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IGATE-HINTS: further birthday paradox clarification

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Heikki Hannikainen 2017-04-17 00:29:52 +03:00
parent dc9fcd397e
commit dd470e2d7c
1 changed files with 6 additions and 3 deletions
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doc/IGATE-HINTS.md
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@ -98,9 +98,12 @@ the same checksum).
different packet may have the same checksum and may get dropped. With 16
bits, there are 65536 different checksum values. Given two different random
packets, there is a 1-in-65536 chance that they have the same checksum.
Given 100 random packets, there is a whopping 7.3% chance that two packets
will have the same checksum (for proof, see the
[Birthday paradox](https://en.wikipedia.org/wiki/Birthday_problem)).
However, given 100 random packets, there is a 7.3% probability that two
packets will have the same checksum. Given 300 random packets, 49.6%
probability that two *different* packets have the same CRC. For proof, see
the [Birthday paradox](https://en.wikipedia.org/wiki/Birthday_problem).
When the igate is left running for weeks and months, some hash collisions
and unnecessary packet drops will absolutely happen.
The implementation on the APRS-IS servers is more complicated. It takes
into account various common packet corruptions, and is not as likely to do