Wednesday, July 18, 2012

Research paper: "Lessons from the PSTN for Dependable Computing"

I came across this paper while reading about self-healing systems. The authors of the paper (Enriquez, Brown, Patterson) are doing analysis of FCC disruption reports in order to find out the causes of faults in PSTN. Additionally, PSTN is large and complex networks and certainly experiences from maintaining this network can help a lot in maintaining Internet infrastrcture.

I'll emphasize the following key points from this paper that I find interesting:
  • PSTN operators are required to fill disruption report when 30,000 people are affected and/or the disruption is longer than 30 minutes. There is a screen shot of report in the paper, even though it probably can be downloaded from FCC site. But, it seems that reports themselves are not publicly available?
  • They analyzed reports from year 2000. There is a reference in the paper with older, similar, analysis.
  • They used three metrics for comparison: number of outages, customer minutes and blocked calls. Number of outages is a simple count of outages, customer minutes is a multiplication of duration and total number of customers affected (disregarding the fact if they tried to make a call during disruption). Finally, blocked calls is a multiplication of duration and number of customers that really tried to make a call during disruption.
  • The prevailing cause of disruption is human error, more than 50% in any case. Human error is further subdivided into those made by persons affiliated in some way with the operator and those that are not. Those affiliated with the operator are cause of a larger number of disruptions.

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