On Thu, Jul 18, 2002 at 01:07:06PM -0700, Chris Whyte wrote:
> It's actually a bit more than that. Remember, the interconnect from the
> LC to the fabric is 5Gbps (including overhead). The overhead varies, of
> course, due to cellification but you can actually get around 2.8Gbps to
> possibly 3.0Gbps (subtracting overhead), if I remember correctly.
You're using cisco math. I intentionally quoted all figures
as full-duplex, because that tends to be a more useful number for
capacity planning purposes. I probably should have clarified that
in the original email.
So:
5.0 Gbps (which is 2.5 Gbps full-duplex)
A cisco cell is 64 bytes, 16 of which are header and CRC,
and the remaining 48 bytes are payload. Probably works great for
ATM (gah). So, 25% of our theoretical capacity is gone before we
factor in any other overhead.
We're down to 3.75 Gbps, or 1.875 full-duplex. You can
fill this thing without using the third port. And after real
world overhead and other inefficiencies (CEF updates, etc.)
I'd call this 1.5G full-duplex or so maximum.
Note that in the installation and configuration guide
for the 3GE-GBIC-SC, cisco clearly states:
"The 3-Port Gigabit Ethernet Line card supports full line
rate with two ports in service while the third port is shutdown.
With three ports turned on, the 3-Port Gigabit Ethernet line card
throughput is limited to the line card forwarding engine limit of
4 million packets per second (4 Mpps)."
None of this changes my original assertion that trying
to do some type of load balancing across multiple ports on this
card can get you into trouble at high traffic volumes.
--msa
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