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Re: [HSSG] The List


Jack,
thank you for chiming in.  We need more of this type of input.  Your response is provocative on several points, so consequently I have some questions and comments about your statements:  

1) First, SFP+ achieves the 300m SR objective with similar ease as XFP.

What is absorbing or mitigating the jitter that is handled by the CDR in the XFP?  Is it an external CDR, and EDC function, reduced temperature range, or improved signal quality from the upper level divides to which the SFP+ interfaces?  Or was the presence of the CDR in the XFP unwarranted in the first place?  Or are you saying that SFP+ supports a 300m link despite being noncompliant to 10GBASE-S specs?

2) 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.

I completely agree that this is a retreating approach that is not a preferred solution if it can be avoided, especially if all that is required is a simple (low cost and power) EDC function built into the receiver's TIA.  

3) A reduced operating temperature range offers immediate cost savings for some customers without compromising reach and without any new standards specifications.

I do not think that the 802.3 standard specifies operating temperature range.  If so, this improvement is available without violation of the 10GBASE-S spec.  But then there is the market requirement on temp range to consider, which can be just as imposing as the standards specs.  This leads back to the questions of item 1.

4) 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.

The crosstalk in a transceiver is another source of jitter.  I accept that the crosstalk in a single lane transceiver is likely to be easier to mitigate than that in a multi-lane transceiver that shares a common housing/circuit board between the transmit and receive functions. The degree of added impairment is the issue, and whether the jitter impairment causes a reduction in reach or other parameter trade-offs will need to be sorted out during the setting of specifications.  But if EDC and reduced temp range are means to lower cost for SFP+, then they will be as well for QSFP.  I think this may need to be sorted out in the lab as companies design these components into their test fixtures and systems.  That is why I encourage those with experience in this area to afford us the benefit of that experience.  Existence proof is a powerful argument.

5) Comparing costs, the SFP+ will be lower than QSFP for the foreseeable future (per lane for the same spec).

Does this claim rely on volumes favoring SFP+?  From what I can tell, the intrinsic costs favor QSFP relative to 4xSFP+.  If you disagree with this, please provide the particulars of where we differ by addressing the constituent comparisons in kolesar_01_0507.

Thanks for helping to increase understanding of these issues.

Regards,
Paul Kolesar
CommScope Inc.
EnterpriseŽ Solutions
1300 East Lookout Drive
Richardson, TX 75082
Phone:  972.792.3155
Fax:      972.792.3111
eMail:   pkolesar@commscope.com


Jack Jewell <Jack.Jewell@PICOLIGHT.COM>

06/27/2007 11:41 AM
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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.
EnterpriseŽ Solutions
1300 East Lookout Drive
Richardson, TX 75082
Phone:  972.792.3155
Fax:      972.792.3111
eMail:   pkolesar@commscope.com
"Dove, Dan" <dan.dove@HP.COM>

06/26/2007 09:24 PM
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"Dove, Dan" <dan.dove@HP.COM>
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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.
EnterpriseŽ Solutions
1300 East Lookout Drive
Richardson, TX 75082
Phone:  972.792.3155
Fax:      972.792.3111
eMail:   pkolesar@commscope.com
"Dove, Dan" <dan.dove@HP.COM>

06/26/2007 02:45 PM
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"Dove, Dan" <dan.dove@HP.COM>
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Re: [HSSG] The List






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