Technical information

File Transfer Protocol (FTP) Theory of Operation
2-92 AT+i Commands Reference Manual May 31, 2008
File Transfer Protocol (FTP) Theory of Operation
Introduction
The FTP client component in W24 extends W24's general-purpose sockets to incorporate an
additional, dedicated socket for FTP activities. From the host's perspective, the FTP capabilities
are a logical extension of the capabilities of e-mail and direct socket manipulation.
As in all other W24 protocol implementations, host involvement in the specifics of FTP is
minimal. W24 needs to deal with non-standard FTP issues, such as possible differences between
FTP server responses, on its own. Multi-stage FTP protocol sequences are atomized under W24
control to minimize complexity and need for host processor intervention.
The FTP protocol is described in RFC 959.
W24 Family FTP Client Command Set
• Open FTP link to FTP Server
• Retrieve File List from Server
• Change Directory on Server
• Retrieve File Contents from Server
• Open a New File on Server
• Open an existing File on Server for Append
• Send Binary Data to an open File on Server
• Close a File on Server After Binary Data Send
• Delete File on Server
• Close FTP Session
W24 FTP Client Operation Mode
FTP specifies several operational modes. The RFC calls for a minimum implementation, which
should be observed by all FTP servers. W24 restricts its operation mode to the minimum
implementation to assure best intersystem compatibility.
FTP Command Socket
The FTP command socket is normally on port 21 (decimal) of an FTP server. However, other
ports can be specified to support special cases.
Character Types: ASCII Non-print
Structure: File
Mode: Stream