Creating or exploiting positive feedback loops or under-damped
oscillatory behaviors so as to overload a system. Examples include electrical
or acoustic wave enhancement, the creation of packets in the Internet which
form infinite communications loops, and protocol errors causing cascade
failures in telephone systems.
Complexity: In some under-damped systems,
sympathetic vibration is easily induced. It sometimes even happens
accidentally. In over-damped systems, sympathetic vibration requires
additional energy. In logical systems - such as protocol driven networks -
the complexity of finding an oscillatory behavior is often very low. A
simple search of the Internet protocols leads to several such cases. More
generally, finding such cases may involve N-fold combinations of protocol
elements which is exponential in time and linear in space. Proving that
protocols are free of such behaviors is known to be at least NP-complete.