SFTP is a secure file transfer protocol sending data over encripted SSH transport. One should notice that it's a single-stream protocol. It can also be significantly slower than bbcp or Globus Online due to its internal data encription. The protocol doesn't seem to be optimized for transferring data over a Wide Area Network (WAN).
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The main benefit of sftp (or scp) is that it's very easy to use.
Here is a basic example of an interactive session (a password for SLAC UNIX user 'user' is being requested):
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