Q. How does InterMapper calculate bandwidth utilization?

A. To compute utilization, InterMapper does the following:

1. It queries ifInOctets (and ifOutOctets) and the sysUpTime and ifSpeed variables.
2. It subtracts the octet counts from successive samples, and divides by the difference in the sysUpTime samples to compute a byte/second rate.
3. It divides the result by the ifSpeed variable to compute a percentage of the link's capacity/bandwidth. (If the user has overridden the ifSpeed variable, InterMapper uses the user-entered value.)
4. If a network is using a shared baseband link (such as Ethernet, wireless, etc.) InterMapper compares the sum of the transmitted and received bytes/second against the link speed to get the utilization. If it's a full-duplex link (such as a frame relay, T-1 or T3, ATM, etc.) then InterMapper compares the higher of the transmitted or received data rate against the link speed. The default is to use the full-duplex settings, which can be changed using the Set Link Speed option for the interface.