Re: [pilc] Re: How many bytes should a CRC-32 protect?

From: Aaron Falk (falk@ISI.EDU)
Date: Tue May 07 2002 - 12:57:16 EDT

  • Next message: Matt Mathis: "Re: [pilc] Re: How many bytes should a CRC-32 protect?"

    Matt-

    You're assuming a uniform distribution of errors, aren't you? If you have
    bursty errors (as in most wireless channels), you win with bigger packets
    since errors are concentrated in a smaller number of packets.

    --aaron

    > The logic behind the calculation seems to be flawed in the following way:
    > If you have a large quantity of data to move (say a Peta Byte, 1e+15
    > Bytes) then the total undetected error rate is independent of the packet
    > size across a huge range of sizes. This is because changes in
    > per-packet exposure to undetected errors are exactly offset by the change
    > in the number of packets.
    >
    > For example if I send 1e+15 bytes over a link that has a raw error rate
    > of 1E-12 then I compute:
    >
    > Using 1000 byte packets:
    > Raw bit error rate: 1.0e-12
    > Per packet error rate: 1.0e-09
    > Undetected packet errors: 2.5e-19
    > Packets per data set: 1.0e+12
    > Total undetected errors per data set: 2.5e-07
    >
    > Using 10000000 byte packets:
    > Raw bit error rate: 1.0e-12
    > Per packet error rate: 1.0e-05
    > Undetected packet errors: 2.5e-15
    > Packets per data set: 1.0e+08
    > Total undetected errors per data set: 2.5e-07
    >

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