The Interval Reliability, its Usage and Calculation for Information and Communication Systems and Networks

The quality of information and communication service includes such important aspects as service accessibility and service retainability, which depend on dependability of systems and networks. The paper considers a dependability measure called interval reliability. It is defined as the probability that an item is in a state to perform as required at a given instant and, starting from this moment, continues to be in this state for a required time interval. The interval reliability simultaneously takes into account availability and reliability, describing the impact of dependability on service accessibility and service retainability at once. Special attention is paid to systems with redundancy, where it may be necessary to take into account situations when failover can lead to the premature termination (interruption) of a service session. A method for calculating the interval reliability for such systems is proposed. The presentation is illustrated by numerical examples for a network that can use protection with non-interrupting failover and restoration with interrupting failover.