Only if the client sends back something on completion.
A given file could pass through any number of machines on its way from the server to the client, all of them operating at different speeds under different loads on different bandwidths. Any one of these machines could finish "downloading" the file from the machine immediately upstream through its humping great T3 connection long before the client's own box is able to suck it down through its 56k dialup line. So your server could be finished with its part of the transaction long before the client.
