The reliability target on the WeCo 5ESS was/is 99.999% (the famous "five nines"). Actually, it comes out to 99.99943% "up time". That calculates to two hours (not seconds) of down time in 40 years.
Regards.
Charles G. Gray Senior Lecturer, Telecommunications Oklahoma State University - Tulsa (918) 594-8433
It also requires a definition of "down time" and "up time." I recall a line module failure on an early No 1ESS that took three days to diagnose, then repair. 1,000 customers assigned to that module (frame) were out of service for those three days. But, the other 20,000-plus subscribers assigned to that switch were unaffected.
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