It is configured with a single file system deployment target, which places the contents of the deployment onto a flat file system, and is typically served up by a web or application server. For performance reasons, only the difference between the old version and the new version is sent.
The destination file server receiver has to be running with its RMI registry port and service port (by default, 44100 and 44101, respectively) accessible, unless you have configured it to run over another transport.