Data Compression

Data compression may reduce file transfer times. The level of improvement, if any, depends on your CPU speed, network speed, and the type file being compressed.

Compression can often reduce the size of files containing plain text by more than 50 percent. Some examples include XML, HTML, CSV, and tab delimited data files. Conversely it is also possible that the total file transfer times could increase if time is wasted attempting to compress media files or other files that are already compressed like ZIP or RAR files.

Data compression modifies file transfer times by shifting some of the effort away from the network and onto the CPU. Transfer times benefit the most when your network connection is slow (modem) and your CPU is fast.

With connection-level compression, Robo-FTP automatically negotiates a compression/decompression agreement with the remote computer and then reduces the size of all data transferred across the connection. The remote computer automatically decompresses the data as it arrives.

Connection-level compression is disabled by default but may be enabled by setting the /compression=x option of the FTPLOGON command or by modifying the Compression property of a Managed Site in the Configurator.

The compression algorithm used by Robo-FTP depends on the connection type as follows:

FTP and FTPS	MODE Z compression is used for FTP and FTPS connections. Valid zlib levels 0 through 9 are supported where 0 is no compression and 9 is maximum compression.
SFTP	The compression Robo-FTP uses for SFTP connections is equivalent to the –C switch in command line SFTP programs. Valid zlib levels 0 through 9 are supported where 0 is no compression and 9 is maximum compression.
HTTP and HTTPS	Robo-FTP automatically uses GZIP or ZLIB depending on the capabilities of the remote server. HTTP(s) Compression does not have multiple levels; it is either off or on (zero or non-zero).

With file-level compression, each file must be explicitly compressed and you must use external means to ensure that the recipient will be able to properly decompress the files. The ZIP script command creates a zip archive from one or more files. The PGPENCRYPT script command encrypts and compresses files.