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Re: [HSSG] 40G MAC Rate Discussion


A very real factor in 10GBASE-T power reduction and multiple PHY integration is already present and pushing hard without regard to 10GBASE-T use in a 40G context. That is the very real market need for high port density in switches. The volume switch market doesn't get real at any speed until you can put multiple Cu PHYs on a single chip. Thus the multiple PHY chip is, by necessity, already a high priority item for 10GBASE-T vendors (even though power is a significant challenge at this point). I say this with only a knowledge of history and no insider information. I'm sure that a more intimately affected party (e.g. Bill) can comment further.

Thus, I am in violent agreement that time is on our side, especially in this particular area. It might facilitate things for 40G copper vendors to nurture MSAs on the RJ-45 side of a multi 10GBASE-T chip to better support some sort of (to be) standardized 16 pair ribbon cable for 40G.


At 03:44 PM 4/10/2007 , Paul Kolesar wrote:

First, let me apologize for misspelling Scott Kipp's last name in my previous note. Sorry Scott.

I think you have touched on the key issue facing 10GBASE-T: power dissipation.  While we can look forward to lower power consumption with future IC feature reductions, these will be muted by the need for multiple 10GBASE-T PMDs in a LAG or other parallel scenario.  Such power reductions will also enable lower power consumption by the optical PMDs, although by relatively smaller power reduction ratios.  In my estimation it will be difficult, or far into the future, to deliver a 4x 10GBASE-T device that dissipates the equivalent dissipation of 40G parallel optical transceivers. 

The cost of the copper cabling will also be 4x higher than for a single 10GBASE-T link.  So here it would loose its most of its competitive edge. 

The relative PMD cost factors are unknown, since I am not aware of 10GBASE-T ports in the market at this time.  But it is very likely that once 10GBASE-T become highly integrated, they will compete with the parallel optical transceivers where their application spaces overlap.  It is unclear if that overlap will include 40G applications, since LAG deployments will fade as the single PMD solutions become available.

Time appears to be one of the variables with the greatest influence on the optimal choice.  Will that play best to copper or fiber?  Somebody with a better crystal ball than mine on the issues outlined above needs to weigh in. 

Paul Kolesar
CommScope Inc.
EnterpriseŽ Solutions
1300 East Lookout Drive
Richardson, TX 75082
Phone:  972.792.3155
Fax:      972.792.3111

Mikael Abrahamsson <swmike@SWM.PP.SE>

04/10/2007 03:04 PM
Please respond to
Mikael Abrahamsson <swmike@SWM.PP.SE>

Re: [HSSG] 40G MAC Rate Discussion

On Tue, 10 Apr 2007, Ali Ghiasi wrote:

> I know there is readily available solution based on QSFP that could do
> 40G copper with twin-ax cables.  Copper solution are very attractive for
> sub-10m as they offer order of magnitude cost advantage.  Longer reach
> cable not as attractive as you have to use heavier gage which increase
> the cable size, weight, cost, and the complexity of receiver increases.

Well, my idea was to compare 4*10GE LAG and whatever 40GE solution is
being proposed. I understand now I should have written this outright,

My thoughts were that operational cost and CAPEX of doing 4*10GE LAG using
10GBASE-T for servers would be quite a lot lower than any new proposed
40GE solution, since I only saw coaxial and fiber proposed for 40GE
physical media.

Or have I misunderstood 10GBASE-T when it comes to power and reach (100M
over CAT7 or ~50 on CAT6)? Does it require a lot more power than fiber
based solution?

From a pure end-user perspective CAT6-7 based cabling has the lowest
operational cost (physical only) since it's abundant and there is a lot of
experience with that kind of cabling. But perhaps it uses a lot more power
than the other proposed solutions for 40GE?

Mikael Abrahamsson    email: