NEC NEAX 2000 IPS Reference Manual page 59

Mean Time To Repair (MTTR)
The Mean Time To Repair has been studied with the following conditions:
1. A mid to high-level technical person will attend to the site for the detection of the fault and
replacement of the faulty circuit board.
2. All critical circuit boards for replacement are stocked at each Fault Dispatch Center (FDC).
3. All non-critical circuit boards for FDCs are stocked at NEC. The calculation result of the MTTR is
1.0 hour.
Reliability Calculations
The following information is to show you how to calculate the reliability for the system you are
configuring. Remember that these calculations are used to determine a partial system outage.
1Defect
1FIT=
1,000,000,000Hours•Parts
To calculate the MTBF of a single system, obtain the sum of the FITs from each component.
For example: Assume you have a complete system that consists of two components:
Item A FIT=31,700, Item B FIT=80,000
TotalFit = 31,700 + 80,000 = 111,700
10
MTBF=
111,700
8,952.22 Hours
8,760Hours / Year
Availability Calculations
MTBF
Availability=
MTBF+MTTR
NEAX2000 IPS Request For Proposal (RFP) Reference Guide
NDA-24349 Issue 4
System Calculation
9
= 8952.55 Hours
= 1.02 Years
=.9XXXXX
Reliability Calculation
1FIT
MTBF= =
TotalFITS TotalFITS
Chapter 3 System Highlights
9
10
Page 3-7