Q. What is the purpose of the "Set Link Speed..." window?
A. The "Set Link Speed..." window helps InterMapper compute link utilization. It does not change the speed or duplex setting of the real interface. This window has settings for the expected transmit and receive speeds for the link so you can override the ifSpeed reported by the interface.
Example: Let's say you have a 100 mbps interface on your router going into an assymetric DSL link with a max of 16mbps download and 2 mbps upload. It's useful to compute utilization separately for each direction based on those speeds, not 100 mbps of the actual interface. Setting those speeds in the "Set Link Speed..." window will do this.
InterMapper has a single number for the utilization of an interface. It always reports the highest utilization on the interface. There are two cases:
a) If you have checked "Full duplex", InterMapper computes the actual transmit/receive rates as a percentage of the customer-entered rates, and then reports the larger percentage. Thus if the DSL link above is receiving and sending 1.0 mbps in each direction simultaneously, InterMapper will calculate the transmit utilization as 50% and the receive utilization as 6.25%, and show the link as 50% used.
b) If you have checked "Baseband", InterMapper adds the transmit and receive data rates to calculate the utilization. Thus a 10BaseT (half-duplex) link that's transmitting 3 mbps and receiving 3 mbps would be shown with a utilization of 60%. (3 mbps + 3 mpbs = 6 mbps = 60% of a 10 mbps interface.)