Reliability prediction is an important element in the process of selecting equipment. This prediction provides necessary input to system-level reliability modes for predicting expected downtime per year and system availability.

SR-332 provides all the tools needed for predicting device and unit hardware reliability. The Telcordia Reliability Prediction Procedure has a long and distinguished history of use within and outside the telecommunications industry. SR-332 provides the only hardware reliability prediction procedure developed from the input and participation of a cross-section of major industrial companies. This lends the procedure and the predictions derived from it a high level of credibility free from the bias of any individual supplier or service provider. 


  • FIT (λ): Failure in Time is the rate of random failures, usually expressed in components per giga-hour 
  • CL: Confidence level (60% or 90%  is commonly used for the calculation)
  • MTTF: Mean Time To Failure 
  • MTBF: Mean Time Between Failure 
  • MDT: Mean Down Time 
  • MUT: Mean Up Time 
In many cases, MDT is very week compared to MUT, we can say that MTTF = MTBF
In many cases, MDT is very week compared to MUT, we can say that MTTF = MTBF


Assumptions for calculation 

  • The field failures are random failures and can be modeled with the exponential distribution 
  • The failure rate (λ) is constant and is expressed in FIT [10-9 h-1 

 proportion of failed components x 10(ex 9) accumulated device hours


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