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. The strongest value
of this or the corresponding circuit setting will be used.