At 01:14 PM 11/18/2009, Michael Sokolov wrote...
As I have learned in school from a department head, mean time between failures (MTBF) means anything only if you are being mean. If you are not being mean, it means nothing.
There is at least one practical use for MTBF, at least the real-world statistical form.
If one has a reasonably large population of devices to maintain, the number of spare devices needed to stay operational is a function of the MTBF.
If you've got 10,000 cell sites, each with an Rb timebase, MTBF figures can provide a pretty accurate estimate of how often one will fail and need to be replaced, at least during the normal lifetime (between the infant mortality and wearout stages). Coupled with MTTR statistics, one can figure out how many spares should be stocked.
Manufacturers invest a lot of effort into using such statistical measures to determine how many spare parts should be kept at various points in the supply chain. Unnecessary parts on shelves = wasted capital. Manufacturers also use MTBF statistics to price service contracts on equipment.
This only works when one is dealing with a large population of devices, so MTBF is meaningless at the individual unit level.
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