The current Secure File Transfer Protocol (SFTP) does not transfer any information about the files to be transferred, only the file contents as a byte stream. This is sufficient for Unix-type files if the sender and receiver use the same CCS.
SSH Tectia Server for IBM z/OS needs more information: which transfer format to use, what code sets are involved, and what the file characteristics are. SSH Tectia introduces some extensions to SFTP and the information can be relayed by using the Site commands of scpg3 and sftpg3. Alternatively file transfer profiles can be used.
For command descriptions, see the site and lsite command on the sftpg3 man page and the --dst-site and --src-site options on the scpg3 man page.
A file transfer profile is a mechanism for pre-configuring different types of secure file transfers. Both the mainframe clients (scpg3, sftpg3) and the server use the same profile mechanism. There are two types of profiles: named profiles and filename-matched profiles.