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Re: [802.3_100GCU] FW: Discussion of Objectives



At the last meeting we discussed briefly what is the “legacy” channels we should attempt to cover.

Obviously it’s not a 10GBASE-KR channel – not enough lanes.

As has been suggested by others, I agree that we should look at 40GBASE-KR4 channels as the ‘legacy’ we should attempt to support… especially for the bladeserver market.  Kinda funny, because KR4 is not common in the market yet, but will be soon… so it’s a “future legacy.”

 

As Rich points out PCB technology moves at a snail’s pace compared to silicon.  I started designing boards in 1988 and the technology – especially for volume PCs & servers - is largely unchanged.  In fact, your Smart Phone uses much more advanced PCB tech than an IA server.     Look at the size of a Server motherboard – if we force a technology that doubles (or more) the square-inch cost of the PCB, that is not a good fit for this market.  Relating this to the objectives terminology below, if “improved FR4” means Megtron-6, that is impractical.

 

We have another external force is this market: regulatory requirements for RoHS (restriction of hazardous substances).    Over the last few years the PC/Server market made the transition to lead-free PCBs in support of RoHS.  Our next exciting challenge is Halogen Free.  That includes getting rid of the bromine & chlorine flame retardant common in FR4 today.  This makes a fundamental change in the epoxy dielectric properties.   (Actually the transition to lead-free was easier electrically – it was primarily a change in surface finish away from HASL; didn’t affect the dielectric.)  There is active industry effort underway to improve the electrical performance of HF PCBs… but the first stop along that path is just getting them up to “common” FR4 performance.  Finding a cost-effective, manufacturable, Halogen Free PCB solution with the electrical performance of Megtron-6 (or -4, or Nelco-13SI) may be a long way off… but more investigation is needed here.   For more background on HF, see: http://thor.inemi.org/webdownload/projects/ELSC/HFR-Free_PVC-Free_Timeline.pdf

 

Tying this back to a length objective for backplane channels is difficult, but I think we had the same issue in 802.3ap.  We assumed “improved” FR4 to achieve 1m.  But in practice I think most implementers chose to stay with lower cost PCB material & implement shorter channels.  In 802.3 we are used to having an objective for length – but that’s an awkward fit.

 

Dave

 

 


From: Mellitz, Richard [mailto:richard.mellitz@xxxxxxxxx]
Sent: Thursday, January 27, 2011 8:06 AM
To: STDS-802-3-100GCU@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_100GCU] FW: Discussion of Objectives

 

How about dielectric material that is projected to be used in X percent of the market in 201#?  That plays to broad market potential. Silicon technology is expected to still have exponential growth.  Changing “backplane/line card” board technology on the other hand is like turning a battle ship.   Given that,  we should at least evaluate how much of legacy product present in 201# we can cover given the disparity of the silicon vs. board technology pace.  Simply put, coverage could be one of the metric to compare proposals. Unfortunately it’s still crystal ball. 

 

… Rich

 

From: Havermann, Gert [mailto:Gert.Havermann@xxxxxxxxxxx]
Sent: Thursday, January 27, 2011 2:58 AM
To: STDS-802-3-100GCU@xxxxxxxxxxxxxxxxx
Subject: [802.3_100GCU] AW: [802.3_100GCU] FW: Discussion of Objectives

 

All,

 

besides the grammar I would like to have some kind of reference to the "enhanced FR-4 Material". There are so many different anhanced materials available (low loss, ultra low loss, low dk glass...) all having a different influence on the length factor we are trying to fix (not to mention the cost differenve between materials).

 

Regards

Gert Havermann

 

 


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Von: John D'Ambrosia [mailto:jdambrosia@xxxxxxxxxxxxxxx]
Gesendet: Mittwoch, 26. Januar 2011 19:07
An: STDS-802-3-100GCU@xxxxxxxxxxxxxxxxx
Betreff: [802.3_100GCU] FW: Discussion of Objectives

All,

Not sure this message got forwarded to the reflector, so forwarding.

 

Regards,

 

John

 

From: Kolesar, Paul [mailto:PKOLESAR@xxxxxxxxxxxx]
Sent: Wednesday, January 26, 2011 11:53 AM
To: John D'Ambrosia; STDS-802-3-100GCU@xxxxxxxxxxxxxxxxx
Subject: RE: Discussion of Objectives

 

John and group,

The objectives are on the right track, but there are a few grammatical and clarity issues.

 

The first is an issue with the wording at the end of each.  The phrase “up to at least” is illogical and confusing because it combines words that specify maxima (i.e. up to) with words that specify minima (i.e. at least).  While this phraseology may be following some precedent of former objectives, it only serves to cloud the real intent.  In the past these objectives have always been interpreted as the requirements for minimum reach.  Therefore I propose that they each simply state it as such by replacing “lengths up to at least” with “lengths of at least”.  

 

Further, I do not know what is intended by the phrase “for links consistent with lengths”.  Why use the word “consistent”?  Is there a perception of some increased flexibility or some other advantage?  Please explain.  If the advantage is ambiguity, I would prefer stating objectives more crisply. 

 

Unless your rationale for this word choice is compelling, I propose combining these two issues into the following new phrase: “for link lengths of at least”.  

 

Lastly, it would be simpler and clearer to place all the adjectives describing “traces” before the noun rather than some before and some after.  Rearranging these yields ”over improved FR-4 copper traces”.

 

With all three of these changes, the two draft objectives become:

 

·         Define a 4-lane 100 Gb/s PHY for operation over improved FR-4 copper traces for links lengths of at least “X” m.

 

·         Define a 4-lane 100 Gb/s PHY for operation over copper twin-axial cables for links lengths of at least “Y” m.

 

Of course all these grammatical improvements do not address the main issues which are the values of X and Y.  But that is what study groups are for.

 

Regards,

Paul Kolesar

 


From: John D'Ambrosia [mailto:jdambrosia@xxxxxxxxxxxxxxx]
Sent: Monday, January 24, 2011 12:00 PM
To: STDS-802-3-100GCU@xxxxxxxxxxxxxxxxx
Subject: [802.3_100GCU] Discussion of Objectives

 

All,

I wanted to try and foster some discussion on the reflector regarding objectives for the project to help all focus their planning of presentations for March. 

 

So what do we appear to have consensus on so far?

a)      We are in a  study group looking at 100GbE over backplane and copper twin-ax

b)      Legacy support indicates broad market potential would be aided by 4 lane solutions

 

What appears to need further consensus building?  Well the big ones would seem to be reach for both backplane and cu cabling objectives. 

 

So if we can combine where we appear to have consensus with what we need to resolve, the following two statements could be used as strawmans for objectives for the group to work towards (leaving the reach #’s as variables for now):

 

·         Define a 4-lane 100 Gb/s PHY for operation over copper traces on improved FR-4 for links consistent with lengths up to at least “X” m.

 

·         Define a 4-lane 100 Gb/s PHY for operation over copper twin-axial cables for links consistent with lengths up to at least “Y” m.

 

Feedback?

 

John