There is no published RFC that describes SCP protocol. There are several implementations of SCP, with some variation in the features implemented. WS_FTP Server with SSH supports SCP2 protocol (i.e. SCP over SSH2).
In addition, the WS_FTP implementation of SCP2 has the benefit of leveraging any users, rules, and notifications created for the WS_FTP server host.
Supported SSH clients include: