Is this an Interface or an Interconnection?
Interfaces have formal Application Program Interfaces (API). Interfaces are the handshake between functions and procedures from one software application to another. Interfaces are managed at the application level. There are internal and external interfaces. Internal interfaces do not require a network connection; external interfaces sometimes require a network connection.
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On the other hand ,SFTP is also known as Secure File Transfer Protocol (SFTP). SFTP is at the file level, providing file to file transfer from folder to folder. It is a software application all to itself. SFTP usually requires a network connection (i.e., interconnection) in order to work.
SFTP is not an interface, it is a software application that provides secure file transfer within a computer (folder to folder) or over a network.