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SUMMARYIn 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.

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PurposeThe purpose of this paper is to derive the user‐perceived availability of M‐for‐N shared protection systems composed of multiple user groups, each with a protection‐switching priority.Design/methodology/approachThe paper assumes a shared protection system with M protection units and N working units. The memoryless state transition diagram viewed from the system administrator, combined with combinatorial analysis of state probabilities on protection switching, yields a generic formula of the availability viewed from an arbitrary end user.FindingsThe numerical examples of availability reveal the effect of prioritized protection switching. It is observed that the total protection capacity is constant regardless of the ways of priority grouping. The shared protection system with multiple protection units enables more flexible availability allocation compared with the case of a single protection unit.Research limitations/implicationsUser‐perceived reliability is still an unexplored research area. Many variations of the system treated in this paper can be applied to various applications.Practical implicationsThe analysis provides useful information for the design and operation of, for example, telecommunication network devices. The analysis is applicable to general shared protection systems that are subject to service level agreement (SLA) involving user‐perceived reliability measures.Originality/valueThis paper establishes the model of the priority shared protection systems for the first time and shows a practical computation method of prioritized user‐perceived availability.

In this paper, we investigate service-level assurance in high-availability multi-unit systems using the M-for-N backup scheme. M-for-N shared protection (backup) systems with priority control (i.e. prioritized protection switching and prioritized re-housing of repaired units) can be applied to actual telecommunication devices that are subject to service-level agreement (SLA) involving reliability measures. A priority level is assigned to each end user in such a system and the switching and unit re-housing process is subject to the priority. The main contribution of this paper is to give a practical computation method of the user-perceived availability under the priority control. Our case studies for real telecommunication systems reveal the effect of priority control on the user-perceived availability. Copyright