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Re: [HSSG] 40G MAC Rate Discussion

Hi colleagues,
Sorry for interrupting (I may not know all the details; sorry I could
not make it to last month's plenary). I was just wondering, is it
possible that we define a single spec (say 100Gbps) that could possibly
run at lower datarates (40G, or other multiples of 10Gbps in this case)?
I guess the main reason for having the "magical" 40Gbps is just to get
the most out of the present hardware without incurring significant cost
overheads, so defining a 100Gbps spec that could run at reduced
datarates, might also see possible adoption by present hardware.

Also, I am curious about the 10Gbps/lane datarate that we are holding on
to. Are there any plans to increase this per-lane datarate for 40Gbps or
100Gbps? Probably 2x20G or 5x20G? This may be a bad idea, I am just


-----Original Message-----
From: Shimon Muller [mailto:Shimon.Muller@Sun.COM] 
Sent: Wednesday, April 04, 2007 10:43 AM
Subject: Re: [HSSG] 40G MAC Rate Discussion

> 1) What is so magical about 40Gps number for servers?
> Why any other multiple of 10 between 10Gbps - 100Gbps is not
> good for servers?

Nothing magic about 40Gb for servers, just as there is nothing magic
a 10x scaling factor, except for tradition.
40Gb happens to be in the right ballpark for server needs in that
and it will be at the right cost.

> 2) Do one really think that a processor (MC/MT included) and memory
> could meaningfully fill the 40Gbps pipe and still do some useful work?

> I mean
> by 2011 or may be beyond?

Absolutely. I would be more than happy to demonstrate that to you.

> 3) What is PCIe affinity to 40Gbps as I/O? PCIe doesn't seem to tied 
> to 40Gbps.
> It supports or could support any multiple of 10 (or may be 2.5) 
> between 2.5Gbps - 100Gbps.

Today, PCI-Ex 1.0 can do 32Gb raw, but at most 24Gb usable.
By 2010, PCI-Ex 2.0 will double that to 64Gb raw, 48Gb usable.
By 2015, PCI-Ex 3.0 will double that again to 128Gb raw, 96Gb usable.
It's all about timing.

> 4) Extending flexibility, if flexibility is desired then why limit to 
> just 40G and 100G? If flexibility of
> multi-rate is a goal why not option for 20G or 50G (if not more)?

Some (very reasonable) people would argue that infinite flexibility is a
good thing. I am not one of them. Life is about trade-offs.