Q. How does InterMapper find the byte/second and bits/second that it displays when you click on a link??
A. In general, InterMapper uses ifInOctets and ifOutOctets from MIB-II for SNMPv1, and the high capacity variants (ifHCInOctets and ifHCOutOctets, when available) for SNMPv2c/v3.
This link may provide helpful information related to Cisco's implementation