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Is OC3MON really fast enough for 150 Mbits/s?

OC3MON was tested by NLANR on an OC3c link fully occupied with single cell packets (as would occur in the admittedly unlikely event of continuous TCP ACKs with no data and LLC/SNAP disabled on the routers), which yields 353207.5 packets per second (or in the single-cell packet case, the same number of cells) across each half-duplex link. Each header, including timestamp, ATM, LLC/SNAP, IP and TCP headers consumes 60 bytes, so the internal bus bandwidth required would be

\begin{displaymath}
353207.5 * 2 * 60 * 8 = 339 \mbox{ Mbit/s}.\end{displaymath}

The 32-bit, 33 MHz bus in the PC is slated at 1.056 gigabits, so bus bandwidth wont be a bottleneck until OC12 is to be supported.

Generic internet environments exhibit average packet sizes closer to 250 bytes (about 5 cells), and rarely full utilization in both directions of a link. If we estimate 66% utilization in one direction and full utilization in the other, we get a more realistic:

353207.5 * 1.6666 / 5 = 117731

headers per second, or 56.5 Mbits per second across the internal bus. This estimation shows that OC3MON can be used to monitor a full-duplex 150 Mbit/s ATM connection without suffering any capacity problems.


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Next: Flow Definition the OC3MON Up: The OC3MON Software Previous: Usage
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8/4/1997