consensus on the issue in the group, hence the discussion. Cheers, Jack From:
Chris Cole <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 |