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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
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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8/4/1997