Forum: Reliability & Maintainability Questions and Answers

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Posted by: Mark Chapman
Date posted: Fri Jul 29 4:44:29 US/Eastern 2005
Subject: Software Reliability Courses
Message:
Hello all.
Can anyone recommend a software reliability course in the UK. Thanks.

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Posted by: Sadat
Organization:Nortel
Date posted: Thu Jul 28 16:56:00 US/Eastern 2005
Subject: Early Life Prediction
Message:
I am wondering if anyone has done any early life failure rate predictions. If yes, then what methodology did you use?
Telcordia SR-332 has First Year Multiplier (FYM) operating on the steady-state failure rate. I need to predict the first year and second year failure rates based on my long-term MTBF number.

Replies:
Credible failure rate prediction
Larry George Sun Jul 31 13:22:34 US/Eastern 2005

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Posted by: Alex Olson (agolson@sandia.gov )
Date posted: Tue Jul 19 19:03:35 US/Eastern 2005
Subject: Markov Models for Relability
Message:
I'm trying to develop a model to measure the average execution time/efficiency of a large computer system under various fault-tolerance techniques (e.g. checkpointing).
I came across one paper that used a Markov Cost model to model a repairable computer system. They used three states (start,failed segment,successful segment). I understand how they determined the probabilities and costs for each transition, but not the average cost of all paths. They derived the average execution time/efficiency from the average cost of the START->SUCCESS path. Of two other papers (that give the same result), this derivation seems cleaner [I wish to add more states]. Can anyone direct me to an online reference for this type of material?

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Posted by: Amir Saeed (amir.saeed@gd-ais.com )
Organization:GD
Date posted: Wed Jul 13 9:20:00 US/Eastern 2005
Subject: Mission Phases and specified FRs in Relex
Message:
I am using vendor specified failure rates in Relex v7.7 for the system. I have many mission phases. The program does not allow me to specify different failure rates for the different phases or it does not do the calculations itself either. Once the different phases are identified in the "mission profile" file, it uses the same failure rate for all mission phases. How can i work around this?
One way I thought about is to have multiple project files for the system and have the different phases in each of those files with updated calculated failure rates. Is there another way to do this? Any Relex experts who know how to do this in a different manner? I have spoken to Relex too about this, they are absolutely of no help.

Replies:
MTBF with phased failure rates
Larry George Sat Jul 16 13:42:20 US/Eastern 2005

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Posted by: Mark Chapman
Date posted: Tue Jul 12 7:43:19 US/Eastern 2005
Subject: Connection/Interconnection FR
Message:
I need some help please.
I am doing a 217F N2 prediction using MILSTRESS and there are different component connection failure rates that are being generated. One is IR (interconnection rate) and the CR (connection rate). I know that CR is dependant upon the number of pins and whether the components connection is through hole or SMT and it is what I have always used. My customer is asking me to create a separate block category keyword ST - IA,Surface Mount Tech and then put all of the components under it. This automatically creates a FR of 0.592 fpmh and does not take into consideration the component-board soldering. Section 16.2 of 217F N2 states that this failure rate does not include soldering!! IMHO I would have thought that the components should be created in the normal way taking into consideration soldering and then the SMT board FR of 0.592 fphm added at the end. Can anyone please comment on this. Thanks.

Replies:
Connection Reliability Models
bwd Wed Aug 3 11:40:58 US/Eastern 2005

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