Re: [HSSG] The List
a transceiver vendor with experience and interest in both serial and
First, SFP+ achieves the 300m SR objective
with similar ease as
XFP. While a reduced-reach 10G PMD might reduce costs, it's a
retreating approach that requires the customer to purchase higher-cost
transceivers to fill in the reach gap, e.g. for reaches between 100m
and 300m.. A reduced operating temperature range offers immediate
cost savings for some customers without compromising reach and without any
new standards specifications. Use of a linear receiver and EDC and relaxed Tx specs can also achieve
the 300m reach at reduced cost.
For this application, the amount of compensation required is far
less than what is required for LRM. EDC is
becoming widely available, to the point of being a standard feature of PHY ICs,
so the cost of this EDC is becoming
insignificant. Forward-looking standards efforts will achieve their
full impact by making use of EDC.
For QSFP,. Here again, EDC offers great advantage, and ignoring it
would be a mistake. But crosstalk introduces module-level limitations that
might motivate reach reduction or other modification to the
Comparing costs, the SFP+ will be lower than QSFP
for the forseeable future (per lane for the
same spec). The only advantage of QSFP over SFP+ is density
and possibly simpler cabling.
However, a 12-channel parallel module
pair, e.g. SNAP12, offers greater density than QSFP and 2.5-3X the
bandwidth at <2X the cost.
Regarding SFP+, I am very familiar with the technology and
have been tracking the SFF-8431 development. The architecture re-distribution of
cost that SFP+ offers will have a substantial impact on cost, especially when
combined with the higher density we can achieve with smaller geometry ASICs and
multiport PHYs that will come with it.
As for QSFP, I am less familiar with whether or not it will
provide a cost improvement over SFP+ or be capable of meeting the existing SR
spec. This is something for the QSFP experts to consider, but like I said, a
shorter 10G PMD might be the avenue to take rather than an identity challenged
Regarding LAG, my conversation with HP Server architects
indicates there are a number of avenues for improvement of LAG under
cited these areas in my earlier message and would appreciate them being
addressed rather than ignored.
I can't tell how successfully SFP+ and QSFP will be
at meeting the existing 10GBASE-S spec. If they can, a new shorter
distance 10G PMD would not be of value. If they can't, then a new PMD spec
may be worth while. Those attempting to implement these lower cost
platforms need to weigh in to provide guidance. In the event that either
the QSFP and/or SFP+ can meet 10GBASE-S specs in multiple vendor's platforms, or
that a new shorter distance spec is developed that allows lower cost, the
performance issues of LAG will remain. I believe Howard's presentations on
LAG have indicated that improving LAG would not be without compromise, leading
me to conclude that, however improved, LAG performance could not become
equivalent to a 40G pipe. Developing a 40G spec would ensure a solution
that simultaneously addresses these cost and performance issues.
1300 East Lookout Drive
06/26/2007 09:24 PM
|Re: [HSSG] The
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 development.
From: Paul Kolesar
Sent: Tuesday, June 26, 2007 6:16
Subject: Re: [HSSG]
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
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
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
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 NICs.
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
volumes / commoditization of 10G driving cost down much faster than the current
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
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
appears 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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