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Hi, I have a GbE device that cannot forward the full 1Gbps
rate for frames of odd-byte sizes, but can forward the full
1Gbps rate for frames of even-byte sizes. I hope to get other
experts comments on this situation.

I'm using IXIA traffic generator to test the GbE device.
With the even-byte-sized frames (say, 64, 512), the device
can receive full-rate traffic and forward back to IXIA.
However, with the odd-byte-sized frames (say, 65, 511), the
device can receive full-rate traffic, but fails to forward
all the traffic back to IXIA. Overflow happens inside the device.

The nominal traffic generation speed for 511-byte frames can
be calculated like the following;
1Gbps / (511 + 8 + 12) * 8 = 235,404.89642

And the IXIA's input rate is 235,405 frames/sec.
The forwarding rate of the device is limited to 234,932 fps due to
the overflow.

The device company claims that IXIA is generating too much
traffic, that is, IXIA has a faster ineternal clock than the device
clock. Is this valid claim or not?

Thanks for any comments.

Regards,
Jay Kim

<jaymkim@gmail.com> wrote in message
news:1130986054.275889.110630@g49g2000cwa.googlegroups.com...

Hi, I have a GbE device that cannot forward the full 1Gbps
rate for frames of odd-byte sizes, but can forward the full
1Gbps rate for frames of even-byte sizes. I hope to get other
experts comments on this situation.

I'm using IXIA traffic generator to test the GbE device.
With the even-byte-sized frames (say, 64, 512), the device
can receive full-rate traffic and forward back to IXIA.
However, with the odd-byte-sized frames (say, 65, 511), the
device can receive full-rate traffic, but fails to forward
all the traffic back to IXIA. Overflow happens inside the device.

The nominal traffic generation speed for 511-byte frames can
be calculated like the following;
1Gbps / (511 + 8 + 12) * 8 = 235,404.89642

And the IXIA's input rate is 235,405 frames/sec.
The forwarding rate of the device is limited to 234,932 fps due to
the overflow.

The device company claims that IXIA is generating too much
traffic, that is, IXIA has a faster ineternal clock than the device
clock. Is this valid claim or not?

it shouldnt matter - if the clock is wrong the the generated data would be
arriving @ faster than 1 Gbps - 1/5 frame / sec or 1 part per million should
be well with allowed clock tolerance

i suggest is you try this with different length tests - internal buffering
probably takes up the slack up to some limit.

you have to ask whether it really matters that the device cannot handle that
last 0.2% of continuous wirespeed thruput.

i suggest you run the traffic generator with 510 / 511 / 512 byte frames and
see if 510 is OK as well - that should point out the anomaly on odd length
frames.

FWIW odd transfers inside the device memory may have some extra overhead -
but if the design is that close to the edge you should be having other
issues.

Maybe they misalign internal frame transfers, so for odd length frames they
do 2 DMA cycles per x bytes rather than 1? in which case this is likely a
bug or hardware programming issue.

Thanks for any comments.

Regards,
Jay Kim
--

Regards

stephen_hope@xyzworld.com - replace xyz with ntl

In article <1130986054.275889.110630@g49g2000cwa.googlegroups.com>,
jaymkim@gmail.com writes:

Hi, I have a GbE device that cannot forward the full 1Gbps
rate for frames of odd-byte sizes, but can forward the full
1Gbps rate for frames of even-byte sizes. I hope to get other
experts comments on this situation.

I'm using IXIA traffic generator to test the GbE device.
With the even-byte-sized frames (say, 64, 512), the device
can receive full-rate traffic and forward back to IXIA.
However, with the odd-byte-sized frames (say, 65, 511), the
device can receive full-rate traffic, but fails to forward
all the traffic back to IXIA. Overflow happens inside the device.

The nominal traffic generation speed for 511-byte frames can
be calculated like the following;
1Gbps / (511 + 8 + 12) * 8 = 235,404.89642

And the IXIA's input rate is 235,405 frames/sec.
The forwarding rate of the device is limited to 234,932 fps due to
the overflow.

The device company claims that IXIA is generating too much
traffic, that is, IXIA has a faster ineternal clock than the device
clock. Is this valid claim or not?

Hmm, from the numbers I would rather guess the device under test
can only send even length frames and pads if asked to forward odd
length ones.

--
Manfred Kwiatkowski kwiatkowski@zrz.tu-berlin.de

Thanks for any comments.

Regards,
Jay Kim

Thanks for your comments.
Yes, it seems that the device has some kind of internal bug when
odd-sized frames
are injected with the full 1Gbps rate. I tried 510, it was ok, tried
509, it failed.

The device company claimed that Ethernet standard allows 200ppm clock
difference
(+-100ppm) among different Ethernet devices.

I'm wondering this kind of odd-byte problem is common in Ethernet
devices.
I think it's not, is it?

Regards,
Jay Kim

In article <1131071781.266720.312060@g44g2000cwa.googlegroups.com>,
"Jay Kim" <jaymkim@gmail.com> writes:

Thanks for your comments.
Yes, it seems that the device has some kind of internal bug when
odd-sized frames
are injected with the full 1Gbps rate. I tried 510, it was ok, tried
509, it failed.

The device company claimed that Ethernet standard allows 200ppm clock
difference
(+-100ppm) among different Ethernet devices.

200ppm is 1 byte in 5000, you are loosing 1 in 500.

I'm wondering this kind of odd-byte problem is common in Ethernet
devices.
I think it's not, is it?

Who knows. As it makes no difference in everyday operation
you will only notice by looking at the wire.

--
Manfred Kwiatkowski kwiatkowski@zrz.tu-berlin.de