Editing UUCP (section)

====File requests====
If the two systems successfully handshake, the caller will now begin to send a series of file requests. There are four types:

:'''S''' causes a file to be Sent from the caller to the called system (upload). The from and to names are provided, allowing the filename to be changed on the receiver. When the S command is received on the called system, it responds with SY if it succeeded and it is ready to accept the file, or SNx if it failed, where x is a failure code. If an SY is received by the caller, it begins uploading the file using the protocol selected during the initial handshake (see below). When the transfer is complete, the called system responds with CY if it successfully received the file, or CN5 if it failed.
:'''R''' is a Request for the called system to send a file to the caller (download). It is otherwise similar to S, using RY and RN to indicate the command was accepted and it will begin to send data or had a problem, and expecting a CY and CN5 from the caller at the end of the transfer.
:'''X''' uploads commands to be eXecuted on the called system. This can be used to make that system call another and deliver files to it. The called system responds with XY if it succeeded, or XN if it failed.
:'''H''', for Hangup, indicates the caller is done. The called system responds with HY if it succeeded, or HN if it failed.