This appendix discusses mathematical calculations to calculate network availability. The percentage method specifies the expected amount of system downtime. The defects-per-million method specifies the actual system performance. The availability method enables you to calculate theoretical availability based on manufacture information. This appendix also includes an availability-calculation example for a simple network topology.
The percentage method describes availability based on a percentage of the total number of minutes in one year (525,960 minutes, a figure that takes leap years into account). Table A-1 shows the availability percentages.