  In a 2002 paper, Che and co-authors proposed a simple approach for estimating
the hit rates of a cache operating the least recently used (LRU) replacement
policy. The approximation proves remarkably accurate and is applicable to quite
general distributions of object popularity. This paper provides a mathematical
explanation for the success of the approximation, notably in configurations
where the intuitive arguments of Che, et al clearly do not apply. The
approximation is particularly useful in evaluating the performance of current
proposals for an information centric network where other approaches fail due to
the very large populations of cacheable objects to be taken into account and to
their complex popularity law, resulting from the mix of different content types
and the filtering effect induced by the lower layers in a cache hierarchy.
