Re: [HSSG] The List
Paul,
With regard to the point I made about a "relaxed spec for
10G" vs writing an "entirely new Ethernet spec with multiple PMDs for 40G",
it was in response to your contention that 10GBASE-SR would be more expensive to
build than one channel of a new, unwritten, and parametrically relaxed 40G PMD.
My point was not that it is *necessary* to have a relaxed spec for 10G, but
rather that if such a relaxation is to be done, it would be less conflictive
with existing projects to do a 10G PMD than an entire set of PMDs and a 40G MAC
spec that lacks distinction from 100G in the market place. (ie: Two higher speed
Ethernets coming out at the same time with only a slight difference in
speed)
It is my firm opinion that we can build 10GBASE-SR
compliant SFP+ transceivers and that the total solution cost compared to X2 or
XFP will be significantly lower in cost than today's solution cost because of
the repartitioning of the functionality, the rapidly diminishing cost of EDC,
and the port density improvements which will allow system vendors to distribute
infrastructure cost into more ports than is possible today.
Dan
Ali,
there seems to be a theme throughout your response that
implies that cost is paramount and compliance to 10GBASE-S is of secondary
importance. This subtle but very significant posture may be pervasive with
others as well. In my comparisons I have been holding 10G LAG
implementations to the requirements of 10GBASE-S. Dan suggested that a
relaxed spec version of 10GBASE-S could be an alternative that makes LAG more
attractive from a cost perspective. And I am asking Jack to clarify his
statements with respect to compliance. Now you make similar intonations.
While this may be an alternative, it is one that distorts the reality of
the day. We do not have a relaxed spec, and although it is possible to
conceive of such a change, there is no study group activity in that direction.
So it seems mostly academic at this point because proprietary solutions of
this sort do not ensure interoperability. We need to be very clear on this
assumption in our comparisons going forward.
Regards,
Paul Kolesar
CommScope Inc.
Enterprise®
Solutions
1300 East Lookout Drive
Richardson, TX 75082
Phone:
972.792.3155
Fax: 972.792.3111
eMail:
pkolesar@commscope.com
| "Ali Ghiasi"
<aghiasi@broadcom.com>
06/27/2007 12:33 PM
|
|
To
| "Jack Jewell"
<Jack.Jewell@PICOLIGHT.COM>, "Paul Kolesar"
<pkolesar@systimax.com>
|
|
cc
| STDS-802-3-HSSG@listserv.ieee.org
|
|
Subject
| Re: [HSSG] The
List |
|
Jack
and Paul
The question is not whether SFP+ can achieve 300 m SR reach
similar to XFP, but how do we get to 10G SFP+
at 2.5x the cost of 1G classic
SFP for DCE (Data Center Ethernet) with max reach of 100 m.
If we can get
to 10G SFP+ at 2.5x the cost of 1G at 300 m then the 10G PAR objective is
complete, but how long
do we wait the need is know. But I do know the
combination of lower cost optics with EDC can deliver
the 2.5x cost
objective for DCE applications near term. To get to these cost the
transmitter very likely
will not be fully SR compliant and in that case it
does not matter if the reach is 100 or 300 m.
The current assumption
in the HSSG is that you can achieve SFP+ limiting performance with 4 or 10
channels without the
use of CDR in the module, with more crosstalk, less
optimum layout, SerDes having more jitter and less tolerance compare
to
small port count PHYs, optics ??? You will get small benefit from reducing
fiber reach to 100m but not enough to close the
link budget. As Dan
mentioned EDC is becoming an standard feature on PHYs and we definitely need to
leverage it for 40G/100G.
Use of linear interface is an approach that
can close the link budget without the use of CDR in the module, relax the optics
specifications, and the same interface can support passive copper Twin-ax up
to 10m.
Ali
Jack Jewell wrote:
Input from a transceiver vendor with experience and interest
in both serial and parallel modules:
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 PMD.
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.
Jack
From: Dove, Dan [mailto:dan.dove@HP.COM]
Sent: Wednesday, June 27, 2007 9:32 AM
To: STDS-802-3-HSSG@listserv.ieee.org
Subject: Re: [HSSG] The List
Paul,
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 40G
spec.
Regarding LAG, my conversation with HP Server architects indicates there
are a number of avenues for improvement of LAG under development.
I cited
these areas in my earlier message and would appreciate them being addressed
rather than ignored.
Dan
From: Paul Kolesar [mailto:PKOLESAR@SYSTIMAX.COM]
Sent: Wednesday, June 27, 2007 8:04 AM
To: STDS-802-3-HSSG@listserv.ieee.org
Subject: Re: [HSSG] The List
Dan,
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.
Regards,
Paul Kolesar
CommScope Inc.
Enterprise®
Solutions
1300 East Lookout Drive
Richardson, TX 75082
Phone:
972.792.3155
Fax: 972.792.3111
eMail:
pkolesar@commscope.com
Hi
Paul,
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.
Thanks,
Dan
From: Paul Kolesar [mailto:PKOLESAR@SYSTIMAX.COM]
Sent: Tuesday, June 26, 2007 6:16 PM
To: STDS-802-3-HSSG@listserv.ieee.org
Subject: Re: [HSSG] The List
Dan,
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.
Regards,
Paul Kolesar
CommScope Inc.
Enterprise®
Solutions
1300 East Lookout Drive
Richardson, TX 75082
Phone:
972.792.3155
Fax: 972.792.3111
eMail:
pkolesar@commscope.com
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 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 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).
This 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
performance analysis.
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.
Respectfully,
Dan Dove
Dove Networking Solutions - Serving ProCurve Networking by
HP