Recent Trends and Some Lessons for Serious Network Failures in Japan

Due to significant environmental changes in the telecommunications market, network failures affect socioeconomic activities more than ever before. In this paper, we investigate the statistical characteristics of interval, duration, and number of users affected for serious network failures, which are defined as network failures that last for more than two hours and affect more than 30,000 users, that occurred in Japan during Japanese fiscal years 2008-2013 (April 2008 to March 2014). The results show that (i) the interval follows a Poisson process, (ii) the duration follows a Pareto distribution, (iii) the number of users affected follows a piecewise Pareto distribution, (iv) the product of duration and number of users affected roughly follows a distribution that can be derived from a convolution of two distributions of duration and number of users affected, (v) the relationship between duration and number of users affected differs from service to service, and (vi) the impact of recent serious network failures is getting more severe.