We propose to improve existing techniques and tools, and to test and integrate them into DOE and other network infrastructures. The proposed effort will overcome limitations of existing algorithms whose estimates degrade as the distance from the probing host increases. The experience of the investigators with both VPS (Variable Packet Size) and PTD (Packet Train Dispersion) probing techniques makes us uniquely qualified to take on this research challenge. As we improve the algorithms for both techniques, we will incorporate our knowledge into an integrated tool suite that offers insights into both hop-by-hop and end-to-end network characteristics. We also will investigate mechanisms for incorporating bandwidth measurement methodologies into applications or operating systems, so that the applications quickly reach the highest throughput a path can provide. Finally, we will examine ways in which routing protocols, traffic engineering, and network resource management systems can use accurate bandwidth estimation techniques in order to improve overall network efficiency.