10GE TOR port buffers (was Re: 10G switch recommendaton)

Joel jaeggli joelja at bogus.com
Sat Jan 28 00:00:36 UTC 2012

On 1/27/12 15:40 , bas wrote:
> Hi All,
> On Sat, Jan 28, 2012 at 12:32 AM, Joel jaeggli <joelja at bogus.com> wrote:
>> On 1/27/12 14:53 , bas wrote:
>>> While I agree _again_!!!!!
>>> It does not explain why TOR boxes have little buffers and chassis box
>>> have many.....
>> you need purportionally more buffer when you need to drain 16 x 10 gig
>> into 4 x 10Gig then when you're trying to drain 10Gb/s into 2 x 1Gb/s
>> there's a big incentive bom wise to not use offchip dram buffer in a
>> merchant silicon single chip switch vs something that's more complex.
> I'm almost ready to throw the towel in the ring, and declare myself a looney..
> I can imagine at least one vendor ingnoring the extra BOM capex, and
> simpky try to please #$%^#@! like me.
> C NSP has been full with threads about appalling microburst
> performance of the 6500 for years..

And people who care have been using something other than a c6500 for
years. it's a 15 year old architecture, and it's had a pretty good run,
but it's 2012.

An ex8200 has 512MB per port on non-oversuscribed 10Gig ports and 42MB
per port on 1Gig ports. that's a lot of ram.

to take this back to actual tors.

a broadcom 56840 based switch has something in the neighborhood of 9MB
available for packet buffer on chip if you need more then more drams are
in order. while the TOR can cut-through-switch the chassis can't. the
tor is also probably not built with offchip cam (there are examples of
off chip cam as well) for much the same reason.

> One would think a vendor would jump to a copetitive edge like this...

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