Measuring Bandwidth

We measure bandwidth using the SNMP network protocol on our backbone switches. Each server is connected to the switches via a 100Mbit Ethernet connection. The switches keep a running count of each byte into and out of each port along with other network statistics. Our monitoring system reads the byte count every 5 minutes from the switches. This gives us an average transfer rate through your switch port every 5 minutes. We keep this data in a set of database tables and use it to report your usage to you.

Plotting Usage

We create a set of bandwidth plots for each client every 5 minutes using this data. When you set up your account, we give you a private URL which allows you to view these usage plots. Four plots are generated: A daily plot which uses 5 minute averages, a weekly plot which uses 30 minute averages, a monthly plot which uses 2 hour averages, and a yearly plot which uses 1 day averages. Below is an example of a daily plot.
Below the plot are some usage stats which give numerical measures to correlate with what is on the plot.

Calculating Usage

We calculate bandwidth usage using the "95th percentile of 5 minute averages" method. This is a method frequently used by service providers as it is a realistic measure of real bandwidth usage. While many hosting companies use the simpler MB/month method, this serves neither the hosting company nor the client well. By measuring (and plotting) bandwidth usage, you have a better view into what your server sees in the real world. Are you getting a few very high traffic periods or is your traffic consistent. Both may have the same MB/month, but with one, your server performance may be suffering during the high traffic periods.

To arrive at the final usage figure, we stack up all of your 5 minute measurements for the month (about 8600 samples), arranging them from highest to lowest. Then we toss out the top 5% (about 430 samples). The next highest sample is your usage figure for the month. This approach allows you to burst at very high traffic rates for 1/20 of the time without cost penalty.

You can estimate the usage from the daily plots (assuming that your traffic is similar day-to-day throughout the month). Visually pick out a level which removes 5% of the peaks. In the example plot above, the 95th percentile point is 273 Kpbs