Heterogeneous communication networks with their variety of application demands, uncertain time-varying trafc load, and mixture of wired and wireless links pose several challenging problem in modeling and control. In this paper we focus on bandwidth estimation and elucidate why estimates based directly on bandwidth samples are biased. Previously, this phenomenon has been observed but not properly explained, it seems. Standard techniques for bandwidth estimation are based on measurements of inter-arrival times of packets as the bandwidth is proportional to the inverse of the  nterarrival time. Two main classes of bandwidth estimators are analyzed wrt how variations in the inter-arrival times affect the estimates. It is shown that linear time-invariant ltering of instantaneous bandwidth estimates does not change the bias. In contrast to this, smoothing the inter-arrival-time samples does give a bias reduction which depends on the properties of the smoothing lter. Hence, with such approach, noise attenuation can be traded against tracking ability wrt changes in the actual bandwidth.