NEC NEAX NDA-24349 - Manual (Page 59)

Chapter 3 System Highlights
NEAX2000 IPS Request For Proposal (RFP) Reference Guide Page 3-7
NDA-24349 Issue 4
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.
Reliability Calculation
1Defect
1FIT 10
9
1FIT= MTBF= =
1,000,000,000Hours•Parts TotalFITS TotalFITS
System Calculation
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 9
MTBF= = 8952.55 Hours
111,700
8,952.22 Hours
= 1.02 Years
8,760Hours / Year
Availability Calculations
MTBF
Availability=
MTBF+MTTR
=.9XXXXX