Re: [HSSG] The List
Good points. I was not really expecting to see a significant cost
differential at the PMD although its a good argument that a 100m PMD would be
less expensive. If this is the case, why not do another 10G PMD
focused on lowering the cost of server interconnect? I believe that would be a smaller project
and have a much less significant impact on 100G
thanks for your detailed thoughts and proposals. I
appreciate the points you made regarding the volume effect of 10G components on
the cost comparison. The presentation I submitted for the May interim
looked at the intrinsic cost factors and did not attempt to include volume in
the equation. But volume certainly can be a significant factor. Your
suggestion to look into its impact when comparing 4x10G LAG to 40G is
reasonable, but complicated at the PMD level. As my May presentation shows
there are a few ways to implement LAG on MMF. One uses the XFP, another
the SFP+, still another the QSFP. Today the XFP is shipping to the
10GBASE-S spec, and supports 300m transmission. Designs using SFP+ and
QSFP will be more challenged to meet this spec due to jitter, so it remains to
be seen how successfully these lower cost form factors can substitute for the
XFP in 10GBASE-S compliant LAG. However, a reduced distance requirement,
such as that stated in the HSSG objectives, would greatly improve the chances
that QSFP will suffice for "40GBASE-S". So while volume is important,
these unanswered questions on suitability make it impossible from my vantage
point to determine how the volumes for 10GBASE-S will be divided among XFP,
SFP+, and QSFP. And the effects of volume on production costs are better
left to those who manufacture the devices. Perhaps individuals with such
insights will offer some scenarios.
1300 East Lookout Drive
Richardson, TX 75082
06/26/2007 02:45 PM
|Re: [HSSG] The
My fellow colleagues ,
Last week I sent out a list of items that I felt need to be
addressed to ensure that a 40G PAR would be justified. At a subsequent EA
teleconference intended to build concensus in the HSSG, I offered to review the
presentations made in support of 40G Economic Feasibility and comparing 40G vs
4x10 LAG performance to ensure that I was not being too harsh in my
consideration of the material that was presented.
Over the weekend, I reviewed
every presentation I could find on these subjects so that I could be comfortable
that I was not being unfair in my concerns. Fortunately, it was not a huge task
as there are not that many to review.
After doing so, I found myself less convinced
in the validity of some presentations that were made. This statement is not made
to criticize my colleagues, but to honor the concept of peer review which
requires that we review and criticize, otherwise we might as well just upload
them to a server and forget about them.
Specifically, I disagreed with cost arguments made
on the assumption that 10G cost remains a constant, when in fact I anticipate
substantial reductions in 10G cost over the next few years at a rate much faster
than today due to a few factors;
1) Higher density/lower cost optical form factors (SFP+)
allowing better utilization of switch infrastructural cost and QSFP for
2) Smaller geometry CMOS allowing
higher port densities to work in synergy with PMD cost reductions.
3) Integration of XFI / SFI interfaces directly into
ASICs or multi-port PHYs driving 10G cost further downward.
4) Higher volumes / commoditization of 10G driving cost down
much faster than the current trajectory.
While 40G can leverage some of these elements, it
cannot leverage the volume that feeds the downward cost spiral. So in 4 years, a
40G switch port cost is going to be based on low-volume, freshly designed and
un-amortized silicon used primarily for server interconnect, whereas a 10G port
cost will be based on amortized, high-volume silicon being used in a huge array
of applications. Having different trajectories, the relative cost for 40G will
be higher than presented. This is true for 100G as well, but who is arguing a
need for 100G based on cost? It is bandwidth that drives 100G demand.
In addition, I found
presentations claiming that LAG was insufficient to address server I/O bandwidth
needs, yet those presentations failed to address upcoming technology
enhancements like TRILL and its impact combined with I/O Virtualization, perhaps
with a physical manifestation of QSFP and MPO optics which I believe can lead to
graceful performance scaling for servers that does not demand an intermediate
IEEE standard. In other words, activities and technologies are advancing which
will parse server network access into multiple conversations that can then be
put onto a LAG group with much higher than presented performance levels.
Now, I realize that I
am swimming upstream here by asking that the proponents for "40G now" to
complete a task that took the 100G proponents almost a year to accomplish, in
less than 6 months, but then I am not asking them to do that. My first
choice, the one I proposed in Geneva, was that we move 100G forward (because
it is DONE) and that we continue to work on 40G (until it is done).
to be a minority position because apparently some people will accept an unproven
40G proposal rather than risk 100G. Others think that 40G is proven sufficiently
and are demanding "40G now" or they will not allow a 100G PAR to go forward.
Those in the latter camp must either be unconvinced of my concerns, or they
think my concerns are insufficient to justify any further work being done to
justify a 40G project.
I can accept differences of opinion.
What I cannot do, however, is
pretend that these issues do not exist, or that the work we would have to spend
getting a 40G standard done is not going to delay the much needed 100G
aggregation solution our customers demand. I cannot ignore what I perceive as
holes in the 40G presentations.
So, to provide a little more direction to my colleagues in the
"40G now or the HSSG stalls" crowd, I am asking you to include relative cost
trajectories in your analysis of 40G vs 10G cost models, and to include
technology enhancements to LAG (TRILL, I/O Virtualization, QSFP, MPO) in your
If you feel that this is unnecessary, I am requesting that you
communicate this position to me as soon as possible so that I can prepare a
presentation on these areas of concern for the July meeting.
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