> So assuming that you're running on copper with 40.000 Gbps, this is the > on-wire bit rate, that includes the 8-byte preamble, the visible eth frame, > the FCS (4 bytes) and the IFG (12 bytes), hence 1538 bytes for the regular > 1514 bytes. This gives a maximum frame rate of 3250975 pps for such frames, > which is what you'd get if by 1518 you included the FCS, or 3242542 pps if > by 1518 you included a VLAN header (hence 1542 bytes on the wire). > > If we take that last example that sounds like the most plausible, that > gives you a layer2 max bit rate of 3242542*1518*8 = 39.377 Gbps. As such, > depending on how and where you measure, it's very possible that you've > totally filled the wire. Yes, I'm using 40G copper. 1518 byte is including FCS and no VLANs, so the pps expected to fully fill the pipe as you calculate rightly is 3250975 or 3.25 Mpps. The rate I get varies continuously between 3.19 and 3.22 Mpps and very rarely goes up to 3.24 Mpps. The few times I've seen 3.24 Mpps is at the immediate start of a run, but not afterwards - a behaviour I'm not able to explain. I'm trying to understand why I get a lower rate than 3.250975 Mpps and what I need to do to get the full pps rate. Srivats
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