Frequency of traffic encryption key change, based upon number
of bytes encrypted; in operation, this is effectively rounded
up to the next full packet. Note that the key change rate is
also influenced by time. The so-called 'best' value will be
dependent upon the algorithms that use the TEK; also, for a
given algorithm the 'best' value will change over time due to
the progresses made in cryptanalysis. This is the value used,
which is the strongest value of the corresponding line or
circuit setting.