Example of Grid file transfer: a grid scheduler determines that a copy of a given file needs to be copied to site A before a job can be run. Several copies of this file are ina Grid Replica Catalogue so there is a choice of where to copy the file from. The Grid Scheduler needs to determine the optimal method to create this new file copy, and to estimate how long this file creation will take. To make this selection the scheduler must have determined what is the best source (or sources) to copy the data from. Selecting the best source to copy the data from requires a prediction of future end-to-end path characteristics between the destination and each possible source. Accurate prediction of the performance obtainable from each source requires measurement of available bandwidth (both end-to-end and hop-by-hop), latency, loss, and other characteristics important to transfer performance. Profile for Network Performance Measurements for Grids, GGF NMWG group.