Hi Tom,

> Well that's where I disagree. And where I am looking for clarification.

> We were NOT using systems with Buses limited to 32bit/33Mhz or Basic PCI.
The routers that we used for testing were using the Intel 7501 chipset,
spec'd at allowing 3GB of throughput, and PCI-X Bus.

> There are actually three potential limits...
> 1) Hardware

Depending on the Ethernet card, this is still a real possibility.

> 2) Software

This is definitely a limitation.

> 3) Ethernet Protocol theoretical limit.

> My understanding, although not confirmed, was that there was an Ethernet
(cdma) timing Limitation, that prevented the Full 1GB from being reached
using a < 1500MTU.

There is no such limitation on Ethernet.  I'm assuming that when you say <
1500 MTU you mean < 1500 byte packets and not < 1500 MTU.  In any case, a
quick Google search can confirm that equipment does exist that passes GigE
at wirespeed.  I remember Network World magazine doing tests back in 1999 or
2000 and passing wirespeed GigE over a variety of equipment with an array of
packet sizes.

> Myhardware can handle it. I'm investigating whether the limit is related
to my Linux Software config versus Ethernet theoretical limits.  

Given our experiences, I know that the former is affecting you.  The latter
limits you mention do not exist.

> > If you want wirespeed GigE performance with multiple packet streams at a
more reasonable packet size (remember that 1500 byte packets aren't
realistic), you'll need to make some adjustments to the kernel.

> Well, thats my point... 1500MTU is a requirement that is usually beyond
the control of the ISP. The ISP may may control the GB connection for Higher
MTU, but NOT necessarily backend Transit or Front End last mile connections.

> The Internet is full of less than 384K average size packets, and not much
an ISP can do about that.

> Part of the question becomes, can near 1GB be acheived at 1500MTU?

Yes, without question.

> > > With the 1500MTU frame acheiving only 200kbps, our routers CPU
utilization was less than 20%, so it was not a saturated router.

> > Actually, it is.  Utilities top and vmstat don't necessarily reflect all
of the CPU utilization, and can't account for PCI bus contention/overhead.

> Excellent Point. Any way to tell that (FULL CPU utilization)?

You would need a debugger to see the amount of time that the CPU was waiting
for various operations.  That would be the only way that I know to ferret
out everything.

> > > The second we changed MTU to 9600, we got over 800 mbps, and CPU
utilization was still very low, forget exact number but under 40%.

> > Well, sure...you've just taken your packet rate down significantly.

> The reason we thought this was an Ethernet limitation and not a
CPU/hardware limitation is that, we were able to pass a larger speed by
combining multiple 100 mbps connections.  For example, we were able to get
400 mbps with 4- 100mbps connections simultaneously.(didn't have more
machines to test.)

You've changed too many variables at once (drivers, hardware) to make any
conclusions.

> Does ImageStream have any data, from live tests, proving the speed they
can get across their GB routers at < 1500 MTU?

Again, I'm assuming that you mean packet size when you're saying MTU and not
actually setting the MTU to less than 1500 bytes.  We have tested our GigE
performance on routers with GigE wirespeed specs to ensure that we can pass
1 Gbps at various packet sizes.

Regards,

Jeff




Tom DeReggi

> Regards,
>
> Jeff
>
>
>
> Tom DeReggi
> RapidDSL & Wireless, Inc
> IntAirNet- Fixed Wireless Broadband
>
> --
> WISPA Wireless List: wireless@wispa.org
>
> Subscribe/Unsubscribe:
> http://lists.wispa.org/mailman/listinfo/wireless
>
> Archives: http://lists.wispa.org/pipermail/wireless/
>
>
> --
> WISPA Wireless List: wireless@wispa.org
>
> Subscribe/Unsubscribe:
> http://lists.wispa.org/mailman/listinfo/wireless
>
> Archives: http://lists.wispa.org/pipermail/wireless/

--
WISPA Wireless List: wireless@wispa.org

Subscribe/Unsubscribe:
http://lists.wispa.org/mailman/listinfo/wireless

Archives: http://lists.wispa.org/pipermail/wireless/


-- 
WISPA Wireless List: wireless@wispa.org

Subscribe/Unsubscribe:
http://lists.wispa.org/mailman/listinfo/wireless

Archives: http://lists.wispa.org/pipermail/wireless/

Reply via email to