User-Perceived Reliability of M-for-N (M:N) Shared Protection Systems

Hirokazu OZAKI  Atsushi KARA  Zixue CHENG  

IEICE TRANSACTIONS on Information and Systems   Vol.E92-D   No.3   pp.443-450
Publication Date: 2009/03/01
Online ISSN: 1745-1361
DOI: 10.1587/transinf.E92.D.443
Print ISSN: 0916-8532
Type of Manuscript: PAPER
Category: Dependable Computing
user-perceived reliability,  shared protection systems,  availability,  MTTFF,  MTTF,  TTFF,  probability distribution,  

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In this paper we investigate the reliability of general type shared protection systems i.e. M for N (M:N) that can typically be applied to various telecommunication network devices. We focus on the reliability that is perceived by an end user of one of N units. We assume that any failed unit is instantly replaced by one of the M units (if available). We describe the effectiveness of such a protection system in a quantitative manner. The mathematical analysis gives the closed-form solution of the availability, the recursive computing algorithm of the MTTFF (Mean Time to First Failure) and the MTTF (Mean Time to Failure) perceived by an arbitrary end user. We also show that, under a certain condition, the probability distribution of TTFF (Time to First Failure) can be approximated by a simple exponential distribution. The analysis provides useful information for the analysis and the design of not only the telecommunication network devices but also other general shared protection systems that are subject to service level agreements (SLA) involving user-perceived reliability measures.