A monitoring technique is provided for diagnosing delays in file transfers between a server and a client via a network, which monitoring technique operates to make measurements of ordinary network traffic on a link unique to a given client/server pair connection. In particular, the invention operates to apply a set of rules to partition the file transfer time into increments attributable to specific identified causes. To that end, the invention intercepts and sorts traffic traversing a predetermined monitor point into a set of flows, wherein each flow consists of all of the traffic between one client and one server. For each flow the packet headers and timestamps of all packets passing in each direction are read. The partitioning of the file transfer times is based on the resulting data.