How does 95th percentile bandwidth monitoring work?
The 95th percentile is a widely used mathematical calculation to evaluate the regular and sustained utilization of a network connection. The 95th percentile method more closely reflects the needed capacity of the link in question than tracking by other methods such as mean or maximum rate..
The 95th percentile allows for short (less than 36 hours total for the month) bursts in traffic without overage charges. Basically the 95th percentile says that 95% of the time, the usage is at or below this amount. Conversely, 5% of the samples may be bursting above this rate.
The sampling interval, or how often samples (or data points) are taken, is an important factor in percentile calculation. A percentile is calculated on some set of data points. Every data point represents the average bandwidth used during the sampling interval (e.g., five minutes) and is calculated as the number of bits transferred throughout the interval divided by the duration of the interval (e.g., 300 seconds). The resulting value represents the average utilization rate for a single sampling interval and is expressed as bits per second (see below).