Communication over wireless heterogeneous networks is still a challenging task. The underlying reason beneath this is in the waste of available bandwidth or the bursts of packet drops that may occur during handoff due to the disparity in the amount of available bandwidths among wireless cells. In mobile environments, the fundamental challenge upon a handoff phenomenon consists in an efficient probing of the availability of the new network resources and an appropriate rate adjustment in the new network cell. As a remedy to the above issue, this paper argues the usage of low-priority dummy packets to probe the availability of the new network resources. Indeed, when a mobile node enters a cell overlapping area and is about to change its point-of-attachment to the network, two connections are simultaneously set between the mobile node and the sender: one through the old point-of-attachment and another through the new one. The sender transmits actual data through the old connection. Meanwhile, it sends dummy segments through the new connection to verify the bandwidth availability of the new network. The proposed scheme is dubbed Dummy Segment based Bandwidth Probing (DSBP). The performance of the DSBP scheme is evaluated and compared with existing schemes through extensive simulations. The simulation results show that the DSBP scheme substantially improves the system efficiency, reduces the number of packet drops, and makes better utilization of the network bandwidth.